Fri·Apr 30, 2021Friday·April 30, 2021

1. 01*

   A bound on the nucleon Druck-term from chiral EFT in curved space-time and mechanical stability conditions

   Jambul Gegelia🇩🇪 · Maxim V. Polyakov🇩🇪

   Using dispersive representations of the nucleon gravitational form factors, the results for their absorptive parts from chiral effective field theory in curved space-time, and the mechanical stability conditions, we obtain a model independent inequality for the value of the gravitational $D(t)$ form factor at zero momentum transfer (Druck-term). In particular, the obtained inequality leads to a conservative bound on the Druck-term in the chiral limit $D\le -0.95(9)$. This bound implies the restriction on the low-energy constant $c_8$ of the effective chiral action for nucleons and pions in the presence of an external gravitational field, $c_8\le -1.1(1)$ GeV${}^{-1}$. For the physical pion mass we obtain a model independent bound $D\le -0.20(2)$.

   hep-phhep-exnucl-thPLB(2021)·28 citations
2. 02*

   Freeze-in production of sterile neutrino dark matter in a gauged U$(1{)}^{\prime }$ model with inverse seesaw

   Arindam Das🇰🇷 · Srubabati Goswami🇮🇳 · Vishnudath K.N. · Tanmay Kumar Poddar🇮🇳

   We consider a general, anomaly free U$(1{)}^{\prime }$ extension of the Standard Model (SM) where the neutrino mass is generated at the tree level via the inverse seesaw mechanism. The model contains three right handed neutrinos, three additional singlet fermions, one extra complex scalar and a neutral gauge boson $(Z^{\prime })$. Instead of resorting to a specific $U(1)$ extension, we consider a class of models by taking the $U(1{)}^{\prime }$ charges of the scalars to be free parameters. Here, we assign one pair of the pseudo-Dirac degenerate sterile neutrinos as Dark Matter (DM) candidates which are produced by the freeze-in mechanism. Considering different mass regimes of the DM, $Z^{\prime }$ and reheating temperature, we obtain constraints on the $U(1{)}^{\prime }$ charges giving the correct relic abundance. We have also obtained constraints on $Z^{\prime }$ mass and coupling from consideration of relic density as well as high energy collider experiments like ATLAS in case of heavy $Z^{\prime }$ or in intensity and lifetime frontier experiments like DUNE, FASERs, and ILC beam dump which are looking for light $Z^{\prime }$. Additionally, in this model, the decay of pseudo-Dirac DM into active neutrinos can explain the 511 keV line observed by the INTEGRAL satellite.

   hep-phNPB(2024)·20 citations
3. 03*

   Survival probabilities of charmonia as a clue to measure transient magnetic fields

   Sachio Iwasaki🇯🇵 · Daisuke Jido🇯🇵 · Makoto Oka🇯🇵 · Kei Suzuki🇯🇵

   We investigate time evolution of $S$-wave charmonium populations under a time-dependent homogeneous magnetic field and evaluate survival probabilities of the low-lying charmonia to the goal of estimating the magnetic field strength at heavy-ion collisions. Our approach implements mixing between different spin eigenstates and transitions to radially excited states. We show that the survival probabilities can change even by an extremely short magnetic field. Furthermore, we find that the survival probabilities depend on the initial spin states. We propose the sum of the survival probabilities over spin partners as an observable insensitive to the initial states. We also find that the sum can be approximately given as a function of $\sigma B_0^2$ with a duration time $\sigma$ and the maximum strength of the magnetic field $B_0$.

   hep-phhep-exnucl-exnucl-thPLB(2021)·9 citations
4. 04*

   A review of quarkonia under strong magnetic fields

   Sachio Iwasaki🇯🇵 · Makoto Oka🇯🇵 · Kei Suzuki🇯🇵

   We review the properties of quarkonia under strong magnetic fields. The main phenomena are (i) mixing between different spin eigenstates, (ii) quark Landau levels and deformation of wave function, (iii) modification of $\bar{Q}Q$ potential, and (iv) the motional Stark effect. For theoretical approaches, we review (i) constituent quark models, (ii) effective Lagrangians, (iii) QCD sum rules, and (iv) holographic approaches.

