Mon·Jul 16, 2018Monday·July 16, 2018

1. 01*

   Reports of My Demise Are Greatly Exaggerated: $N$-subjettiness Taggers Take On Jet Images

   Liam Moore🇧🇪 · Karl Nordström🇳🇱 · Sreedevi Varma🇬🇧 · Malcolm Fairbairn🇬🇧

   We compare the performance of a convolutional neural network (CNN) trained on jet images with dense neural networks (DNNs) trained on n-subjettiness variables to study the distinguishing power of these two separate techniques applied to top quark decays. We find that they perform almost identically and are highly correlated once jet mass information is included, which suggests they are accessing the same underlying information which can be intuitively understood as being contained in 4-, 5-, 6-, and 8-body kinematic phase spaces depending on the sample. This suggests both of these methods are highly useful for heavy object tagging and provides a tentative answer to the question of what the image network is actually learning.

   hep-phSciPost Phys.(2019)·53 citations
2. 02*

   In-medium spectral functions and dilepton rates with the Functional Renormalization Group

   Ralf-Arno Tripolt🇮🇹 · Christopher Jung🇩🇪 · Naoto Tanji🇮🇹 · Lorenz von Smekal🇩🇪 · Jochen Wambach🇮🇹

   We present recent results on in-medium spectral functions of vector and axial-vector mesons, the electromagnetic (EM) spectral function and dilepton rates using the Functional Renormalization Group (FRG) approach. Our method is based on an analytic continuation procedure that allows us to calculate real-time quantities like spectral functions at finite temperature and chemical potential. As an effective low-energy model for Quantum Chromodynamics (QCD) we use an extended linear-sigma model including quarks where (axial-)vector mesons as well as the photon are introduced as gauge bosons. In particular, it is shown how the $\rho$ and the $a_1$ spectral function become degenerate at high temperatures or chemical potentials due to the restoration of chiral symmetry. Preliminary results for the EM spectral function and the dilepton production rate are discussed with a focus on the possibility to identify signatures of the chiral crossover and the critical endpoint (CEP) in the QCD phase diagram.

   hep-phnucl-thNPA(2019)·23 citations
3. 03*

   Right sneutrino with $\Delta L=2$ masses as non-thermal dark matter

   Avirup Ghosh🇮🇳 · Tanmoy Mondal🇮🇳 · Biswarup Mukhopadhyaya🇮🇳

   We consider MSSM with right-chiral neutrino superfields with Majorana masses, where the lightest right-handed sneutrino dominated scalars constitutes non-thermal dark matter (DM). The $\Delta L=2$ masses are subject to severe constraints coming from freeze-in relic density of such DM candidates as well as from sterile neutrino $\text{freeze-in}$. In addition, big-bang Nucleosynthesis and $\text{freeze-out}$ of the next-to-lightest superparticle shrink the viable parameter space of such a scenario. We examine various $\Delta L=2$ mass terms for families other than that $\Delta L=2$ masses are difficult to reconcile with a right-sneutrino DM, unless there is either (a) a hierarchy of about 3 orders of magnitudes among various supersymmetry-breaking mass parameters, or, (b) strong cancellation between the higgsino mass and the trilinear supersymmetry breaking mass parameter for sneutrinos.

   hep-phPRD(2019)·9 citations
4. 04*

   On the use of a running coupling in the calculation of forward hadron production at next-to-leading order

   B. Ducloué🇫🇷 · E. Iancu🇫🇷 · T. Lappi🇫🇮 · A. H. Mueller🇺🇸 · G. Soyez🇫🇷 · D. N. Triantafyllopoulos🇮🇹 · Y. Zhu🇩🇪

   We study a puzzle raised recently regarding the running coupling prescription used in the calculation of forward particle production in proton-nucleus collisions at next-to-leading order: using a coordinate space prescription which is consistent with the one used in the high energy evolution of the target leads to results which can be two orders of magnitude larger than the ones obtained with a momentum space prescription. We show that this is an artefact of the Fourier transform involved when passing between coordinate and momentum space and propose a new coordinate space prescription which avoids this problem.

   hep-phNPA(2019)·2 citations
5. 05*

   CoLoRFulNNLO for LHC processes

   Adam Kardos🇭🇺 · Giuseppe Bevilacqua🇭🇺 · Gábor Somogyi🇭🇺 · Zoltán Trócsányi🇭🇺 · Zoltán Tulipánt🇭🇺

