Thu·Dec 31, 2015Thursday·December 31, 2015

1. 01*

   Light-front ${\varphi }_{1+1}^4$ theory using a many-boson symmetric-polynomial basis

   S.S. Chabysheva🇺🇸

   We extend earlier work on fully symmetric polynomials for three-boson wave functions to arbitrarily many bosons and apply these to a light-front analysis of the low-mass eigenstates of ${\varphi }^4$ theory in 1+1 dimensions. The basis-function approach allows the resolution in each Fock sector to be independently optimized, which can be more efficient than the preset discrete Fock states in DLCQ. We obtain an estimate of the critical coupling for symmetry breaking in the positive mass-squared case.

   hep-phFew Body Syst.(2016)·6 citations
2. 02*

   A Megaxion at 750 GeV as a First Hint of Low Scale String Theory

   Luis E. Ibanez🇪🇸 · Victor Martin-Lozano🇪🇸

   Low scale string models naturally have axion-like pseudoscalars which couple directly to gluons and photons (but not $W$s) at tree level. We show how they typically get tree level masses in the presence of closed string fluxes, consistent with the axion discrete gauge symmetry, in a way akin of the axion monodromy of string inflation and relaxion models. We discuss the possibility that the hints for a resonance at 750 GeV recently reported at ATLAS and CMS could correspond to such a heavy axion state (megaxion). Adjusting the production rate and branching ratios suggests the string scale to be of order $M_s$ ~ $7-10^4$ TeV, depending on the compactification geometry. If this interpretation was correct, one extra $Z^{\prime }$ gauge boson could be produced before reaching the string threshold at LHC and future colliders.

   hep-phhep-exhep-thJHEP(2016)·68 citations
3. 03*

   Oscillating Asymmetric Sneutrino Dark Matter from the Maximally $U(1{)}_L$ Supersymmetric Inverse Seesaw

   Shao-Long Chen🇨🇳 · Zhaofeng Kang🇰🇷

   The inverse seesaw mechanism provides an attractive approach to generate small neutrino mass, which origins from a tiny $U(1{)}_L$ breaking. In this paper, we work in the supersymmetric version of this mechanism, where the singlet-like sneutrino could be an asymmetric dark matter (ADM) candidate in the maximally $U(1{)}_L$ symmetric limit. However, even a tiny $\delta m$, the mass splitting between sneutrino and anti-sneutrino as a result of the tiny $U(1{)}_L$ breaking effect, could lead to fast oscillation between sneutrino and anti-sneutrino and thus spoils the ADM scenario. We study the evolution of this oscillation and find that a weak scale sneutrino, which tolerates a relatively larger $\delta m\sim 10^{-5}$ eV, is strongly favored. We also investigate possible natural ways to realize that small $\delta m$ in the model.

   hep-phastro-ph.COPLB(2016)·13 citations
4. 04*

   Radiative Model of Neutrino Mass with Neutrino Interacting MeV Dark Matter

   Abdesslam Arhrib🇲🇦 · Céline Bœhm🇫🇷 · Ernest Ma🇺🇸 · Tzu-Chiang Yuan🇹🇼

   We consider the radiative generation of neutrino mass through the interactions of neutrinos with MeV dark matter. We construct a realistic renormalizable model with one scalar doublet and one complex singlet together with three light singlet Majorana fermions, all transforming under a dark U(1) symmetry which breaks softly to Z_2. We study in detail the scalar sector which supports this specific scenario and its rich phenomenology.

   hep-phJCAP(2016)·41 citations
5. 05*

   D mesons in a magnetic field

   Philipp Gubler🇮🇹 · Koichi Hattori🇯🇵 · Su Houng Lee🇰🇷 · Makoto Oka🇯🇵 · Sho Ozaki🇯🇵 · Kei Suzuki🇯🇵