   hep-phhep-exhep-latnucl-ex+1EPJA(2021)·46 citations
5. 05*

   Thermomagnetic modification of the anomalous magnetic moment of quarks using the NJL model

   Snigdha Ghosh🇮🇳 · Nilanjan Chaudhuri🇮🇳 · Pradip Roy🇮🇳 · Sourav Sarkar🇮🇳

   The effective photon-quark-antiquark ($\gamma q\overline{q}$) vertex function is evaluated at finite temperature in the presence of an arbitrary external magnetic field using the two-flavor gauged Nambu--Jona-Lasinio (NJL) model in the mean field approximation. The lowest order diagram contributing to the magnetic form factor and the anomalous magnetic moment (AMM) of the quarks is calculated at finite temperature and external magnetic field using the imaginary time formalism of finite temperature field theory and the Schwinger proper time formalism. The Schwinger propagator including all the Landau levels with non-zero AMM of the dressed quarks is considered while calculating the loop diagram. Using sharp as well as smooth three momentum cutoff, we regularize the UV divergences arising from the vertex function and the parameters of our model are chosen to reproduce the well known phenomenological quantities at zero temperature and zero magnetic field, such as pion-decay constant ($f_{\pi }$), vacuum quark condensate, vacuum pion mass ($m_{\pi }$) as well as the magnetic moments of proton and neutron. We then study the temperature and magnetic field dependence of the AMM and constituent mass of the quark. We found that, the AMM as well as the constituent quark mass are large at the chiral symmetry broken phase in the low temperature region. Around the pseudo-chiral phase transition they decrease rapidly and at high temperatures both of them approach vanishingly small values in the symmetry restored phase.

   hep-phnucl-thPRD(2021)·19 citations
6. 06*

   Elastic and inelastic $J/\psi$ photoproduction in $p$-$p$ collisions at LHC energies: the feature of Weizsäcker-Williams approximation

   Zhi-Lei Ma🇨🇳 · Zhun Lu🇨🇳 · Jia-Qing Zhu🇨🇳 · Li Zhang🇨🇳

   The $J/\psi$ production originating from elastic and inelastic photoproduction processes in p-p collisions at LHC energies is investigated, where the fragmentation processes are involved. An exact treatment is performed, which adopts the Martin-Ryskin method to weight the contribution from different channels, and can return to Weizsäcker-Williams approximation (WWA) when $Q^2\to 0$. The relevant kinematical relations are also achieved. We present a comprehensive analysis for the feature of WWA by comparing with the exact treatment. The results are expressed in $Q^2$, $y$, $z$, $p_T$, and $y_r$ (rapidity) distributions, and the total cross sections are also estimated. The numerical results indicate that, the incoherent-photon emission can provide the meaningful contribution to elastic photoproduction, and starts to play a very important role in the inelastic processes. The photoproduction and fragmentation processes can improve the contribution of $J/\psi$ production in $p$-$p$ collisions at LHC energies. Moreover, the WWA is only effective in very restricted domains, and the exact treatment is needed to deal accurately with the $J/\psi$ photoproduction, which can naturally avoid double counting and WWA errors.

   hep-phPRD(2022)·1 citation
7. 07*

   Baryon number non-conservation as Peccei-Quinn mechanism

   Takahiro Ohata🇯🇵 · Kengo Takeuchi🇯🇵 · Koji Tsumura🇯🇵

   Baryon number is an accidental symmetry in the standard model, while Peccei-Quinn symmetry is hypothetical symmetry which is introduced to solve the strong CP problem. We study the possible connections between Peccei-Quinn symmetry and baryon number symmetry. In this framework, an axion is identified as the Nambu-Goldstone boson of baryon number violation. As a result, characteristic baryon number violating processes are predicted. We developed the general method to determine the baryon number and lepton number of new scalar in the axion model.

   hep-phPRD(2021)·2 citations
8. 08*

   Unveiling the pole structure of S-matrix using deep learning

   Denny Lane B. Sombillo🇵🇭 · Yoichi Ikeda🇯🇵 · Toru Sato🇯🇵 · Atsushi Hosaka🇯🇵

   Particle scattering is a powerful tool to unveil the nature of various subatomic phenomena. The key quantity is the scattering amplitude whose analytic structure carries the information of the quantum states. In this work, we demonstrate our first step attempt to extract the pole configuration of inelastic scatterings using the deep learning method. Among various problems, motivated by the recent new hadron phenomena, we develop a curriculum learning method of deep neural network to analyze coupled channel scattering problems. We show how effectively the method works to extract the pole configuration associated with resonances in the $\pi N$ scatterings.

