Fri·Dec 18, 2015Friday·December 18, 2015

1. 01*

   The QCD Axion from Aligned Axions and Diphoton Excess

   Tetsutaro Higaki🇯🇵 · Kwang Sik Jeong🇰🇷 · Naoya Kitajima🇰🇷 · Fuminobu Takahashi🇯🇵

   We argue that the QCD axion can arise from many aligned axions with decay constants much smaller than the conventional axion window. If the typical decay constant is of {\cal O}{(100)} GeV to 1 TeV, one or more of the axions or saxions may account for the recently found diphoton excess at \sim 750 GeV. Our scenario predicts many axions and saxions coupled to gluons with decay constants of order the weak scale, and therefore many collider signatures by heavy axions and saxions will show up at different energy scales. In particular, if the inferred broad decay width is due to multiple axions or saxions, a non-trivial peak structure may become evident when more data is collected. We also discuss cosmological implications of the aligned QCD axion scenario. In the Appendix we give a possible UV completion and argue that the high quality of the Peccei-Quinn symmetry is naturally explained in our scenario.

   hep-phPLB(2016)·206 citations
2. 02*

   Singlet Scalar Resonances and the Diphoton Excess

   Samuel D. McDermott🇺🇸 · Patrick Meade🇺🇸 · Harikrishnan Ramani🇺🇸

   ATLAS and CMS recently released the first results of searches for diphoton resonances in 13 TeV data, revealing a modest excess at an invariant mass of approximately 750 GeV. We find that it is generically possible that a singlet scalar resonance is the origin of the excess while avoiding all other constraints. We highlight some of the implications of this model and how compatible it is with certain features of the experimental results. In particular, we find that the very large total width of the excess is difficult to explain with loop-level decays alone, pointing to other interesting bounds and signals if this feature of the data persists. Finally we comment on the robust Z-gamma signature that will always accompany the model we investigate.

   hep-phPLB(2016)·197 citations
3. 03*

   On the Interpretation of a Possible $\sim 750$ GeV Particle Decaying into $\gamma \gamma$

   John Ellis🇬🇧 · Sebastian A. R. Ellis🇺🇸 · Jérémie Quevillon🇬🇧 · Veronica Sanz🇬🇧 · Tevong You🇬🇧

   We consider interpretations of the recent $\sim 3\sigma$ reports by the CMS and ATLAS collaborations of a possible $X(\sim 750\mathrm{GeV})$ state decaying into $\gamma \gamma$ final states. We focus on the possibilities that this is a scalar or pseudoscalar electroweak isoscalar state produced by gluon-gluon fusion mediated by loops of heavy fermions. We consider several models for these fermions, including a single vector-like charge $2/3$ T quark, a doublet of vector-like quarks $(T,B)$, and a vector-like generation of quarks, with or without leptons that also contribute to the $X\to \gamma \gamma$ decay amplitude. We also consider the possibility that $X(750)$ is a dark matter mediator, with a neutral vector-like dark matter particle. These scenarios are compatible with the present and prospective direct limits on vector-like fermions from LHC Runs 1 and 2, as well as indirect constraints from electroweak precision measurements, and we show that the required Yukawa-like couplings between the $X$ particle and the heavy vector-like fermions are small enough to be perturbative so long as the $X$ particle has dominant decay modes into $gg$ and $\gamma \gamma$. The decays $X\to ZZ,Z\gamma$ and $W^{+}{W}^{-}$ are interesting prospective signatures that may help distinguish between different vector-like fermion scenarios.

   hep-phhep-exJHEP(2016)·253 citations
4. 04*

   A pseudoscalar decaying to photon pairs in the early LHC Run 2 data

   Matthew Low🇺🇸 · Andrea Tesi🇺🇸 · Lian-Tao Wang🇺🇸

   In this paper we explore the possibility of a pseudoscalar resonance to account for the 750 GeV diphoton excess observed both at ATLAS and at CMS. We analyze the ingredients needed from the low energy perspective to obtain a sufficiently large diphoton rate to explain the signal while avoiding constraints from other channels. Additionally, we point out composite Higgs models in which one can naturally obtain a pseudoscalar at the 750 GeV mass scale and we estimate the pseudoscalar couplings to standard model particles that one would have in such models. A generic feature of models that can explain the excess is the presence of new particles in addition to the 750 GeV state. Finally, we note that due to the origin of the coupling of the resonance to photons, one expects to see comparable signals in the $Z\gamma$, $ZZ$, and $WW$ channels.

   hep-phhep-exJHEP(2016)·204 citations
5. 05*

   Goldstones in Diphotons

   Brando Bellazzini🇫🇷 · Roberto Franceschini🇨🇭 · Filippo Sala🇫🇷 · Javi Serra🇨🇭

   We study the conditions for a new scalar resonance to be observed first in diphotons at the LHC Run-2. We focus on scenarios where the scalar arises either from an internal or spacetime symmetry broken spontaneously, for which the mass is naturally below the cutoff and the low-energy interactions are fixed by the couplings to the broken currents, UV anomalies, and selection rules. We discuss the recent excess in diphoton resonance searches observed by ATLAS and CMS at 750 GeV, and explore its compatibility with other searches at Run-1 and its interpretation as Goldstone bosons in supersymmetry and composite Higgs models. We show that two candidates naturally emerge: a Goldstone boson from an internal symmetry with electromagnetic anomalies, and the scalar partner of the Goldstone of supersymmetry breaking: the sgoldstino. The dilaton from conformal symmetry breaking is instead disfavoured by present data, in its minimal natural realization.

   hep-phhep-exJHEP(2016)·204 citations
6. 06*

   Interpreting a 750 GeV Diphoton Resonance

   Rick S. Gupta🇮🇱 · Sebastian Jäger🇬🇧 · Yevgeny Kats🇮🇱 · Gilad Perez🇮🇱 · Emmanuel Stamou🇮🇱