   We investigate the mass spectra of open heavy flavor mesons in an external constant magnetic field within QCD sum rules. Spectral ansätze on the phenomenological side are proposed in order to properly take into account mixing effects between the pseudoscalar and vector channels, and the Landau levels of charged mesons. The operator product expansion is implemented up to dimension-5 operators. As a result, we find for neutral D mesons a significant positive mass shift that goes beyond simple mixing effects. In contrast, charged D mesons are further subject to Landau level effects, which together with the mixing effects almost completely saturate the mass shifts obtained in our sum rule analysis.

   hep-phhep-latnucl-exnucl-thPRD(2016)·89 citations
6. 06*

   Bose-Einstein Condensation of Bound Pairs of Relativistic Fermions in a Magnetic Field

   Bo Feng🇨🇳 · Defu Hou🇨🇳 · Hai-cang Ren🇨🇳 · Ping-ping Wu🇨🇳

   The Bose-Einstein condensation of bound pairs made of equally and oppositely charged fermions in a magnetic field is investigated using a relativistic model. The Gaussian fluctuations have been taken into account in order to study the spectrum of bound pairs in the strong coupling region. We found, in weak coupling reagion, the condensation temperature increases with an increasing magnetic field displaying the magnetic catalysis effect. In strong coupling region, the inverse magnetic catalysis appears when the magnetic field is low and is replaced by the usual magnetic catalysis effect when magnetic field is sufficiently high, in contrast to the nonrelativistic case where the inverse magnetic catalysis prevails in strong coupling region regardless of the strength of the magnetic field. The resulting response to the magnetic field is the consequence of the competition between the dimensional reduction by Landau orbitals in pairing dynamics and the anisotropy of the kinetic spectrum of the bound pairs. We thus conclude that dimensional reduction dominates in weak domain and strong coupling one except the small magnetic field region, where the enhanced fluctuations dominates.

   hep-phnucl-thPRD(2016)·11 citations
7. 07*

   Revisiting Scalar Quark Hidden Sector in Light of 750-GeV Diphoton Resonance

   Cheng-Wei Chiang🇹🇼 · Masahiro Ibe🇯🇵 · Tsutomu T. Yanagida🇯🇵

   In this short note, we revisit the model of a CP-even singlet scalar resonance proposed in arXiv:1507.02483, where the resonance appears as the lightest composite state made of scalar quarks participating in hidden strong dynamics. We show that the model can consistently explain the excess of diphoton events with an invariant mass around 750GeV reported by both the ATLAS and CMS experiments. We also discuss the nature of the charged composite states in the TeV range which accompany to the neutral scalar. Due to inseparability of the dynamical scale and the mass of the resonance, the model also predicts signatures associated with the hidden dynamics such as leptons, jets along with multiple photons at future collider experiments. We also associate the TeV-scale dynamics behind the resonance with an explanation of dark matter.

   hep-phJHEP(2016)·60 citations
8. 08*

   Electroweak Baryogenesis with Anomalous Higgs Couplings

   Archil Kobakhidze🇦🇺 · Lei Wu🇦🇺 · Jason Yue🇦🇺

   We investigate feasibility of efficient baryogenesis at the electroweak scale within the effective field theory framework based on a non-linear realisation of the electroweak gauge symmetry. In this framework the LHC Higgs boson is described by a singlet scalar field, which, therefore, admits new interactions. Assuming that Higgs couplings with the eletroweak gauge bosons are as in the Standard Model, we demonstrate that the Higgs cubic coupling and the CP-violating Higgs-top quark anomalous couplings alone may drive the a strongly first-order phase transition. The distinguished feature of this transition is that the anomalous Higgs vacuum expectation value is generally non-zero in both phases. We identify a range of anomalous couplings, consistent with current experimental data, where sphaleron rates are sufficiently fast in the 'symmetric' phase and are suppressed in the 'broken' phase and demonstrate that the desired baryon asymmetry can indeed be generated in this framework. This range of the Higgs anomalous couplings can be further constrained from the LHC Run 2 data and be probed at high luminosity LHC and beyond.

