Fri·May 4, 2018Friday·May 4, 2018

1. 01*

   Effective kinetic description of event-by-event pre-equilibrium dynamics in high-energy heavy-ion collisions

   Aleksi Kurkela🇨🇭 · Aleksas Mazeliauskas🇩🇪 · Jean-François Paquet🇺🇸 · Sören Schlichting🇺🇸 · Derek Teaney🇺🇸

   We develop a macroscopic description of the space-time evolution of the energy-momentum tensor during the pre-equilibrium stage of a high-energy heavy-ion collision. Based on a weak coupling effective kinetic description of the microscopic equilibration process (à la "bottom-up"), we calculate the non-equilibrium evolution of the local background energy-momentum tensor as well as the non-equilibrium linear response to transverse energy and momentum perturbations for realistic boost-invariant initial conditions for heavy ion collisions. We demonstrate how this framework can be used on an event-by-event basis to propagate the energy momentum tensor from far-from-equilibrium initial state models, e.g. IP-Glasma, to the time ${\tau }_{\text{hydro}}$ when the system is well described by relativistic viscous hydrodynamics. The subsequent hydrodynamic evolution becomes essentially independent of the hydrodynamic initialization time ${\tau }_{\text{hydro}}$ as long as ${\tau }_{\text{hydro}}$ is chosen in an appropriate range where both kinetic and hydrodynamic descriptions overlap. We find that for $\sqrt{s_{NN}}=2.76\text{TeV}$ central Pb-Pb collisions, the typical time scale when viscous hydrodynamics with shear viscosity over entropy ratio $\eta /s=0.16$ becomes applicable is ${\tau }_{\text{hydro}}\sim 1\text{fm/c}$ after the collision.

   hep-phnucl-thPRC(2019)·257 citations
2. 02*

   N2HDECAY: Higgs Boson Decays in the Different Phases of the N2HDM

   Isabell Engeln🇩🇪 · Margarete Mühlleitner🇩🇪 · Jonas Wittbrodt🇩🇪

   The program N2HDECAY calculates the branching ratios and decay widths of the Higgs bosons of the Next-to-Two-Higgs-Doublet Model (N2HDM). The code incorporates the dominant higher-order effects by including QCD corrections and off-shell decay modes. The N2HDM is an extension of the Standard Model by a Higgs doublet and a real Higgs singlet. Its phenomenology can change dramatically depending on which global symmetries are broken by electroweak symmetry breaking. It can feature a large visible Higgs sector in the broken phase, behave like a 2HDM with scalar singlet dark matter in the dark singlet phase, or, in the inert doublet phase, extend an inert doublet model by mixing a singlet with the SM Higgs boson. N2HDECAY provides precise predictions for the decays of the Higgs bosons in all of these phases.

   hep-phComput.Phys.Commun.(2019)·53 citations
3. 03*

   Eta Decay and Muonic Puzzles

   Yu-Sheng Liu🇨🇳 · Ian C. Cloët🇺🇸 · Gerald A. Miller🇺🇸

   New physics motivated by muonic puzzles (proton radius and muon $g-2$ discrepancies) is studied. Using a light scalar boson $\varphi$, assuming Yukawa interactions, accounts for these muonic puzzles simultaneously. Our previous work limits the existence of such a scalar boson's mass $m_{\varphi }$ from about 160 keV to 60 MeV. We improve this result by including the influence of all of the possible particles that couple to the $\varphi$ in computing the decay rate. Doing this involves including the strong interaction physics, involving quarks, necessary to compute the $\eta \pi \varphi$ vertex function. The Nambu-Jona-Lasinio model, which accounts for the spontaneous symmetry breaking that yields the constituent mass is employed to represent the relevant strong-interaction physics. We use the $\eta \pi \varphi$ vertex function to reanalyze the electron beam dump experiments. The result is that the allowed range of $m_{\varphi }$ lies between about 160 keV and 3.5 MeV. This narrow range represents an inviting target for ruling out or discovering this scalar boson. A possible UV completion of our phenomenological model is discussed.

   hep-phhep-exnucl-exnucl-th+1NPB(2019)·11 citations
4. 04*

   Threshold resummation of the rapidity distribution for Drell-Yan production at NNLO+NNLL