   We discuss the implications of the significant excesses in the diphoton final state observed by the LHC experiments ATLAS and CMS around a diphoton invariant mass of 750 GeV. The interpretation of the excess as a spin-zero s-channel resonance implies model-independent lower bounds on both its branching ratio and its coupling to photons, which stringently constrain dynamical models. We consider both the case where the excess is described by a narrow and a broad resonance. We also obtain model-independent constraints on the allowed couplings and branching fractions to final states other than diphotons, by including the interplay with 8 TeV searches. These results can guide attempts to construct viable dynamical models of the resonance. Turning to specific models, our findings suggest that the anomaly cannot be accounted for by the presence of only an additional singlet or doublet spin-zero field and the Standard Model degrees of freedom; this includes all two-Higgs-doublet models. Likewise, heavy scalars in the MSSM cannot explain the excess if stability of the electroweak vacuum is required, at least in a leading-order analysis. If we assume that the resonance is broad we find that it is challenging to find a weakly coupled explanation. However, we provide an existence proof in the form of a model with vectorlike quarks with large electric charge that is perturbative up to the 100 TeV scale. For the narrow-resonance case a similar model can be perturbative up to high scales also with smaller charges. We also find that, in their simplest form, dilaton models cannot explain the size of the excess. Some implications for flavor physics are briefly discussed.

   hep-phhep-exJHEP(2016)·228 citations
7. 07*

   The 750 GeV diphoton excess from the goldstino superpartner

   Christoffer Petersson🇧🇪 · Riccardo Torre🇨🇭

   We interpret the di-photon excess recently reported by the ATLAS and CMS collaborations as a new resonance arising from the sgoldstino scalar, which is the superpartner of the Goldstone mode of spontaneous supersymmetry breaking, the goldstino. The sgoldstino is produced at the LHC via gluon fusion and decays to photons, with interaction strengths proportional to the corresponding gaugino masses over the supersymmetry breaking scale. Fitting the excess, while evading bounds from searches in the di-jet, $Z\gamma$, $ZZ$ and $WW$ final states, selects the supersymmetry breaking scale to be a few TeV, and particular ranges for the gaugino masses. The two real scalars, corresponding to the CP-even and CP-odd parts of the complex sgoldstino, both have narrow widths, but their masses can be split of the order 10-30 GeV by electroweak mixing corrections, which could account for the preference of a wider resonance width in the current low-statistics data. In the parameter space under consideration, tree-level $F$-term contributions to the Higgs mass arise, in addition to the standard $D$-term contribution proportional to the $Z$-boson mass, which can significantly enhance the tree level Higgs mass.

   hep-phPRL(2016)·174 citations
8. 08*

   Minimal Composite Dynamics versus Axion Origin of the Diphoton excess

   Emiliano Molinaro🇩🇰 · Francesco Sannino🇩🇰 · Natascia Vignaroli🇩🇰

   ATLAS and CMS observe deviations from the expected background in the diphoton invariant mass searches of new resonances around 750 GeV. We show that a simple realization in terms of a new pseudoscalar state can accommodate the observations. The model leads to further footprints that can be soon observed. The new state can be interpreted both as an axion or as a {highly natural} composite state arising from minimal models of dynamical electroweak symmetry breaking. We further show how to disentangle the two scenarios. Beyond the possible explanation of the diphoton excess the results show that it is possible to directly test and constrain composite dynamics via processes stemming from its distinctive topological sector.

   hep-phhep-exhep-latMod.Phys.Lett.A(2016)·199 citations
9. 09*

   Millicharge or Decay: A Critical Take on Minimal Dark Matter

   Eugenio Del Nobile🇺🇸 · Marco Nardecchia🇬🇧 · Paolo Panci🇫🇷

   Minimal Dark Matter (MDM) is a theoretical framework highly appreciated for its minimality and yet its predictivity. Of the two only viable candidates singled out in the original analysis, the scalar eptaplet has been found to decay too quickly to be around today, while the fermionic quintuplet is now being probed by indirect Dark Matter (DM) searches. It is therefore timely to critically review the MDM paradigm, possibly pointing out generalizations of this framework. We propose and explore two distinct directions. One is to abandon the assumption of DM electric neutrality in favor of absolutely stable, millicharged DM candidates which are part of $SU(2{)}_{\text{L}}$ multiplets with integer isospin. Another possibility is to lower the cutoff of the model, which was originally fixed at the Planck scale, to allow for DM decays. We find new viable MDM candidates and study their phenomenology in detail.

   hep-phastro-ph.COJCAP(2016)·83 citations
10. 10*

    Singlet Extensions of the Standard Model at LHC Run 2: Benchmarks and Comparison with the NMSSM

    Raul Costa🇵🇹 · Margarete Mühlleitner🇩🇪 · Marco O. P. Sampaio🇵🇹 · Rui Santos🇵🇹

    The Complex singlet extension of the Standard Model (CxSM) is the simplest extension that provides scenarios for Higgs pair production with different masses. The model has two interesting phases: the dark matter phase, with a Standard Model-like Higgs boson, a new scalar and a dark matter candidate; and the broken phase, with all three neutral scalars mixing. In the latter phase Higgs decays into a pair of two different Higgs bosons are possible. In this study we analyse Higgs-to-Higgs decays in the framework of singlet extensions of the Standard Model (SM), with focus on the CxSM. After demonstrating that scenarios with large rates for such chain decays are possible we perform a comparison between the NMSSM and the CxSM. We find that, based on Higgs-to-Higgs decays, the only possibility to distinguish the two models at the LHC run 2 is through final states with two different scalars. This conclusion builds a strong case for searches for final states with two different scalars at the LHC run 2. Finally, we propose a set of benchmark points for the real and complex singlet extensions to be tested at the LHC run 2. They have been chosen such that the discovery prospects of the involved scalars are maximised and they fulfil the dark matter constraints. Furthermore, for some of the points the theory is stable up to high energy scales. For the computation of the decay widths and branching ratios we developed the Fortran code, sHDECAY, which is based on the implementation of the real and complex singlet extensions of the SM in HDECAY.