   hep-phhep-exnucl-exnucl-th+1Rev.Mex.Fis.Suppl.(2022)·10 citations
9. 09*

   Phenomenology of ultralight scalars in leptonic observables

   Pablo Escribano🇪🇸

   Ultralight scalars, which are states that are either exactly massless or much lighter than any other massive particle in the model, appear in many new physics scenarios. Axions and majorons constitute well-motivated examples of this type of particle. In this work, we explore the phenomenology of these states in low-energy leptonic observables adopting a model independent approach that includes both scalar and pseudoscalar interactions. Then, we consider processes in which the ultralight scalar $\varphi$ is directly produced, such as $\mu \to e\varphi$, or acts as a mediator, as in $\tau \to \mu \mu \mu$. Finally, contributions to the charged leptons magnetic and electric moments are studied as well. In particular, it is shown that the muon $g-2$ anomaly can be explained provided a mechanism for suppressing the experimental bounds on the coupling between the ultralight scalar and a pair of muons is introduced.

   hep-ph0 citations
10. 10*

    Asymmetric accidental composite dark matter

    Salvatore Bottaro🇮🇹 · Marco Costa🇮🇹 · Oleg Popov🇰🇷

    The goal of this work is to find the simplest UV completion of Accidental Composite Dark Matter Models (ACDM) that can dynamically generate an asymmetry for the DM candidate, the lightest \textit{dark baryon} (DCb), and simultaneously annihilate the symmetric component. In this framework the DCb is a bound state of a confining $\text{SU}(N{)}_{\text{DC}}$ gauge group, and can interact weakly with the visible sector. The constituents of the DCb can possess non-trivial charges under the Standard Model gauge group. The generation of asymmetry for such candidate is a two-flavor variation of the \emph{out-of-equilibrium} decay of a heavy scalar, with mass $M_{\varphi }\gtrsim 10^{10}$ GeV. Below the scale of the scalars, the models recover accidental stability, or long-livedness, of the DM candidate. The symmetric component is annihilated by residual confined interactions provided that the mass of the DCb $m_{\text{DCb}}\lesssim 75$ TeV. We implement the mechanism of asymmetry generation, or a variation of it, in all the original ACDM models, managing to generate the correct asymmetry for DCb of masses in this range. For some of the models found, the stability of the DM candidate is not spoiled even considering generic GUT completions or asymmetry generation mechanisms in the visible sector.

    hep-phastro-ph.COJHEP(2021)·19 citations
11. 11*

    On systematic effects in the numerical solutions of the JIMWLK equation

    Salvatore Cali🇺🇸 · Krzysztof Cichy🇵🇱 · Piotr Korcyl🇵🇱 · Piotr Kotko🇵🇱 · Krzysztof Kutak🇵🇱 · Cyrille Marquet🇫🇷

    In the high energy limit of hadron collisions, the evolution of the gluon density in the longitudinal momentum fraction can be deduced from the Balitsky hierarchy of equations or, equivalently, from the nonlinear Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner (JIMWLK) equation. The solutions of the latter can be studied numerically by using its reformulation in terms of a Langevin equation. In this paper, we present a comprehensive study of systematic effects associated with the numerical framework, in particular the ones related to the inclusion of the running coupling. We consider three proposed ways in which the running of the coupling constant can be included: "square root" and "noise" prescriptions and the recent proposal by Hatta and Iancu. We implement them both in position and momentum spaces and we investigate and quantify the differences in the resulting evolved gluon distributions. We find that the systematic differences associated with the implementation technicalities can be of a similar magnitude as differences in running coupling prescriptions in some cases, or much smaller in other cases.

    hep-phEPJC(2021)·22 citations
12. 12*

    Initial- and final-state temperatures of emission source from differential cross-section in squared momentum transfer in high energy collisions