   hep-phJHEP(2016)·46 citations
9. 09*

   Boosting Higgs pair production in the $b\bar{b}b\bar{b}$ final state with multivariate techniques

   J. Katharina Behr🇬🇧 · Daniela Bortoletto🇬🇧 · James A. Frost🇬🇧 · Nathan P. Hartland🇬🇧 · Cigdem Issever🇬🇧 · Juan Rojo🇬🇧

   The measurement of Higgs pair production will be a cornerstone of the LHC program in the coming years. Double Higgs production provides a crucial window upon the mechanism of electroweak symmetry breaking and has a unique sensitivity to the Higgs trilinear coupling. We study the feasibility of a measurement of Higgs pair production in the $b\bar{b}b\bar{b}$ final state at the LHC. Our analysis is based on a combination of traditional cut-based methods with state-of-the-art multivariate techniques. We account for all relevant backgrounds, including the contributions from light and charm jet mis-identification, which are ultimately comparable in size to the irreducible $4b$ QCD background. We demonstrate the robustness of our analysis strategy in a high pileup environment. For an integrated luminosity of $\mathcal{L}=3$ ab${}^{-1}$, a signal significance of $S/\sqrt{B}\simeq 3$ is obtained, indicating that the $b\bar{b}b\bar{b}$ final state alone could allow for the observation of double Higgs production at the High-Luminosity LHC.

   hep-phhep-exEPJC(2016)·86 citations
10. 10*

    Pion's valence-quark GPD and its extension beyond DGLAP region

    C. Mezrag🇺🇸 · H. Moutarde🇫🇷 · J. Rodríguez-Quintero🇪🇸

    We briefly report on a recent computation, with the help of a fruitful algebraic model, sketching the pion valence dressed-quark generalized parton distribution and, very preliminary, discuss on a possible avenue to get reliable results in both Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and Efremov-Radyushkin-Brodsky-Lepage (ERBL) kinematial regions.

    hep-phEPJ Web Conf.(2016)·0 citations
11. 11*

    A data-driven approach to pile-up at high luminosity

    F. Hautmann🇬🇧

    We discuss recent results on pile-up based on a data-driven jet-mixing method. We illustrate prospects for experimental searches and precision studies in high pile-up regimes at high-luminosity hadron colliders, showing how the jet mixing approach can be used, also outside tracker acceptances, to treat correlation observables and effects of hard jets from pile-up.

    hep-phFrascati Phys.Ser.(2016)·2 citations
12. 12*

    Top-phobic heavy Higgs boson as the 750 GeV diphoton resonance

    Sin Kyu Kang🇰🇷 · Jeonghyeon Song🇰🇷

    A hint of a new resonance at a mass of 750\,GeV has been observed in the diphoton channel of LHC Run 2 at $\sqrt{s}=13$ TeV. The signal rate is too large to interpret it as a new Higgs boson in the context of weakly-coupled renormalizable models. One way is to reduce its total decay rate, which is possible if the CP-even heavy Higgs boson $H^0$ in the aligned two Higgs doublet model becomes top-phobic. To ensure sufficient gluon fusion production, we introduce vector-like quarks (VLQ). The Higgs precision data as well as the exclusion limits from no excesses in other 8 TeV LHC searches of $Z\gamma$, $b\bar{b}$, ${\tau }^{+}{\tau }^{-}$, and $jj$ channels are simultaneously included. In Type I, top-phobic $H^0$ cannot explain the 750\,GeV diphoton signal and the Higgs precision data simultaneously since the universal Yukawa couplings of the up-type and down-type VLQs always make more contribution to $h^0$ than to $H^0$. In Type II, small Yukawa coupling of the up-type VLQ but sizable Yukawa coupling for the down-type VLQ is shown to explain the signal while satisfying other LHC exclusion limits.

