Tue·Dec 22, 2015Tuesday·December 22, 2015

1. 01*

   Electron-positron pair production in inhomogeneous electromagnetic fields

   Christian Kohlfürst🇦🇹

   The process of electron-positron pair production is investigated within the phase-space Wigner formalism. The similarities between atomic ionization and pair production for homogeneous, but time-dependent linearly polarized electric fields are examined mainly in the regime of multiphoton absorption (field-dependent threshold, above-threshold pair production). Characteristic signatures in the particle spectra are identified (effective mass, channel closing). The non-monotonic dependence of the particle yield on the carrier frequency is discussed as well. The investigations are then extended to spatially inhomogeneous electric fields. New effects arising due to the spatial dependence of the effective mass are discussed in terms of a semi-classical interpretation. An increase in the normalized particle yield is found for various field configurations. Pair production in inhomogeneous electric and magnetic fields is also studied. The influence of a time-dependent spatially inhomogeneous magnetic field on the momentum spectrum and the particle yield is investigated. The Lorentz invariants are identified to be crucial in order to understand pair production by strong electric fields in the presence of strong magnetic fields.

   hep-ph43 citations
2. 02*

   A resonance without resonance: scrutinizing the diphoton excess at 750 GeV

   J. S. Kim🇪🇸 · J. Reuter🇩🇪 · K. Rolbiecki🇪🇸 · R. Ruiz de Austri🇪🇸

   Motivated by the recent diphoton excesses reported by both ATLAS and CMS collaborations, we suggest that a new heavy spinless particle is produced in gluon fusion at the LHC and decays to a couple of lighter pseudoscalars which then decay to photons. The new resonances could arise from a new strongly interacting sector and couple to Standard Model gauge bosons only via the corresponding Wess-Zumino-Witten anomaly. We present a detailed recast of the newest 13 TeV data from ATLAS and CMS together with the 8 TeV data to scan the consistency of the parameter space for those resonances.

   hep-phhep-exPLB(2016)·120 citations
3. 03*

   The 750 GeV $S$-cion: Where else should we look for it?

   Alexandre Alves🇧🇷 · Alex G. Dias🇧🇷 · Kuver Sinha🇺🇸

   The resonance $S$ at $\sim 750$ GeV in the diphoton channel observed by ATLAS and CMS, if it holds up, is almost certainly the ($S$)cion of a larger dynasty in a UV completion that may very well be connected to the hierarchy problem. At this stage, however, an effective field theory framework provides a useful way to parametrize searches for this resonance in other channels. Assuming that the excess is due to a new scalar or pseudoscalar boson, we study associated production of $S$ ("$S$-strahlung") at the LHC and propose searches in several clean channels like $\gamma \gamma \ell \ell$, $\gamma \gamma \ell \text{eslash}$ and $\ell \ell \ell \gamma \text{eslash}$ to probe dimension-5 operators coupling $S$ to Standard Model gauge bosons. We consider a range of widths for $S$, from 5 GeV to 45 GeV, and find that the three channels probe complementary regions of parameter space and the suppression scale $\Lambda$. The finding of most immediate relevance is that with 3 fb${}^{-1}$, the LHC might already reveal new excesses in the $\gamma \gamma \ell \ell$ channel and a 5(3) $\sigma$ discovery may already be possible after collecting 65(25) fb${}^{-1}$ of data with $\ell \ell \ell \gamma \text{eslash}$ events if the scale of the new physics is within $\sim$ 9 TeV for couplings respecting 8 TeV LHC bounds and compatible with the observed excess in diphotons for a wide resonance as suggested by the ATLAS Collaboration. Beyond the EFT parametrization, we found realizations of models with heavy vector-like quarks and leptons which can simultaneously fit the diphoton excess and be discovered in the channels proposed here.

   hep-phPLB(2016)·145 citations
4. 04*

   Automated Calculation of Dijet Soft Functions in Soft-Collinear Effective Theory

   Guido Bell🇬🇧 · Rudi Rahn🇬🇧 · Jim Talbert🇬🇧

   We present a systematic framework for the calculation of dijet soft functions, which are defined as a matrix element of two light-like Wilson lines that is weighted by a generic measurement function. Based on a universal parametrisation of the phase-space integrals, we isolate the singular terms in Laplace space and evaluate the observable-dependent integrations numerically. We discuss the implementation of our algorithm into the public program SecDec, and present results for various SCET-1 soft functions to two-loop order. In particular, we obtain new predictions for the C-parameter and the angularity variables. Finally, we discuss ongoing extensions and the future outlook of the project.

   hep-phPoS(2016)·19 citations
5. 05*

   On dilatons and the LHC diphoton excess

   Eugenio Megias🇩🇪 · Oriol Pujolas🇪🇸 · Mariano Quiros🇪🇸

   We study soft wall models that can embed the Standard Model and a naturally light dilaton. Exploiting the full capabilities of these models we identify the parameter space that allows to pass Electroweak Precision Tests with a moderate Kaluza-Klein scale, around $2$ TeV. We analyze the coupling of the dilaton with Standard Model (SM) fields in the bulk, and discuss two applications: i) Models with a light dilaton as the first particle beyond the SM pass quite easily all observational tests even with a dilaton lighter than the Higgs. However the possibility of a 125 GeV dilaton as a Higgs impostor is essentially disfavored; ii) We show how to extend the soft wall models to realize a 750 GeV dilaton that could explain the recently reported diphoton excess at the LHC.

   hep-phhep-thJHEP(2016)·137 citations
6. 06*

   Supersoft SUSY Models and the 750 GeV Diphoton Excess, Beyond Effective Operators

   Linda M. Carpenter🇺🇸 · Russell Colburn🇺🇸 · Jessica Goodman🇺🇸

   We propose that the sbino, the scalar partner of a Dirac bino can explain the 750 GeV diphoton excess observed by ATLAS and CMS . We analyze a model in which the sbino couples to pairs of Standard Model (SM) gauge bosons. We analyze an effective operator model, as well as a completion in which the sbino couples to pairs of gauge bosons through loops of heavy sfermions. We find that the sbino may be given an appreciable decay width through tree level coupling in the Higgs or Higgsino sector and additionally fit the 750 GeV excess by considering gluon fusion processes with decay to diphotons.

   hep-phPRD(2016)·115 citations
7. 07*

   Could the width of the diphoton anomaly signal a three-body decay ?

   Jérémy Bernon🇫🇷 · Christopher Smith🇫🇷

   The recently observed diphoton anomaly at the LHC appears to suggest the presence of a rather broad resonance. In this note, it is pointed out that this does not hold if the two photons are produced along with an extra state. Specifically, the diphoton invariant mass arising from various $A\to B\gamma \gamma$ processes, with $A,B$ being scalars, fermions, or vectors, though peaked at a rather large value, would naturally be broad and could fit rather well the observed deviations. This interpretation has a number of advantages over the two-photon resonance hypothesis, for example with respect to the compatibility with the 8 TeV diphoton, dilepton or dijet searches, and opens many new routes for New Physics model construction.

   hep-phPLB(2016)·113 citations
8. 08*

   Gauge Mediated Mini-Split

   Timothy Cohen🇺🇸 · Nathaniel Craig🇺🇸 · Simon Knapen🇺🇸

   We propose a simple model of split supersymmetry from gauge mediation. This model features gauginos that are parametrically a loop factor lighter than scalars, accommodates a Higgs boson mass of 125 GeV, and incorporates a simple solution to the $\mu -b_{\mu }$ problem. The gaugino mass suppression can be understood as resulting from collective symmetry breaking. Imposing collider bounds on $\mu$ and requiring viable electroweak symmetry breaking implies small $a$-terms and small $\tan \beta$ -- the stop mass ranges from $10^5$ to $10^8\text{mbox}GeV$. In contrast with models with anomaly + gravity mediation (which also predict a one-loop loop suppression for gaugino masses), our gauge mediated scenario predicts aligned squark masses and a gravitino LSP. Gluinos, electroweakinos and Higgsinos can be accessible at the LHC and/or future colliders for a wide region of the allowed parameter space.

   hep-phJHEP(2016)·6 citations
9. 09*

   Pseudo-observables in electroweak Higgs production

   Admir Greljo🇨🇭 · Gino Isidori🇨🇭 · Jonas M. Lindert🇨🇭 · David Marzocca🇨🇭

   We discuss how the leading electroweak Higgs production processes at the LHC, namely vector-boson fusion and Higgs+W/Z associated production, can be characterized in generic extensions of the Standard Model by a proper set of pseudo-observables (PO). We analyze the symmetry properties of these PO and their relation with the PO set appearing in Higgs decays. We discuss in detail the kinematical studies necessary to extract the production PO from data, and present a first estimate of the LHC sensitivity on these observables in the high-luminosity phase. The impact of QCD corrections and the kinematical studies necessary to test the validity of the momentum expansion at the basis of the PO decomposition are also discussed.

   hep-phhep-exEPJC(2016)·62 citations
10. 10*

    Dark Matter Direct Detection with Accelerometers

    Peter W. Graham🇺🇸 · David E. Kaplan🇺🇸 · Jeremy Mardon🇺🇸 · Surjeet Rajendran🇺🇸 · William A. Terrano🇺🇸

    The mass of the dark matter particle is unknown, and may be as low as ~$10^{-22}$ eV. The lighter part of this range, below ~eV, is relatively unexplored both theoretically and experimentally but contains an array of natural dark matter candidates. An example is the relaxion, a light boson predicted by cosmological solutions to the hierarchy problem. One of the few generic signals such light dark matter can produce is a time-oscillating, EP-violating force. We propose searches for this using accelerometers, and consider in detail the examples of torsion balances, atom interferometry, and pulsar timing. These approaches have the potential to probe large parts of unexplored parameter space in the next several years. Thus such accelerometers provide radically new avenues for the direct detection of dark matter.

    hep-phastro-ph.COhep-exquant-phPRD(2016)·309 citations
11. 11*

    Conciliating SUSY with the Z-peaked excess

    Vasiliki A. Mitsou (U. Valencia, IFIC)🇪🇸

    The ATLAS experiment observed an excess at the $3\sigma$ level in the channel of $Z$ boson, jets and high missing transverse momentum in the full 2012 dataset at 8 TeV while searching for SUSY. The question arises whether the abundance and the kinematical features of this excess are compatible with the yet unconstrained supersymmetric realm, respecting at the same time the measured Higgs boson properties and dark matter density. By trying to explain this signal with SUSY we find that only relatively light gluinos together with a heavy neutralino NLSP decaying predominantly to a $Z$ boson plus a light gravitino could reproduce the excess. We construct an explicit general gauge mediation model able to match the observed signal. More sophisticated models could also reproduce the signal, as long as it features light gluinos, or heavy particles with a strong production cross section, producing at least one $Z$ boson in its decay chain. The implications of our findings for the Run II at LHC with the scaling on the $Z$ peak, as well as for the direct search of gluinos and other SUSY particles, are also discussed.