    Qi Wang🇨🇳 · Fu-Hu Liu🇨🇳 · Khusniddin K. Olimov🇺🇿

    The differential cross-section in squared momentum transfer of $\rho$, ${\rho }^0$, $\omega$, $\varphi$, $f_0(980)$, $f_1(1285)$, $f_0(1370)$, $f_1(1420)$, $f_0(1500)$, and $J/\psi$ produced in high energy virtual photon-proton ($\gamma$${}^{\ast }p$), photon-proton ($\gamma p$), and proton-proton ($pp$) collisions measured by the H1, ZEUS, and WA102 Collaborations are analyzed by the Monte Carlo calculations. In the calculations, the Erlang distribution, Tsallis distribution, and Hagedorn function are separately used to describe the transverse momentum spectra of the emitted particles. Our results show that the initial- and final-state temperatures increase from lower squared photon virtuality to higher one, and decrease with increasing of center-of-mass energy.

    hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2021)·12 citations
13. 13*

    Improved Treatment of Dark Matter Capture in White Dwarfs

    Nicole F. Bell🇦🇺 · Giorgio Busoni🇩🇪 · Maura E. Ramirez-Quezada🇬🇧 · Sandra Robles🇦🇺 · Michael Virgato🇦🇺

    White dwarfs, the most abundant stellar remnants, provide a promising means of probing dark matter (DM) interactions, complimentary to terrestrial searches. The scattering of dark matter from stellar constituents leads to gravitational capture, with important observational consequences. In particular, white dwarf heating occurs due to the energy transfer in the dark matter capture and thermalisation processes, and the subsequent annihilation of captured dark matter. We consider the capture of dark matter by scattering on either the ion or the degenerate electron component of white dwarfs. For ions, we account for the stellar structure, the star opacity, realistic nuclear form factors that go beyond the simple Helm approach, and finite temperature effects pertinent to sub-GeV dark matter. Electrons are treated as relativistic, degenerate targets, with Pauli blocking, finite temperature and multiple scattering effects all taken into account. We also estimate the dark matter evaporation rate. The DM-nucleon/electron scattering cross sections can be constrained by comparing the heating rate due to dark matter capture with observations of cold white dwarfs in dark matter-rich environments. We apply this technique to observations of old white dwarfs in the globular cluster Messier 4, which we assume to be located in a DM subhalo. For DM-nucleon scattering, we find that white dwarfs can probe the sub-GeV mass range inaccessible to direct detection searches, with the low mass reach limited only by either evaporation or dominant DM annihilation to neutrinos, and can be competitive with direct detection in the $1-10^4$ GeV range. White dwarf limits on dark matter-electron scattering are found to outperform current electron recoil experiments over the full mass range considered, and extend well beyond the $\sim 10$ GeV mass regime where the sensitivity of electron recoil experiments is reduced.

    hep-phastro-ph.COastro-ph.SRJCAP(2021)·77 citations
14. 14*

    The properties of strange quark matter under strong rotation

    Fei Sun🇨🇳 · Anping Huang🇨🇳

    We investigate the rotating quark matter in the three-flavor Nambu and Jona-Lasinio (NJL) model. The chiral condensation, spin polarization and number susceptibility of the light and strange quarks are carefully studied at finite temperature without or with finite chemical potential in this model. We find that the rotation suppresses the chiral condensation and enhances the first-order quark spin polarization, however for the second-order quark spin polarization and quark number susceptibility the effect is complicated and interesting. When extending to the situation with finite chemical potential, we find the angular velocity also plays a crucial role, at small angular velocity the chemical potential enhances the susceptibility, however in the middle region of angular velocity the effect of the chemical potential is suppressed by the angular velocity and susceptibility can be changed considerably, it can be observed that at very low temperature in the presence of quark chemical potential the quark number susceptibility has two maxima with increasing angular velocity. Furthermore, it is found that at sufficiently large angular velocity the contributions played by light quark and strange quark to these phenomena are almost equal. we also explored the phase diagram in the $T$-$\omega$ plane, we observe that there exist first order phase transitions for the rotating system and the first order phase transition lines move toward a higher temperature for decreasing angular velocity. It is also found that the different chemical potentials change the boundary of phase diagram, and that a larger chemical potential shifts down the critical temperature. We expect these studies to be used to understand the chiral symmetry breaking and restoration as well as probe the QCD phase transition.