    hep-phhep-exJHEP(2016)·149 citations
11. 11*

    Three Twin Neutrinos: Evidence from LSND and MiniBooNE

    Yang Bai🇺🇸 · Ran Lu🇺🇸 · Sida Lu🇺🇸 · Jordi Salvado🇪🇸 · Ben A. Stefanek🇺🇸

    We construct a neutrino model of three twin neutrinos in light of the neutrino appearance excesses at LSND and MiniBooNE. The model, which includes a twin parity, naturally predicts identical lepton Yukawa structures in the Standard Model and the twin sectors. As a result, a universal mixing angle controls all three twin neutrino couplings to the Standard Model charged leptons. This mixing angle is predicted to be the ratio of the electroweak scale over the composite scale of the Higgs boson and has the right order of magnitude to fit the data. The heavy twin neutrinos decay within the experimental lengths into active neutrinos plus a long-lived Majoron and can provide a good fit, at around $4\sigma$ confidence level, to the LSND and MiniBooNE appearance data while simultaneously satisfying the disappearance constraints. For the Majorana neutrino case, the fact that neutrinos have a larger scattering cross section than anti-neutrinos provides a natural explanation to MiniBooNE's observation of a larger anti-neutrino appearance excess.

    hep-phhep-exPRD(2016)·57 citations
12. 12*

    CP Violating Baryon Oscillations

    David McKeen🇺🇸 · Ann E. Nelson🇺🇸

    We enumerate the conditions necessary for $CP$ violation to be manifest in $n$-$\bar{n}$ oscillations, and build a simple model that can give rise to such effects. We discuss a possible connection between neutron oscillations and dark matter, provided the mass of the latter lies between $m_p-m_e$ and $m_p+m_e$. We apply our results to a possible baryogenesis scenario involving $CP$ violation in the oscillations of the ${\Xi }^0$.

    hep-phPRD(2016)·68 citations
13. 13*

    Universal structure of the Drell-Yan process beyond threshold

    Domenico Bonocore🇳🇱

    We review recent results in the investigation of threshold logarithms at next-to-leading power considering the case of the Drell-Yan cross section at NNLO. We first show how they can be reproduced with a method of region calculation. Then we move to an approach based on soft- collinear factorization, showing that the entire logarithmic structure can be reproduced by means of universal functions.

    hep-ph3 citations
14. 14*

    Dodelson-Widrow Production of Sterile Neutrino Dark Matter with Non-Trivial Initial Abundance

    Alexander Merle🇩🇪 · Aurel Schneider🇨🇭 · Maximilian Totzauer🇩🇪

    The simplest way to create sterile neutrinos in the early Universe is by their admixture to active neutrinos. However, this mechanism, connected to the Dark Matter (DM) problem by Dodelson and Widrow (DW), cannot simultaneously meet the relic abundance constraint as well as bounds from structure formation and X-rays. Nonetheless, unless a symmetry forces active-sterile mixing to vanish exactly, the DW mechanism will unavoidably affect the sterile neutrino DM population created by any other production mechanism. We present a semi-analytic approach to the DW mechanism acting on an arbitrary initial abundance of sterile neutrinos, allowing to combine DW with any other preceding production mechanism in a physical and precise way. While previous analyses usually assumed that the spectra produced by DW and another mechanism can simply be added, we use our semi-analytic results to discuss the validity of this assumption and to quantify its accurateness, thereby also scrutinising the DW spectrum and the derived mass bounds. We then map our results to the case of sterile neutrino DM from the decay of a real SM singlet coupled to the Higgs. Finally, we will investigate aspects of structure formation beyond the usual simple free-streaming estimates in order to judge on the effects of the DW modification on the sterile neutrino DM spectra generated by scalar decay.

    hep-phastro-ph.COJCAP(2016)·62 citations
15. 15*

    TMDs and SSAs in hadronic interactions

    E.C. Aschenauer (1)🇺🇸 · U. D'Alesio (2,3)🇮🇹 · F. Murgia (3) ((1) BNL, USA, (2) University of Cagliari, Italy, (3) INFN, Cagliari, Italy)🇮🇹

    We present an overview on the current experimental and phenomenological status of transverse single spin asymmetries (tSSAs) in proton-proton collisions. In particular, we focus on large-$p_T$ inclusive pion, photon, jet, pion-jet production and Drell-Yan processes. For all of them theoretical estimates are given in terms of a generalised parton model (GPM) based on a transverse momentum dependent (TMD) factorisation scheme. Comparisons with the corresponding results in a collinear twist-3 formalism and in a modified GPM approach are also made. On the experimental side, a selection of the most interesting and recent results from RHIC is presented.

    hep-phEPJA(2016)·41 citations
16. 16*

    Eikonal gluon bremsstrahlung at finite N_c beyond two loops

    Yazid Delenda🇩🇿 · Kamel Khelifa-Kerfa🇩🇿

    We present a general formalism for computing the matrix-element squared for the emission of soft energy-ordered gluons beyond two loops in QCD perturbation theory at finite $N_c$. Our formalism is valid in the eikonal approximation. A Mathematica program has been developed for the automated calculation of all real/virtual eikonal squared amplitudes needed at a given loop order. For the purpose of illustration we show the explicit forms of the eikonal squared amplitudes up to the fifth-loop order. In the large-$N_c$ limit our results coincide with those previously reported in literature.

    hep-phPRD(2016)·15 citations
17. 17*

    Interpretation of the diphoton excess at CMS and ATLAS

    Bhaskar Dutta🇺🇸 · Yu Gao🇺🇸 · Tathagata Ghosh🇺🇸 · Ilia Gogoladze🇺🇸 · Tianjun Li🇨🇳

    We consider the diphoton resonance at the 13 TeV LHC in a consistent model with new scalars and vector-like fermions added to the Standard Model (SM), which can be constructed from orbifold grand unified theories and string models. The gauge coupling unification can be achieved, neutrino masses can be generated radiatively, and electroweak vacuum stability problem can be solved. To explain the diphoton resonance, we study a spin-0 particle, and discuss various associated final states.