    hep-phEPJ Web Conf.(2016)·2 citations
12. 12*

    PARTONS: PARtonic Tomography Of Nucleon Software. A computing framework for the phenomenology of Generalized Parton Distributions

    B. Berthou🇫🇷 · D. Binosi🇮🇹 · N. Chouika🇫🇷 · L. Colaneri🇫🇷 · M. Guidal🇫🇷 · C. Mezrag🇺🇸 · H. Moutarde🇫🇷 · J. Rodríguez-Quintero🇪🇸 · F. Sabatié🇫🇷 · P. Sznajder🇵🇱 · J. Wagner🇵🇱

    We describe the architecture and functionalities of a C++ software framework, coined PARTONS, dedicated to the phenomenology of Generalized Parton Distributions. These distributions describe the three-dimensional structure of hadrons in terms of quarks and gluons, and can be accessed in deeply exclusive lepto- or photo-production of mesons or photons. PARTONS provides a necessary bridge between models of Generalized Parton Distributions and experimental data collected in various exclusive production channels. We outline the specification of the PARTONS framework in terms of practical needs, physical content and numerical capacity. This framework will be useful for physicists - theorists or experimentalists - not only to develop new models, but also to interpret existing measurements and even design new experiments.

    hep-phhep-exnucl-exnucl-th+1EPJC(2018)·136 citations
13. 13*

    FRBs and dark matter axions

    Aiichi Iwazaki🇯🇵

    We have proposed a model of a progenitor of fast radio bursts (FRBs): The FRBs are emitted by electrons in atmospheres of neutron stars when neutron stars collide with dark matter axion stars. We reexamine the model by taking account of the tidal forces of the neutron stars. The axion stars are distorted by the forces so that they become like long sticks when they are close to the neutron stars. Although the tidal forces fairly distort the axion stars, our model is still consistent with present observations. We explain a distinctive feature of our model that the FRBs are not broadband, but narrowband. We also show that two-component FRBs may arise when the axion stars collide with binary neutron stars. FRBs would most frequently arise in centers of galaxies since the dark matter concentrates in the centers.

    hep-phastro-ph.HE9 citations
14. 14*

    Phenomenology of dark matter-nucleon effective interactions

    Riccardo Catena🇸🇪

    I compare the non-relativistic effective theory of one-body dark matter-nucleon interactions to current dark matter direct detection experiments and neutrino telescope observations, presenting exclusion limits on the coupling constants of the theory. In the analysis of direct detection experiments, I focus on the interference of different dark matter-nucleon interaction operators and on predictions observable at directional detectors. Interpreting neutrino telescope observations, I use new nuclear response functions recently derived through nuclear structure calculations and show that hydrogen is not the most important element in the exclusion limit calculation for the majority of the spin-dependent dark matter-nucleon interaction operators

    hep-phastro-ph.COJ.Phys.Conf.Ser.(2016)·2 citations
15. 15*

    Cancellation of Infrared Divergence in Inclusive Production of Heavy Quarkonia

    Gao-Liang Zhou🇨🇳

    A scheme is presented here to cancel out the topologically unfactorized infrared divergences in the inclusive production of heavy quarkonia, which affect the NRQCD factorization of these processes. The heavy quarkonia are defined as resonance states of QCD instead of color singlet heavy quark pair. Thus the final heavy quark pair is nor necessarily to be color singlet. In addition, the heavy quarkonia are reconstructed by their decay products. As the result, transition between states containing containing heavy quarks caused by exchanges of soft gluons are also taken into account here. Such cancellation is crucial for the NRQCD factorization of these processes.

    hep-phPRD(2016)·1 citation
16. 16*

    Symmetries Behind the 750 GeV Diphoton Excess

    Wei Chao🇺🇸

    A 750 GeV resonance has been observed at the Run 2 LHC in the diphoton channel. In this paper, we explain this resonance as a CP-even scalar, S, that triggers the spontaneous breaking of local $U(1{)}_B$ or $U(1{)}_{B+L}$ gauge symmetries. S couples to gluon and photon pairs at the one-loop level, where particles running in the loop are originally introduced to cancel anomalies. The gluon fusion is the dominate production channel of S at the LHC. The model automatically contains a scalar dark matter candidate, stabilized by the new gauge symmetry. Our study shows that both the observed production cross section at the LHC and the best fit decay width of S can be explained in this concrete model, without conflicting with any experimental data. Constraints on couplings of S are studied, which shows a negligible mixing with the standard model Higgs boson but sizable coupling with the dark matter.

    hep-phPRD(2016)·136 citations
17. 17*

    Gravitons in multiply warped scenarios - at 750 GeV and beyond

    Mathew Thomas Arun🇮🇳 · Pratishruti Saha🇨🇦

    The search for extra dimensions has so far yielded no positive results at the LHC. Along with the discovery of a 125 GeV Higgs boson, this implies a moderate degree of fine tuning in the parameter space of the Randall-Sundrum model. Within a 6-dimensional warped compactification scenario, with its own interesting phenomenological consequences, the parameters associated with the additional spatial direction can be used to eliminate the need for fine tuning. We examine the constraints on this model due to the 8 TeV LHC data and survey the parameter space that could be probed at the 14 TeV run of the LHC. We also identify the region of parameter space that is consistent with the recently reported excess in the diphoton channel in the 13 TeV data. Finally, as an alternative explanation for the observed excess, we discuss a scenario with brane-localized Einstein-Hilbert terms with Standard Model fields in the bulk.

    hep-phhep-exPramana(2017)·121 citations
18. 18*

    Explorations of two empirical formulae for fermion masses

    Guan-Hua Gao🇺🇸 · Nan Li🇨🇳

    Two empirical formulae for the lepton and quark masses (i.e. Kartavtsev's extended Koide formulae), $K_l=({\sum }_l{m}_l)/({\sum }_l\sqrt{m_l}{)}^2=2/3$ and $K_q=({\sum }_q{m}_q)/({\sum }_q\sqrt{m_q}{)}^2=2/3$, are explored in this paper. For the lepton sector, we show that $K_l=2/3$, only if the uncertainty of the tauon mass is relaxed to about $2\sigma$ confidence level, and the neutrino masses can consequently be extracted with the current experimental data. For the quark sector, the extended Koide formula should only be applied to the running quark masses, and $K_q$ is found to be rather insensitive to the renormalization effects in a large range of energy scales from GeV to $10^{12}$ GeV. However, $K_q$ is always slightly larger than $2/3$, but the discrepancy is merely about $5\%$.

    hep-phEPJC(2016)·6 citations
19. 19*

    Detectable Gravitational Waves from Very Strong Phase Transitions in the General NMSSM

    Stephan J. Huber🇬🇧 · Thomas Konstandin🇩🇪 · Germano Nardini🇩🇪 · Ingo Rues🇩🇪

    We study the general NMSSM with an emphasis on the parameter regions with a very strong first-order electroweak phase transition (EWPT). In the presence of heavy fields coupled to the Higgs sector, the analysis can be problematic due to the existence of sizable radiative corrections. In this paper we propose a subtraction scheme that helps to circumvent this problem. For simplicity we focus on a parameter region that is by construction hidden from the current collider searches. The analysis proves that (at least) in the identified parameter region the EWPT can be very strong and striking gravitational wave signals can be produced. The corresponding gravitational stochastic background can potentially be detected at the planned space-based gravitational wave observatory eLISA, depending on the specific experiment design that will be approved.

    hep-phastro-ph.COJCAP(2016)·99 citations
20. 20*

    The diphoton resonance as a gravity mediator of dark matter

    Chengcheng Han🇯🇵 · Hyun Min Lee🇰🇷 · Myeonghun Park🇰🇷 · Veronica Sanz🇬🇧

    We consider the possibility of interpreting the recently reported diphoton excess at 750 GeV as a spin-two massive particle (such as a Kaluza-Klein graviton in warped extra-dimensions) which serves as a mediator to Dark Matter via its gravitational couplings to the dark sector and to the Standard Model (SM). We model non-universal couplings of the resonance to gauge bosons in the SM and to Dark Matter as a function on their localization in the extra dimension. We find that scalar, fermion or vector dark matter can saturate the dark matter relic density by the annihilation of dark matter into a pair of the SM particles or heavy resonances, in agreement with the diphoton resonance signal strength. We check the compatibility of our hypothesis with other searches for the KK graviton. We show that the invisible decay rate of the resonance into a pair of dark matter is subdominant in the region of the correct relic density, hence leading to no constraints from the mono-jet bound at 8 TeV via the gluon coupling. We also discuss the kinematic features of the decay products of a KK graviton to distinguish the KK graviton from the SM backgrounds or a scalar particle interpretation of the diphoton resonance.

    hep-phhep-exPLB(2016)·175 citations
21. 21*

    Resonant mono Higgs at the LHC

    Lorenzo Basso🇫🇷

    In recent years, the production of a SM particle with large missing transverse momentum, dubbed mono-X searches, have gained increasing attention. After the discovery of the Higgs boson in 2012, the run-II of the LHC will now scrutinise its properties, looking for BSM physics. In particular, one could search for mono-Higgs signals, that are typically studied in models addressing dark matter. However, this signal can appear also in models addressing the neutrino masses, if additional heavier neutrinos with masses at the electroweak scale are present. The latter will couple to the SM neutrinos and the Higgs boson, yielding a type of mono-Higgs signal not considered for dark matter: the resonant production of a Higgs boson and missing energy. In this paper, we address the LHC exclusion power of the latter with dedicated detector simulations, and reinterpret it in a benchmark scenario for neutrino mass generation.

    hep-phJHEP(2016)·15 citations
22. 22*

    PDFs and Top Physics

    R.S. Thorne🇬🇧

    I present the results from the recent PDF4LHC study, and the resulting new recommendation for combining PDFs sets for LHC calculations. In order to put this into context I summarise continuing updates in PDFs. This includes improvements and recent updates of particular PDF sets due to theory improvements and a variety of new data sets, including most of the up-to-date LHC data. I will emphasise particular issues relevant for top physics.

