Thu·Oct 31, 2019Thursday·October 31, 2019

1. 01*

   Vector Leptoquarks Beyond Tree Level

   Javier Fuentes-Martin🇨🇭 · Gino Isidori🇨🇭 · Matthias König🇨🇭 · Nudzeim Selimovic🇨🇭

   Models with massive vector leptoquarks, resulting from an $SU(4)$ gauge symmetry spontaneously broken at the TeV scale, are of great phenomenological interest given the current "anomalies" in semileptonic $B$ decays. We analyze the relations between low- and high-energy observables in such class of models to next-to-leading order accuracy in the $SU(4)$ gauge coupling $g_4$. For large values of $g_4$, motivated by recent $B$-physics data, one-loop corrections are sizeable. The main effect is an enhanced contribution at low-energy, at fixed on-shell couplings. This result has important implications for current and future high-energy searches of vector leptoquark models.

   hep-phPRD(2020)·73 citations
2. 02*

   BSM Physics from Enlarged Gauge Symmetry: the 331 Model, a case of study

   Antonio Costantini🇮🇹

   We discuss the most relevant features of a BSM model with extra gauge symmetry, the so called 331 model. The gauge group is $SU(3{)}_c\times SU(3{)}_L\times U(1{)}_X$ impling the presence of extra gauge bosons, both charged and neutral, as well as extra/exotic fermions and an enlarged scalar sector. We present the relevant phenomenology of doubly-charged gauge bosons, which are a distinctive feature of a version of the 331 model, and discuss the role of BSM phenomenology as a tool for testing GUT (inspired) theories.

   hep-phPoS(2020)·1 citation
3. 03*

   Quasi normal modes for Heavy Vector Mesons in a Finite Density Plasma

   Nelson R. F. Braga🇧🇷 · Rodrigo da Mata🇧🇷

   There are strong indications that ultra-relativistic heavy ion collisions, produced in accelarators, lead to the formation of a new state of matter: the quark gluon plasma (QGP). This deconfined QCD matter is expected to exist just for very short times after the collision. All the information one can get about the plasma is obtained from the particles that reach the detectors. Among them, heavy vector mesons are particularly important. The abundance of $c\bar{c}$ and $b\bar{b}$ states produced in a heavy ion collision is a source of information about the plasma. In contrast to the light mesons, that completely dissociate when the plasma is formed, heavy mesons presumably undergo a partial thermal dissociation. The dissociation degree depends on the temperature and also on the presence of magnetic fields and on the density (chemical potential). So, in order to get information about the plasma out of the quarkonium abundance data, one needs to resort to models that provide the dependence of the dissociation degree on these factors. Holographic phenomenological models provide a nice description for charmonium and bottomonium quasi-states in a plasma. In particular, quasi-normal modes associated with quarkonia states have been studied recently for a plasma with magnetic fields. Here we extend this analysis of quasinormal models to the case when charmonium and bottomonium are inside a plasma with finite density. The complex frequencies obtained are then compared with a Breit Wigner approximation for the peaks of the corresponding thermal spectral functions, in order to investigate the quantitative agreement of the different descriptions of quarkonium quasi-states.

   hep-phhep-thPLB(2020)·15 citations
4. 04*

   Multiplicity distributions as probes of quarkonia production mechanisms

   Marat Siddikov🇨🇱 · Eugene Levin🇮🇱 · Ivan Schmidt🇨🇱

   In this paper we demonstrate that the vigorously growing multiplicity distributions measured by STAR and ALICE present a strong evidence in favor of multigluon fusion mechanisms of the quarkonia production in CGC approach. We analyze the contribution of 3-gluon fusion mechanism and demonstrate that it gives a sizeable contribution to quarkonia yields, as well as predicts correctly the multiplicity distributions for $J/\psi$ at RHIC and LHC. We also make predictions for other quarkonia states, such as $\psi (2S)$ and ${\rm Y}(1S)$, and find that the multiplicity dependence of these states should be comparable to similar dependence for $J/\psi$. Finally, we discuss an experimental setup in which very strong multiplicity dependence could be observed. This observation would be a strong evidence in favor of CGC approach.