   Pulak Banerjee🇮🇳 · Goutam Das🇩🇪 · Prasanna K. Dhani🇮🇳 · V. Ravindran🇮🇳

   We consider the production of pairs of lepton through the Drell-Yan process at the LHC and present the most accurate prediction on their rapidity distribution. While the fixed order prediction is already known to next-to-next-to-leading order in perturbative QCD, the resummed contribution coming from threshold region of phase space up to next-to-next-to-leading logarithmic (NNLL) accuracy has been computed in this article. The formalism developed in [1-3] has been used to resum large threshold logarithms in the two dimensional Mellin space to all orders in perturbation theory. We have done a detailed numerical comparison against other approaches that resum certain threshold logarithms in Mellin-Fourier space. Our predictions at NNLL level are close to theirs even though at leading logarithmic and next-to-leading logarithmic level we differ. We have also investigated the impact of these threshold logarithms on the stability of perturbation theory against factorisation and renormalisation scales. While the dependence on these scales does not get better with resummed results, the convergence of the perturbative series shows a better trend compared to the fixed order predictions. This is evident from the reduction in the K-factor for the resummed case compared to fixed order. We also present the uncertainties on the predictions resulting from parton distribution functions.

   hep-phPRD(2018)·54 citations
5. 05*

   Radiative bound-state formation in unbroken perturbative non-Abelian theories and implications for dark matter

   Julia Harz🇫🇷 · Kalliopi Petraki🇫🇷

   We compute the cross-sections for the radiative capture of non-relativistic particles into bound states, in unbroken perturbative non-Abelian theories. We find that the formation of bound states via emission of a gauge boson can be significant for a variety of dark matter models that feature non-Abelian long-range interactions, including multi-TeV scale WIMPs, dark matter co-annihilating with coloured partners and hidden-sector models. Our results disagree with previous computations, on the relative sign of the Abelian and non-Abelian contributions. In particular, in the case of capture of a particle-antiparticle pair into its tightest bound state, we find that these contributions add up, rather than partially canceling each other. We apply our results to dark matter co-annihilating with particles transforming in the (anti)fundamental of SU(3)c, as is the case in degenerate stop-neutralino scenarios in the MSSM. We show that the radiative formation and decay of particle-antiparticle bound states can deplete the dark matter density by (40-240)%, for dark matter heavier than 500 GeV. This implies a larger mass difference between the co-annihilating particles, and allows for the dark matter to be as heavy as 3.3 TeV.

   hep-phJHEP(2018)·90 citations
6. 06*

   Electroweak and QCD corrections to $Z$-boson production with one $b$ jet in a massive 5 Flavor Scheme

   Diogenes Figueroa🇺🇸 · Steven Honeywell🇺🇸 · Seth Quackenbush🇺🇸 · Laura Reina🇺🇸 · Christian Reuschle🇺🇸 · Doreen Wackeroth🇺🇸

   We compute the $O({\alpha }_s{\alpha }^2)$ and $O({\alpha }_s^2\alpha )$ contributions to the production cross section of a $Z$ boson with one $b$ jet at the Large Hadron Collider (LHC), and study their phenomenological relevance for LHC physics. The accurate prediction of hadronic $Z+b$-jet production is needed to control a background that greatly affects both the measurement of Higgs-boson properties and searches of new physics at the LHC. At the same time it could enable the first precise measurement of the $b$-quark parton distribution function. In this context $b$-quark mass effects become relevant and need to be studied with care, both at the level of the hard process and at the level of the initial- and final-state parton evolution. It is the aim of this paper to explore some of these issues in the framework of a massive 5 Flavor Scheme and to assess the need for both the inclusion of electroweak corrections, in addition to QCD corrections, and $b$-quark mass effects in the prediction of total and differential cross sections for hadronic $Z+b$-jet production.

   hep-phPRD(2018)·22 citations
7. 07*

   The ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\mu }^{+}{\mu }^{-}$ decay in the ${\text{RS}}_c$ model

   Aqsa Nasrullah🇵🇰 · Faisal Munir Bhutta🇨🇳 · M. Jamil Aslam🇵🇰

   We study the four body decay ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\mu }^{+}{\mu }^{-}$ in the Randall-Sundrum model with custodial protection $({\text{RS}}_c)$. By considering the constraints coming from the direct searches of the lightest Kaluza-Klein (KK) excitation of the gluon, electroweak precision tests, the measurements of the Higgs signal strengths at the LHC and from $\Delta F=2$ flavor observables, we perform a scan of the parameter space of the ${\text{RS}}_c$ model and obtain the maximum allowed deviations of the Wilson coefficients $\Delta C_{7,9,10}^{(\prime )}$ for different values of the lightest KK gluon mass $M_{g^{(1)}}$. Later, their implications on the observables such as differential branching fraction, longitudinal polarization of the daughter baryon $\Lambda$, forward-backward asymmetry with respect to leptonic, hadronic and combined lepton-hadron angles are discussed where we present the analysis of these observables in different bins of di-muon invariant mass squared $s(=q^2)$. It is observed that with the current constraints the Wilson coefficients in ${\text{RS}}_c$ model show slight deviations from their Standard Model values and hence can not accommodate the discrepancies between the Standard Model calculations of various observables and the LHCb measurements in ${\Lambda }_b$ decays.