    hep-phPRD(2016)·69 citations
13. 13*

    Analogy between rotation and density for Dirac fermions in a magnetic field

    Hao-Lei Chen🇨🇳 · Kenji Fukushima🇯🇵 · Xu-Guang Huang🇨🇳 · Kazuya Mameda🇯🇵

    We analyse the energy spectra of Dirac fermions in the presence of rotation and magnetic field. We find that the Landau degeneracy is resolved by rotation. A drastic change in the energy dispersion relation leads to the "rotational magnetic inhibition" that is a novel phenomenon analogous to the inverse magnetic catalysis in a magnetic system at finite chemical potential.

    hep-phPRD(2016)·179 citations
14. 14*

    An O(750) GeV Resonance and Inflation

    Yuta Hamada🇯🇵 · Toshifumi Noumi🇨🇳 · Gary Shiu🇺🇸 · Sichun Sun🇨🇳

    We study the possibility of a heavy scalar or pseudoscalar in TeV-scale beyond the Standard Model scenarios being the inflaton of the early universe in light of the recent O(750) GeV diphoton excess at the LHC. We consider a scenario in which the new scalar or pseudoscalar couples to the Standard Model gauge bosons at the loop level through new massive Standard Model charged vectorlike fermions with or without dark fermions. We calculate the renormalization group running of both the Standard Model and the new scalar couplings, and present two different models that are perturbative and with a stabilized vacuum up to near the Planck scale. Thus, the Standard Model Higgs and this possible new resonance may still preserve the minimalist features of Higgs inflation.

    hep-phastro-ph.COPRD(2016)·77 citations
15. 15*

    A 750 GeV dark matter messenger at the Galactic Center

    Xian-Jun Huang🇨🇳 · Wei-Hong Zhang🇨🇳 · Yu-Feng Zhou🇨🇳

    The first data from the LHC Run-2 have shown a possible excess in diphoton events with invariant mass $\sim 750$ GeV, suggesting the existence of a new resonance which may decay dominantly into dark matter (DM) particles. We show in a simple model that the reported diphoton excess at the LHC is consistent with another photon excess, the $2$ GeV excess in cosmic gamma-ray fluxes towards the Galactic Center observed by the Fermi-LAT. Both the excesses can be simultaneously explained by a $\sim 60$ GeV scalar DM particle annihilating dominantly into two gluons with a typical thermal annihilation cross section, which leads to the prediction of a large width to mass ratio $\Gamma /M\approx \mathcal{O}(10^{-2})$ of the resonance. The upper limit on the dijet search at LHC Run-1 leads to a $lower$ limit on the predicted cross section for DM annihilating into $\gamma \gamma$ final states $⟨\sigma v{⟩}_{\gamma \gamma }\gtrsim \mathcal{O}(10^{-30})\text{mbox}{cm}^3\text{mbox}{s}^{-1}$. Both the predictions can be tested by the LHC, Fermi-LAT and future experiments.

    hep-phastro-ph.COPRD(2016)·66 citations
16. 16*

    Effects produced by multi-parton interactions and color reconnection in small systems

    Eleazar Cuautle🇲🇽 · Antonio Ortiz🇲🇽 · Guy Paic🇲🇽

    Multi-parton interactions and color reconnection can produce QGP-like effects in small systems, specifically, radial flow-like patterns. For pp collisions simulated with Pythia 8.212, in this work we investigate their effects on different observables like event multiplicity, event shapes and transverse momentum distributions.

    hep-phnucl-thNPA(2016)·12 citations
17. 17*

    Description and interpretation of DVCS measurements

    Krešimir Kumerički🇭🇷 · Dieter Müller🇭🇷

    Having in mind the well-known limitations of certain models of generalized parton distributions (GPDs), we show that the allegedly universal GPDs, describing both deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP) data, fail to describe measurements of deep inelastic scattering. We present a new global DVCS fit that describes reasonably the world data set, which includes now also new measurements from Hall A and CLAS collaborations. We also explicitly illustrate that Compton form factors (CFFs) cannot be unambiguously extracted from photon electroproduction measurements off unpolarized proton alone and we argue that it is more reliable to interpret such measurements in terms of certain CFF combinations, where still some care is needed in order to estimate the propagated error.