   hep-phhep-exEPJC(2020)·50 citations
5. 05*

   Two-body hadronic weak decays of antitriplet charmed baryons

   Jinqi Zou🇨🇳 · Fanrong Xu🇨🇳 · Guanbao Meng🇹🇼 · Hai-Yang Cheng🇹🇼

   We study Cabibbo-favored (CF) and singly Cabibbo-suppressed (SCS) two-body hadronic weak decays of the antitriplet charmed baryons ${\Lambda }_c^{+}$, ${\Xi }_c^0$ and ${\Xi }_c^{+}$ with more focus on the last two. Both factorizable and nonfactorizable contributions are considered in the topologic diagram approach. The estimation of nonfactorizable contributions from $W$-exchange and inner $W$-emission diagrams relies on the pole model and current algebra. The non-perturbative parameters in both factorizable and nonfactorizable parts are calculated in the MIT bag model. Branching fractions and up-down decay asymmetries for all the CF and SCS decays of antitriplet charmed baryons are presented. The prediction of $\mathcal{B}({\Xi }_c^{+}\to {\Xi }^0{\pi }^{+})$ agrees well with the measurements inferred from Belle and CLEO, while the calculated $\mathcal{B}({\Xi }_c^0\to {\Xi }^{-}{\pi }^{+})$ is too large compared to the recent Belle measurement. We conclude that these two ${\Xi }_c\to \Xi {\pi }^{+}$ modes cannot be simultaneously explained within the current-algebra framework for $S$-wave amplitudes. This issue needs to be resolved in future study. The long-standing puzzle with the branching fraction and decay asymmetry of ${\Lambda }_c^{+}\to {\Xi }^0{K}^{+}$ is resolved by noting that only type-II $W$-exchange diagram will contribute to this mode. We find that not only the calculated rate agrees with experiment but also the predicted decay asymmetry is consistent with the SU(3)-flavor symmetry approach in sign and magnitude. Likewise, the CF mode ${\Xi }_c^0\to {\Sigma }^{+}{K}^{-}$ and the SCS decays ${\Xi }_c^0\to p{K}^{-},{\Sigma }^{+}{\pi }^{-}$ proceed only through type-II $W$-exchange. They are predicted to have large and {\it positive} decay asymmetries. These features can be tested in the near future.

   hep-phhep-exPRD(2020)·71 citations
6. 06*

   Masses of Heavy Flavour mesons in a space with one finite extra-dimension

   D. K. Choudhury🇮🇳 · Jugal Lahkar🇮🇳

   Motivated by the recent developments in stability of hydrogen atom in a space with one finite extra-dimension,we consider that physical mesons are also stable in such a space and estimate their masses in a QCD inspired potential model. Our analysis suggests that a model of mesons with linear plus coulomb potential in a space with one finite extra-dimension of size very very less than 10^{-18} m is compatible with the present experimental data of heavy flavour mesons.

   hep-ph0 citations
7. 07*

   A Composite 2-Higgs Doublet Model

   Stefania De Curtis🇮🇹 · Luigi Delle Rose🇮🇹 · Stefano Moretti🇬🇧 · Key Yagyu🇯🇵

   In the context of Composite Higgs Models we consider the realisation of an extended Higgs sector with two Higgs doublets arising as pseudo Nambu-Goldstone bosons from a $\text{SO}(6)\to \text{SO}(4)\times \text{SO}(2)$ breaking. The properties of the Higgses are obtained in terms of the fundamental parameters of the composite sector, such as masses, Yukawa and gauge couplings of the new spin-1/2 and spin-1 resonances. After computing the Higgs potential from the explicit breaking of the $\text{SO}(6)$ global symmetry by the partial compositeness of fermions and gauge bosons, the main focus is to derive the phenomenological properties of the Higgs bosons and to highlight the main signatures of the Composite 2-Higgs Doublet Model at the Large Hadron Collider, including modifications to the SM-like Higgs couplings, production and decay channels of heavier Higgs states.

   hep-phPoS(2020)·6 citations
8. 08*

   Calculation of anisotropic transport coefficients for an ultrarelativistic Boltzmann gas in a magnetic field within a kinetic approach

   Zhengyu Chen🇨🇳 · Carsten Greiner🇩🇪 · Anping Huang🇨🇳 · Zhe Xu🇨🇳

   According to the Kubo formulas we employ the (3+1)-d parton cascade, Boltzmann approach of multiparton scatterings (BAMPS), to calculate the anisotropic transport coefficients (shear viscosity and electric conductivity) for an ultrarelativistic Boltzmann gas in the presence of a magnetic field. The results are compared with those recently obtained by using the Grad's approximation. We find good agreements between both results, which confirms the general use of the derived Kubo formulas for calculating the anisotropic transport coefficients of quark-gluon plasma in a magnetic field.

   hep-phPRD(2020)·25 citations
9. 09*

   Polarization observables in WZ production at the 13 TeV LHC: Inclusive case

   Julien Baglio🇨🇭 · Le Duc Ninh🇻🇳

   We present a study of the polarization observables of the $W$ and $Z$ bosons in the process $pp\to W^{\pm }Z\to e^{\pm }{\nu }_e{\mu }^{+}{\mu }^{-}$ at the 13 TeV Large Hadron Collider. The calculation is performed at next-to-leading order, including the full QCD corrections as well as the electroweak corrections, the latter being calculated in the double-pole approximation. The results are presented in the helicity coordinate system adopted by ATLAS and for different inclusive cuts on the di-muon invariant mass. We define left-right charge asymmetries related to the polarization fractions between the $W^{+}Z$ and $W^{-}Z$ channels and we find that these asymmetries are large and sensitive to higher-order effects. Similar findings are also presented for charge asymmetries related to a P-even angular coefficient.

   hep-phhep-exCommun.in Phys.(2020)·25 citations
10. 10*

    Production of Z'-Boson Resonances with Large Width at the LHC

    E. Accomando🇬🇧 · F. Coradeschi🇬🇧 · T. Cridge🇬🇧 · J. Fiaschi🇩🇪 · F. Hautmann🇧🇪 · S. Moretti🇬🇧 · C. Shepherd-Themistocleous🇬🇧 · C. Voisey🇬🇧