    hep-phhep-exPoS(2016)·0 citations
23. 23*

    Strong-coupling effects in a plasma of confining gluons

    Wojciech Florkowski🇵🇱 · Radoslaw Ryblewski🇵🇱 · Nan Su🇩🇪 · Konrad Tywoniuk🇪🇸

    The plasma consisting of confining gluons resulting from the Gribov quantization of the SU(3) Yang-Mills theory is studied using non-equilibrium fluid dynamical framework. Exploiting the Bjorken symmetry and using linear response theory a general analytic expressions for the bulk and shear viscosity coefficients are derived. It is found that the considered system exhibits a number of properties similar to the strongly-coupled theories, where the conformality is explicitly broken. In particular, it is shown that, in the large temperature limit, bulk to shear viscosity ratio, scales linearly with the difference $1/3-c_s^2$, where $c_s$ is the speed of sound. Results obtained from the analysis are in line with the interpretation of the quark-gluon plasma as an almost perfect fluid.

    hep-phhep-thnucl-thNPA(2016)·3 citations
24. 24*

    Warm Dark Matter via Ultra-Violet Freeze-In: Reheating Temperature and Non-Thermal Distribution for Fermionic Higgs Portal Dark Matter

    John McDonald🇬🇧

    Warm dark matter (WDM) of order keV mass may be able to resolve the disagreement between structure formation in cold dark matter simulations and observations. The detailed properties of WDM will depend upon its energy distribution, in particular how it deviates from the thermal distribution usually assumed in WDM simulations. Here we focus on WDM production via the Ultra-Violet (UV) freeze-in mechanism, for the case of fermionic Higgs portal dark matter $\psi$ produced via the portal interaction $\bar{\psi }\psi H^{†}H/\Lambda$. We introduce a new method to simplify the computation of the non-thermal energy distribution of dark matter from freeze-in. We show that the non-thermal energy distribution from UV freeze-in is hotter than the corresponding thermal distribution and has the form of a Bose-Einstein distribution with a non-thermal normalization. The resulting range of dark matter fermion mass consistent with observations is 5-7 keV. The reheating temperature must satisfy $T_R\gtrsim 120$ GeV in order to account for the observed dark matter density when $m_{\psi }\approx 5$ keV, where the lower bound on $T_R$ corresponds to the limit where the fermion mass is entirely due to electroweak symmetry breaking via the portal interaction. The corresponding bound on the interaction scale is $\Lambda \gtrsim 6.0\times 10^9$ GeV.

    hep-phastro-ph.COJCAP(2016)·38 citations
25. 25*

    A Simple $U(1)$ Gauge Theory Explanation of the Diphoton Excess

    Spencer Chang🇺🇸

    The recent ATLAS and CMS diphoton resonance excesses are explored in a simple $U(1)$ gauge theory extension of the Standard Model where the resonance is the Higgs boson of the $U(1)$ symmetry breaking, $\varphi$. This particle couples to exotic quarks which, through loops, can produce a large enough rate to explain the excess. Due to the choice of $U(1)$ charges, flavor constraints are naturally suppressed, allowing arbitrary flavor violation in the decays of the new quarks to up-type quarks, modifying their signal topologies. An additional heavy quark in the model decays to the lighter exotic quark by emitting either $\varphi$ or the $U(1)$ gauge boson, $A_x$, giving extra signals containing diphoton and digluon resonances. Finally, the new Higgs can decay into $\gamma A_x$ and $Z{A}_x$, followed by $A_x$ decaying into Standard Model fermions through kinetic mixing. Thus, this model gives interesting modified signals to the general class of exotic quark models explaining the diphoton resonance.

    hep-phhep-exPRD(2016)·105 citations
26. 26*

    Axion dark matter in the post-inflationary Peccei-Quinn symmetry breaking scenario

    Andreas Ringwald🇩🇪 · Ken'ichi Saikawa🇩🇪

    We consider extensions of the Standard Model in which a spontaneously broken global chiral Peccei-Quinn (PQ) symmetry arises as an accidental symmetry of an exact $Z_N$ symmetry. For $N=9$ or $10$, this symmetry can protect the accion - the Nambu-Goldstone boson arising from the spontaneous breaking of the accidental PQ symmetry - against semi-classical gravity effects, thus suppressing gravitational corrections to the effective potential, while it can at the same time provide for the small explicit symmetry breaking term needed to make models with domain wall number $N_{\mathrm{DW}}>1$, such as the popular Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) model ($N_{\mathrm{DW}}=6$), cosmologically viable even in the case where spontaneous PQ symmetry breaking occurred after inflation. We find that $N=10$ DFSZ accions with mass $m_A\approx 3.5$-$4.2\mathrm{meV}$ can account for cold dark matter and simultaneously explain the hints for anomalous cooling of white dwarfs. The proposed helioscope International Axion Observatory - being sensitive to solar DFSZ accions with mass above a few meV - will decisively test this scenario.

    hep-phastro-ph.COPRD(2016)·146 citations
27. 27*

    The Inert Doublet Model and its extensions

    Maria Krawczyk🇵🇱 · Neda Darvishi🇵🇱 · Dorota Sokolowska🇵🇱

    The Inert Doublet Model and its extension with an additional complex singlet is considered. The CP violation aspects are analysed in the simplified case, with one SM-like Higgs doublet and a complex singlet.

    hep-phActa Phys.Polon.B(2016)·20 citations
28. 28*

    Combined analysis of effective Higgs portal dark matter models

    Ankit Beniwal🇦🇺 · Filip Rajec🇦🇺 · Christopher Savage🇸🇪 · Pat Scott🇬🇧 · Christoph Weniger🇳🇱 · Martin White🇦🇺 · Anthony G. Williams🇦🇺

    We combine and extend the analyses of effective scalar, vector, Majorana and Dirac fermion Higgs portal models of dark matter (DM), in which DM couples to the Standard Model (SM) Higgs boson via an operator of the form ${\mathcal{O}}_{\text{DM}}{H}^{†}H$. For the fermion models, we take an admixture of scalar $\overline{\psi }\psi$ and pseudoscalar $\overline{\psi }i{\gamma }_5\psi$ interaction terms. For each model, we apply constraints on the parameter space based on the Planck measured DM relic density and the LHC limits on the Higgs invisible branching ratio. For the first time, we perform a consistent study of the indirect detection prospects for these models based on the WMAP7/Planck observations of the cosmic microwave background, a combined analysis of 15 dwarf spheroidal galaxies by Fermi-LAT and the upcoming Cherenkov Telescope Array (CTA). We also perform a correct treatment of the momentum-dependent direct search cross section that arises from the pseudoscalar interaction term in the fermionic DM theories. We find, in line with previous studies, that current and future direct search experiments such as LUX and XENON1T can exclude much of the parameter space, and we demonstrate that a joint observation in both indirect and direct searches is possible for high mass weakly interacting massive particles. In the case of a pure pseudoscalar interaction of a fermionic DM candidate, future gamma-ray searches are the only class of experiment capable of probing the high mass range of the theory.

    hep-phastro-ph.COPRD(2016)·127 citations
29. 29*

    Mass of \emph{Y}(4140) in Bethe-Salpeter equation for quarks

    Xiaozhao Chen🇨🇳 · Xiaofu Lü🇨🇳 · Renbin Shi🇨🇳 · Xiurong Guo🇨🇳

    Using the general form of the Bethe-Salpeter wave functions for the bound states consisting of two vector fields given in our previous work, we investigate the molecular state composed of $D_s^{\ast +}$$D_s^{\ast -}$. However, for the SU(3) symmetry the component $D_s^{\ast +}$$D_s^{\ast -}$ is coupled with the other components $D^{\ast 0}$${\bar{D}}^{\ast 0}$ and $D^{\ast +}$$D^{\ast -}$. Then we interpret the internal structure of the observed \emph{Y}(4140) state as a mixed state of pure molecule states $D^{\ast 0}$${\bar{D}}^{\ast 0}$, $D^{\ast +}$$D^{\ast -}$ and $D_s^{\ast +}$$D_s^{\ast -}$ with quantum numbers $J^P=0^{+}$. In this paper, the operator product expansion is used to introduce the nonperturbative contribution from the vacuum condensates into the interaction between two heavy mesons. The calculated mass of \emph{Y}(4140) is consistent with the experimental value, and we conclude that it is a more reasonable scenario to explain the structure of Y (4140) as a mixture of pure molecule states.

    hep-ph19 citations
30. 30*

    Chiral Phase Transition in the Soft-Wall Model of AdS/QCD

    Kaddour Chelabi🇩🇿 · Zhen Fang🇨🇳 · Mei Huang🇨🇳 · Danning Li🇨🇳 · Yue-Liang Wu🇨🇳

    We investigate the chiral phase transition in the soft-wall model of AdS/QCD at zero chemical potential for two-flavor and three-flavor cases, respectively. We show that there is no spontaneous chiral symmetry breaking in the original soft-wall model. After detailed analysis, we find that in order to realize chiral symmetry breaking and restoration, both profiles for the scalar potential and the dilaton field are essential. The scalar potential determines the possible solution structure of the chiral condensate, except the mass term, it takes another quartic term for the two-flavor case, and for the three-flavor case, one has to take into account an extra cubic term due to the t'Hooft determinant interaction. The profile of the dilaton field reflects the gluodynamics, which is negative at a certain ultraviolet scale and approaches positive quadratic behavior at far infrared region. With this set-up, the spontaneous chiral symmetry breaking in the vacuum and its restoration at finite temperature can be realized perfectly. In the two-flavor case, it gives a second order chiral phase transition in the chiral limit, while the transition turns to be a crossover for any finite quark mass. In the case of three-flavor, the phase transition becomes a first order one in the chiral limit, while above sufficient large quark mass it turns to be a crossover again. This scenario agrees exactly with the current understanding on chiral phase transition from lattice QCD and other effective model studies.

    hep-phhep-lathep-thJHEP(2016)·88 citations
31. 31*

    Diphoton excess at 750 GeV: Singlet scalars confront triviality

    Indrani Chakraborty🇮🇳 · Anirban Kundu🇮🇳

    We suggest that the recently observed diphoton excess at 750 GeV comes from a quasi-degenerate bunch of gauge singlet scalars produced and decaying through one or more vector-like fermions. This explains the broad nature of the resonance, even though the decay is loop-mediated. At the same time, the model keeps the new Yukawa couplings in the perturbative region, which is necessary for the stability of the potential.