    hep-phhep-exEPJ Web Conf.(2016)·78 citations
18. 18*

    Pseudoscalar transition form factors: $(g-2)$ of the muon, pseudoscalar decays into lepton pairs, and the $\eta -{\eta }^{\prime }$ mixing

    Pere Masjuan🇩🇪 · Pablo Sanchez-Puertas🇩🇪

    We present our model-independent and data-driven method to describe pseudoscalar meson transition form factors in the space- and (low-energy) time-like regions. The method is general and conforms a toolkit applicable to any other form factor, of one and two variables, with the potential to include both high- and low-energy QCD constraints altogether. The method makes use of analyticity and unitary properties of form factors, it is simple, systematic and can be improved upon by including new data. In the present discussion, the method is used to show the impact of experimental data for precision calculations in the low-energy sector of the Standard Model. In particular, due to its relevance for New Physics searches, we have considered the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon (the pseudoscalar exchange contribution), the pseudoscalar decays into lepton pairs, and the determination of the mixing parameters of the $\eta$ and ${\eta }^{\prime }$ system. For all of them we provide the most updated results in a data-driven manner.

    hep-phhep-exnucl-thEPJ Web Conf.(2016)·2 citations
19. 19*

    Derivation of Functional Equations for Feynman Integrals from Algebraic Relations

    O. V. Tarasov🇩🇪

    New methods for obtaining functional equations for Feynman integrals are presented. Application of these methods for finding functional equations for various one- and two- loop integrals described in detail. It is shown that with the aid of functional equations Feynman integrals in general kinematics can be expressed in terms of simpler integrals.

    hep-phJHEP(2017)·14 citations
20. 20*

    Z'-induced FCNC decays of top, beauty and strange quarks

    Kaori Fuyuto🇯🇵 · Wei-Shu Hou🇹🇼 · Masaya Kohda🇹🇼

    Anomalous b --> s transitions from LHCb data may suggest a new massive gauge boson Z' that couples to the left-handed b --> s current, which in turn implies a coupling to the t --> c current. In this paper, we study flavor-changing neutral current (FCNC) decays of the top quark induced by a Z' boson, namely t --> c Z', based on a model of the gauged L_mu - L_tau symmetry (the difference between the muon and tauon numbers) with vector-like quarks, which was introduced to explain the anomalous LHCb data. We illustrate that searching for t --> c Z' via Z' --> mu^+ mu^- with LHC Run 1 data can already probe a parameter region which is unexplored by B physics for the Z' mass around O(10) GeV or more. We further extend the model to very light Z' with mass below 400 MeV, which is motivated by the muon g-2 anomaly. Taking rare B and K meson decay data into account, we give upper limits on the t --> c Z' branching ratio for the light Z' case, and discuss about its observability at the LHC. We also scrutinize the possibility that the decay K_L --> pi^0 Z' with Z' --> nu nubar may lead to apparent violation of the usual Grossman-Nir bound of B(K_L --> pi^0 nu nubar) < 1.4 x 10^-9.

    hep-phPRD(2016)·66 citations
21. 21*

    LHC 750 GeV Diphoton excess in a radiative seesaw model

    Shinya Kanemura🇯🇵 · Kenji Nishiwaki🇰🇷 · Hiroshi Okada🇹🇼 · Yuta Orikasa🇰🇷 · Seong Chan Park🇰🇷 · Ryoutaro Watanabe🇰🇷

    We investigate a possibility for explaining the recently announced 750\,GeV diphoton excess by the ATLAS and the CMS experiments at the CERN LHC in a model with multiple doubly charged particles, which was originally suggested for explaining tiny neutrino masses through a three-loop effect in a natural way. The enhanced radiatively generated effective coupling of a new singlet scalar $S$ with diphoton with multiple charged particles in the loop enlarges the production rate of $S$ in $pp\to S+X$ via photon fusion process and also the decay width $\Gamma (S\to \gamma \gamma )$ even without assuming a tree level production mechanism. We provide detailed analysis on the cases with or without allowing the mixing between $S$ and the standard model Higgs doublet.