   In my talk I gave a status update on the extension of the CoLoRFulNNLO subtraction method for computing QCD jet cross sections with hadrons in the initial state. The scheme has been fully worked out previously for electron-positron collisions and recently important steps have been made towards generalizing it to be able to deliver corrections of the same order for LHC processes as well. In particular, the important bottleneck of regularizing multiple real emissions has been addressed. We demonstrate the numerical stability of the CoLoRFulNNLO method by computing the doubly real contribution for Higgs-boson production in gluon-gluon fusion and for W production.

   hep-phPoS(2018)·5 citations
6. 06*

   b-s Anomaly Decays in Covariant Quark Model

   Aidos Issadykov🇷🇺 · Mikhail A. Ivanov🇷🇺

   The work is devoted to the study of b-s anomaly decays. We evaluated branching fractions of $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$, $B_s^0\to \varphi {\mu }^{+}{\mu }^{-}$ and $B_s\to {\mu }^{+}{\mu }^{-}$ decays and compared them with available experimental data and with results from other theoretical approaches.

   hep-phPhys.Part.Nucl.Lett.(2018)·3 citations
7. 07*

   Direct Detection is testing Freeze-in

   Thomas Hambye🇧🇪 · Michel H.G. Tytgat🇧🇪 · Jérôme Vandecasteele🇧🇪 · Laurent Vanderheyden🇧🇪

   Dark Matter (DM) may belong to a hidden sector that is only feebly interacting with the Standard Model (SM) and may have never been in thermal equilibrium in the Early Universe. In this case, the observed abundance of dark matter particles could have built up through a process known as Freeze-in. We show that, for the first time, direct detection experiments are testing this DM production mechanism. This applies to scenarios where the SM and hidden sectors communicate through a light mediator particle of mass less than a few MeV. Through the exchange of such light mediator, the very same FIMP candidates can have self-interactions that are in the range required to address the small scale structure issues of collisionless cold dark matter.

   hep-phastro-ph.COPRD(2018)·103 citations
8. 08*

   Nonequilibrium quark production in the expanding QCD plasma

   Naoto Tanji🇮🇹 · Juergen Berges🇩🇪

   We present real-time lattice simulation results for nonequilibrium quark production from an over-occupied gluon plasma in longitudinally expanding geometry. The quark number density per unit transverse area and rapidity shows almost linear growth in time, and its growth rate appears to be consistent with a simple kinetic theory estimate involving only two-to-two scattering processes in small-angle approximation. We also find that quarks produced at early times satisfy a nonequilibrium scaling law.

   hep-phnucl-thNPA(2019)·1 citation
9. 09*

   Forward rapidity isolated photon production in proton-nucleus collisions

   B. Ducloué🇫🇷 · T. Lappi🇫🇮 · H. Mäntysaari🇫🇮

   We calculate isolated photon production at forward rapidities in proton-nucleus collisions in the Color Glass Condensate framework. Our calculation uses dipole cross sections solved from the running coupling Balitsky-Kovchegov equation with an initial condition fit to deep inelastic scattering data and extended to nuclei with an optical Glauber procedure that introduces no additional parameters beyond the basic nuclear geometry. We present predictions for future forward RHIC and LHC measurements. The predictions are also compared to updated results for the nuclear modification factors for pion production, Drell-Yan dileptons and $J/\psi$ mesons in the same forward kinematics, consistently calculated in the same theoretical framework. We find that leading order, running coupling high energy evolution in the CGC picture leads to a significant nuclear suppression at forward rapidities. This nuclear suppression is stronger for photons than for pions. We also discuss how this might change with next-to-leading order high energy evolution.

   hep-phnucl-thNPA(2019)·0 citations
10. 10*

    Scrutinizing Right-Handed Neutrino Portal Dark Matter With Yukawa Effect

    Priyotosh Bandyopadhyay🇮🇳 · Eung Jin Chun🇰🇷 · Rusa Mandal🇮🇳 · Farinaldo S. Queiroz🇧🇷