    hep-phPRD(2016)·98 citations
32. 32*

    Interpreting $750$ GeV Diphoton Excess with R-parity Violating Supersymmetry

    Ran Ding🇨🇳 · Li Huang🇨🇳 · Tianjun Li🇨🇳 · Bin Zhu🇨🇳

    We propose an supersymmetric explanation of the diphoton excess in the Minimal Supersymmetric Standard Model with the leptonic R-parity violation. Where the sneutrino serves as the 750 GeV resonance and produced through quark anti-quark annihilation. With introducing appropriate trilinear soft parameters, we show that the diphoton branching ratio is significantly enhanced compared with the conventional MSSM. The parameter space favored by diphoton excess strongly indicates the mass of smuon and stau fall into the range $375-410$ (375-480) GeV, which depending on the electroweakino masses. In addition, the $R$-parity-violating trilinear couplings involved with second generation quarks are both favored by compatibility of diphoton excess and low-energy constraints.

    hep-phInt.J.Mod.Phys.A(2017)·132 citations
33. 33*

    Scalar Explanation of Diphoton Excess at LHC

    Huayong Han🇨🇳 · Shaoming Wang🇨🇳 · Sibo Zheng🇨🇳

    Inspired by the diphoton signal excess observed in the latest data of 13 TeV LHC, we consider either a 750 GeV real scalar or pseudo-scalar responsible for this anomaly. We propose a concrete vector-like quark model, in which the vector-like fermion pairs directly couple to this scalar via Yukawa interaction. For this setting the scalar is mainly produced via gluon fusion, then decays at the one-loop level to SM diboson channels $gg,\gamma \gamma ,ZZ,WW$. We show that for the vector-like fermion pairs with exotic electric charges, such model can account for the diphoton excess and is consistent with the data of 8 TeV LHC simultaneously in the context of perturbative analysis.

    hep-phhep-exNPB(2016)·114 citations
34. 34*

    Implication of the 750 GeV diphoton resonance on two-Higgs-doublet model and its extensions with Higgs field

    Xiao-Fang Han🇨🇳 · Lei Wang🇨🇳

    We examine the implication of the 750 GeV diphoton resonance on the two-Higgs-doublet model imposing various theoretical and experimental constraints. The production rate of two-Higgs-doublet model is smaller than the cross section observed at the LHC by two order magnitude. In order to accommodate the 750 GeV diphoton resonance, we extend the two-Higgs-doublet model by introducing additional Higgs fields, and focus on two different extensions, an inert complex Higgs triplet and a real scalar septuplet. With the 125 GeV Higgs being agreement with the observed data, the production rate for the 750 GeV diphoton resonance can be enhanced to 0.6 fb for the former and 4.5 fb for the latter. The results of the latter are well consistent with the 750 GeV diphoton excess at the LHC.

    hep-phPRD(2016)·136 citations
35. 35*

    Exclusive processes with a leading neutron in $ep$ collisions

    V. P. Goncalves🇧🇷 · F. S. Navarra🇧🇷 · D. Spiering🇧🇷

    In this paper we extend the color dipole formalism to the study of exclusive processes associated with a leading neutron in $ep$ collisions at high energies. The exclusive $\rho$, $\varphi$ and $J/\Psi$ production, as well as the Deeply Virtual Compton Scattering, are analysed assuming a diffractive interaction between the color dipole and the pion emitted by the incident proton. We compare our predictions with the HERA data on $\rho$ production and estimate the magnitude of the absorption corrections. We show that the color dipole formalism is able to describe the current data. Finally, we present our estimate for the exclusive cross sections which can be studied at HERA and in future electron-proton colliders.

    hep-phhep-exnucl-thPRD(2016)·19 citations
36. 36*

    Oblique corrections from less-Higgsless models in warped space

    Hisaki Hatanaka🇰🇷

    The Higgsless model in warped extra dimension is reexamined. Dirichlet boundary conditions on the TeV brane are replaced with Robin boundary conditions which are parameterized by a mass parameter $M$. We calculate the Peskin-Takeuchi precision parameters $S$, $T$ and $U$ at tree level. We find that to satisfy the constraints on the precision parameters at $99\%$ [$95\%$] confidence level (CL) the first Kaluza-Klein excited $Z$ boson, $Z^{\prime }$, should be heavier than 5 TeV [8 TeV]. The Magnitude of $M$, which is infinitely large in the original model, should be smaller than 200 GeV (70 GeV) for the curvature of the warped space $R^{-1}=10^{16}$ GeV ($10^8$ GeV) at $95\%$ CL. If the Robin boundary conditions are induced by the mass terms localized on the TeV brane, from the $99\%$ [$95\%$] bound we find that the brane mass interactions account for more than $97\%$ [$99\%$] of the masses of $Z$ and $W$ bosons. Such a brane mass term is naturally interpreted as a vacuum expectation value of the Higgs scalar field in the standard model localized on the TeV brane. If so, the model can be tested by precise measurements of $HWW$, $HZZ$ couplings and search for 1st Kaluza-Klein excited states.

    hep-ph10 citations
37. 37*

    Aharonov-Bohm Phase in High Density Quark Matter

    Chandrasekhar Chatterjee🇯🇵 · Muneto Nitta🇯🇵

    Stable non-Abelian vortices, which are color magnetic flux tubes as well as superfluid vortices, are present in the color-flavor locked phase of dense quark matter with diquark condensations. We calculate the Aharanov-Bohm phases of charged particles, that is, electrons, muons, and color-flavor locked mesons made of tetraquarks around a non-Abelian vortex.

    hep-phhep-thPRD(2016)·21 citations
38. 38*

    Quark Flavor Mixings from Hierarchical Mass Matrices

    Rohit Verma🇮🇳 · Shun Zhou🇨🇳

    In this paper, we extend the Fritzsch ansatz of quark mass matrices while retaining their hierarchical structures and show that the main features of the Cabibbo-Kobayashi-Maskawa (CKM) matrix $V$, including $|V_{us}^{}|\simeq |V_{cd}^{}|$, $|V_{cb}^{}|\simeq |V_{ts}^{}|$ and $|V_{ub}^{}|/|V_{cb}^{}|<|V_{td}^{}|/|V_{ts}^{}|$, can be well understood. This agreement is observed especially when the mass matrices have non-vanishing $(1,3)$ and $(3,1)$ off-diagonal elements. The phenomenological consequences of these for the allowed texture content and gross structural features of `hierarchical' quark mass matrices are addressed from a model independent prospective under the assumption of factorizable phases in these. The approximate and analytical expressions of the CKM matrix elements are derived, and a detailed analysis reveals that such structures are in good agreement with the observed quark flavor mixing angles and the CP-violating phase at the $1\sigma$ level and call upon a further investigation of the realization of these structures from a top-down prospective.

    hep-phEPJC(2016)·9 citations
39. 39*

    Constituent-counting rule in photoproduction of hyperon resonances

    Wen-Chen Chang (Taiwan, Inst. Phys.)🇹🇼 · S. Kumano (KEK, Tsukuba and J-PARC, Tokai)🇯🇵 · Takayasu Sekihara (RCNP, Osaka U.)🇯🇵

    We analyze the CLAS data on the photoproduction of hyperon resonances, as well as the available data for the ground state $\Lambda$ and ${\Sigma }^0$ of the CLAS and SLAC-E84 collaborations, by considering constituent-counting rule suggested by perturbative QCD. The counting rule emerges as a scaling behavior of cross sections in hard exclusive reactions with large scattering angles, and it enables us to determine the number of elementary constituents inside hadrons. Therefore, it could be used as a new method for identifying internal constituents of exotic-hadron candidates. From the analyses of the $\gamma p\to K^{+}\Lambda$ and $K^{+}{\Sigma }^0$ reactions, we find that the number of the elementary constituents is consistent with $n_{\gamma }=1$, $n_p=3$, $n_{K^{+}}=2$, and $n_{\Lambda }=n_{{\Sigma }^0}=3$. Then, the analysis is made for the photoproductions of the hyperon resonances $\Lambda (1405)$, $\Sigma (1385{)}^0$, and $\Lambda (1520)$, where $\Lambda (1405)$ is considered to be a $\bar{K}N$ molecule and hence its constituent number could be five. However, we find that the current data are not enough to conclude the numbers of their constituent. It is necessary to investigate the higher-energy region at $\sqrt{s}>2.8$ GeV experimentally beyond the energy of the available CLAS data for counting the number of constituents clearly. We also mention that our results indicate energy dependence in the constituent number, especially for $\Lambda (1405)$. If an excited hyperon is a mixture of three-quark and five-quark states, the energy dependence of the scaling behavior could be valuable for finding its composition and mixture.

    hep-phhep-exnucl-exnucl-thPRD(2016)·24 citations
40. 40*

    Pion correlation functions in position space from chiral perturbation theory with resonance exchange

    Peter C. Bruns🇩🇪

    Explicit expressions for pion correlators are derived in position-space, employing Chiral Perturbation Theory (ChPT). Resonance exchange contributions are included to test the range of applicability of the leading-order ChPT expressions. The obtained results will be useful for a forthcoming Lattice-QCD study of double parton distributions in the pion.

    hep-phhep-lat1 citation
41. 41*

    Dyson-Schwinger equations and $\mathcal{N}=4$ SYM in Landau gauge

    Axel Maas🇦🇹 · Stefan Zitz🇦🇹

    $\mathcal{N}=4$ Super Yang-Mills theory is a highly constrained theory, and therefore a valuable tool to test the understanding of less constrained Yang-Mills theories. Our aim is to use it to test our understanding of both the Landau gauge beyond perturbation theory as well as truncations of Dyson-Schwinger equations in ordinary Yang-Mills theories. We derive the corresponding equations within the usual one-loop truncation for the propagators after imposing the Landau gauge. We find a conformal solution in this approximation, which surprisingly resembles many aspects of ordinary Yang-Mills theories. We furthermore identify which role the Gribov-Singer ambiguity in this context could play, should it exist in this theory.

    hep-phEPJC(2016)·1 citation
42. 42*

    A direct probe of the intrinsic charm content of the proton

    Tom Boettcher🇺🇸 · Philip Ilten🇺🇸 · Mike Williams🇺🇸

    Measurement of $Z$ bosons produced in association with charm jets $(Zc)$ in proton-proton collisions in the forward region provides a direct probe of a potential non-perturbative (intrinsic) charm component in the proton wave function. We provide a detailed study of the potential to measure $Zc$ production at the LHCb experiment in Runs 2 and 3 of the LHC. The sensitivity to valence-like (sea-like) intrinsic charm is predicted to be $⟨x{⟩}_{\mathrm{IC}}\gtrsim 0.3\%(1\%)$. The impact of intrinsic charm on Higgs production at the LHC, including $Hc$, is also discussed in detail.