    hep-phPTEP(2016)·101 citations
22. 22*

    Diphoton excess at 750 GeV in an extended scalar sector

    Shinya Kanemura🇯🇵 · Naoki Machida🇯🇵 · Shinya Odori🇯🇵 · Tetsuo Shindou🇯🇵

    We discuss an extended scalar model which explains the recent results of diphoton excess at 750 GeV at LHC Run II experiments. An additional singlet scalar boson with the mass of 750 GeV, which couples to top quarks via a dimension five operator, is produced via gluon fusion and decays into two photons via loop contributions of a number of (multiply) charged scalar bosons. Origin of such a dimension five operator would be, for example, in the context of composite Higgs models. The excess can be explained without contradicting the data from LHC Run I and also theoretical consistencies such as perturbative unitarity and charge non-breaking.

    hep-ph69 citations
23. 23*

    Lepton asymmetry from mixing and oscillations

    Alexander Kartavtsev🇩🇪 · Peter Millington🇬🇧 · Hendrik Vogel🇩🇪

    We show how the two physically-distinct sources of CP-asymmetry relevant to scenarios of leptogenesis: (i) resonant mixing and (ii) oscillations between different flavours can be unambiguously identified within the Kadanoff-Baym formalism. These contributions are isolated by analyzing the spectral structure of the non-equilibrium propagators without relying on the definition of particle number densities. The mixing source is associated with the usual mass shells, whereas the oscillation source is identified with a third intermediate shell. In addition, we identify terms lying on the oscillation shell that can be interpreted as the destructive interference between mixing and oscillation. We confirm that identical shell structure is obtained in both the Heisenberg- and interaction-picture realizations of the Kadanoff-Baym formalism. In so doing, we illustrate the self-consistency and complementarity of these two approaches. The interaction-picture approach in particular has the advantage that it may be used to analyze all forms of mass spectra from quasi-degenerate through to hierarchical.

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

    Direct-photon+hadron correlations to study parton energy loss with the STAR experiment

    Nihar Ranjan Sahoo (STAR collaboration)🇺🇸

    We report new results of ${\gamma }_{dir}$+hadron and ${\pi }^0$+hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment from years 2011 and 2009 of data taking, respectively. The charged-hadron per-trigger yields at mid-rapidity $(|\eta |<1)$ and for transverse momenta $p_T^{assoc}>1.2$ ~GeV/$c$ associated with ${\gamma }_{dir}$~ and ${\pi }^0$~(for triggers $|\eta |<$0.9, 12 $<p_T^{trig}<$ 20 GeV/$c$) in central Au+Au collisions are compared with p+p collisions. The $z_T$ ($=\frac{p_T^{assoc}}{p_T^{trig}}$) dependence, now extending down to $z_T$=0.1, of the suppression of the away-side associated yields is presented. We observed that the suppression of away-side associated yields tends to vanish at lower \zT. The dependence of the suppression on both $p_T^{assoc}$ and $p_T^{trig}$ is also discussed. Finally, these results are compared with various model predictions.

    ↳ nucl-exhep-exhep-phnucl-thNPA(2016)·3 citations
25. 25*

    Measurements of jet quenching with semi-inclusive charged jet distributions in $Au+Au$ collisions at $\sqrt{s_{NN}}$=200 GeV

    P. M. Jacobs🇺🇸 · A. Schmah (STAR Collaboration)🇺🇸

    We report measurements of jet quenching in $Au+Au$ collisions at $\sqrt{s_{NN}}$=200 GeV, based on the semi-inclusive distribution of reconstructed charged particle jets recoiling from a high $p_T$ hadron trigger. Jets are reconstructed with the anti-k${}_T$ algorithm ($R$=0.2 to 0.5), with low IR-cutoff of track constituents ($p_T>0.2$ GeV/c). Uncorrelated background is corrected using a novel mixed-event technique, with no fragmentation bias imposed by the correction procedure on the accepted recoil jet population. Corrected recoil jet distributions, reported in the range $0<p_{T,jet}^{ch}<30$ GeV/c, are used to measure jet yield suppression, jet energy loss, and intra-jet broadening. The first search for QCD Molière scattering of jets in hot QCD matter at RHIC is reported.