    hep-phhep-thPRD(2022)·21 citations
15. 15*

    A complete effective field theory for dark matter

    Juan Carlos Criado🇬🇧 · Abdelhak Djouadi🇪🇸 · Manuel Perez-Victoria🇪🇸 · Jose Santiago🇪🇸

    We present an effective field theory describing the relevant interactions of the Standard Model with an electrically neutral particle that can account for the dark matter in the Universe. The possible mediators of these interactions are assumed to be heavy. The dark matter candidates that we consider have spin 0, 1/2 or 1, belong to an electroweak multiplet with arbitrary isospin and hypercharge and their stability at cosmological scales is guaranteed by imposing a ${\mathbb{Z}}_2$ symmetry. We present the most general framework for describing the interaction of the dark matter with standard particles, and construct a general non-redundant basis of the gauge-invariant operators up to dimension six. The basis includes multiplets with non-vanishing hypercharge, which can also be viable DM candidates. We give two examples illustrating the phenomenological use of such a general effective framework. First, we consider the case of a scalar singlet, provide convenient semi-analytical expressions for the relevant dark matter observables, use present experimental data to set constraints on the Wilson coefficients of the operators, and show how the interplay of different operators can open new allowed windows in the parameter space of the model. Then we study the case of a lepton isodoublet, which involves co-annihilation processes, and we discuss the impact of the operators on the particle mass splitting and direct detection cross sections. These examples highlight the importance of the contribution of the various non-renormalizable operators, which can even dominate over the gauge interactions in certain cases.

    hep-phJHEP(2021)·42 citations
16. 16*

    Following in Tini's Giant Footsteps

    John Ellis🇬🇧

    This paper describes my personal appreciation of some of Tini Veltman's great research achievements and how my own research career has followed the pathways he opened. Among the topics where he has been the most influential have been the pursuit and study of the Higgs boson and the calculation of radiative corrections that enabled the masses of the top quark and the Higgs boson to be predicted ahead of their discoveries. The search for physics beyond the Standard Model may require a complementary approach, such as the search for non-renormalizable interactions via the Standard Model Effective Field Theory.

    hep-phhep-exphysics.hist-phActa Phys.Polon.B(2021)·0 citations
17. 17*

    Low scale leptogenesis and dark matter in the presence of primordial black holes

    Suruj Jyoti Das🇮🇳 · Devabrat Mahanta🇮🇳 · Debasish Borah🇮🇳

    We study the possibility of low scale leptogenesis along with dark matter (DM) in the presence of primordial black holes (PBH). For a common setup to study both leptogenesis and DM we consider the minimal scotogenic model which also explains light neutrino mass at radiative level. While PBH in the mass range of $0.1-10^5$ g can, in principle, affect leptogenesis, the required initial PBH fraction usually leads to overproduction of scalar doublet DM whose thermal freeze-out occurs before PBH evaporation. PBH can lead to non-thermal source of leptogenesis as well as dilution of thermally generated lepton asymmetry via entropy injection, with the latter being dominant. The parameter space of scotogenic model which leads to overproduction of baryon or lepton asymmetry in standard cosmology can be made consistent in the presence of PBH with appropriate initial mass and energy fraction. On the other hand, for such PBH parameters, the scalar DM is constrained to be in light mass regime where its freeze-out occurs after PBH evaporation. We then discuss the possibility of fermion singlet DM with $N_2$ leptogenesis in the same model where due to singlet nature of DM, its connection with PBH parameters and hence leptogenesis becomes stronger compared to the previous case.

    hep-phastro-ph.COJCAP(2021)·70 citations
18. 18*

    A model for mixed warm and hot right-handed neutrino dark matter

    Maíra Dutra🇨🇦 · Vinícius Oliveira🇧🇷 · C. A. de S. Pires🇧🇷 · Farinaldo S. Queiroz🇧🇷

    We discuss a model where a mixed warm and hot keV neutrino dark matter rises naturally. We arrange active and sterile neutrinos in the same $SU(3{)}_L$ multiplet, with the lightest sterile neutrino being dark matter. The other two heavy sterile neutrinos, through their out-of-equilibrium decay, contribute both to the dilution of dark matter density and its population, after freeze-out. We show that this model features all ingredients to overcome the overproduction of keV neutrino dark matter, and explore the phenomenological implications for Big Bang Nucleosynthesis and the number of relativistic degrees of freedom.