    hep-phhep-exPRD(2016)·47 citations
43. 43*

    On the effect of time-dependent inhomogeneous magnetic fields in electron-positron pair production

    Christian Kohlfürst🇩🇪 · Reinhard Alkofer🇦🇹

    Electron-positron pair production in space- and time-dependent electromagnetic fields is investigated. Especially, the influence of a time-dependent, inhomogeneous magnetic field on the particle momenta and the total particle yield is analyzed for the first time. The role of the Lorentz invariant ${\mathbf{E}}^2-{\mathbf{B}}^2$, including its sign and local values, in the pair creation process is emphasized.

    hep-phPLB(2016)·36 citations
44. 44*

    Squarkonium, diquarkonium and octetonium at the LHC and their di-photon decays

    Ming-xing Luo🇨🇳 · Kai Wang🇨🇳 · Tao Xu🇨🇳 · Liangliang Zhang🇨🇳 · Guohuai Zhu🇨🇳

    Motivated by the recent di-photon excess by both ATLAS and CMS collaborations at the LHC, we systematically investigate the production and di-photon decay of onia formed by pair of all possible color exotic scalars in minimal extension. When such scalar massive meta-stable colored and charged (MMCC) particles are produced in pair near threshold, $\eta$ onium can be formed and decay into di-photon through annihilation as $pp\to \eta \to \gamma \gamma$. Squarkonium is formed by meta-stable squarks in supersymmetric models such as stoponium. Diquarkonium is formed by meta-stable color sextet diquarks which may be realized in the Pati-Salam model. Octetonium is formed by color octet scalars bosons as in the Manohar-Wise model. Stoponium prediction is much smaller than the required signal to account for the di-photon excess. Due to the enhancement factor from color and electric charge, predictions of diquarkonium and octetonium are of $\mathcal{O}$(10 fb) which are significantly greater than the stoponium prediction. Since the color enhancement also results in large production at the colliders, such light color exotic states of $\mathcal{O}$(375 GeV) suffer from severe direct search constraints. On the other hand, if their dominant decay mode involve top quark, they may be buried in the $t\bar{t}$ plus jets samples and can potentially be searched via $t+j$ resonance.

    hep-phhep-exPRD(2016)·104 citations
45. 45*

    Interpreting the 750 GeV Di-photon Resonance using photon-jets in Hidden-Valley-like models

    Jung Chang🇹🇼 · Kingman Cheung🇹🇼 · Chih-Ting Lu🇹🇼

    Motivated by the di-photon resonance recently reported by the ATLAS and CMS collaborations at $\sqrt{s}=13$ TeV, we interpret the resonance as a scalar boson $X(750)$ in hidden-valley-like models. The scalar boson $X$ can mix with the standard model Higgs boson and thus can be produced via gluon fusion. It then decays into a pair of very light hidden particles $Y$ of sub-GeV, each of which in turn decays to a pair of collimated ${\pi }^0$'s, and these two ${\pi }^0$'s decay into photons which then form photon-jets. A photon-jet ($\gamma$-jet) is a special feature that consists of a cluster of collinear photons from the decay of a fast moving light particle (sub-GeV). Because these photons inside the photon-jet are so collimated that it cannot be distinguished from a single photon, and so in the final state of the decay of $X(750)$ a pair of photon-jets look like a pair of single photons, which the experimentalists observed and formed the 750 GeV di-photon resonance. Prospects for the LHC Run-2 about other new and testable features are also discussed.

    hep-phhep-exPRD(2016)·124 citations
46. 46*

    Radion Candidate for the LHC Diphoton Resonance

    Debjyoti Bardhan🇮🇳 · Disha Bhatia🇮🇳 · Amit Chakraborty🇮🇳 · Ushoshi Maitra🇮🇳 · Sreerup Raychaudhuri🇮🇳 · Tousik Samui🇮🇳

    The recent observation of a modest excess in diphoton final states at the LHC, by both the ATLAS and CMS Collaborations, has sparked off the expected race among theorists to find the right explanation for this proto-resonance, assuming that the signal will survive and not prove to be yet another statistical fluctuation. We carry out a general analysis of this `signal' in the case of a scalar which couples only to pairs of gluons (for production) and photons (for diphoton decay modes), and establish that an explanation of the observed resonance, taken together with the null results of new physics searches in all the other channels, requires a scalar with rather exotic behaviour. We then demonstrate that a fairly simple-minded extension of the minimal Randall-Sundrum model can yield a radion candidate which might reproduce this exotic behaviour.

    hep-phhep-ex116 citations
47. 47*

    Radiative Neutrino Model with Inert Triplet Scalar

    Hiroshi Okada🇹🇼 · Yuta Orikasa🇰🇷

    We study a one-loop induced radiative neutrino model with an inert isospin triplet scalar field, in which we discuss current neutrino oscillation data, lepton flavor violations, muon anomalous magnetic moment, and a dark matter candidate. We show global analysis combining all the constraints, and briefly mention another possibility.

    hep-phPRD(2016)·39 citations
48. 48*

    The LHC 750 GeV diphoton excess in supersymmetry with gauged baryon and lepton numbers

    Tai-Fu Feng🇨🇳 · Xue-Qian Li🇨🇳 · Hai-Bin Zhang🇨🇳 · Shu-Min Zhao🇨🇳

    The significance of discovering the boson of 750 GeV is beyond finding a single heavy boson, because it may hint the location of the scale for new physics beyond the standard model which is the target of long-time exploration. There have been many models to explain the diphoton excess observed by the ATLAS and CMS collaborations and the BLMSSM is one of them. The BLMSSM is an extension of the minimal supersymmetric model where baryon and lepton numbers are local gauge symmetries. We analyze the decay channels $\Phi \to gg$, $\Phi \to \gamma \gamma$, $\Phi \to Z\gamma$, and $\Phi \to \bar{t}t,VV(V=Z,W)$ with the mass of the CP-odd scalar $\Phi =A_{{}_B}^0$ being around $750\mathrm{GeV}$ in this model. Within a certain parameter space, the scenario can account for the experimental data on the diphoton excess.

    hep-phhep-ex119 citations
49. 49*

    S-wave nonleptonic hyperon decays and ${\Xi }_b^{-}\to {\pi }^{-}{\Lambda }_b$

    Michael Gronau🇮🇱 · Jonathan L. Rosner🇺🇸

    The decay ${\Xi }_b^{-}\to {\pi }^{-}{\Lambda }_b$ has recently been observed by the LHCb Collaboration at CERN. In contrast to most weak decays of $b$-flavored baryons, this process involves the decay of the strange quark in ${\Xi }_b$, and thus has features in common with nonleptonic weak decays of hyperons. Thanks to the expected pure S-wave nature of the decay in question in the heavy $b$ quark limit, we find that its amplitude may be related to those for S-wave nonleptonic decays of $\Lambda$, $\Sigma$, and $\Xi$ in a picture inspired by duality. The calculated branching fraction $\mathcal{B}({\Xi }_b^{-}\to {\pi }^{-}{\Lambda }_b)=(6.3\pm 4.2)\times 10^{-3}$ is consistent with the range allowed in the LHCb analysis. The error is dominated by an assumed 30\% uncertainty in the amplitude due to possible U(3) violation. A more optimistic view based on sum rules involving nonleptonic hyperon decay S-wave amplitudes reduces the error on the branching fraction to $2.0\times 10^{-3}$.

    hep-phhep-exPRD(2016)·13 citations
50. 50*

    On light dilaton extensions of the Standard Model

    Eugenio Megias🇩🇪 · Oriol Pujolas🇪🇸 · Mariano Quiros🇪🇸

    We discuss the presence of a light dilaton in Conformal Field Theories deformed by a single scalar operator, in the holographic realization consisting of confining Renormalization Group flows. Then, we apply this formalism to study the extension of the Standard Model with a light dilaton in a 5D warped model. We study the spectrum of scalar and vector perturbations, compare the model predictions with Electroweak Precision Tests and find the corresponding bounds for the lightest modes. Finally, we analyze the possibility that the Higgs resonance found at the LHC be a dilaton.

    hep-phhep-thEPJ Web Conf.(2016)·16 citations
51. 51*

    No deconfinement in QCD ?

    L. Ya. Glozman🇦🇹

    At a critical temperature QCD in the chiral limit undergoes a chiral restoration phase transition. Above the phase transition the quark condensate vanishes. The Banks-Casher relation connects the quark condensate to a density of the near-zero modes of the Dirac operator. In the Nambu-Goldstone mode the quasi-zero modes condense around zero, \lambda \rightarrow 0, and provide a nonvanishing quark condensate. The chiral restoration phase transition implies that above the critical temperature there is no any longer a condensation of the Dirac modes around zero. If a U(1)_A symmetry is also restored and a gap opens in the Dirac spectrum then the Euclidean correlation functions are SU(2N_f) \supset SU(N_f)_L \times SU(N_f)_R \times U(1)_A- symmetric. This symmetry implies that a free (deconfined) propagation of quarks in Minkowski space-time that perturbatively interact with unconfined gluons is impossible. This means that QCD above the critical temperature is not of a quark-gluon plasma origin and has a more complicated structure.

    hep-phhep-lathep-th5 citations
52. 52*

    A natural Coleman-Weinberg theory explains the diphoton excess

    Oleg Antipin🇭🇷 · Matin Mojaza🇸🇪 · Francesco Sannino🇩🇰

    It is possible to delay the hierarchy problem, by replacing the standard Higgs-sector by the Coleman-Weinberg mechanism, and at the same time ensure perturbative naturalness through the so-called Veltman conditions. As we showed in a previous study, minimal models of this type require the introduction of an extra singlet scalar further coupled to new fermions. In this constrained setup the Higgs mass was close to the observed value and the new scalar mass was below a TeV scale. Here we first extend the previous analysis by taking into account the important difference between running mass and pole mass of the scalar states. We then investigate whether these theories can account for the 750 GeV excess in diphotons observed by the LHC collaborations. New QCD-colored fermions in the TeV mass range coupled to the new scalar state are needed to describe the excess. We further show, by explicit computation of the running of the couplings, that the model is under perturbative control till just above the masses of the heaviest states of the theory. We further suggest related testable signatures and thereby show that the LHC experiments can test these models.