   hep-phJ.Phys.G(2018)·8 citations
8. 08*

   Search for the RS model with a small curvature through photon-induced process at the LHC

   S.C. İnan🇹🇷 · A.V. Kisselev🇷🇺

   In this paper, potential of the LHC to explore the phenomenology of the Randall-Sundrum-like scenario with the small curvature for the process $pp\to p\gamma \gamma p\to p{\mu }^{-}{\mu }^{+}p$ through the subprocess $\gamma \gamma \to {\mu }^{-}{\mu }^{+}$ is examined for two forward detector acceptances, $0.0015<\xi <0.5$ and $0.1<\xi <0.5$. This process is known to be one of the most clean channels. The sensitivity bounds on the anomalous model parameters have been found at the $95\%$ confidence level for various LHC integrated luminosity values.

   hep-phhep-exEPJC(2018)·13 citations
9. 09*

   Phase structure of magnetized 2SC quark matter under compact star conditions

   M. Coppola🇦🇷 · P. Allen🇦🇷 · A. G. Grunfeld🇦🇷 · N. N. Scoccola🇦🇷

   Some properties of magnetized two flavor color superconducting (2SC) cold dense quark matter under compact star conditions (COSC) are investigated within a $SU(2{)}_f$ Nambu Jona-Lasinio type model. We study the phase diagram for several model parametrizations. The features of each phase are analyzed through the behavior of the chiral and superconducting condensates for increasing chemical potential or magnetic field. We show how the phases are modified in the presence of $\beta$-equilibrium as well as color and electric charge neutrality conditions.

   hep-ph0 citations
10. 10*

    Pion-pole contribution to hadronic light-by-light scattering in the anomalous magnetic moment of the muon

    Martin Hoferichter🇺🇸 · Bai-Long Hoid🇩🇪 · Bastian Kubis🇩🇪 · Stefan Leupold🇸🇪 · Sebastian P. Schneider🇩🇪

    The ${\pi }^0$ pole constitutes the lowest-lying singularity of the hadronic light-by-light (HLbL) tensor, and thus provides the leading contribution in a dispersive approach to HLbL scattering in the anomalous magnetic moment of the muon $(g-2{)}_{\mu }$. It is unambiguously defined in terms of the doubly-virtual pion transition form factor, which in principle can be accessed in its entirety by experiment. We demonstrate that, in the absence of a direct measurement, the full space-like doubly-virtual form factor can be reconstructed very accurately based on existing data for $e^{+}{e}^{-}\to 3\pi$, $e^{+}{e}^{-}\to e^{+}{e}^{-}{\pi }^0$, and the ${\pi }^0\to \gamma \gamma$ decay width. We derive a representation that incorporates all the low-lying singularities of the form factor, matches correctly onto the asymptotic behavior expected from perturbative QCD, and is suitable for the evaluation of the $(g-2{)}_{\mu }$ loop integral. The resulting value, $a_{\mu }^{{\pi }^0\text{-pole}}=62.6_{-2.5}^{+3.0}\times 10^{-11}$, for the first time, represents a complete data-driven determination of the pion-pole contribution with fully controlled uncertainty estimates. In particular, we show that already improved singly-virtual measurements alone would allow one to further reduce the uncertainty in $a_{\mu }^{{\pi }^0\text{-pole}}$.

    hep-phhep-exhep-latnucl-thPRL(2018)·201 citations
11. 11*

    Super-cool Dark Matter

    Thomas Hambye🇧🇪 · Alessandro Strumia🇮🇹 · Daniele Teresi🇧🇪

    In dimension-less theories of dynamical generation of the weak scale, the Universe can undergo a period of low-scale inflation during which all particles are massless and super-cool. This leads to a new mechanism of generation of the cosmological Dark Matter (DM) relic density: super-cooling can easily suppress the amount of DM to the desired level. This is achieved for TeV-scale DM, if super-cooling ends when quark condensates form at the QCD phase transition. Along this scenario, the baryon asymmetry can be generated either at the phase transition or through leptogenesis. We show that the above mechanism takes place in old and new dimension-less models.