    hep-phastro-ph.HEhep-thJHEP(2021)·19 citations
19. 19*

    Fifth-Force Screening around Extremely Compact Sources

    Clare Burrage🇬🇧 · Benjamin Elder🇺🇸 · Peter Millington🇬🇧 · Daniela Saadeh🇬🇧 · Ben Thrussell🇬🇧

    Many non-linear scalar field theories possess a screening mechanism that can suppress any associated fifth force in dense environments. As a result, these theories can evade local experimental tests of new forces. Chameleon-like screening, which occurs because of non-linearities in the scalar potential or the coupling to matter, is well understood around extended objects. However, many experimental tests of these theories involve objects with spatial extent much smaller than the scalar field's Compton wavelength, and which could therefore be considered point-like. In this work, we determine how the fifth forces are screened in the limit that the source objects become extremely compact.

    hep-phastro-ph.COgr-qchep-thJCAP(2021)·18 citations
20. 20*

    Axion Production in Pulsar Magnetosphere Gaps

    Anirudh Prabhu🇺🇸

    Pulsar magnetospheres admit non-stationary vacuum gaps that are characterized by non-vanishing $\mathbf{E}\cdot \mathbf{B}$. The vacuum gaps play an important role in plasma production and electromagnetic wave emission. We show that these gaps generate axions whose energy is set by the gap oscillation frequency. The density of axions produced in a gap can be several orders of magnitude greater than the ambient dark matter density. In the strong pulsar magnetic field, a fraction of these axions may convert to photons, giving rise to broadband radio signals. We show that dedicated observations of nearby pulsars with radio telescopes (FAST) and interferometers (SKA) can probe axion-photon couplings that are a few orders of magnitude lower than current astrophysical bounds.

    hep-phastro-ph.HEPRD(2021)·54 citations
21. 21*

    One-loop corrections to light neutrino masses in gauged U(1) extensions of the standard model

    Sho Iwamoto🇭🇺 · Timo J. Kärkkäinen🇭🇺 · Zoltán Péli🇭🇺 · Zoltán Trócsányi🇭🇺

    We consider gauged U(1) extensions of the standard model of particle physics with three right-handed sterile neutrinos and a singlet scalar. The neutrinos obtain mass via the type I seesaw mechanism. We compute the one loop corrections to the elements of the tree level mass matrix of the light neutrinos and show explicitly the cancellation of the gauge dependent terms. We present a general formula for the gauge independent, finite one-loop corrections for arbitrary number new U(1) groups, new complex scalars and sterile neutrinos. We estimate the size of the corrections relative to the tree level mass matrix in a particular extension, the super-weak model.

    hep-phhep-thPRD(2021)·18 citations
22. 22*

    Renormalization Group in Six-derivative Quantum Gravity

    Leslaw Rachwal🇧🇷 · Leonardo Modesto🇨🇳 · Aleksandr Pinzul🇧🇷 · Ilya L. Shapiro🇧🇷

    The exact one-loop beta functions for the four-derivative terms (Weyl tensor squared, Ricci scalar squared and the Gauss-Bonnet) are derived for the minimal six-derivative quantum gravity (QG) theory in four spacetime dimensions. The calculation is performed by means of the Barvinsky and Vilkovisky generalized Schwinger-DeWitt technique. With this result we gain, for the first time, the full set of the relevant beta functions in a super-renormalizable model of QG. The complete set of renormalization group (RG) equations, including also those for the Newton and the cosmological constant, is solved explicitly in the general case and for the six-derivative Lee-Wick (LW) quantum gravity proposed in a previous paper by two of the authors. In the ultraviolet regime, the minimal theory is shown to be asymptotically free and describes free gravitons in Minkowski or (anti-) de Sitter ((A)dS) backgrounds, depending on the initial conditions for the RG equations. The ghostlike states appear in complex conjugate pairs at any energy scale consistently with the LW prescription. However, owing to the running, these ghosts may become tachyons. We argue that an extension of the theory that involves operators cubic in Riemann tensor may change the beta functions and hence be capable of overcoming this problem.