    hep-phPRD(2016)·102 citations
53. 53*

    750 GeV Diphoton Resonance, 125 GeV Higgs and Muon g-2 Anomaly in Deflected Anomaly Mediation SUSY Breaking Scenario

    Fei Wang🇨🇳 · Lei Wu🇦🇺 · Jin Min Yang🇨🇳 · Mengchao Zhang🇨🇳

    We propose to interpret the 750 GeV diphoton excess in deflected anomaly mediation supersymmetry breaking scenarios, which can naturally predict couplings between a singlet field and vector-like messengers. The CP-even scalar component (S) of the singlet field can serve as the 750 GeV resonance. The messenger scale, which is of order the gravitino scale, can be as light as F_\phi \sim {\cal O}(10) TeV when the messenger species N_F and the deflection parameter d are moderately large. Such messengers can induce the large loop decay process S \to \gamma\gamma. Our results show that such a scenario can successfully accommodate the 125 GeV Higgs boson, the 750 GeV diphoton excess and the muon g-2 without conflicting with the LHC constraints. We also comment on the possible explanations in the gauge mediation supersymmetry breaking scenario.

    hep-phPLB(2016)·136 citations
54. 54*

    Predicting the Sparticle Spectrum from GUTs via SUSY Threshold Corrections with SusyTC

    Stefan Antusch🇨🇭 · Constantin Sluka🇨🇭

    Grand Unified Theories (GUTs) can feature predictions for the ratios of quark and lepton Yukawa couplings at high energy, which can be tested with the increasingly precise results for the fermion masses, given at low energies. To perform such tests, the renormalization group (RG) running has to be performed with sufficient accuracy. In supersymmetric (SUSY) theories, the one-loop threshold corrections (TC) are of particular importance and, since they affect the quark-lepton mass relations, link a given GUT flavour model to the sparticle spectrum. To accurately study such predictions, we extend and generalize various formulas in the literature which are needed for a precision analysis of SUSY flavour GUT models. We introduce the new software tool SusyTC, a major extension to the Mathematica package REAP, where these formulas are implemented. SusyTC extends the functionality of REAP by a full inclusion of the (complex) MSSM SUSY sector and a careful calculation of the one-loop SUSY threshold corrections for the full down-type quark, up-type quark and charged lepton Yukawa coupling matrices in the electroweak-unbroken phase. Among other useful features, SusyTC calculates the one-loop corrected pole mass of the charged (or the CP-odd) Higgs boson as well as provides output in SLHA conventions, i.e. the necessary input for external software, e.g. for performing a two-loop Higgs mass calculation. We apply SusyTC to study the predictions for the parameters of the CMSSM (mSUGRA) SUSY scenario from the set of GUT scale Yukawa relations $y_e/y_d=-1/2$, $y_{\mu }/y_s=6$, and $y_{\tau }/y_b=-3/2$, which has been proposed recently in the context of SUSY GUT flavour models.

    hep-phJHEP(2016)·20 citations
55. 55*

    Interpreting the 750 GeV diphoton excess by the singlet extension of the Manohar-Wise Model

    Junjie Cao🇨🇳 · Chengcheng Han🇯🇵 · Liangliang Shang🇨🇳 · Wei Su🇨🇳 · Jin Min Yang🇨🇳 · Yang Zhang🇨🇳

    The evidence of a new scalar particle $X$ from the 750 GeV diphoton excess, and the absence of any other signal of new physics at the LHC so far suggest the existence of new colored scalars, which may be moderately light and thus can induce sizable $Xgg$ and $X\gamma \gamma$ couplings without resorting to very strong interactions. Motivated by this speculation, we extend the Manohar-Wise model by adding one gauge singlet scalar field. The resulting theory then predicts one singlet dominated scalar $\varphi$ as well as three kinds of color-octet scalars, which can mediate through loops the $\varphi gg$ and $\varphi \gamma \gamma$ interactions. After fitting the model to the diphoton data at the LHC, we find that in reasonable parameter regions the excess can be explained at $1\sigma$ level by the process $gg\to \varphi \to \gamma \gamma$, and the best points predict the central value of the excess rate with ${\chi }_{min}^2=2.32$, which corresponds to a $p$-value of $0.68$. We also consider the constraints from various LHC Run I signals, and we conclude that, although these constraints are powerful in excluding the parameter space of the model, the best points are still experimentally allowed.

    hep-phPLB(2016)·119 citations
56. 56*

    Diphoton and Dark Matter from Cascade Decay

    Fa Peng Huang🇨🇳 · Chong Sheng Li🇨🇳 · Ze Long Liu🇨🇳 · Yan Wang🇨🇳

    We propose a simplified model to study the possible new heavy diphoton resonance from cascade decay of a heavier particle at colliders, which may be related to the dark matter or other new physics beyond the standard model. Model-independent constraints and predictions on the allowed couplings for generating the observed diphoton data are studied in detail. We demonstrate that this scenario can be tested by the possible four-photon signal or the $WW/ZZ/Z\gamma$ resonances. Meanwhile, this cascade decay scenario also provides us with the dark matter candidates, which is consistent with the observed dark matter relic density.

    hep-phPRD(2016)·127 citations
57. 57*

    Improved variational approach to QCD in Coulomb gauge

    P. Vastag🇩🇪 · H. Reinhardt🇩🇪 · D. Campagnari🇩🇪

    The variational approach to QCD in Coulomb gauge developed previously by the Tübingen group is improved by enlarging the space of quark trial vacuum wave functionals through a new Dirac structure in the quark-gluon coupling. Our ansatz for the quark vacuum wave functional ensures that all linear divergences cancel in the quark gap equation resulting from the minimization of the energy calculated to two-loop order. The logarithmic divergences are absorbed in a renormalized coupling which is adjusted to reproduce the phenomenological value of the quark condensate. We also unquench the gluon propagator and show that the unquenching effects are generally small and amount to a small reduction in the mid-momentum regime.

    hep-phhep-thPRD(2016)·29 citations
58. 58*

    Supersymmetric $SO(10)$-inspired leptogenesis and a new $N_2$-dominated scenario

    Pasquale Di Bari🇬🇧 · Michele Re Fiorentin🇬🇧

    We study the supersymmetric extension of $SO(10)$-inspired thermal leptogenesis showing the constraints on neutrino parameters and on the reheat temperature $T_{\mathrm{RH}}$ that derive from the condition of successful leptogenesis from next-to-lightest right handed (RH) neutrinos ($N_2$) decays and the more stringent ones when independence of the initial conditions (strong thermal leptogenesis) is superimposed. In the latter case, the increase of the lightest right-handed neutrino ($N_1$) decay parameters helps the wash-out of a pre-existing asymmetry and constraints relax compared to the non-supersymmetric case. We find significant changes especially in the case of large $\tan \beta$ values $(\gtrsim 15)$. In particular, for normal ordering, the atmospheric mixing angle can now be also maximal. The lightest (ordinary) neutrino mass is still constrained within the range $10\lesssim m_1/\mathrm{meV}\lesssim 30$ (corresponding to $75\lesssim {\sum }_i{m}_i/\mathrm{meV}\lesssim 120$). Inverted ordering is still disfavoured, but an allowed region satisfying strong thermal leptogenesis opens up at large $\tan \beta$ values. We also study in detail the lower bound on $T_{\mathrm{RH}}$ finding $T_{\mathrm{RH}}\gtrsim 1\times 10^{10}\mathrm{GeV}$ independently of the initial $N_2$ abundance. Finally, we propose a new $N_2$-dominated scenario where the $N_1$ mass is lower than the sphaleron freeze-out temperature. In this case there is no $N_1$ wash-out and we find $T_{\mathrm{RH}}\gtrsim 1\times 10^9\mathrm{GeV}$. These results indicate that $SO(10)$-inspired thermal leptogenesis can be made compatible with the upper bound from the gravitino problem, an important result in light of the role often played by supersymmetry in the quest of a realistic model of fermion masses.

    hep-phJCAP(2016)·23 citations
59. 59*

    Scalar resonance at 750 GeV as composite of heavy vector-like fermions

    Wei Liao🇨🇳 · Han-qing Zheng🇨🇳

    We study a model of scalars which includes both the SM Higgs and a scalar singlet as composites of heavy vector-like fermions. The vector-like fermions are bounded by the super-strong four-fermion interactions. The scalar singlet decays to SM vector bosons through loop of heavy vector-like fermions. We show that the surprisingly large production cross section of di-photon events at 750 GeV resonance and the odd decay properties can all be explained. This model serves as a good model for both SM Higgs and a scalar resonance at 750 GeV.

    hep-phhep-exCommun.Theor.Phys.(2016)·85 citations
60. 60*

    Warped Seesaw is Physically Inverted

    Kaustubh Agashe🇺🇸 · Sungwoo Hong🇺🇸 · Luca Vecchi🇮🇹

    Warped extra dimensions can address both the Planck-weak and flavor hierarchies of the Standard Model (SM). In this paper we discuss the SM neutrino mass generation in a scenario in which a SM singlet bulk fermion - coupled to the Higgs and the lepton doublet near the IR brane - is given a Majorana mass of order the Planck scale on the UV brane. Despite the resemblance to a type I seesaw mechanism, a careful investigation based on the mass basis for the singlet 4D modes reveals a very different picture. Namely, the SM neutrino masses are generated dominantly by the exchange of the TeV-scale mass eigenstates of the singlet, that are pseudo-Dirac and have a sizable Higgs- induced mixing with the SM doublet neutrino: remarkably, in warped 5D models the anticipated type I seesaw morphs into a natural realization of the so-called "inverse" seesaw. This understanding uncovers an intriguing and direct link between neutrino mass generation (and possibly leptogenesis) and TeV-scale physics. We also perform estimates using the dual CFT picture of our framework, which back-up our 5D calculation.

    hep-phPRD(2016)·33 citations
61. 61*

    Static electromagnetic moments and lepton decay constant of the $\rho$-meson in the instant form of relativistic quantum mechanics

    Alexander Krutov (Samara State University)🇷🇺 · Roman Polezhaev (Samara State University)🇷🇺 · Vadim Troitsky (D.V. Skobeltsyn Institute of Nuclear Physics, M. V. Lomonosov Moscow State University)🇷🇺