    hep-phhep-exPRD(2016)·153 citations
18. 18*

    Searching for charmoniumlike states with hidden $s\bar{s}$

    Xiao-Hai Liu🇯🇵 · Makoto Oka🇯🇵

    We investigate the processes $e^{+}{e}^{-}$$\to$$\gamma J/\psi \varphi$, $\gamma J/\psi \omega$ and ${\pi }^{0}J/\psi \eta$ to search for the charmnium-like states with hidden $s\bar{s}$, such as $Y(4140)$, $Y(4274)$, $X(4350)$ and $X(3915)$. These processes will receive contributions from the charmed-strange meson rescatterings. When the center-of-mass energies of the $e^{+}{e}^{-}$ scatterings are taken around the $D_{s0}(2317)D_s^{\ast }$, $D_{s1}(2460)D_s$ or $D_{s1}(2460)D_s^{\ast }$ threshold, the anomalous triangle singularities can be present in the rescattering amplitudes, which implies a non-resonance explanation about the resonance-like structures. The positions of the anomalous triangle singularities are sensitive to the kinematics, which offers us a criterion to distinguish the kinematic singularities from genuine particles.

    hep-phhep-exnucl-exnucl-thPRD(2016)·21 citations
19. 19*

    New U(1) Gauge Model of Radiative Lepton Masses with Sterile Neutrino and Dark Matter

    Rathin Adhikari🇮🇳 · Debasish Borah🇮🇳 · Ernest Ma🇺🇸

    An anomaly-free U(1) gauge extension of the standard model (SM) is presented. Only one Higgs doublet with a nonzero vacuum expectation is required as in the SM. New fermions and scalars as well as all SM particles transform nontrivially under this U(1), resulting in a model of three active neutrinos and one sterile neutrino, all acquiring radiative masses. Charged-lepton masses are also radiative as well as the mixing between active and sterile neutrinos. At the same time, a residual $Z_2$ symmetry of the U(1) gauge symmetry remains exact, allowing for the existence of dark matter.

    hep-phPLB(2016)·60 citations
20. 20*

    The Extreme Walking Behavior in a 331-TC Model

    A. Doff🇧🇷

    It is quite possible that the Technicolor problems are related to the poorly known self-energy expression, or the way chiral symmetry breaking (CSB) is realized in non-abelian gauge theories. Actually, the only known laboratory to test the CSB mechanism is QCD. The TC dynamics may be quite different from the QCD , this fact has led to the walking TC proposal making the new strong interaction almost conformal and changing appreciably its dynamical behavior. There are different ways to obtain of extreme walking (or quasi-conformal) technicolor theories, in this paper we propose an scheme to obtain this behavior based on an extension of the electroweak sector of the standard model, in the context of so called 331-TC model.

    hep-phEPJC(2016)·5 citations
21. 21*

    Antiproton--proton annihilation into pion pairs within effective meson theory

    Ying Wang🇫🇷 · Yury M. Bystritskiy🇷🇺 · Egle Tomasi-Gustafsson🇫🇷

    Antiproton--proton annihilation into light mesons is revisited in the few GeV energy domain, in view of a global description of the existing data. An effective meson model is developed, with mesonic and baryonic degrees od freedom in $s$, $t$, and $u$ channels. Regge factors are added to reproduce the proper energy behavior and the forward and backward peaked behavior. A comparison with existing data and predictions for angular distributions and energy dependence are done for charged and neutral pion pair production.

    hep-phnucl-thPRC(2017)·5 citations
22. 22*

    Hard Diffraction with Dynamic Gap Survival

    Christine O. Rasmussen🇸🇪 · Torbjörn Sjöstrand🇸🇪

    We present a new framework for the modelling of hard diffraction in pp and ppbar collisions. It starts from the the approach pioneered by Ingelman and Schlein, wherein the single diffractive cross section is factorized into a Pomeron flux and a Pomeron PDF. To this it adds a dynamically calculated rapidity gap survival factor, derived from the modelling of multiparton interactions. This factor is not relevant for diffraction in ep collisions, giving non-universality between HERA and Tevatron diffractive event rates. The model has been implemented in Pythia 8 and provides a complete description of the hadronic state associated with any hard single diffractive process. Comparisons with ppbar and pp data reveal improvement in the description of single diffractive events.

    hep-phJHEP(2016)·43 citations
23. 23*

    Theory status of four-fermion production at e-e+ colliders

    Christian Schwinn🇩🇪

    The status of predictions for four-fermion production at e-e+ colliders is reviewed with an emphasis on the developments after the LEP2 era and an outlook to the challenges posed by the precision program at future colliders.

    hep-phFrascati Phys.Ser.(2016)·0 citations
24. 24*

    A Boost Test of Anomalous Diphoton Resonance at the LHC

    Qing-Hong Cao🇨🇳 · Yandong Liu🇨🇳 · Ke-Pan Xie🇨🇳 · Bin Yan🇨🇳 · Dong-Ming Zhang🇨🇳

    The recently observed diphoton resonance around 750~GeV at the LHC Run-2 could be interpreted as a weak singlet scalar. The scalar might also decay into a pair of $Z$-boson and photon. The $Z$-boson is highly boosted and appears as a fat jet in the detector. We use the jet substructure method to explore the possibility of discovering the singlet scalar in the process of $pp\to S\to Z\gamma$ in the future LHC experiment.

    hep-phhep-ex159 citations
25. 25*

    Direct measurement of alpha_QED(mZ) at the FCC-ee

    Patrick Janot🇨🇭

    When the measurements from the FCC-ee become available, an improved determination of the standard-model "input" parameters will be needed to fully exploit the new precision data towards either constraining or fitting the parameters of beyond-the-standard-model theories. Among these input parameters is the electromagnetic coupling constant estimated at the Z mass scale, alpha_QED(mZ). The measurement of the muon forward-backward asymmetry at the FCC-ee, just below and just above the Z pole, can be used to make a direct determination of alpha_QED(mZ) with an accuracy deemed adequate for an optimal use of the FCC-ee precision data.