    Di-lepton searches for Beyond the Standard Model (BSM) Z' bosons that rely on the analysis of the Breit-Wigner (BW) line shape are appropriate in the case of narrow resonances, but likely not sufficient in scenarios featuring Z' states with large widths. Conversely, alternative experimental strategies applicable to wide Z' resonances are much more dependent than the default bump search analyses on the modelling of QCD higher-order corrections to the production processes, for both signal and background. For heavy Z' boson searches in the di-lepton channel at the CERN Large Hadron Collider (LHC), the transverse momentum q_T of the di-lepton system peaks at q_T \ltap 10^{-2} M_{ll}, where M_{ll} is the di-lepton invariant mass. We exploit this to treat the QCD corrections by using the logarithmic resummation methods in M_{ll} / q_T to all orders in the strong coupling constant \alpha_s. We carry out studies of Z' states with large width at the LHC by employing the program {\tt reSolve}, which performs QCD transverse momentum resummation up to Next-to-Next-to-Leading Logarithmic (NNLL) accuracy. We consider two benchmark BSM scenarios, based on the Sequential Standard Model (SSM) and dubbed `SSM wide' and `SSM enhanced'. We present results for the shape and size of Z' boson signals at the differential level, mapped in both cross section (\sigma) and Forward-Backward Asymmetry (A_{\rm FB}), and perform numerical investigations of the experimental sensitivity at the LHC Run 3 and High-Luminosity LHC (HL-LHC).

    hep-phPLB(2020)·33 citations
11. 11*

    Analytic results for deep-inelastic scattering at NNLO QCD with the nested soft-collinear subtraction scheme

    Konstantin Asteriadis🇩🇪 · Fabrizio Caola🇬🇧 · Kirill Melnikov🇩🇪 · Raoul Röntsch🇨🇭

    We present analytic results that describe fully-differential NNLO QCD corrections to deep-inelastic scattering processes within the nested soft-collinear subtraction scheme. This is the last building block required for the application of this scheme to computations of NNLO QCD corrections to arbitrary processes at hadron colliders.

    hep-phEPJC(2020)·41 citations
12. 12*

    Revisiting the quantum field theory of neutrino oscillations in vacuum

    Walter Grimus🇦🇹

    We consider neutrino oscillations in vacuum in the framework of quantum field theory in which neutrino production and detection processes are part of a single Feynman diagram and the corresponding cross section is computed in the standard way, i.e. with final states represented by plane waves. We use assumptions which are realized in actual experiments and concentrate on the detection process. Moreover, we also allow for a finite time interval of length $\tau$ during which the detector records neutrino events. In this context we are motivated by accelerator-neutrino oscillation experiments where data taking is synchronized in time with the proton spill time of the accelerator. Given the final momenta and the direction of neutrino propagation, we find that in the oscillation amplitude---for all practical purposes---the neutrino energy $Q$ is fixed, apart from an interval of order $2\pi \hslash /\tau$ around a mean energy $\bar{Q}$; this is an expression of energy non-conservation or the time-energy uncertainty relation in the detection process due to $\tau <\infty$. We derive in excellent approximation that in the amplitude the oscillation effect originates from massive neutrinos with the same energy $\bar{Q}$, i.e. oscillations take place in space without any decoherece effect, while the remaining integration over $Q$ in the interval of order $2\pi \hslash /\tau$ around $\bar{Q}$ results in a time-correlation function expressing the time delay between neutrino production and detection.

    hep-phJ.Phys.G(2020)·37 citations
13. 13*

    Nuclear deformation effects on charge radius measurements of the proton and deuteron

    Yonghui Lin🇨🇳 · Bingsong Zou🇨🇳

    Up to now, all charge radius measurements of the proton and deuteron assumed uniform spheroidal charge distribution. We investigate the nuclear deformation effects on these charge radius measurements by assuming a uniform prolate charge distribution for the proton and deuteron. We solve the energy levels of the corresponding muonic and electric atoms with such deformed nucleus and present how the purely quadruple deformation of proton and deuteron affects their Lamb shifts. The numerical results suggest that the deformation of proton and deuteron leads to that the charge radius extracted from the electronic measurement should be smaller than the corresponding one in the muonic measurement which assumed uniform spheroidal charge distribution. If the central values of newest measurements for the proton are adopted, the proton would have a prolate structure with the 0.91 $\mathrm{fm}$ long axis and 0.73 $\mathrm{fm}$ short axis. Further improved precise charge radius measurements of the proton and deuteron will help us to pin down their shape deformation.

    hep-phnucl-exnucl-th1 citation
14. 14*

    Reanalysis of the newly observed ${\Omega }^{\ast }$ state in hadronic molecule model