    ↳ hep-thgr-qchep-phmath-ph+1PRD(2021)·28 citations
23. 23*

    Late Afterglow Bump/Plateau around the Jet Break: Signature of a free-to-shocked wind Environment in Gamma-ray Burst

    Xiao-Yan Li🇨🇳 · Da-Bin Lin🇨🇳 · Jia Ren🇨🇳 · Shu-Jin Hou🇨🇳 · Yu-Fei Li🇨🇳 · Xiang-Gao Wang🇨🇳 · En-Wei Liang🇨🇳

    A number of gamma-ray bursts (GRBs) exhibit the late simultaneous bumps in their optical and Xray afterglows around the jet break. Its origin is unclear. Based on the following two facts, we suggest that this feature may sound a transition of circum-burst environment from a free-wind medium to a homogeneous medium. (I) The late bump followed by a steep decay is strongly reminiscent of the afterglows of GRB 170817A, which is attributed to an off-axis observed external-forward shock (eFS) propagating in an interstellar medium. (II) Observations seem to feature a long shallow decay before the late optical bump, which is different from the afterglow of GRB 170817A. In this paper, we study the emission of an eFS propagating in a free-to-shocked wind for on/off-axis observers, where the mass density in the shocked-wind is almost constant. The late simultaneous bumps/plateaux in the optical and X-ray afterglows are really found around the jet break for high-viewing-angle observers. Moreover, there is a long plateau or shallow decay before the late bump in the theoretical light-curves, which is formed during the eFS propagating in the free-wind. For low-viewing-angle observers, the above bumps appear only in the situation that the structured jet has a low characteristic angle and the deceleration radius of the on-axis jet flow is at around or beyond the free-wind boundary. As examples, the X-ray and optical afterglows of GRBs 120326A, 120404A, and 100814A are fitted. We find that an off-axis observed eFS in a free-to-shocked wind can well explain the afterglows in these bursts.

    ↳ astro-ph.HEhep-phApJ(2021)·7 citations
24. 24*

    Hybrid model with viscous relativistic hydrodynamics: a role of constraints on the shear-stress tensor

    A. S. Khvorostukhin🇷🇺 · E. E. Kolomeitsev🇸🇰 · V. D. Toneev🇷🇺

    We present the hybrid hadron string dynamic (HydHSD) model connecting the parton-hadron-string dynamic model (PHSD) and a hydrodynamic model taking into account shear viscosity within the Israel-Stewart approach. The performance of the code is tested on the pion and proton rapidity and transverse mass distributions calculated for Au+Au and Pb+Pb collision at AGS--SPS energies. The influence of the switch time from transport to hydro models, the viscous parameter, and freeze-out time are discussed. Since the applicability of the Israel-Stewart hydrodynamics assumes the perturbative character of the viscous stress tensor, ${\pi }^{\mu \nu }$, which should not exceed the ideal energy-momentum tensor, $T_{\mathrm{id}}^{\mu \nu }$, hydrodynamical codes usually rescale the shear stress tensor if the inequality $\Vert {\pi }^{\mu \nu }\Vert \ll \Vert T_{\mathrm{id}}^{\mu \nu }\Vert$ is not fulfilled in some sense. We show that the form of the corresponding condition plays an important role in the sensitivity of hydrodynamic calculations to the viscous parameter -- a ratio of the shear viscosity to the entropy density, $\eta /s$. It is shown that the constraints used in the vHLLE and MUSIC models give the same results for the observables. With these constraints, the rapidity distributions and transverse momentum spectra are most sensitive to a change of the $\eta /s$ ratio. As an alternative, a strict condition is used. We performed global fits the rapidity and transverse mass distribution of pion and protons. It was also found that $\eta /s$ as a function of the collision energy monotonically increases from $E_{\mathrm{lab}}=6A$GeV up to $E_{\mathrm{lab}}=40A$GeV and saturates for higher SPS energies. We observe that it is difficult to reproduce simultaneously pion and proton rapidity distribution within our model with the present choice of the equation of state without a phase transition.