    ↳ nucl-exhep-exhep-phNPA(2016)·25 citations
26. 26*

    Why not any tau double bang in Icecube, yet?

    D.Fargion🇮🇹 · P.Oliva🇮🇹 · G. Ucci🇮🇹

    High Energy Neutrino Astronomy has been revealed by a sudden change in the flavor composition around maximal energies since three years of recording in ice km detector. However these discover didn' t led to any clear promised Neutrino Astronomy land yet. No correlation with hard gamma sources was found. Moreover the astrophysical spectra expected at Fermi value, seem to converge to a softer value, also required to avoid any Glashow resonant neutrino signal. We suggest a main solution within a composite flux ruled by prompt atmospheric neutrinos. Nevertheless the recent discover of twentyone crossing muons at hundreds TeVs had shown a first narrow overlapped doublet and a correlated track with a peculiar hard UHECR event clustering pointing to a well known microjet in bynary precession; these first connections hint for a non negligible astrophysical component making neutrino astronomy anyway already more than a hope.

    ↳ astro-ph.HEastro-ph.IMhep-phPoS(2016)·12 citations
27. 27*

    Anisotropic emission of direct photons from Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ with EPOS3 and IP-Glasma

    Fu-Ming Liu🇨🇳 · Sheng-Xu Liu🇨🇳 · Klaus Werner🇫🇷

    The observed large elliptic flow ($v_2$) of direct photons in relativistic heavy ion collisions challenges us to explain. In this paper we consider only two sources of direct photons, prompt photons and thermal photons. Prompt photons are calculated with QCD to next leading order, which fits well the spectra at high transverse momentum ($p_{\mathrm{t}}$) region. Thermal photons are calculated with AMY rate in a 3+1D viscous hydrodynamical evolution of the collision systems. Two types of initial conditions, EPOS3 and IP-Glasma, are employed. Our results with IP-Glasma initial condition agree with results in published work in most cases, and the difference tells the regions effected by the absence of viscous correction in photon emission rate. Because both models are well constrained with hadron data, the hydrodynamic evolution of collision systems in the two models have many common. However, the transverse velocity of the collective motion are quite different. This makes a big difference in the anisotropic emission of direct photon emission. The observed large elliptic flow of direct photons is reproduced with EPOS3 hydrodynamic evolution.

    ↳ nucl-thhep-ph7 citations
28. 28*

    Octet baryon masses and sigma terms in covariant baryon chiral perturbation theory

    Xiu-Lei Ren (Beihang U. and IPN Orsay)🇨🇳 · Li-Sheng Geng (Beihang U.)🇨🇳 · Jie Meng (Peking U., SKLNPT and Beihang U. and Stellenbosch U.)🇨🇳

    We report on a recent study of the ground-state octet baryon masses and sigma terms in covariant baryon chiral perturbation theory with the extended-on-mass-shell scheme up to next-to-next-to-next-to-leading order. To take into account lattice QCD artifacts, the finite-volume corrections and finite lattice spacing discretization effects are carefully examined. We performed a simultaneous fit of all the $n_f=2+1$ lattice octet baryon masses and found that the various lattice simulations are consistent with each other. Although the finite lattice spacing discretization effects up to $\mathcal{O}(a^2)$ can be safely ignored, but the finite volume corrections cannot even for configurations with $M_{\varphi }L>4$. As an application, we predicted the octet baryon sigma terms using the Feynman-Hellmann theorem. In particular, the pion- and strangeness-nucleon sigma terms are found to be ${\sigma }_{\pi N}=55(1)(4)$ MeV and ${\sigma }_{sN}=27(27)(4)$ MeV, respectively.