    Analyzing the neutrino Yukawa effect in the freeze-out process of a generic dark matter candidate with right-handed neutrino portal, we identify the parameter regions satisfying the observed dark matter relic density as well as the current Fermi-LAT and H.E.S.S. limits and the future CTA reach on gamma-ray signals. In this scenario the dark matter couples to the Higgs boson at one-loop level and thus could be detected by spin-independent nucleonic scattering for a reasonable range of the relevant parameters.

    hep-phPLB(2019)·46 citations
11. 11*

    Four-loop results for the cusp anomalous dimension

    R.Brüser🇩🇪 · A.G.Grozin🇷🇺 · J.M.Henn🇩🇪 · M.Stahlhofen🇩🇪

    We review the current status of calculations of the HQET field anomalous dimension and the cusp anomalous dimension. In particular, we give the results at 4 loops for the quartic Casimir contribution, and for the full QED case, up to ${\phi }^6$ in the small angle expansion. Furthermore, we discuss the leading terms in the anti-parallel lines limit at four loops.

    hep-phPoS(2018)·6 citations
12. 12*

    Phenomenology of extra quarks at the LHC

    Hugo Prager🇬🇧

    We study in a model independent way models of new Physics featuring extra quarks (XQs). These XQs are predicted by extensions of the Standard Model (SM) but have never been observed yet even though many searches have been designed to find them at the LHC. After an introduction about the SM and the LHC, we present the main properties of these XQs and a model independent parametrisation that can be used to describe their phenomenology with generic hypotheses about their mixing with SM quarks, both in the case of XQ coupling with SM bosons and with Dark Matter (DM) candidates. In these cases we study the offshellness effects in pair-production and decay and show that if the Narrow-Width Approximation (NWA) is a good approximation of the full result in the small width over mass ratio limit, sizeable differences occur when the XQ width becomes larger. The conclusion of our analysis is that even though the small width assumption is always conservative it is not possible to trivially rescale the mass bounds obtained considering processes of pair production and decay in the NWA to determine constraints for XQs with large widths. We also study the role of interference in the process of pair production of new heavy XQs decaying to SM particles and show that in the NWA the interference contribution can be described by considering a parameter which contains only the relevant couplings and the scalar part of the propagators of the new quarks, both at the cross section level and at the distribution level. Finally, we study how various SUSY searches perform for our simplified model with XQs decaying to DM. We show that the bound for XQs can be obtained from the SUSY ones just by rescaling the exclusion with the XQ cross section.

    hep-ph0 citations
13. 13*

    Electroweak corrections in the Two-Higgs-Doublet Model and a Singlet Extension of the Standard Model

    Lukas Altenkamp🇩🇪 · Michele Boggia🇩🇪 · Stefan Dittmaier🇩🇪 · Heidi Rzehak🇩🇰

    We present the next-to-leading-order calculation of the partial decay widths of light CP-even Higgs bosons decaying into four fermions in the Two-Higgs-Doublet Model and a Singlet Extension of the Standard Model. Different renormalization schemes are applied in the calculation, which is implemented into the analysis tool PROPHECY4F. Some sample results on the Higgs->4fermions decay widths illustrate how the corrections reduce the dependence on the renormalization scale and the choice of the scheme.

    hep-phPoS(2018)·4 citations
14. 14*

    Measurements of directed and elliptic flow for $D^0$ and $\overline{D^0}$ mesons using the STAR detector at RHIC

    Subhash Singha (for the STAR Collaboration)🇺🇸

    We report on the first evidence for a non-zero rapidity-odd directed flow ($v_1$) for $D^0$ and $\overline{D^0}$ mesons in 10-80\% centrality Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200~GeV measured with the STAR detector at RHIC. The slope of the $v_1$ rapidity dependence ($d{v}_1/dy$) averaged over $D^0$ and $\overline{D^0}$ mesons is -0.081 $\pm$ 0.021 $\pm$ 0.017, while that of charged kaons is -0.0030 $\pm$ 0.0001 $\pm$ 0.0002, suggesting significantly larger slope for the $D^0$ mesons. Models indicate that the large $d{v}_1/dy$ of $D^0$ mesons is sensitive to the initially tilted source. We also present a new measurement of the $D^0$ meson elliptic flow ($v_2$) as a function of transverse momentum ($p_T$) in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200~GeV with an improved precision with respect to the previously published results.The $D^0$ $v_2$ results are compared to those of light-flavor hadrons to test the number-of-constituent-quark (NCQ) scaling. Both the $v_1$ and $v_2$ results are compared to recent hydrodynamic and transport model calculations.