    hep-phhep-exJHEP(2016)·65 citations
26. 26*

    Axion Dark Matter Coupling to Resonant Photons via Magnetic Field

    Ben T. McAllister · Stephen R. Parker · Michael E. Tobar

    We show that the magnetic component of the photon field produced by dark matter axions via the two-photon coupling mechanism in a Sikivie Haloscope is an important parameter passed over in previous analysis and experiments. The interaction of the produced photons will be resonantly enhanced as long as they couple to the electric or magnetic mode structure of the Haloscope cavity. For typical Haloscope experiments the electric and magnetic coupling is the same and implicitly assumed in past sensitivity calculations. However, for future planned searches such as those at high frequency, which synchronize multiple cavities, the sensitivity will be altered due to different magnetic and electric couplings. We define the complete electromagnetic form factor and discuss its implications for current and future high and low mass axion searches, including some effects which have been overlooked, due to the assumption that the two couplings are the same.

    hep-phastro-ph.GAgr-qchep-ex+1Phys. Rev. Lett. 116, 161804 (2016)
27. 27*

    Gauge Coupling Unification in Gauge-Higgs Grand Unification

    Naoki Yamatsu🇯🇵

    We discuss renormalization group equations for gauge coupling constants in gauge-Higgs grand unification on five-dimensional Randall-Sundrum warped space. We show that all the four-dimensional Standard Model gauge coupling constants are asymptotically free and are effectively unified in $SO(11)$ gauge-Higgs grand unified theories on 5D Randall-Sundrum warped space.

    hep-phPTEP(2016)·30 citations
28. 28*

    750 GeV Diphoton Signal from One-Family Walking Technipion

    Shinya Matsuzaki🇯🇵 · Koichi Yamawaki🇯🇵

    The ATLAS and CMS groups have recently reported an excess at around 750 GeV with the local significance by about 3 sigma in the diphoton channel at the 13 TeV LHC. We give a possible explanation for the excess by a composite pseudo scalar $(P^0)$ predicted in the one-family model of walking technicolor.

    hep-phhep-exhep-latMod.Phys.Lett.A(2016)·136 citations
29. 29*

    750 GeV diphoton resonance in a top and bottom seesaw model

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

    The top/bottom seesaw model, which extends the top seesaw in order to accomodate a 125 GeV Higgs boson, predicts vector-like top/bottom partners and these partners can be bounded to form several neutral and charged singlet composite scalars by some new strong dynamics. In this letter, we use such a singlet scalar to interpret the 750 GeV diphoton reseanance. This singlet scalar is dominantly produced through the gluon fusion process induced by the partners and its diphoton decay is induced by both the partners and the charged singlet scalars. We show that this scenario can readily account for the observed 750 GeV diphoton signal under the current LHC constraints. Further, this scenario predicts some other phenomenology, such as a strong correlation between the decays to $\gamma \gamma$, $Z\gamma$ and $ZZ$, a three-photon singal from the associate production of a singlet scalar and a photon, as well as some signals from the partner cascade decays. These signals may jointly allow for a test of this framework in future LHC and ILC experiments.

    hep-phhep-exPLB(2016)·177 citations
30. 30*

    Does zero temperature decide on the nature of the electroweak phase transition?

    Christopher P. D. Harman🇬🇧 · Stephan J. Huber🇬🇧

    Taking on a new perspective of the electroweak phase transition, we investigate in detail the role played by the depth of the electroweak minimum ("vacuum energy difference"). We find a strong correlation between the vacuum energy difference and the strength of the phase transition. This correlation only breaks down if a negative eigenvalue develops upon thermal corrections in the squared scalar mass matrix in the broken vacuum before the critical temperature. As a result the scalar fields slide across field space toward the symmetric vacuum, often causing a significantly weakened phase transition. Phenomenological constraints are found to strongly disfavour such sliding scalar scenarios. For several popular models, we suggest numerical bounds that guarantee a strong first order electroweak phase transition. The zero temperature phenomenology can then be studied in these parameter regions without the need for any finite temperature calculations. For almost all non-supersymmetric models with phenomenologically viable parameter points, we find a strong phase transition is guaranteed if the vacuum energy difference is greater than $-8.8\times 10^7$~\text{GeV}${}^4$. For the GNMSSM, we guarantee a strong phase transition for phenomenologically viable parameter points if the vacuum energy difference is greater than $-6.9\times 10^7$~\text{GeV}${}^4$. Alternatively, we capture more of the parameter space exhibiting a strong phase transition if we impose a simultaneous bound on the vacuum energy difference and the singlet mass.

    hep-phhep-thJHEP(2016)·32 citations
31. 31*

    Diphoton decay for a $750$ GeV scalar boson in an $U(1{)}_X$ model

    R. Martinez🇨🇴 · F. Ochoa🇨🇴 · C.F. Sierra🇨🇴

    In the context of a nonuniversal and anomaly free $U(1{)}_X$ extension of the standard model, we examine the decay of a $750$GeV scalar singlet state, ${\xi }_{\chi }$, as a possible explanation of the observed diphoton excess announced by the ATLAS and CMS collaborations at CERN-LHC collider. One-loop decay to photons is allowed through three heavy singlet quarks and one charged Higgs boson into the loop. We obtain, for different width approximations and for masses of the exotic singlet quarks in the region $[900,3000]$ GeV, a production cross section $\sigma (pp\to {\xi }_{\chi }\to \gamma \gamma )$ compatible with ATLAS and CMS collaborations data. We also include another scalar singlet, $\sigma$, as a dark matter candidate that may couple with the 750 GeV scalar at tree level with production cross sections in agreement with ATLAS and CMS.

    hep-phNPB(2016)·132 citations
32. 32*

    Implications of diphoton searches for a Radion in the Bulk-Higgs Scenario

    Peter Cox🇦🇺 · Anibal D. Medina🇫🇷 · Tirtha Sankar Ray🇮🇳 · Andrew Spray🇰🇷

    In this work we point out that the apparent diphoton excess initially presented by the ATLAS and CMS collaborations could have originated from a radion in the bulk Higgs scenario within a warped extra dimension. In this scenario the couplings of the radion to massive gauge bosons are suppressed, allowing it to evade existing searches. In the presence of mixing with the Higgs, due to the strong constraints from diboson searches, only points near what we denominate the alignment region were able to explain the diphoton signal and evade other experimental constraints. In light of the new measurements presented at ICHEP 2016 by both LHC collaborations, which do not confirm the initial diphoton excess, we study the current and future collider constraints on a radion within the bulk-Higgs scenario. We find that searches in the diphoton channel provide the most powerful probe of this scenario and already exclude large regions of parameter space, particularly for smaller warp factors. The radion has a sizeable branching ratio into top pairs and this channel may also give competitive constraints in the future. Finally, diHiggs searches can provide a complementary probe in the case of non-zero radion-Higgs mixing but strong alignment.

    hep-phhep-exInt.J.Mod.Phys.A(2017)·161 citations
33. 33*

    Can the new resonance at LHC be a CP-Odd Higgs boson?