    Yonghui Lin · Fei Wang · Bingsong Zou

    After the discovery of the new ${\Omega }^{\ast }$ state, the ratio of the branching fractions of $\Omega (2012)\to \bar{K}\pi \Xi$ relative to $\bar{K}\Xi$ decay channel was investigated by the Belle Collaboration recently. The measured $11.9\%$ up limit on this ratio is in sharp tension with the $S$-wave $\bar{K}\Xi (1530)$ molecule interpretation for $\Omega (2012)$ which indicates the dominant $\bar{K}\pi \Xi$ three-body decay. In the present work, we try to explore the possibility of the $P$-wave molecule assignments for $\Omega (2012)$ (where $\Omega (2012)$ has positive parity). It is found that the latest experimental measurements are compatible with the $1/2^{+}$ and $3/2^{+}$ $\bar{K}\Xi (1530)$ molecular pictures, while the $5/2^{+}$ $\bar{K}\Xi (1530)$ molecule shows the larger $\bar{K}\pi \Xi$ three-body decay compared with the $\bar{K}\Xi$ decay as the case of $S$-wave molecule. Thus, the newly observed $\Omega (2012)$ can be interpreted as the $1/2^{+}$ or $3/2^{+}$ $\bar{K}\Xi (1530)$ molecule state according to current experiment data.

    hep-phhep-exPRD(2020)·24 citations
15. 15*

    Gravitational production of scalar dark matter

    Jose A. R. Cembranos🇪🇸 · Luis J. Garay🇪🇸 · Jose M. Sánchez Velázquez🇪🇸

    We investigate the gravitational production of scalar dark matter particles during the inflationary and reheating epochs. The oscillatory behavior of the curvature scalar $R$ during the reheating phase generates two different enhancement mechanisms in the particle production. On the one hand, as it has been already discussed in previous works, it induces tachyonic instabilities in the field which are the dominant enhancement mechanism for light masses. On the other hand, we have found that it also provokes a resonant effect in the ultraviolet region of the spectrum which becomes dominant for masses in the range $10^9\mathrm{GeV}$ to $10^{13}\mathrm{GeV}$. We have developed an analytical approximation to describe this resonance effect and its consequences on the ultraviolet regime. Once we have calculated the theoretical gravitational production, we constrain the possible values of the phenomenological field parameters to be considered as a dark matter candidate. We do so by comparing the theoretically predicted abundance with the observed one and ensuring that the theoretical prediction does not lead to overproduction. In particular, we find that there is a region of intermediate masses that is forbidden as they would lead to overproduction.

    hep-phJHEP(2020)·53 citations
16. 16*

    High energy Photon Collider

    Ilya F. Ginzburg🇷🇺 · Gleb L.Kotkin🇷🇺

    We discuss a high-energy photon linear collider (HE PLC) based on the $e^{+}{e}^{-}$ linear collider with cms electron energy $2E=1÷2$ TeV (JLC, CLIC,...). This energy region was previously considered hopeless for experiment. On the contrary, the present study leads to a rather optimistic conclusions. We compare properties of HE PLC with those of the usually discussed {\it standard PLC} with $E\approx 250$ GeV. We show that at the optimal choice of laser the high-energy \ggam luminosity integral is about 1/5, and the maximum luminosity is about 1/4 from similar values for the standard PLC. For this choice, the laser flash energy and laser-optical system should be approximately the same as those prepared for the standard PLC. The photon spectrum of HE PLC is much more monochromatic than that in the standard PLC, it is concentrated near the high-energy limit with an energy spread of about 5\%. It will be well separated from the low energy part.

    hep-ph7 citations
17. 17*

    Gluon Pseudo-Distributions at Short Distances: Forward Case

    Ian Balitsky🇺🇸 · Wayne Morris🇺🇸 · Anatoly Radyushkin🇺🇸

    We present the results that are necessary in the ongoing lattice calculations of the gluon parton distribution functions (PDFs) within the pseudo-PDF approach. We give a classification of possible two-gluon correlator functions and identify those that contain the invariant amplitude determining the gluon PDF in the light-cone $z^2\to 0$ limit. One-loop calculations have been performed in the coordinate representation and in an explicitly gauge-invariant form. We made an effort to separate ultraviolet (UV) and infrared (IR) sources of the $\ln (-z^2)$-dependence at short distances $z^2$. The UV terms cancel in the reduced Ioffe-time distribution (ITD), and we obtain the matching relation between the reduced ITD and the light-cone ITD. Using a kernel form, we get a direct connection between lattice data for the reduced ITD and the normalized gluon PDF. We also show that our results may be used for a rather straightforward calculation of the one-loop matching relations for quasi-PDFs.