    ↳ nucl-exhep-exhep-phnucl-thNPA(2019)·7 citations
15. 15*

    Monopole and instanton effects in QCD

    Masayasu Hasegawa🇷🇺

    We aim to show the effects of the magnetic monopoles and instantons in quantum chromodynamics (QCD) on observables; therefore, we introduce a monopole and anti-monopole pair in the QCD vacuum of a quenched SU(3) by applying the monopole creation operator to the vacuum. We calculate the eigenvalues and eigenvectors of the overlap Dirac operator that preserves the exact chiral symmetry in lattice gauge theory using these QCD vacua. We then investigate the effects of magnetic monopoles and instantons. First, we confirm the monopole effects as follows: (i) The monopole creation operator makes the monopoles and anti-monopoles in the QCD vacuum. (ii) A monopole and anti-monopole pair creates an instanton or anti-instanton without changing the structure of the QCD vacuum. (iii) The monopole and anti-monopole pairs change only the scale of the spectrum distribution without affecting the spectra of the Dirac operator by comparing the spectra with random matrix theory. Next, we find the instanton effects by increasing the number density of the instantons and anti-instantons as follows: (iv) The decay constants of the pseudoscalar increase. (v) The values of the chiral condensate, which are defined as negative numbers, decrease. (vi) The light quarks and the pseudoscalar mesons become heavy. The catalytic effect on the charged pion is estimated using the numerical results of the pion decay constant and the pion mass. (vii) The decay width of the charged pion becomes wider than the experimental result, and the lifetime of the charged pion becomes shorter than the experimental result. These are the effects of the monopoles and instantons in QCD.

    ↳ hep-lathep-exhep-phJHEP(2020)·5 citations
16. 16*

    Heavy-flavor nuclear modification factor and event-by-event azimuthal anisotropy correlations in heavy ion collisions

    Caio Alves Garcia Prado🇧🇷

    Relativistic heavy ion collisions, which are performed at large experimental programs such as Relativistic Heavy Ion Collider's (RHIC) STAR experiment and the Large Hadron Collider's (LHC) experiments, can create an extremely hot and dense state of the matter known as the quark gluon plasma (QGP). A huge amount of sub-nucleonic particles are created in the collision processes and their interaction and subsequent evolution after the collision takes place is at the core of the understanding of the matter that builds up the Universe. It has recently been shown that event-by-event fluctuations in the spatial distribution between different collision events have great impact on the particle distributions that are measured after the evolution of the created system. Specifically, these distributions are greatly responsible for generating the observed azimuthal anisotropy in measurements. Furthermore, the eventual cooling and expansion of the fluctuating system can become very complex due to lumps of energy density and temperature, which affects the interaction of the particles that traverse the medium. In this configuration, heavy flavor particles play a special role, as they are generally created at the initial stages of the process and have properties that allow them to retain "memory" from the interactions within the whole evolution of the system. However, the comparison between experimental data and theoretical or phenomenological predictions on the heavy flavor sector cannot fully explain the heavy quarks coupling with the medium and their subsequent hadronization process. [Full abstract in file]

    ↳ nucl-thhep-phnucl-ex2 citations
17. 17*

    Witnessing Entanglement In Compton Scattering Processes Via Mutually Unbiased Bases

    B. C. Hiesmayr🇦🇹 · P. Moskal🇵🇱

    We present a quantum information theoretic version of the Klein-Nishina formula. This formulation singles out the quantity, the a priori visibility, that quantifies the ability to deduce the polarisation property of single photons. The Kraus-type structure allows a straightforward generalisation to the multiphoton cases, relevant in the decay of positronium which is utilized e.g. for metabolic PET-imaging (Positron-Emission-Tomograph). Predicted by theory but never experimentally proven, the two- or three-photon states should be entangled. We provide an experimentally feasible method to witness entanglement for these processes via MUBs (Mutually Unbiased Bases), exploiting Bohr's complementarity. Last but not least we present explicit cases exemplifying the interrelation of geometry and entanglement including relations to its potentiality for teleportation schemes or Bell inequality violations or in future for detecting cancer in human beings.