    The relativistic calculations of the electromagnetic form factors, static moments and lepton decay constant of the $\rho$-meson are given in the framework of the instant form of the relativistic quantum mechanics with different model wave functions. The modified impulse approximation (MIA) is used for the electroweak current operator. MIA provides Lorentz covariance and conservation law for current operators. The developed approach gives the nonzero quadrupole moment due to the relativistic Wigner spin rotation in the $S$-state of the quarks in $\rho$-meson

    hep-phquant-ph0 citations
62. 62*

    Radiative decays $V\to P{\gamma }^{\ast }$ in the instant form of relativistic quantum mechanics

    Alexander Krutov (Samara State University)🇷🇺 · Roman Polezhaev (Samara State University)🇷🇺 · Vadim Troitsky (D.V. Skobeltsyn Institute of Nuclear Physics, M. V. Lomonosov Moscow State University)🇷🇺

    Calculations of form factor for the radiative decays $V\to P{\gamma }^{\ast }$ process are performed in the framework of an instant form of relativistic quantum mechanics. The electromagnetic current operator for this decay is constructed. The transition form factor is obtained in the so called relativistic modified impulse approximation (MIA). The current operator satisfies the conditions of Lorentz-covariance and current conservation in MIA. The results of the calculations are compared with the analogous results in the light-front dynamics and in the model of vector meson dominance

    hep-phhep-thquant-ph0 citations
63. 63*

    Neutrino mixing and CP violation from Dirac-Majorana mixing

    Junpei Harada🇯🇵

    We consider a minimal condition that predicts the 1-3 lepton mixing angle ${\theta }_{13}\simeq {\theta }_{\mathrm{C}}/\sqrt{2}$ with ${\theta }_{\mathrm{C}}$ the Cabibbo angle, and give the improved prediction of ${\theta }_{13}$. In the case of normal mass ordering, the theoretical value of ${\theta }_{13}$ is predicted as ${\theta }_{13}=8.6^{\circ }$, which is in good agreement with the current global best fit. In the case of inverted mass ordering, the theoretical value is predicted as ${\theta }_{13}=9.7^{\circ }$, which is far from the current global best fit. We also study the leptonic CP violation. We show that any values of the leptonic Dirac CP phase ${\delta }_{\mathrm{CP}}$ can be obtained by fine tuning. Without fine tuning, $|\sin {\delta }_{\mathrm{CP}}|$ should be very small, typically of $\mathcal{O}({\lambda }^2)$ where $\lambda \equiv \sin {\theta }_{\mathrm{C}}$. Furthermore, a model-independent measure of CP violation is proposed, which is applicable to any flavor models.

    hep-ph0 citations
64. 64*

    On the validity of the perturbative description of axions during inflation

    Ricardo Z. Ferreira🇩🇰 · Jonathan Ganc🇩🇰 · Jorge Noreña🇨🇭 · Martin S. Sloth🇩🇰

    Axions play a central role in many realizations of large field models of inflation and in recent alternative mechanisms for generating primordial tensor modes in small field models. If these axions couple to gauge fields, the coupling produces a tachyonic instability that leads to an exponential enhancement of the gauge fields, which in turn can decay into observable scalar or tensor curvature perturbations. Thus, a fully self-consistent treatment of axions during inflation is important, and in this work we discuss the perturbative constraints on axions coupled to gauge fields. We show how the recent proposal of generating tensor modes through these alternative mechanisms is in tension with perturbation theory in the in-in formalism. Interestingly, we point out that the constraints are parametrically weaker than one would estimate based on naive power counting of propagators of the gauge field. In the case of non-Abelian gauge fields, we derive new constraints on the size of the gauge coupling, which apply also in certain models of natural large field inflation, such as alignment mechanisms.

    ↳ astro-ph.COhep-phhep-thJCAP(2016)·94 citations
65. 65*

    Screening of Nucleon Electric Dipole Moments in Nuclei

    Satoru Inoue🇺🇸 · Vladimir Gudkov🇺🇸 · Matthias R. Schindler🇺🇸 · Young-Ho Song🇰🇷

    A partial screening of nucleon electric dipole moments (EDMs) in nuclear systems, which is related to the Schiff mechanism known for neutral atomic systems, is discussed. It is shown that the direct contribution from the neutron EDM to the deuteron EDM is partially screened by about 1% in a zero-range approximation calculation.

    ↳ nucl-thhep-phPRC(2016)·6 citations
66. 66*

    Correlated fluctuations near the QCD critical point

    Lijia Jiang🇨🇳 · Pengfei Li🇨🇳 · Huichao Song (Peking U.)🇨🇳

    In this paper, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy dependent cumulant $C_4$ and $\kappa {\sigma }^2$ of net protons through tuning the related parameters. However, the calculated $C_2$ and $C_3$ with both Poisson and Binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. In order to qualitatively and quantitatively describe the experimental data, the dynamical critical fluctuations and more realistic non-critical fluctuation baselines should be investigated in the near future.

    ↳ nucl-thhep-phnucl-exPRC(2016)·69 citations
67. 67*

    Is the Effective Field Theory of Dark Energy Effective?

    Eric V. Linder🇺🇸 · Gizem Sengör🇺🇸 · Scott Watson🇺🇸

    The effective field theory of cosmic acceleration systematizes possible contributions to the action, accounting for both dark energy and modifications of gravity. Rather than making model dependent assumptions, it includes all terms, subject to the required symmetries, with four (seven) functions of time for the coefficients. These correspond respectively to the Horndeski and general beyond Horndeski class of theories. We address the question of whether this general systematization is actually effective, i.e. useful in revealing the nature of cosmic acceleration when compared with cosmological data. The answer is no and yes: {\it there is no simple time dependence of the free functions} -- assumed forms in the literature are poor fits, but one can derive some general characteristics in early and late time limits. For example, we prove that the gravitational slip must restore to general relativity in the de Sitter limit of Horndeski theories, and why it doesn't more generally. We also clarify the relation between the tensor and scalar sectors, and its important relation to observations; in a real sense the expansion history $H(z)$ or dark energy equation of state $w(z)$ is $1/5$ or less of the functional information! In addition we discuss the de Sitter, Horndeski, and decoupling limits of the theory utilizing Goldstone techniques.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2016)·71 citations
68. 68*

    Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions

    Chiara Caprini🇫🇷 · Mark Hindmarsh🇬🇧 · Stephan Huber🇬🇧 · Thomas Konstandin🇩🇪 · Jonathan Kozaczuk🇨🇦 · Germano Nardini🇨🇭 · Jose Miguel No🇬🇧 · Antoine Petiteau🇫🇷 · Pedro Schwaller🇩🇪 · Geraldine Servant🇩🇪 · David J. Weir🇳🇴

    We investigate the potential for the eLISA space-based interferometer to detect the stochastic gravitational wave background produced by strong first-order cosmological phase transitions. We discuss the resulting contributions from bubble collisions, magnetohydrodynamic turbulence, and sound waves to the stochastic background, and estimate the total corresponding signal predicted in gravitational waves. The projected sensitivity of eLISA to cosmological phase transitions is computed in a model-independent way for various detector designs and configurations. By applying these results to several specific models, we demonstrate that eLISA is able to probe many well-motivated scenarios beyond the Standard Model of particle physics predicting strong first-order cosmological phase transitions in the early Universe.

    ↳ astro-ph.COgr-qchep-phJCAP(2016)·1272 citations
69. 69*

    Does non-monotonic behavior of directed flow signal the onset of deconfinement?

    Yasushi Nara🇯🇵 · Akira Ohnishi🇯🇵

    We investigate the effects of nuclear mean-field as well as the formation and decay of nuclear clusters on the directed flow $v_1$ in high energy nucleus-nucleus collisions from $\sqrt{s_{NN}}=7.7$ GeV to 27 GeV incident energies within a transport model. Specifically, we use the JAM transport model in which potentials are implemented based on the framework of the relativistic quantum molecular dynamics. Our approach reproduces the rapidity dependence of directed flow data up to $\sqrt{s_{NN}}\approx 8$ GeV showing the significant importance of mean-field. However, the slopes of $d{v}_1/dy$ at mid-rapidity are calculated to be positive at $\sqrt{s_{NN}}=11.7$ and 19.6 GeV, and becomes negative above 27 GeV. Thus the result from the JAM hadronic transport model with nuclear mean-field approach is incompatible with the data. Therefore within our approach, we conclude that the excitation function of the directed flow cannot be explained by the hadronic degree of freedom alone.

    ↳ nucl-thhep-phnucl-exNPA(2016)·11 citations
70. 70*

    Extracting shear viscosity of the Quark Gluon Plasma in the presence of bulk viscosity

    Jacquelyn Noronha-Hostler🇺🇸

    One of the most remarkable features of the Quark Gluon Plasma is its nearly perfect fluidity behavior indicated by the small shear viscosity to entropy density ratio obtained from fitting relativistic viscous hydrodynamics flow harmonics to experimental data. In recent years, bulk viscosity has also been considered in the context of event-by-event relativistic hydrodynamics and it has been found to have a non-trivial interplay with shear viscosity. In this paper some of the issues are discussed that require further work when extracting the shear viscosity to entropy density ratio in the presence of a non-zero bulk viscosity.

    ↳ nucl-thhep-ph11 citations
71. 71*

    On post-inflation validity of perturbation theory in Horndeski scalar-tensor models

    Cristiano Germani🇪🇸 · Nina Kudryashova🇩🇪 · Yuki Watanabe🇯🇵

    By using the newtonian gauge, we re-confirm that, as in the minimal case, the re-scaled Mukhanov-Sasaki variable is conserved leading to a constraint equation for the Newtonian potential. However, conversely to the minimal case, in Horndeski theories, the super-horizon Newtonian potential can potentially grow to very large values after inflation exit. If that happens, inflationary predictability is lost during the oscillating period. When this does not happen, the perturbations generated during inflation can be standardly related to the CMB, if the theory chosen is minimal at low energies. As a concrete example, we analytically and numerically discuss the new Higgs inflationary case. There, the Inflaton is the Higgs boson that is non-minimally kinetically coupled to gravity. During the high-energy part of the post-inflationary oscillations, the system is anisotropic and the Newtonian potential is largely amplified. Thanks to the smallness of today's amplitude of curvature perturbations, however, the system stays in the linear regime, so that inflationary predictions are not lost. At low energies, when the system relaxes to the minimal case, the anisotropies disappear and the Newtonian potential converges to a constant value. We show that the constant value to which the Newtonian potential converges is related to the frozen part of curvature perturbations during inflation, precisely like in the minimal case.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2016)·11 citations
72. 72*

    Plasma dark matter direct detection

    Jackson D. Clarke🇦🇺 · Robert Foot🇦🇺

    Dark matter in spiral galaxies like the Milky Way may take the form of a dark plasma. Hidden sector dark matter charged under an unbroken $U(1{)}^{\prime }$ gauge interaction provides a simple and well defined particle physics model realising this possibility. The assumed $U(1{)}^{\prime }$ neutrality of the Universe then implies (at least) two oppositely charged dark matter components with self-interactions mediated via a massless "dark photon" (the $U(1{)}^{\prime }$ gauge boson). In addition to nuclear recoils such dark matter can give rise to keV electron recoils in direct detection experiments. In this context, the detailed physical properties of the dark matter plasma interacting with the Earth is required. This is a complex system, which is here modelled as a fluid governed by the magnetohydrodynamic equations. These equations are numerically solved for some illustrative examples, and implications for direct detection experiments discussed. In particular, the analysis presented here leaves open the intriguing possibility that the DAMA annual modulation signal is due primarily to electron recoils (or even a combination of electron recoils and nuclear recoils). The importance of diurnal modulation (in addition to annual modulation) as a means of probing this kind of dark matter is also emphasised.