    hep-phhep-latPLB(2020)·81 citations
18. 18*

    Di-Higgs Production in SUSY models at the LHC

    Peisi Huang🇺🇸 · Yu Hang Ng🇺🇸

    We study the modification to di-Higgs production via gluon fusion within the context of the Minimal Supersymmetric Standard Model(MSSM) and the Next-to-Minimal Supersymmetric Standard Model(NMSSM) in the parameter space allowed by current experimental and theoretical constraints, and also relevant to the Large Hadron Collider(LHC) experiments in the near future. The calculation is based on the analytical expression of the leading order Feynman amplitudes (which includes both quark and squark loops). We separate the di-Higgs production cross section into resonant, non-resonant, and interference parts, in order to better understand the mechanisms that are responsible for the modification to di-Higgs production rate in different regions of the allowed parameter space. We also investigate the sensitivity of High-Luminosity LHC (HL-LHC) to the di-Higgs production in these low energy supersymmetry(SUSY) models. Furthermore, we examine the complementarity between di-Higgs searches and direct searches for BSM particles and precision Higgs couplings measurements at the HL-LHC. We found that the di-Higgs production cross section can be enhanced significantly through resonant production. In the region where the resonant production cross section is small, di-Higgs receives a moderate enhancement due to the modifications in the Higgs couplings. In addition, there is a strong correlation between di-Higgs production and single Higgs production, and di-Higgs is not as sensitive as single Higgs at the HL-LHC.

    hep-phhep-exEur.Phys.J.Plus(2020)·16 citations
19. 19*

    $\text{HEPfit}$: a Code for the Combination of Indirect and Direct Constraints on High Energy Physics Models

    Jorge de Blas🇮🇹 · Debtosh Chowdhury🇫🇷 · Marco Ciuchini🇮🇹 · Antonio M. Coutinho🇨🇭 · Otto Eberhardt🇪🇸 · Marco Fedele🇪🇸 · Enrico Franco🇮🇹 · Giovanni Grilli di Cortona🇵🇱 · Victor Miralles🇪🇸 · Satoshi Mishima🇯🇵 · Ayan Paul🇩🇪 · Ana Penuelas🇪🇸 and 6 other authors

    $\text{HEPfit}$ is a flexible open-source tool which, given the Standard Model or any of its extensions, allows to $\text{i)}$ fit the model parameters to a given set of experimental observables; $\text{ii)}$ obtain predictions for observables. $\text{HEPfit}$ can be used either in Monte Carlo mode, to perform a Bayesian Markov Chain Monte Carlo analysis of a given model, or as a library, to obtain predictions of observables for a given point in the parameter space of the model, allowing $\text{HEPfit}$ to be used in any statistical framework. In the present version, around a thousand observables have been implemented in the Standard Model and in several new physics scenarios. In this paper, we describe the general structure of the code as well as models and observables implemented in the current release.

    hep-phhep-exEPJC(2020)·198 citations
20. 20*

    The Soft Quark Sudakov

    Ian Moult🇺🇸 · Iain W. Stewart🇺🇸 · Gherardo Vita🇺🇸 · Hua Xing Zhu🇨🇳

    There has been recent interest in understanding the all loop structure of the subleading power soft and collinear limits, with the goal of achieving a systematic resummation of subleading power infrared logarithms. Most of this work has focused on subleading power corrections to soft gluon emission, whose form is strongly constrained by symmetries. In this paper we initiate a study of the all loop structure of soft fermion emission. In $\mathcal{N}=1$ QCD we perform an operator based factorization and resummation of the associated infrared logarithms, and prove that they exponentiate into a Sudakov due to their relation to soft gluon emission. We verify this result through explicit calculation to $\mathcal{O}({\alpha }_s^3)$. We show that in QCD, this simple Sudakov exponentiation is violated by endpoint contributions proportional to $(C_A-C_F{)}^n$ which contribute at leading logarithmic order. Combining our $\mathcal{N}=1$ result and our calculation of the endpoint contributions to $\mathcal{O}({\alpha }_s^3)$, we conjecture a result for the soft quark Sudakov in QCD, a new all orders function first appearing at subleading power, and give evidence for its universality. Our result, which is expressed in terms of combinations of cusp anomalous dimensions in different color representations, takes an intriguingly simple form and also exhibits interesting similarities to results for large-x logarithms in the off diagonal splitting functions.

    hep-phhep-thnucl-thJHEP(2020)·77 citations
21. 21*

    Electron-Positron Annihilation Freeze-Out in the Early Universe

    Luke C. Thomas🇺🇸 · Ted Dezen🇺🇸 · Evan B. Grohs🇺🇸 · Chad T. Kishimoto🇺🇸

    Electron-positron annihilation largely occurs in local thermal and chemical equilibrium after the neutrinos fall out of thermal equilibrium and during the Big Bang Nucleosynthesis (BBN) epoch. The effects of this process are evident in BBN yields as well as the relativistic degrees of freedom. We self-consistently calculate the collision integral for electron-positron creation and annihilation using the Klein-Nishina amplitude and appropriate statistical factors for Fermi-blocking and Bose-enhancement. Our calculations suggest that this annihilation freezes out when the photon-electron-positron-baryon plasma temperature is approximately 16 keV, after which its rate drops below the Hubble rate. In the temperature regime near 16 keV, we break the assumption of chemical equilibrium between the electrons, positrons, and photons to independently calculate the evolution of the chemical potentials of the electrons and positrons while computing the associated collision integrals at every time step. We find that the electron and positron chemical potentials deviate from the case with chemical equilibrium. While our results do not affect the interpretation of precision cosmological measurements in elucidating the standard cosmological model, these out of equilibrium effects may be important for testing physics beyond the standard model.