    ↳ quant-phhep-phSci.Rep.(2019)·57 citations
18. 18*

    Non-Equilibrium Quantum Transport of Chiral Fluids from Kinetic Theory

    Yoshimasa Hidaka🇯🇵 · Shi Pu🇯🇵 · Di-Lun Yang🇯🇵

    We introduce the quantum-field-theory (QFT) derivation of chiral kinetic theory (CKT) from the Wigner-function approach, which manifests side jumps and non-scalar distribution functions associated with Lorentz covariance and incorporates both background fields and collisions. The formalism is utilized to investigate second-order responses of chiral fluids near local equilibrium. Such non-equilibrium anomalous transport is dissipative and affected by interactions. Contributions from both quantum corrections in anomalous hydrodynamic equations (EOM) of motion and those from the CKT and Wigner functions (WF) are considered in a relaxation-time approximation (RTA). Anomalous charged Hall currents engendered by background electric fields and temperature/chemical-potential gradients are obtained. Furthermore, chiral magnetic/vortical effects (CME/CVE) receive viscous corrections as non-equilibrium modifications stemming from the interplay between side jumps, magnetic-moment coupling, and chiral anomaly.

    ↳ nucl-thhep-phhep-thNPA(2019)·19 citations
19. 19*

    Mass splittings in a linear sigma model for multiflavor gauge theories

    Diego De Floor🇺🇸 · Erik Gustafson🇺🇸 · Yannick Meurice🇺🇸

    We calculate the tree-level mass spectrum for a linear sigma model describing the scalar and pseudoscalar mesons of a $SU(3)$ local gauge theory with Dirac fermions in the fundamental representation. $N_1$ fermions have a mass $m_1$ and $N_2$ a mass $m_2$. Using recent lattice data with $m_1=m_2$ and $N_1+N_2$= 8 or 12, we predict the mass splittings for $m_2=m_1+\delta m$. At first order in $\delta m$, an interesting inverted pattern appears in the $0^{++}$ sector, where mesons with lighter fermions are heavier. This feature could be tested in ongoing calculations provided that $m_1$ and $\delta m$ are sufficiently small. We discuss possible improvements of the approach.

    ↳ hep-lathep-phhep-thPRD(2018)·8 citations
20. 20*

    Resummation in QFT with Meijer G-functions

    Oleg Antipin🇭🇷 · Alessio Maiezza🇭🇷 · Juan Carlos Vasquez🇨🇱

    We employ a recent resummation method to deal with divergent series, based on the Meijer G-function, which gives access to the non-perturbative regime of any QFT from the first few known coefficients in the perturbative expansion. Using this technique, we consider in detail the ${\varphi }^4$ model where we estimate the non-perturbative $\beta -$function and prove that its asymptotic behavior correctly reproduces instantonic effects calculated using semiclassical methods. After reviewing the emergence of the renormalons in this theory, we also speculate on how one can resum them. Finally, we resum the non-perturbative $\beta -$function of abelian and non-abelian gauge-fermion theories and analyze the behavior of these theories as a function of the number of fermion flavors. While in the former no fixed points are found, in the latter, a richer phase diagram is uncovered and illustrated by the regions of confinement, large-distance conformality, and asymptotic safety.

    ↳ hep-thhep-lathep-phNPB(2019)·16 citations
21. 21*

    Theoretical study of the ${\Delta }^{++}-{\Delta }^{-}$ configuration in the deuteron using antiproton beam

    A.B. Larionov🇩🇪 · A. Gillitzer🇩🇪 · J. Haidenbauer🇩🇪 · M. Strikman🇺🇸

    We study the manifestation of the ${\Delta }^{++}-{\Delta }^{-}$ component of the deuteron wave function in the exclusive reaction $\bar{p}d\to {\pi }^{-}{\pi }^{-}{\Delta }^{++}$. Due to the large binding energy the internal motion in the $\Delta -\Delta$ system is relativistic. We take this into account within the light-cone (LC) wave function formalism and, indeed, found large differences between calculations based on the LC and non-relativistic (NR) wave functions. We demonstrate, that the consistent LC treatment of the $\Delta -\Delta$ system plays the key role in the separation of the signal and background. Within the LC approach, the characteristic shape of the momentum distribution of the $\Delta -\Delta$ bound system predicted by the meson-exchange model is well visible on the background of usual annihilations at beam momenta between 10 and 15 GeV/c.