    ↳ nucl-thhep-lathep-phPoS(2016)·1 citation
29. 29*

    Hadronic final states at HERA

    P. J. Bussey🇬🇧

    Measurements of hadronic final states by H1 and ZEUS at HERA are presented. The H1 measurements consist of measurements of charged particle spectra in deep -inelastic $ep$ scattering and of forward photons and neutrons. The ZEUS results consist of a series of measurements of prompt photons in photoproduction.

    ↳ hep-exhep-phNucl.Part.Phys.Proc.(2016)·0 citations
30. 30*

    Gravitational waves from a very strong electroweak phase transition

    Leonardo Leitao🇦🇷 · Ariel Megevand🇦🇷

    We investigate the production of a stochastic background of gravitational waves in the electroweak phase transition. We consider extensions of the Standard Model which can give very strongly first-order phase transitions, such that the transition fronts either propagate as detonations or run away. To compute the bubble wall velocity, we estimate the friction with the plasma and take into account the hydrodynamics. We track the development of the phase transition up to the percolation time, and we calculate the gravitational wave spectrum generated by bubble collisions, magnetohydrodynamic turbulence, and sound waves. For the kinds of models we consider, we find parameter regions for which the gravitational waves are potentially observable at the planned space-based interferometer eLISA. In such cases, the signal from sound waves is generally dominant, while that from bubble collisions is the least significant of them. Since the sound waves and turbulence mechanisms are diminished for runaway walls, the models with the best prospects of detection at eLISA are those which do not have such solutions. In particular, we find that heavy extra bosons provide stronger gravitational wave signals than tree-level terms.

    ↳ astro-ph.COhep-phJCAP(2016)·70 citations
31. 31*

    Direct search for features in the primordial bispectrum

    Stephen Appleby🇰🇷 · Jinn-Ouk Gong🇰🇷 · Dhiraj Kumar Hazra🇫🇷 · Arman Shafieloo🇰🇷 · Spyros Sypsas🇰🇷

    We study features in the bispectrum of the primordial curvature perturbation correlated with the reconstructed primordial power spectrum from the observed cosmic microwave background temperature data. We first show how the bispectrum can be completely specified in terms of the power spectrum and its first two derivatives, valid for any configuration of interest. Then using a model-independent reconstruction of the primordial power spectrum from the Planck angular power spectrum of temperature anisotropies, we compute the bispectrum in different triangular configurations. We find that in the squeezed limit at k ~ 0.06/Mpc and k ~ 0.014/Mpc there are marginal 2sigma deviations from the standard featureless bispectrum, which meanwhile is consistent with the reconstructed bispectrum in the equilateral configuration.

    ↳ astro-ph.COgr-qchep-phhep-thPLB(2016)·21 citations
32. 32*

    Calculation of the hadronic vacuum polarization disconnected contribution to the muon anomalous magnetic moment

    T. Blum🇺🇸 · P.A. Boyle🇬🇧 · T. Izubuchi🇺🇸 · L. Jin🇺🇸 · A. Jüttner🇬🇧 · C. Lehner🇺🇸 · K. Maltman🇨🇦 · M. Marinkovic🇨🇭 · A. Portelli🇬🇧 · M. Spraggs🇬🇧

    We report the first lattice QCD calculation of the hadronic vacuum polarization disconnected contribution to the muon anomalous magnetic moment at physical pion mass. The calculation uses a refined noise-reduction technique which enabled the control of statistical uncertainties at the desired level with modest computational effort. Measurements were performed on the $48^3\times 96$ physical-pion-mass lattice generated by the RBC and UKQCD collaborations. We find $a_{\mu }^{\mathrm{HVP}(\mathrm{LO})\mathrm{DISC}}=-9.6(3.3)(2.3)\times 10^{-10}$, where the first error is statistical and the second systematic.

    ↳ hep-lathep-phPRL(2016)·98 citations

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