    Damir Becirevic🇫🇷 · Enrico Bertuzzo🇧🇷 · Olcyr Sumensari🇫🇷 · Renata Zukanovich Funchal🇧🇷

    A plausible explanation of the recent experimental indication of a resonance in the two-photon spectrum at LHC is that it corresponds to the CP-odd Higgs boson. We explore such a possibility in a generic framework of the two Higgs doublet models (2HDM), and combine $m_A\approx 750$GeV with the known $m_h=125.7(4)$~GeV to show that the charged Higgs boson and the other CP-even scalar masses become bounded from bellow and from above. We show that this possibility is also consistent with the electroweak precision data and the low energy observables, which we test in a few leptonic and semileptonic decay modes.

    hep-phPLB(2016)·154 citations
34. 34*

    Scalar Bosons and Supersymmetry

    Pierre Fayet🇫🇷

    The recent discovery of a spin-0 Brout-Englert-Higgs boson leads to further enquire about other fundamental scalars. Supersymmetric theories involve, in relation with the electroweak breaking, five such scalars at least, two charged and three neutral ones, usually denoted as H${}^{\pm }$, H, h and A. They also introduce spin-0 squarks and sleptons as the superpartners of quarks and leptons. Supersymmetric extensions of the standard model lead to the possibility of gauge/BEH unification by providing spin-0 bosons as extra states for spin-1 gauge bosons within massive gauge multiplets. Depending on its properties the 125 GeV boson observed at CERN may then also be interpreted, up to a mixing angle induced by supersymmetry breaking, as the spin-0 partner of the Z under two supersymmetry transformations, i.e. as a Z that would be deprived of its spin.

    hep-phhep-exSeminaire Poincare(2014)·3 citations
35. 35*

    The iterated structure of the all-order result for the two-loop sunrise integral

    Luise Adams🇩🇪 · Christian Bogner🇩🇪 · Stefan Weinzierl🇩🇪

    We present a method to compute the Laurent expansion of the two-loop sunrise integral with equal non-zero masses to arbitrary order in the dimensional regularisation $\epsilon$. This is done by introducing a class of functions (generalisations of multiple polylogarithms to include the elliptic case) and by showing that all integrations can be carried out within this class of functions.

    hep-phhep-thmath-phmath.MPJ.Math.Phys.(2016)·167 citations
36. 36*

    Starobinsky-Type Inflation With Products of Kaehler Manifolds

    C. Pallis🇨🇾 · N. Toumbas🇨🇾

    We present a novel realization of Starobinsky-type inflation within Supergravity using two chiral superfields. The proposed superpotential is inspired by induced-gravity models. The Kaehler potential contains two logarithmic terms, one for the inflaton T and one for the matter-like field S, parameterizing the SU(1,1)/U(1)x SU(2)/U(1) Kaehler manifold. The two factors have constant curvatures -m/n and 2/n2, where n, m are the exponents of T in the superpotential and Kaehler potential respectively, and 0<n2<=6. The inflationary observables depend on the ratio 2n/m only. Essentially they coincide with the observables of the original Starobinsky model. Moreover, the inflaton mass is predicted to be 3x10^13 GeV.

    hep-phastro-ph.COhep-thJCAP(2016)·32 citations
37. 37*

    See-Saw Composite Higgses at the LHC: Linking Naturalness to the $750$ GeV Di-Photon Resonance

    Jose Miguel No🇬🇧 · Veronica Sanz🇬🇧 · Jack Setford🇬🇧

    We explore the possibility of explaining the recent $\sim 750$ GeV excesses observed by ATLAS and CMS in the $\gamma \gamma$ spectrum in the context of a compelling theory of Naturalness. The potential spin-zero resonance responsible for the excesses also requires the existence of new heavy charged states. We show that both such features are naturally realized in a see-saw Composite Higgs model for EWSB, where the new pseudo-Goldstone bosons are expected to be comparatively heavier than the SM Higgs, and the new fermions have masses in the TeV range. If confirmed, the existence of this new resonance could be the first stone in the construction of a new theory of Naturalness.

    hep-phPRD(2016)·168 citations
38. 38*

    Low-Energy QCD in the Delta Regime

    Matthew E. Matzelle🇺🇸 · Brian C. Tiburzi🇺🇸

    We investigate properties of low-energy QCD in a finite spatial volume, but with arbitrary temperature. In the limit of small temperature and small cube size compared to the pion Compton wavelength, Leutwyler has shown that the effective theory describing low-energy QCD reduces to that of quantum mechanics on the coset manifold, which is the so-called delta regime of chiral perturbation theory. We solve this quantum mechanics analytically for the case of a $U(1{)}_L\times U(1{)}_R$ subgroup of chiral symmetry, and numerically for the case of $SU(2{)}_L\times SU(2{)}_R$. We utilize the quantum mechanical spectrum to compute the mass gap and chiral condensate, and investigate symmetry restoration in a finite spatial volume as a function of temperature. Because we obtain the spectrum for non-zero values of the quark mass, we are able to interpolate between the rigid rotor limit, which emerges at vanishing quark mass, and the harmonic approximation, which is referred to as the p-regime. We find that the applicability of perturbation theory about the rotor limit largely requires lighter-than-physical quarks. As a stringent check of our results, we raise the temperature to that of the inverse cube size. When this condition is met, the quantum mechanics reduces to a matrix model. The condensate we obtain in this limit agrees with that determined analytically in the epsilon regime.