    ↳ nucl-thhep-exhep-phnucl-exPRC(2018)·8 citations
22. 22*

    Dynamical initialization and hydrodynamic modeling of relativistic heavy-ion collisions

    Chun Shen🇺🇸 · Björn Schenke🇺🇸

    We present a fully three-dimensional model providing initial conditions for energy and conserved charge density distributions in heavy ion collisions at RHIC Beam Energy Scan (BES) collision energies. The model includes the dynamical deceleration of participating nucleons or valence quarks. It provides a realistic estimation of the initial baryon stopping during the early stage of collisions. We also present the implementation of the model with 3+1 dimensional hydrodynamics, which involves the addition of source terms that deposit energy and net-baryon densities produced by the initial state model at proper times greater than the initial time for the hydrodynamic simulation. The importance of this dynamical initialization stage on hadronic flow observables at the RHIC BES is quantified.

    ↳ nucl-thhep-phnucl-exNPA(2019)·35 citations
23. 23*

    Limits on Neutrino Lorentz Violation from Multimessenger Observations of TXS 0506+056

    John Ellis🇬🇧 · Nikolaos E. Mavromatos🇬🇧 · Alexander S. Sakharov🇺🇸 · Edward K. Sarkisyan-Grinbaum🇨🇭

    The observation by the IceCube Collaboration of a high-energy ($E\gtrsim 200$ TeV) neutrino from the direction of the blazar TXS 0506+056 and the coincident observations of enhanced $\gamma$-ray emissions from the same object by MAGIC and other experiments can be used to set stringent constraints on Lorentz violation in the propagation of neutrinos that is linear in the neutrino energy: $\Delta v=-E/M_1$, where $\Delta v$ is the deviation from the velocity of light, and $M_1$ is an unknown high energy scale to be constrained by experiment. Allowing for a difference in neutrino and photon propagation times of $\sim 10$ days, we find that $M_1\gtrsim 3\times 10^{16}$ GeV. This improves on previous limits on linear Lorentz violation in neutrino propagation by many orders of magnitude, and the same is true for quadratic Lorentz violation.

    ↳ astro-ph.HEastro-ph.COgr-qchep-ph+1PLB(2019)·53 citations
24. 24*

    On Possibility of Determining Neutrino Mass Hierarchy by the Charged-Current and Neutral-Current Events of Supernova Neutrinos in Scintillation Detectors

    Fei-Fan Lee🇨🇳 · Feng-Shiuh Lee🇹🇼 · Kwang-Chang Lai🇹🇼

    One of the unresolved mysteries in neutrino physics is the neutrino mass hierarchy. We present a new method to determine neutrino mass hierarchy by comparing the events of inverse beta decays (IBD), ${\bar{\nu }}_e+p\to n+e^{+}$, and neutral current (NC) interactions, $\nu (\overline{\nu })+p\to \nu (\overline{\nu })+p$, of supernova neutrinos from accretion and cooling phases in scintillation detectors. Supernova neutrino flavor conversions depend on the neutrino mass hierarchy. On account of Mikheyev-Smirnov-Wolfenstein effects, the full swap of ${\bar{\nu }}_e$ flux with the ${\bar{\nu }}_x$ ($x=\mu ,\tau$) one occurs in the inverted hierarchy, while such a swap does not occur in the normal hierarchy. In consequence, the ratio of high energy IBD events to NC events for the inverted hierarchy is higher than in the normal hierarchy. Since the luminosity of ${\bar{\nu }}_e$ is larger than that of ${\nu }_x$ in accretion phase while the luminosity of ${\bar{\nu }}_e$ becomes smaller than that of ${\nu }_x$ in cooling phase, we calculate this ratio for both accretion and cooling phases. By analyzing the change of this event ratio from accretion phase to cooling phase, one can determine the neutrino mass hierarchy.