    hep-phastro-ph.COhep-thJHEP(2018)·152 citations
12. 12*

    A Light Higgs at the LHC and the B-Anomalies

    Da Liu🇺🇸 · Jia Liu🇺🇸 · Carlos E.M. Wagner🇺🇸 · Xiao-Ping Wang🇺🇸

    After the Higgs discovery, the LHC has been looking for new resonances, decaying into pairs of Standard Model (SM) particles. Recently, the CMS experiment observed an excess in the di-photon channel, with a di-photon invariant mass of about 96~GeV. This mass range is similar to the one of an excess observed in the search for the associated production of Higgs bosons with the $Z$ neutral gauge boson at LEP, with the Higgs bosons decaying to bottom quark pairs. On the other hand, the LHCb experiment observed a discrepancy with respect to the SM expectations of the ratio of the decay of $B$-mesons to $K$-mesons and a pair of leptons, $R_{K^{(\ast )}}=BR(B\to K^{(\ast )}{\mu }^{+}{\mu }^{-})/BR(B\to K^{(\ast )}{e}^{+}{e}^{-})$. This observation provides a hint of the violation of lepton-flavor universality in the charged lepton sector and may be explained by the existence of a vector boson originating form a $U(1{)}_{L_{\mu }-L_{\tau }}$ symmetry and heavy quarks that mix with the left-handed down quarks. Since the coupling to heavy quarks could lead to sizable Higgs di-photon rates in the gluon fusion channel, in this article we propose a common origin of these anomalies identifying a Higgs associated with the breakdown of the $U(1{)}_{L_{\mu }-L_{\tau }}$ symmetry and at the same time responsible to the quark mixing, with the one observed at the LHC. We also discuss the constraints on the identification of the same Higgs with the one associated with the bottom quark pair excess observed at LEP.

    hep-phhep-exJHEP(2018)·44 citations
13. 13*

    Unitarity of the Box Diagram

    Roji Pius🇨🇦 · Ashoke Sen🇮🇳

    The complete proof of cutting rules needed for proving perturbative unitarity of quantum field theories usually employs the largest time equation or old fashioned perturbation theory. None of these can be generalized to string field theory that has non-local vertices. In arXiv:1604.01783 we gave a proof of cutting rules in string field theory, which also provides an alternative proof of cutting rules in ordinary quantum field theories. In this note we illustrate how this works for the box diagram of ${\varphi }^4$ field theory, avoiding the contributions from anomalous thresholds.

    ↳ hep-thhep-phJHEP(2018)·28 citations
14. 14*

    What symmetry is actually broken in the Higgs phase of a gauge-Higgs theory?

    Jeff Greensite🇺🇸 · Kazue Matsuyama🇺🇸

    In SU($N$) gauge-Higgs theories, with a single Higgs field in the fundamental representation, there exists in addition to the local gauge symmetry a global SU(2) symmetry, at $N=2$, and a global U(1) symmetry, for $N\ne 2$. We construct a gauge-invariant order parameter for the breaking of these global symmetries in the Higgs sector, and calculate numerically the transition lines, in coupling-constant space, for SU(2) and SU(3) gauge theories with unimodular Higgs fields. The order parameter is non-local, and therefore its non-analyticity does not violate the theorem proved by Osterwalder and Seiler. We then show that there exists a transition, in gauge-Higgs theories, between two types of confinement: ordinary color neutrality in the Higgs region, and a stronger condition, which we have called "separation-of-charge confinement," in the confinement region. We conjecture that the symmetry-breaking transition coincides with the transition between these two physically different types of confinement.

    ↳ hep-thcond-mat.supr-conhep-lathep-phPRD(2018)·27 citations
15. 15*

    Cosmology in scalar-vector-tensor theories

    Lavinia Heisenberg🇨🇭 · Ryotaro Kase🇯🇵 · Shinji Tsujikawa🇯🇵

    We study the cosmology on the Friedmann-Lemaitre-Robertson-Walker background in scalar-vector-tensor theories with a broken $U(1)$ gauge symmetry. For parity-invariant interactions arising in scalar-vector-tensor theories with second-order equations of motion, we derive conditions for the absence of ghosts and Laplacian instabilities associated with tensor, vector, and scalar perturbations at linear order. This general result is applied to the computation of the primordial tensor power spectrum generated during inflation as well as to the speed of gravity relevant to dark energy. We also construct a concrete inflationary model in which a temporal vector component $A_0$ contributes to the dynamics of cosmic acceleration besides a scalar field $\varphi$ through their kinetic mixings. In this model, we show that all the stability conditions of perturbations can be consistently satisfied during inflation and subsequent reheating.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2018)·50 citations
16. 16*