    ↳ hep-lathep-phnucl-thPRD(2016)·10 citations
39. 39*

    Testing distance duality with CMB anisotropies

    Syksy Rasanen🇫🇮 · Jussi Valiviita🇫🇮 · Ville Kosonen

    We constrain deviations of the form $T\propto (1+z{)}^{1+ϵ}$ from the standard redshift-temperature relation, corresponding to modifying distance duality as $D_L=(1+z{)}^{2(1+ϵ)}{D}_A$. We consider a consistent model, in which both the background and perturbation equations are changed. For this purpose, we introduce a species of dark radiation particles to which photon energy density is transferred, and assume $ϵ\ge 0$. The Planck 2015 release high multipole temperature plus low multipole data give the limit $ϵ<4.5\times 10^{-3}$ at 95% C.L. The main obstacle to improving this CMB-only result is strong degeneracy between $ϵ$ and the physical matter densities ${\omega }_{\mathrm{b}}$ and ${\omega }_{\mathrm{c}}$. A constraint on deuterium abundance improves the limit to $ϵ<1.8\times 10^{-3}$. Adding the Planck high-multipole CMB polarisation and BAO data leads to a small improvement; with this maximal dataset we obtain $ϵ<1.3\times 10^{-3}$. This dataset constrains the present dark radiation energy density to at most 12% of the total photon plus dark radiation density. Finally, we discuss the degeneracy between dark radiation and the effective number of relativistic species $N_{\mathrm{eff}}$, and consider the impact of dark radiation perturbations and allowing $ϵ<0$ on the results.

    ↳ astro-ph.COgr-qchep-phJCAP(2016)·20 citations
40. 40*

    Weak and strong coupling equilibration in nonabelian gauge theories

    Liam Keegan🇨🇭 · Aleksi Kurkela🇨🇭 · Paul Romatschke🇺🇸 · Wilke van der Schee🇺🇸 · Yan Zhu🇫🇮

    We present a direct comparison studying equilibration through kinetic theory at weak coupling and through holography at strong coupling in the same set-up. The set-up starts with a homogeneous thermal state, which then smoothly transitions through an out-of-equilibrium phase to an expanding system undergoing boost-invariant flow. This first apples-to-apples comparison of equilibration provides a benchmark for similar equilibration processes in heavy-ion collisions, where the equilibration mechanism is still under debate. We find that results at weak and strong coupling can be smoothly connected by simple, empirical power-laws for the viscosity, equilibration time and entropy production of the system.

    ↳ hep-thhep-phnucl-thJHEP(2016)·105 citations
41. 41*

    Testing Hydrodynamic Descriptions of of p+p Collisions at \sqrt{s}=7 TeV

    M. Habich🇺🇸 · G.A. Miller🇺🇸 · P. Romatschke🇺🇸 · W. Xiang🇺🇸

    In high energy collisions of heavy-ions, experimental findings of collective flow are customarily associated with the presence of a thermalized medium expanding according to the laws of hydrodynamics. Recently, the ATLAS, CMS and ALICE experiments found signals of the same type and magnitude in ultrarelativistic proton-proton collisions. In this study, the state-of-the-art hydrodynamic model SONIC is used to simulate the systems created in p+p collisions. By varying the size of the second-order transport coefficients, the range of applicability of hydrodynamics itself to the systems created in p+p collisions is quantified. It is found that hydrodynamics can give quantitatively reliable results for the particle spectra and the elliptic momentum anisotropy coefficient $v_2$. Using a simple geometric model of the proton based on the elastic form factor leads to results of similar type and magnitude to those found in experiment when allowing for a small bulk viscosity coefficient.

    ↳ nucl-thhep-phnucl-exEPJC(2016)·42 citations
42. 42*

    Beyond $\Lambda$CDM: Problems, solutions, and the road ahead

    Philip Bull · Yashar Akrami · Julian Adamek · Tessa Baker · Emilio Bellini · Jose Beltrán Jiménez · Eloisa Bentivegna · Stefano Camera · Sébastien Clesse · Jonathan H. Davis · Enea Di Dio · Jonas Enander and 28 other authors

    Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, $\Lambda$CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of $\Lambda$CDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.

    ↳ astro-ph.COastro-ph.GAgr-qchep-ph+1Phys.Dark Univ.(2016)·664 citations
43. 43*

    The Role of Möbius Constants and Scattering Functions in CHY Scalar Amplitudes

    C.S. Lam🇨🇦 · York-Peng Yao🇺🇸

    The integrations leading to the Cachazo-He-Yuan (CHY) double-color $n$-point massless scalar amplitude are carried out one integral at a time. Möbius invariance dictates the final amplitude to be independent of the three Möbius constants ${\sigma }_r,{\sigma }_s,{\sigma }_t$, but their choice affects integrations and the intermediate results. The effect of the Möbius constants, the two colors, and the scattering functions on each integration is investigated. A systematic way to carry out the $n-3$ integrations is explained, each exposing one of the $n-3$ propagators of the Feynman diagrams. Two detailed examples are shown to illustrate the procedure, one a five-point amplitude, and the other a nine-point amplitude.

    ↳ hep-thhep-phPRD(2016)·24 citations
44. 44*

    Particles within extended-spin space: Lagrangian connection

    J. Besprosvany🇲🇽 · R. Romero🇲🇽

    A spin-space extension is reviewed, which provides information on the standard model. Its defining feature is a common matrix space that describes symmetries and representations, and leads to limits on these, for given dimension. The model provides additional information on the standard model, whose interpretation requires an interactive formulation. Within this program, we compare the model's lepton-W generated interactive Lagrangian in (5+1)-dimensions, and that of the standard model. We derive the conditions for this matching, which apply to other Lagrangian terms. We also discuss the advantages of this extension, as compared to others.