    ↳ astro-ph.HEhep-phEPJC(2019)·1 citation
25. 25*

    Holographic Collisions across a Phase Transition

    Maximilian Attems🇪🇸 · Yago Bea🇪🇸 · Jorge Casalderrey-Solana🇪🇸 · David Mateos🇪🇸 · Miquel Triana🇪🇸 · Miguel Zilhao🇪🇸

    We use holography to analyse relativistic collisions in a one-parameter family of strongly coupled gauge theories with thermal phase transitions. For a critical value of the parameter the transition is second order, for subcritical values it is first order, and for super-critical values it is a smooth crossover. We extract the gauge theory stress tensor from collisions of gravitational shock waves on the dual geometries. Regardless of the nature of the transition, for values of the parameter close to the critical value almost all the energy of the projectiles is deposited into a long-lived, quasi-static blob of energy at mid-rapidity. This configuration is well described by the constitutive relations of second-order hydrodynamics that include all second-order gradients that are purely spatial in the local rest frame. In contrast, a Müller-Israel-Stewart-type formulation of hydrodynamics fails to provide a good description. We discuss possible implications for searches of the QCD critical point.

    ↳ hep-thhep-phnucl-thPRL(2018)·59 citations
26. 26*

    Bounds on Slow Roll and the de Sitter Swampland

    Sumit K. Garg🇮🇳 · Chethan Krishnan🇮🇳

    The recently introduced swampland criterion for de Sitter (arXiv:1806.08362) can be viewed as a (hierarchically large) bound on the smallness of the slow roll parameter ${ϵ}_V$. This leads us to consider the other slow roll parameter ${\eta }_V$ more closely, and we are lead to conjecture that the bound is not necessarily on ${ϵ}_V$, but on slow roll itself. A natural refinement of the de Sitter swampland conjecture is therefore that slow roll is violated at $\mathcal{O}(1)$ in Planck units in any UV complete theory. A corollary is that ${ϵ}_V$ need not necessarily be $\mathcal{O}(1)$, if ${\eta }_V\lesssim -\mathcal{O}(1)$ holds. We consider various tachyonic tree level constructions of de Sitter in IIA/IIB string theory (as well as closely related models of inflation), which superficially violate arXiv:1806.08362, and show that they are consistent with this refined version of the bound. The phrasing in terms of slow roll makes it plausible why both versions of the conjecture run into trouble when the number of e-folds during inflation is high. We speculate that one way to evade the bound could be to have a large number of fields, like in $N$-flation.

    ↳ hep-thastro-ph.COgr-qchep-phJHEP(2019)·749 citations
27. 27*

    Features of the IP-Glasma

    Björn Schenke🇺🇸 · Chun Shen🇺🇸 · Prithwish Tribedy🇺🇸

    We discuss differences between the IP-Glasma model and typical wounded-nucleon model like initial conditions. We point out that the IP-Glasma initial state is more compact in the transverse plane and produces a significant initial flow, both of which contribute to an increased radial flow in the subsequent hydrodynamic evolution. A larger bulk viscosity, compared to calculations that use other initial state models, is required to compensate for these effects and find agreement with experimental data. We further demonstrate the importance of the initial momentum anisotropy of the glasma for anisotropy measures in small collision systems such as p+Pb.

    ↳ nucl-thhep-phNPA(2019)·24 citations
28. 28*

    Studying the Milky Way Pulsar Population with Cosmic-Ray Leptons

    Ilias Cholis🇺🇸 · Tanvi Karwal🇺🇸 · Marc Kamionkowski🇺🇸

    Recent measurements of cosmic-ray electron and positron spectra at energies from a GeV to 5 TeV, as well as radio, X-ray and a wide range of gamma-ray observations of pulsar-wind nebulae, indicate that pulsars are significant sources of high-energy cosmic-ray electrons and positrons. Here we calculate the local cosmic-ray $e^{\pm }$ energy spectra from pulsars taking into account models for (a) the distribution of the pulsars spin-down properties; (b) the cosmic-ray source spectra; and (c) the physics of cosmic-ray propagation. We then use the measured cosmic-ray fluxes from AMS-02, CALET and DAMPE to constrain the space of pulsar and cosmic-ray-propagation models and in particular, local cosmic-ray diffusion and energy losses, the pulsars' energy-loss time-dependence, and the injected $e^{\pm }$ spectra. We find that the lower estimates for the local $e^{\pm }$ energy losses are inconsistent with the data. We also find that pulsar braking indexes of 2.5 or less for sources with ages more than 10 kyr are strongly disfavored. Moreover, the cosmic-ray data are consistent with a wide range of assumptions on the $e^{\pm }$ injection spectral properties and on the distribution of initial spin-down powers. Above a TeV in energy, we find that pulsars can easily explain the observed change in the $e^{+}+e^{-}$ spectral slope. These conclusions are valid as long as pulsars contribute $\gtrsim 10\%$ of the observed cosmic-ray $e^{\pm }$ at energies $\gtrsim 100$ GeV.