    hep-phastro-ph.COPRD(2020)·27 citations
22. 22*

    The Myriad Uses of Instantons

    Robert D. Pisarski🇺🇸 · Fabian Rennecke🇺🇸

    In quantum chromodynamics (QCD), the role which topologically non-trivial configurations play in splitting the singlet pseudo-Goldstone meson, the ${\eta }^{\prime }$, from the octet is familiar. In addition, such configurations contribute to other processes which violate the axial $U(1{)}_A$ symmetry. While the nature of topological fluctuations in the confined phase is still unsettled, at temperatures well above that for the chiral phase transition, they can be described by a dilute gas of instantons. We show that instantons of arbitrary topological charge $Q$ generate anomalous interactions between $2N_f|Q|$ quarks, which for $Q=1$ make the ${\eta }^{\prime }$ heavy. For two flavors we compute an anomalous quartic meson coupling and discuss its implications for the phenomenology of the chiral phase transition. A dilute instanton gas suggests that for cold, dense quarks, instantons do not evaporate until very high densities, when the baryon chemical potential is $\gtrsim 2$ GeV.

    hep-phhep-thnucl-thPRD(2020)·26 citations
23. 23*

    Contrast data mining for the MSSM from strings

    Erik Parr🇩🇪 · Patrick K.S. Vaudrevange🇩🇪

    We apply techniques from data mining to the heterotic orbifold landscape in order to identify new MSSM-like string models. To do so, so-called contrast patterns are uncovered that help to distinguish between areas in the landscape that contain MSSM-like models and the rest of the landscape. First, we develop these patterns in the well-known ${\mathbb{Z}}_6$-II orbifold geometry and then we generalize them to all other ${\mathbb{Z}}_N$ orbifold geometries. Our contrast patterns have a clear physical interpretation and are easy to check for a given string model. Hence, they can be used to scale down the potentially interesting area in the landscape, which significantly enhances the search for MSSM-like models. Thus, by deploying the knowledge gain from contrast mining into a new search algorithm we create many novel MSSM-like models, especially in corners of the landscape that were hardly accessible by the conventional search algorithm, for example, MSSM-like ${\mathbb{Z}}_6$-II models with $\Delta (54)$ flavor symmetry.

    ↳ hep-thhep-phNPB(2020)·20 citations
24. 24*

    Relic neutrinos: local clustering and consequences for direct detection

    S. Gariazzo🇪🇸

    The Cosmic Neutrino Background is a prediction of the standard cosmological model, but it has been never observed directly. Experiments with the aim of detecting relic CNB neutrinos are under development. For such experiments, the expected event rate depends on the local number density of relic neutrinos. Since massive neutrinos can be attracted by the gravitational potential of our galaxy and cluster locally, a local overdensity of relic neutrinos should exist at Earth. We report the status of our knowledge on the clustering of neutrinos and the consequences for future direct detection experiments.

    ↳ astro-ph.COhep-phPoS(2020)·0 citations
25. 25*

    Scalarization of compact stars in the scalar-Gauss-Bonnet gravity

    Yan Peng🇨🇳

    We study scalarization of horizonless neutral compact reflecting stars. In our model, the scalar hair can be induced by the coupling of static scalar fields to the Gauss-Bonnet invariant. We analytically obtain lower bounds on the coupling parameter. Below the bound, the static scalar hair cannot form. And above the bound, we numerically get the discrete coupling parameter that can support scalar hairs outside stars. We also disclose effects of model parameters on the discrete coupling parameter.

    ↳ gr-qchep-phhep-thJHEP(2019)·15 citations
26. 26*

    Anomalous Gravitational TTT Vertex, Temperature Inhomogeneity, and Pressure Anisotropy

    M. N. Chernodub🇫🇷 · Claudio Corianò🇮🇹 · Matteo Maria Maglio🇮🇹

    The conformal anomaly in curved spacetime generates a nontrivial anomalous vertex, given by the three-point correlation function $TTT$ of the energy-momentum tensor $T^{\mu \nu }$. We show that a temperature inhomogeneity in a gas of charged massless particles generates, via the $TTT$ vertex, a pressure anisotropy with respect to the axis of the temperature variation. This very particular signature may provide an experimental access to the elusive gravitational coefficient $b$ which determines the anomaly contribution of the Weyl tensor to the trace of the energy-momentum tensor in curved spacetime. We present an estimate of the pressure anisotropy both for fermionic quasiparticles in the solid-state environment of Dirac semimetals as well as for a quark-gluon plasma in relativistic heavy-ion collisions. In both cases, the pressure anisotropy is small compared to the mean thermal pressure.