    ↳ astro-ph.GAhep-phJCAP(2016)·26 citations
73. 73*

    An estimate of the bulk viscosity of the hadronic medium

    Golam Sarwar🇮🇳 · Sandeep Chatterjee🇮🇳 · Jan-e Alam🇮🇳

    The bulk viscosity ($\zeta$) of the hadronic medium has been estimated within the ambit of the Hadron Resonance Gas (HRG) model including the Hagedorn density of states. The HRG thermodynamics within a grand canonical ensemble provides the mean hadron number as well as its fluctuation. The fluctuation in the chemical composition of the hadronic medium in the grand canonical ensemble can result in non-zero divergence of the hadronic fluid flow velocity, allowing us to estimate the $\zeta$ of the hadronic matter upto a relaxation time. We study the influence of the hadronic spectrum on $\zeta$ and find its correlation with the conformal symmetry breaking (CSB) measure, $ϵ-3P$. We estimate $\zeta$ along the contours with constant, $S/N_B$ (total entropy/net baryon number) in the $T-\mu$ plane (temperature-baryonic chemical potential) for $S/N_B=30,45$ and 300. We also assess the value of $\zeta$ on the chemical freezeout curve for various centre of mass energy ($\sqrt{s_{NN}}$) and find that the bulk viscosity to entropy density ratio, $\zeta /s$ is larger at FAIR than LHC energies.

    ↳ nucl-thhep-phJ.Phys.G(2017)·17 citations
74. 74*

    Conical singularities and the Vainshtein screening in full GLPV theories

    Ryotaro Kase🇯🇵 · Shinji Tsujikawa🇯🇵 · Antonio De Felice🇯🇵

    In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, it is known that the conical singularity arises at the center of a spherically symmetric body ($r=0$) in the case where the parameter ${\alpha }_{\mathrm{H}4}$ characterizing the deviation from the Horndeski Lagrangian $L_4$ approaches a non-zero constant as $r\to 0$. We derive spherically symmetric solutions around the center in full GLPV theories and show that the GLPV Lagrangian $L_5$ does not modify the divergent property of the Ricci scalar $R$ induced by the non-zero ${\alpha }_{\mathrm{H}4}$. Provided that ${\alpha }_{\mathrm{H}4}=0$, curvature scalar quantities can remain finite at $r=0$ even in the presence of $L_5$ beyond the Horndeski domain. For the theories in which the scalar field $\varphi$ is directly coupled to $R$, we also obtain spherically symmetric solutions inside/outside the body to study whether the fifth force mediated by $\varphi$ can be screened by non-linear field self-interactions. We find that there is one specific model of GLPV theories in which the effect of $L_5$ vanishes in the equations of motion. We also show that, depending on the sign of a $L_5$-dependent term in the field equation, the model can be compatible with solar-system constraints under the Vainshtein mechanism or it is plagued by the problem of a divergence of the field derivative in high-density regions.

    ↳ gr-qcastro-ph.COhep-phhep-thJCAP(2016)·19 citations
75. 75*

    Photon and dilepton production at the Facility for Antiproton and Ion Research and the beam energy scan program at the Relativistic Heavy-Ion Collider using coarse-grained microscopic transport simulations

    Stephan Endres🇩🇪 · Hendrik van Hees🇩🇪 · Marcus Bleicher🇩🇪

    We present calculations of dilepton and photon spectra for the energy range $E_{\text{lab}}=2-35$ $A$GeV which will be available for the Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-Proton and Ion Research (FAIR). The same energy regime will also be covered by phase II of the Beam Energy Scan at the Relativistic Heavy-Ion Collider (RHIC-BES). Coarse-grained dynamics from microscopic transport calculations of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to determine temperature and chemical potentials, which allows for the use of dilepton and photon-emission rates from equilibrium quantum-field theory calculations. The results indicate that non-equilibrium effects, the presence of baryonic matter and the creation of a deconfined phase might show up in specific manners in the measurable dilepton invariant mass spectra and in the photon transverse momentum spectra. However, as the many influences are difficult to disentangle, we argue that the challenge for future measurements of electromagnetic probes will be to provide a high precision with uncertainties much lower than in previous experiments. Furthermore, a systematic study of the whole energy range covered by CBM at FAIR and RHIC-BES is necessary to discriminate between different effects, which influence the spectra, and to identify possible signatures of a phase transition.

    ↳ nucl-thhep-phPRC(2016)·35 citations
76. 76*

    SIDIS transverse spin azimuthal asymmetries at COMPASS: Multidimensional analysis

    Bakur Parsamyan🇮🇹

    Exploration of transverse spin structure of the nucleon via study of the spin (in)dependent azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan (DY) reactions is one of the main aspects of the broad physics program of the COMPASS experiment (CERN, Switzerland). In past decade COMPASS has collected a considerable amount of polarized deuteron and proton SIDIS data, while recent 2014 and 2015 runs were dedicated to the Drell-Yan measurements. Results on SIDIS azimuthal effects provided so far by COMPASS play an important role in general understanding of the three-dimensional nature of the nucleon. Giving access to the entire "twist-2" set of transverse momentum dependent (TMD) parton distribution functions (PDFs) and fragmentation functions (FFs) COMPASS data are being widely used in phenomenological analyses and experimental data fits. Recent unique and first ever x-$Q^2$-z-pT multidimensional results for transverse spin asymmetries obtained by COMPASS serve as a direct and unprecedented input for one of the hottest topics in the field of spin-physics: the TMD $Q^2$-evolution related studies. In addition, extraction of the Sivers and all other azimuthal effects from first ever polarized Drell-Yan data collected recently by COMPASS will reveal another side of the spin-puzzle clarifying the link between SIDIS and Drell-Yan branches. This will be a unique possibility to test predicted universality and key-features of TMD PDFs using essentially the same experimental setup and exploring the same kinematical domain. In this review main focus will be given to the very recent results from COMPASS multi-dimensional analysis of transverse spin asymmetries and to the physics aspects of COMPASS polarized Drell-Yan program.

    ↳ hep-exhep-phPoS(2015)·3 citations
77. 77*

    Extending the truncated Dyson-Schwinger equation to finite temperatures

    S. M. Dorkin🇷🇺 · M. Viebach🇩🇪 · L. P. Kaptari🇷🇺 · B. Kampfer🇩🇪

    In view of the properties of mesons in hot strongly interacting matter the properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail. In Euclidean space within the Matsubara imaginary time formalism the quark propagator is not longer a O(4) symmetric function and possesses a discrete spectra of the fourth component of the momentum. This makes the treatment of the Dyson-Schwinger and Bethe-Salpeter equations conceptually different from the vacuum and technically much more involved. The question whether the interaction kernel known from vacuum calculations can be applied at finite temperatures remains still open. We find that, at low temperatures, the model interaction with vacuum parameters provides a reasonable description of the quark propagator, while at temperatures higher than a certain critical value $T_c$ the interaction requires stringent modifications. The general properties of the quark propagator at finite temperatures can be inferred from lattice QCD calculations. We argue that, to achieve a reasonable agreement of the model calculations with that from lattice QCD, the kernel is to be modified in such a way as to screen the infra-red part of the interaction at temperatures larger than $T_c$. For this, we analyse the solutions of the truncated Dyson-Schwinger equation with existing interaction kernels in a large temperature range with particular attention on high temperatures in order to find hints to an adequate temperature dependence of the interaction kernel to be further implemented in to the Bethe-Salpeter equation for mesons. This will allow to investigate the possible in medium modifications of the meson properties as well as the conditions of quark deconfinement in hot matter.

    ↳ nucl-thhep-phJ.Mod.Phys.(2016)·6 citations
78. 78*

    In search of chiral magnetic effect: separating flow-driven background effects and quantifying anomaly-induced charge separations

    Xu-Guang Huang🇨🇳 · Yi Yin🇺🇸 · Jinfeng Liao🇺🇸

    We report our recent progress on the search of Chiral Magnetic Effect (CME) by developing new measurements as well as by hydrodynamic simulations of CME and background effects, with both approaches addressing the pressing issue of separating flow-driven background contributions and possible CME signal in current heavy ion collision measurements.

    ↳ nucl-thhep-phNPA(2016)·17 citations
79. 79*

    Axion phenomenology and $\theta$-dependence from $N_f=2+1$ lattice QCD

    Claudio Bonati🇮🇹 · Massimo D'Elia🇮🇹 · Marco Mariti🇮🇹 · Guido Martinelli🇮🇹 · Michele Mesiti🇮🇹 · Francesco Negro🇮🇹 · Francesco Sanfilippo🇬🇧 · Giovanni Villadoro🇮🇹

    We investigate the topological properties of $N_f=2+1$ QCD with physical quark masses, both at zero and finite temperature. We adopt stout improved staggered fermions and explore a range of lattice spacings $a\sim 0.05-0.12$ fm. At zero temperature we estimate both finite size and finite cut-off effects, comparing our continuum extrapolated results for the topological susceptibility $\chi$ with predictions from chiral perturbation theory. At finite temperature, we explore a region going from $T_c$ up to around $4T_c$, where we provide continuum extrapolated results for the topological susceptibility and for the fourth moment of the topological charge distribution. While the latter converges to the dilute instanton gas prediction the former differs strongly both in the size and in the temperature dependence. This results in a shift of the axion dark matter window of almost one order of magnitude with respect to the instanton computation.

    ↳ hep-lathep-phJHEP(2016)·233 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.