    ↳ astro-ph.HEhep-phPRD(2018)·44 citations
29. 29*

    Counting of States in Higgs Theories

    Mark P. Hertzberg🇺🇸 · Mudit Jain🇺🇸

    We enumerate the micro-states in Higgs theories, addressing (i) the number of vacuum states and (ii) the appropriate measure in the quantum path integral. To address (i) we explicitly construct the set of ground state wave-functionals in the field basis focussing on scalar modes $\theta (x)$. Firstly, we show that in the limit in which the gauge coupling is zero, we obtain an infinite set of degenerate ground states at large volume distinguished by $\theta (x)\to \theta (x)+{\theta }_0$, spontaneously breaking the global symmetry, as is well known. We then show that at finite gauge coupling there is a unique ground state at large volume since the wave-functional only depends on $\nabla \theta$ in the IR, and we explain this at the level of the Lagrangian. Since gauge fields fall off exponentially from sources there are no conserved charges or symmetries in the Higgs phase; so the Higgs mechanism is the removal of symmetry from the theory. We show how physical features of defects, such as cosmic strings in the abelian Higgs model, are best understood in this context. Since there is a unique ground state, we address (ii) whether the path integral is a volume measure for the radial Higgs field $\mathcal{D}\rho {\rho }^{N-1}$ from the $N$ components of the Higgs multiplet, or a line measure $\mathcal{D}\rho$ as the $N-1$ would-be Goldstones can be removed in unitary gauge. We prove that the need to avoid quartic divergences demands a tower of counter terms that resum to exactly give the volume measure. So the size of the Hilbert space in the zero gauge coupling case and finite gauge coupling case are in one-to-one correspondence, despite the degeneracy of the ground state being lifted in the latter. As a cosmological application, we point out that the volume measure can make it exponentially more unlikely in $N(=4)$ for the Standard Model Higgs to relax to the electroweak vacuum in the early universe.

    ↳ hep-thastro-ph.COhep-phPRD(2019)·11 citations
30. 30*

    Beam energy dependence of the relativistic retardation effects of electrical fields on the ${\pi }^{-}/{\pi }^{+}$ ratio in heavy-ion collisions

    Gao-Feng Wei · Gao-Chan Yong · Li Ou · Qi-Jun Zhi · Zheng-Wen Long

    In this article we investigate the beam energy dependence of relativistic retardation effects of electrical fields on the single and double ${\pi }^{-}/{\pi }^{+}$ ratios in three heavy-ion reactions with an isospin- and momentum-dependent transport model IBUU11. With the beam energy increasing from 200 to 400 MeV/nucleon, effects of the relativistically retarded electrical fields on the ${\pi }^{-}/{\pi }^{+}$ ratio are found to increase gradually from negligibly to considerably significant as expectedly; it is however, the interesting observation is the relativistic retardation effects of electrical fields on the ${\pi }^{-}/{\pi }^{+}$ ratio are becoming gradually insignificant as the beam energy further increasing from 400 to 800 MeV/nucleon. Moreover, we also investigate the isospin dependence of relativistic retardation effects of electrical fields on the ${\pi }^{-}/{\pi }^{+}$ ratio in two isobar reaction systems of ${}^{96}$Ru+${}^{96}$Ru and ${}^{96}$Zr+${}^{96}$Zr at the beam energies from 200 to 800 MeV/nucleon. It is shown that the relativistic retardation effects of electrical fields on the ${\pi }^{-}/{\pi }^{+}$ ratio are independent of the isospin of reaction. Furthermore, we also examine the double ${\pi }^{-}/{\pi }^{+}$ ratio in reactions of ${}^{96}$Zr+${}^{96}$Zr over ${}^{96}$Ru+${}^{96}$Ru at the beam energies from 200 to 800 MeV/nucleon with the static field and retarded field, respectively. It is shown the double ${\pi }^{-}/{\pi }^{+}$ ratio from two reactions is still an effective observable of symmetry energy without the interference of electrical field due to using the relativistic calculation compared to the nonrelativistic calculation.

    ↳ nucl-thhep-phPRC(2018)·9 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.