    ↳ hep-thcond-mat.mes-hallhep-phPLB(2020)·15 citations
27. 27*

    Role of chiral symmetry in the nucleon excitation spectrum

    Adam Virgili🇦🇺 · Waseem Kamleh🇦🇺 · Derek Leinweber (University of Adelaide)🇦🇺

    The origin of the low-lying nature of the $N$*(1440), or Roper resonance, has been the subject of significant interest for many years, including several investigations using lattice QCD. The majority of lattice studies have not observed a low-lying excited state energy level in the region of the Roper resonance. However, it has been claimed that chiral symmetry could play an important role in our understanding of this resonance. The purpose of this study is to systematically examine the role of chiral symmetry in the low-lying nucleon spectrum by directly comparing the clover and overlap fermion actions. To ensure any differences in results are attributable to the choice of fermion action, simulations are performed on the same set of gauge field configurations at matched pion masses. Correlation matrix techniques are employed to determine the excitation energy of the first positive-parity excited state for each action. The clover and overlap actions show a remarkable level of agreement. We do not find any evidence that fermion action chiral symmetry plays a significant role in understanding the Roper resonance on the lattice.

    ↳ hep-lathep-phnucl-thPRD(2020)·11 citations
28. 28*

    Resonance study of SU(2) model with 2 fundamental flavours of fermions

    Tadeusz Janowski🇬🇧 · Vincent Drach🇬🇧 · Sasa Prelovsek🇸🇮

    Composite Higgs models are promising candidate models to address the long-standing naturalness problem in the Standard Model. Among them, the most minimal one is the SU(2) with 2 flavours of fermions in the fundamental representation of the gauge group. An important prediction in these models is the existence of resonance spectrum in vector boson scattering. Here we study the lowest such resonance, which is the equivalent of rho resonance in QCD. We describe the scan of the parameter space using the clover-improved Wilson fermions with Symanzik improved gauge action and then show the first results for the mass and width of the rho resonance in this model.

    ↳ hep-lathep-phPoS(2019)·7 citations
29. 29*

    Exploiting weak field gravity-Maxwell symmetry in superconductive fluctuations regime

    Giovanni Alberto Ummarino🇮🇹 · Antonio Gallerati🇮🇹

    We study the behaviour of a superconductor in a weak static gravitational field for temperatures slightly greater than its transition temperature (fluctuation regime). Making use of the time-dependent Ginzburg-Landau equations, we find a possible short time alteration of the static gravitational field in the vicinity of the superconductor, providing also a qualitative behaviour in the weak field condition. Finally, we compare the behaviour of various superconducting materials, investigating which parameters could enhance the gravitational field alteration.

    ↳ gr-qccond-mat.supr-conhep-phSymmetry(2019)·14 citations
30. 30*

    Scattering length from holographic duality

    Carlos Hoyos🇪🇸 · Niko Jokela🇫🇮 · Daniel Logares🇪🇸

    Interesting theories with short range interactions include QCD in the hadronic phase and cold atom systems. The scattering length in two-to-two elastic scattering process captures the most elementary features of the interactions, such as whether they are attractive or repulsive. However, even this basic quantity is notoriously difficult to compute from first principles in strongly coupled theories. We present a method to compute the two-to-two amplitudes and the scattering length using the holographic duality. Our method is based on the identification of the residues of Green's functions in the gravity dual with the amplitudes in the field theory. To illustrate the method we compute a contribution to the scattering length in a hard wall model with a quartic potential and find a constraint on the scaling dimension of a scalar operator $\Delta >d/4$. For $d<4$ this is more stringent than the unitarity constraint and may be applicable to an extended family of large-$N$ theories with a discrete spectrum of massive states. We also argue that for scalar potentials with polynomial terms of order $K$, a constraint more restrictive than the unitarity bound will appear for $d<2K/(K-2)$.

    ↳ hep-thcond-mat.stat-mechcond-mat.str-elhep-lat+1PRD(2020)·9 citations
31. 31*

    Inflation model selection revisited after a 1.91% measurement of the Hubble constant

    Rui-Yun Guo🇨🇳 · Jing-Fei Zhang🇨🇳 · Xin Zhang🇨🇳

    The recent local measurement of the Hubble constant based on the distance-ladder method has reached a $1.91\%$ precision, but this result is in tension with the early-universe measurements at the more than 4$\sigma$ level, bringing a crisis to the contemporary cosmology. In addition to the end-to-end test of the $\Lambda$CDM model in the late universe, it is also of great interest to see how the local $H_0$ measurement affects the determination of the primordial power spectra, and further to test the influences for the inflation model selection. Here, we constrain the primordial power spectra of scalar and tensor perturbations by using a series of observational data, including the Planck 2015 cosmic microwave background (CMB) temperature and polarization power spectra data, the Planck 2018 lensing power spectrum data, the BICEP2/Keck Array CMB B-mode data, and also the prior of optical depth $\tau =0.054\pm 0.007$, as well as the late-universe measurements (baryon acoustic oscillations and type Ia supernovae). In particular, we use the latest $1.91\%$ measurement of the Hubble constant, $H_0=74.03\pm 1.42$ km s${}^{-1}$ Mpc${}^{-1}$, in this cosmological test. We find that considering the latest local $H_0$ measurement in the data combination will lead to a larger fit value of $n_{\mathrm{s}}$. With the addition of the latest local measurement of $H_0$, it is found that the natural inflation model is totally excluded at the $2\sigma$ level, the Starobinsky $R^2$ inflation model is marginally favored at around the $2\sigma$ level, and the spontaneously broken SUSY inflation model is the most favored model.