    ↳ nucl-thhep-phEPJA(2021)·8 citations
25. 25*

    Interferences in the Stochastic Gravitational Wave Background

    Disrael Camargo Neves da Cunha🇧🇪 · Christophe Ringeval🇧🇪

    Although the expansion of the Universe explicitly breaks the time-translation symmetry, cosmological predictions for the stochastic gravitational wave background (SGWB) are usually derived under the so-called stationary hypothesis. By dropping this assumption and keeping track of the time dependence of gravitational waves at all length scales, we derive the expected unequal-time (and equal-time) waveform of the SGWB generated by scaling sources, such as cosmic defects. For extinct and smooth enough sources, we show that all observable quantities are uniquely and analytically determined by the holomorphic Fourier transform of the anisotropic stress correlator. Both the strain power spectrum and the energy density parameter are shown to have an oscillatory fine structure, they significantly differ on large scales while running in phase opposition at large wavenumbers $k$. We then discuss scaling sources that are never extinct nor smooth and which generate a singular Fourier transform of the anisotropic stress correlator. For these, we find the appearance of interferences on top of the above-mentioned fine-structure as well as atypical behaviour at small scales. For instance, we expect the rescaled strain power spectrum $k^2{\mathcal{P}}_h$ generated by long cosmic strings in the matter era to oscillate around a scale invariant plateau. These singular sources are also shown to produce orders of magnitude difference between the rescaled strain spectra and the energy density parameter suggesting that only the former should be used for making reliable observable predictions. Finally, we discuss how measuring such a fine structure in the SGWB could disambiguate the possible cosmological sources.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2021)·6 citations
26. 26*

    Hints for a gravitational constant transition in Tully-Fisher data

    George Alestas🇬🇷 · Ioannis Antoniou🇬🇷 · Leandros Perivolaropoulos🇬🇷

    We use an up to date compilation of Tully-Fisher data to search for transitions in the evolution of the Tully-Fisher relation. Using an up to date data compilation, we find hints at $\approx 3\sigma$ level for a transition at critical distances $D_c\simeq 9Mpc$ and $D_c\simeq 17Mpc$. We split the full sample in two subsamples according to the measured galaxy distance with respect to a splitting distance $D_c$ and identify the likelihood of the best fit slope and intercept of one sample with respect to the best fit corresponding values of the other sample. For $D_c\simeq 9Mpc$ and $D_c\simeq 17Mpc$ we find a tension between the two subsamples at a level of $\Delta {\chi }^2>17(3.5\sigma )$. Using a Monte-Carlo simulation we demonstrate that this result is robust with respect to random statistical and systematic variations of the galactic distances. If the tension is interpreted as due to a gravitational strength transition, it would imply a shift of the effective gravitational constant to lower values for distances larger than $D_c$ by $\frac{\Delta G}{G}\simeq -0.1$. Such a shift is of the anticipated sign and magnitude but at somewhat lower distance (redshift) than the gravitational transition recently proposed to address the Hubble and growth tensions ($\frac{\Delta G}{G}\simeq -0.1$ at transition redshift $z_t\lesssim 0.01$ ($D_c\lesssim 40Mpc$)).

    ↳ astro-ph.COastro-ph.GAgr-qchep-ph+1Universe(2021)·54 citations
27. 27*

    Floccinaucinihilipilification: Semisimple extensions of the Standard Model gauge algebra

    B C Allanach🇬🇧 · Ben Gripaios🇬🇧 · Joseph Tooby-Smith🇬🇧

    We show how one may classify all semisimple algebras containing the $\mathfrak{su}(3)\oplus \mathfrak{su}(2)\oplus \mathfrak{u}(1)$ symmetry of the Standard Model and acting on some given matter sector, enabling theories beyond the Standard Model with unification (partial or total) of symmetries (gauge or global) to be catalogued. With just a single generation of Standard Model fermions plus a singlet neutrino, the only {gauge} symmetries correspond to the well-known algebras $\mathfrak{su}(5),\mathfrak{so}(10),$ and $\mathfrak{su}(4)\oplus \mathfrak{su}(2)\oplus \mathfrak{su}(2)$, but with two or more generations a limited number of exotic symmetries mixing flavour, colour, and electroweak degrees of freedom become possible. We provide a complete catalogue in the case of 3 generations or fewer and outline how our method generalizes to cases with additional matter.

    ↳ hep-thhep-phPRD(2021)·28 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.