    New constraints on axion-mediated P,T-violating interaction from electric dipole moments of diamagnetic atoms

    V. A. Dzuba🇦🇺 · V. V. Flambaum🇦🇺 · I. B. Samsonov🇦🇺 · Y. V. Stadnik🇩🇪

    The exchange of an axion-like particle between atomic electrons and the nucleus may induce electric dipole moments (EDMs) of atoms and molecules. This interaction is described by a parity- and time-reversal-invariance-violating potential which depends on the product of a scalar $g^s$ and a pseudoscalar $g^p$ coupling constant. We consider the interaction with the specific combination of these constants, $g_e^s{g}_N^p$, which gives significant contributions to the EDMs of diamagnetic atoms. In this paper, we calculate these contributions to the EDMs of ${}^{199}$Hg, ${}^{129}$Xe, ${}^{211}$Rn and ${}^{225}$Ra for a wide range of axion masses. Comparing these results with recent experimental EDM measurements, we place new constraints on $g_e^s{g}_N^p$. The most stringent atomic EDM limits come from ${}^{199}$Hg and improve on existing laboratory limits from other experiments for axion masses exceeding $10^{-2}$ eV.

    ↳ physics.atom-phhep-phPRD(2018)·48 citations
17. 17*

    Monte Carlo approach to the excluded-volume hadron resonance gas in grand canonical and canonical ensembles

    Volodymyr Vovchenko🇩🇪 · Mark I. Gorenstein🇺🇦 · Horst Stoecker🇩🇪

    The Monte Carlo (MC) procedure for sampling the hadron yields within hadron resonance gas (HRG) model is presented. The effects of excluded-volume due to the finite hadron eigenvolumes and of exact charge conservation within the canonical ensemble (CE) formulation are simultaneously taken into account with the help of the importance sampling technique combined with the rejection sampling. The MC procedure allows one to calculate arbitrary moments of the event-by-event hadron yields. Note that the CE formulation for the excluded-volume HRG has not been considered before. The MC simulations coincide with the known analytic results in the thermodynamic limit for the excluded-volume HRG in the grand canonical ensemble and for the CE of non-interacting particles. The MC procedure is applied to study the simultaneous excluded-volume and CE effects. These effects are considered within the full HRG to calculate the particle number fluctuations and to estimate the finite size effects.

    ↳ nucl-thhep-phPRC(2018)·18 citations
18. 18*

    Concerns about Modelling of the EDGES Data

    Richard Hills🇬🇧 · Girish Kulkarni🇬🇧 · P. Daniel Meerburg🇬🇧 · Ewald Puchwein🇬🇧

    It is predicted that the spectrum of radio emission from the whole sky should show a dip arising from the action of the light from the first stars on the hydrogen atoms in the surrounding gas, which causes the 21-cm line to appear in absorption against the cosmic microwave background. Bowman et al. 2018 identified a broad flat-bottomed absorption profile centred at 78 MHz, which could be this feature, although the depth of the profile is much larger than expected. We have examined the modelling process they used and find that their data implies unphysical parameters for the foreground emission and also that their solution is not unique in the sense that we found other simple formulations for the signal that are different in shape but that also fit their data. We argue that this calls into question the interpretation of these data as an unambiguous detection of the cosmological 21-cm absorption signature.

    ↳ astro-ph.COastro-ph.IMhep-phNature(2018)·277 citations
19. 19*

    New exact solutions of relativistic hydrodynamics for longitudinally expanding fireballs

    T. Csorgo🇭🇺 · G. Kasza🇭🇺 · M. Csanad🇭🇺 · Z. Jiang🇨🇳

    We present new, exact, finite solutions of relativistic hydrodynamics for longitudinally expanding fireballs for arbitrary constant value of the speed of sound. These new solutions generalize earlier, longitudinally finite, exact solutions, from an unrealistic to a reasonable equation of state, characterized by a temperature independent (average) value of the speed of sound. Observables like the rapidity density and the pseudorapidity density are evaluated analytically, resulting in simple and easy to fit formulae that can be matched to the high energy proton-proton and heavy ion collision data at RHIC and LHC. In the longitudinally boost-invariant limit, these new solutions approach the Hwa-Bjorken solution and the corresponding rapidity distributions approach a rapidity plateaux.

    ↳ nucl-thhep-exhep-phnucl-exUniverse(2018)·22 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.