    ↳ astro-ph.COgr-qchep-phSCPMA(2020)·29 citations
32. 32*

    Signatures of Chiral Magnetic Effect in the Collisions of Isobars

    Shuzhe Shi🇨🇦 · Hui Zhang🇨🇳 · Defu Hou🇨🇳 · Jinfeng Liao🇺🇸

    Quantum anomaly is a fundamental feature of chiral fermions. In chiral materials the microscopic anomaly leads to nontrivial macroscopic transport processes such as the Chiral Magnetic Effect (CME), which has been in the spotlight lately across disciplines of physics. The quark-gluon plasma (QGP) created in relativistic nuclear collisions provides the unique example of a chiral material consisting of intrinsically relativistic chiral fermions. Potential discovery of CME in QGP is of utmost significance, with extensive experimental searches carried out over the past decade. A decisive new collider experiment, dedicated to detecting CME in the collisions of isobars, was performed in 2018 with analysis now underway. In this paper, we develop the state-of-the-art theoretical tool for describing CME phenomenon in these collisions and propose an appropriate isobar subtraction strategy for best background removal. Based on that, we make quantitative predictions for signatures of CME in the collisions of isobars. A new and robust observable that is independent of axial charge uncertainty -- the ratio between isobar-subtracted $\gamma -$ and $\delta -$ correlators, is found to be $-(0.41\pm 0.27)$ for event-plane measurement and $-(0.90\pm 0.45)$ for reaction-plane measurement.

    ↳ nucl-thhep-phnucl-exPRL(2020)·69 citations
33. 33*

    Dark-Energy Instabilities induced by Gravitational Waves

    Paolo Creminelli🇮🇹 · Giovanni Tambalo🇮🇹 · Filippo Vernizzi🇫🇷 · Vicharit Yingcharoenrat🇮🇹

    We point out that dark-energy perturbations may become unstable in the presence of a gravitational wave of sufficiently large amplitude. We study this effect for the cubic Horndeski operator (braiding), proportional to ${\alpha }_{\mathrm{B}}$. The scalar that describes dark-energy fluctuations features ghost and/or gradient instabilities for gravitational-wave amplitudes that are produced by typical binary systems. Taking into account the populations of binary systems, we conclude that the instability is triggered in the whole Universe for $|{\alpha }_{\mathrm{B}}|\gtrsim 10^{-2}$, i.e. when the modification of gravity is sizeable. The instability is triggered by massive black-hole binaries down to frequencies corresponding to $10^{10}$ km: the instability is thus robust, unless new physics enters on even longer wavelengths. The fate of the instability and the subsequent time-evolution of the system depend on the UV completion, so that the theory may end up in a state very different from the original one. The same kind of instability is present in beyond-Horndeski theories for $|{\alpha }_{\mathrm{H}}|\gtrsim 10^{-20}$. In conclusion, the only dark-energy theories with sizeable cosmological effects that avoid these problems are $k$-essence models, with a possible conformal coupling with matter.

    ↳ gr-qcastro-ph.COhep-phhep-thJCAP(2020)·116 citations
34. 34*

    A Potential Mechanism for Inflation from Swampland Conjectures

    Hao Geng🇺🇸

    Inflation is the currently accepted paradigm for the beginnings of the Universe. To explain the observed almost scale invariant spectrum of density perturbations with only a slight spectral tilt, inflation must have been "slow roll", that is with a potential with sufficiently small slope. While the origin of inflationary structure is intrinsically quantum mechanical, gravity gets treated semiclassically within inflationary models. Recent work, in terms of the so called de-Sitter swampland conjecture, has called into question whether slow roll inflation is consistent with a complete theory of quantum gravity in the presence of a positive vacuum energy density, which is a key ingredient in the inflationary paradigm. In this work, we show that, in fact, if we understand this conjecture correctly and with another swampland conjecture, the so-called distance conjecture, involved we get a potential mechanism for slow roll inflation and we argue that here fine-tuning is not a technical problem.

    ↳ hep-thastro-ph.COhep-phPLB(2020)·34 citations
35. 35*

    The Cosmological Bootstrap: Weight-Shifting Operators and Scalar Seeds

    Daniel Baumann🇳🇱 · Carlos Duaso Pueyo🇳🇱 · Austin Joyce🇺🇸 · Hayden Lee🇺🇸 · Guilherme L. Pimentel🇳🇱

    A key insight of the bootstrap approach to cosmological correlations is the fact that all correlators of slow-roll inflation can be reduced to a unique building block---the four-point function of conformally coupled scalars, arising from the exchange of a massive scalar. Correlators corresponding to the exchange of particles with spin are then obtained by applying a spin-raising operator to the scalar-exchange solution. Similarly, the correlators of massless external fields can be derived by acting with a suitable weight-raising operator. In this paper, we present a systematic and highly streamlined derivation of these operators (and their generalizations) using tools of conformal field theory. Our results greatly simplify the theoretical foundations of the cosmological bootstrap program.

    ↳ hep-thastro-ph.COgr-qchep-phJHEP(2020)·307 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.