    ↳ hep-thhep-phNucl.Part.Phys.Proc.(2015)·2 citations
45. 45*

    New Spectroscopy with PANDA at FAIR: X, Y, Z and the F-wave Charmonium States

    Elisabetta Prencipe🇩🇪 · Jens Soeren Lange🇩🇪 · Alexander Blinov🇷🇺

    Charm and charmonium physics have gained renewed interest in the past decade. Recent spectroscopic observations strongly motivate these studies. Among the several possible reactions, measurements in proton-antiproton annihilation play an important role, complementary to the studies performed at B-factories. The fixed target PANDA experiment at FAIR (Darmstadt, Germany) will investigate fundamental questions of hadron and nuclear physics in the interactions of antiprotons with nucleons and nuclei. With reaction rates as large as 2*10^7 interactions/s, and a mass resolution 20 times better as compared with the most recent B-factories, PANDA is in a privileged position to successfully perform the measurement of the width of narrow states, such as the X(3872). PANDA will investigate also high spin particles, whose observation was forbidden at B-factories, i.e. F-wave charmonium states. In this report extrapolations on cross sections and rates with PANDA are given.

    ↳ hep-exhep-phAIP Conf.Proc.(2016)·14 citations
46. 46*

    Test of the $X(3872)$ Structure in Antiproton-Nucleus Collisions

    Alexei Larionov🇩🇪 · Mark Strikman🇺🇸 · Marcus Bleicher🇩🇪

    The present day experimental data on the $X(3872)$ decays do not allow to make clear conclusions on the dominating structure of this state. We discuss here an alternative way to study its structure by means of the two-step ${\bar{D}}^{\ast }$ (or $D$) production in $\bar{p}A$ reactions. If this process is mediated by $X(3872)$, the characteristic narrow peaks of the ${\bar{D}}^{\ast }$ (or $D$) distributions in the light cone momentum fraction at small transverse momenta will appear. This would unambiguously signal the $D{\bar{D}}^{\ast }$ + c.c. molecular composition of the $X(3872)$ state.

    ↳ nucl-thhep-exhep-phnucl-exAIP Conf.Proc.(2016)·1 citation
47. 47*

    Hadron Structure and Spectrum from the Lattice

    C. B. Lang🇦🇹

    Lattice calculations for hadrons are now entering the domain of resonances and scattering, necessitating a better understanding of the observed discrete energy spectrum. This is a reviewing survey about recent lattice QCD results, with some emphasis on spectrum and scattering.

    ↳ nucl-thhep-lathep-phnucl-exAIP Conf.Proc.(2016)·7 citations
48. 48*

    Influence of kinematic cuts on the net charge distribution

    Hannah Petersen🇩🇪 · Dmytro Oliinychenko🇺🇦 · Jan Steinheimer🇩🇪 · Marcus Bleicher🇩🇪

    The higher moments of the net charge distributions, e.g. the skewness and kurtosis, are studied within an infinite hadronic matter calculation in a transport approach. By dividing the box into several parts, the volume dependence of the fluctuations is investigated. After confirming that the initial distributions follow the expectations from a binomial distribution, the influence of quantum number conservation in this case the net charge in the system on the higher moments is evaluated. For this purpose, the composition of the hadron gas is adjusted and only pions and $\rho$ mesons are simulated to investigate the charge conservation effect. In addition, the effect of imposing kinematic cuts in momentum space is analysed. The role of resonance excitations and decays on the higher moments can also be studied within this model. This work is highly relevant to understand the experimental measurements of higher moments obtained in the RHIC beam energy scan and their comparison to lattice results and other theoretical calculations assuming infinite matter.

    ↳ nucl-thhep-phnucl-exNPA(2016)·8 citations
49. 49*

    Heavy quark diffusion from coherent color fields in relativistic heavy-ion collisions

    Taesoo Song🇩🇪 · Thomas Epelbaum🇨🇦

    The diffusion coefficients of heavy quarks from the coherent color electromagnetic fields which are generated in the early stage of relativistic heavy-ion collisions are calculated at midrapidity, and compared with those obtained from collisions within a thermalized quark-gluon plasma. The coherent color fields are modeled such that they are initially longitudinal and then become isotropic. We found that the diffusion coefficients from the coherent color fields are larger than those from collisions except for very fast heavy quarks, and the color fields are less effective for heavy-quark energy loss. The importance of coherent color fields for heavy-quark diffusion decreases as energy density decreases.

    ↳ nucl-thhep-ph4 citations
50. 50*

    Post-Inflationary Gravitino Production Revisited

    John Ellis🇬🇧 · Marcos A. G. Garcia🇺🇸 · Dimitri V. Nanopoulos🇺🇸 · Keith A. Olive🇺🇸 · Marco Peloso🇺🇸

    We revisit gravitino production following inflation. As a first step, we review the standard calculation of gravitino production in the thermal plasma formed at the end of post-inflationary reheating when the inflaton has completely decayed. Next we consider gravitino production prior to the completion of reheating, assuming that the inflaton decay products thermalize instantaneously while they are still dilute. We then argue that instantaneous thermalization is in general a good approximation, and also show that the contribution of non-thermal gravitino production via the collisions of inflaton decay products prior to thermalization is relatively small. Our final estimate of the gravitino-to-entropy ratio is approximated well by a standard calculation of gravitino production in the post-inflationary thermal plasma assuming total instantaneous decay and thermalization at a time $t\simeq 1.2/{\Gamma }_{\varphi }$. Finally, in light of our calculations, we consider potential implications of upper limits on the gravitino abundance for models of inflation, with particular attention to scenarios for inflaton decays in supersymmetric Starobinsky-like models.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2016)·102 citations
51. 51*

    Schwinger pair production at nonzero temperatures or in compact directions

    Adam R. Brown🇺🇸

    Electric fields may decay by quantum tunneling: as calculated by Schwinger, an electron-positron pair may be summoned from the vacuum. In this paper I calculate the pair-production rate at nonzero temperatures. I find that at high temperatures the decay rate is dominated by a new instanton that involves both thermal fluctuation and quantum tunneling; this decay is exponentially faster than the rate in the literature. I also calculate the decay rate when the electric field wraps a compact circle (at zero temperature). The same new instanton also governs this rate: I find that for small circles decay is dominated by a process that drops the electric field by one unit, but does not produce charged particles.

    ↳ hep-thhep-phPRD(2018)·39 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.