Fri·May 22, 2020Friday·May 22, 2020

1. 01*

   Muonium-antimuonium oscillations in effective field theory

   Renae Conlin🇺🇸 · Alexey A. Petrov🇺🇸

   Flavor violating processes in the lepton sector have highly suppressed branching ratios in the standard model mainly due to the tiny neutrino mass. This means that observing lepton flavor violation (LFV) in the next round of experiments would constitute a clear indication of physics beyond the standard model (BSM). We revisit a discussion of one possible way to search for LFV, muonium-antimuonium oscillations. This process violates muon lepton number by two units and could be sensitive to the types of BSM physics that are not probed by other types of LFV processes. Using techniques of effective field theory, we calculate the mass and width differences of the mass eigenstates of muonium. We argue that its invisible decays give the parametrically leading contribution to the lifetime difference and put constraints on the scales of new physics probed by effective operators in muonium oscillations.

   hep-phhep-exPRD(2020)·46 citations
2. 02*

   RIP $Hb\bar{b}$: How other Higgs production modes conspire to kill a rare signal at the LHC

   Davide Pagani🇩🇪 · Hua-Sheng Shao🇫🇷 · Marco Zaro🇮🇹

   The hadroproduction of a Higgs boson in association with a bottom-quark pair ($Hb\bar{b}$) is commonly considered as the key process for directly probing the Yukawa interaction between the Higgs boson and the bottom quark ($y_b$). However, in the Standard-Model (SM) this process is also known to suffer from very large irreducible backgrounds from other Higgs production channels, notably gluon-fusion ($gg$F). In this paper we calculate for the first time the so-called QCD and electroweak complete-NLO predictions for $Hb\bar{b}$ production, using the four-flavour scheme. Our calculation shows that not only the $gg$F but also the $ZH$ and even the vector-boson fusion channels are sizeable irreducible backgrounds. Moreover, we demonstrate that, at the LHC, the rates of these backgrounds are very large with respect to the "genuine" and $y_b$-dependent $Hb\bar{b}$ production mode. In particular, no suppression occurs at the differential level and therefore backgrounds survive typical analysis cuts. This fact further jeopardises the chances of measuring at the LHC the $y_b$-dependent component of $Hb\bar{b}$ production in the SM. Especially, unless $y_b$ is significantly enlarged by new physics, even for beyond-the SM scenarios the direct determination of $y_b$ via this process seems to be hopeless at the LHC.

   hep-phhep-exJHEP(2020)·48 citations
3. 03*

   Vector boson fusion at multi-TeV muon colliders

   Antonio Costantini🇮🇹 · Federico De Lillo🇧🇪 · Fabio Maltoni🇧🇪 · Luca Mantani🇧🇪 · Olivier Mattelaer🇧🇪 · Richard Ruiz🇧🇪 · Xiaoran Zhao🇧🇪

   High-energy lepton colliders with a centre-of-mass energy in the multi-TeV range are currently considered among the most challenging and far-reaching future accelerator projects. Studies performed so far have mostly focused on the reach for new phenomena in lepton-antilepton annihilation channels. In this work we observe that starting from collider energies of a few TeV, electroweak (EW) vector boson fusion/scattering (VBF) at lepton colliders becomes the dominant production mode for all Standard Model processes relevant to studying the EW sector. In many cases we find that this also holds for new physics. We quantify the size and the growth of VBF cross sections with collider energy for a number of SM and new physics processes. By considering luminosity scenarios achievable at a muon collider, we conclude that such a machine would effectively be a "high-luminosity weak boson collider," and subsequently offer a wide range of opportunities to precisely measure EW and Higgs coupling as well as to discover new particles.

   hep-phhep-exJHEP(2020)·202 citations
4. 04*

   Interpretation of NO$\nu$A and T2K data in the presence of a light sterile neutrino

   Sabya Sachi Chatterjee🇬🇧 · Antonio Palazzo🇮🇹

   We study in detail the impact of a light sterile neutrino in the interpretation of the latest data of the long baseline experiments NO$\nu$A and T2K, assessing the robustness/fragility of the estimates of the standard 3-flavor parameters with respect to the perturbations induced in the 3+1 scheme. We find that all the basic features of the 3-flavor analysis, including the weak indication ($\sim$1.4$\sigma$) in favor of the inverted neutrino mass ordering, the preference for values of the CP-phase ${\delta }_{13}\sim 1.2\pi$, and the substantial degeneracy of the two octants of ${\theta }_{23}$, all remain basically unaltered in the 4-flavor scheme. Our analysis also demonstrates that it is possible to attain some constraints on the new CP-phase ${\delta }_{14}$. Finally, we point out that, differently from non-standard neutrino interactions, light sterile neutrinos are not capable to alleviate the tension recently emerged between NO$\nu$A and T2K in the appearance channel.

   hep-phhep-ex11 citations
5. 05*

   Inelastic Dark Matter and the SABRE Experiment

   M. J. Zurowski🇦🇺 · E. Barberio🇦🇺 · G. Busoni🇩🇪

   We present here the sensitivity of the SABRE (Sodium iodide with Active Background REjection) experiment to benchmark proto-philic, spin dependent, Inelastic Dark Matter models previously proposed due to their lowered tension with existing experimental results. We perform fits to cross section, mass, and mass splitting values to find the best fit to DAMA/LIBRA data for these models. In this analysis, we consider the Standard Halo Model (SHM), as well as an interesting extension upon it, the SHM+Stream distribution, to investigate the influence of the Dark Matter velocity distribution upon experimental sensitivity and whether or not its consideration may be able to help relieve the present experimental tension. Based on our analysis, SABRE should be sensitive to all the three benchmark models within 3-5 years of data taking.

   hep-phhep-exJCAP(2020)·9 citations
6. 06*

   QCD Axion From a Spontaneously Broken B-L Gauge Symmetry

   Gongjun Choi🇨🇳 · Motoo Suzuki🇨🇳 · Tsutomu T. Yanagida🇨🇳

   In this paper, we show that the Peccei-Quinn (PQ) symmetry with a good quality can be realized in a simple $B-L$ extension of the minimal supersymmetric standard model. The PQ symmetry is a remnant of the $B-L$ gauge symmetry at the renormalizable level. Besides, the sufficient quality of the PQ symmetry is preserved by a non anomalous discrete gauged $R$-symmetry and a small gravitino mass $m_{3/2}\ll 100$GeV. A viable mass range is $m_{3/2}=\mathcal{O}(1)$eV which allows a high reheating temperature and many baryogenesis scenarios typified by the thermal leptogenesis without any astrophysical and cosmological problems. Such a light gravitino may be tested in the future 21cm line observations.

   hep-phJHEP(2020)·11 citations
7. 07*

   Cosmic String in Abelian-Higgs Model with Enhanced Symmetry -- Implication to the Axion Domain-Wall Problem --

   Takashi Hiramatsu🇯🇵 · Masahiro Ibe🇯🇵 · Motoo Suzuki🇨🇳

   In our previous work, we found new types of the cosmic string solutions in the Abelian-Higgs model with an enhanced $U(1)$ global symmetry. We dubbed those solutions as the compensated/uncompensated strings. The compensated string is similar to the conventional cosmic string in the Abrikosov-Nielsen-Olesen (ANO) string, around which only the would-be Nambu-Goldstone (NG) boson winds. Around the uncompensated string, on the other hand, the physical NG boson also winds, where the physical NG boson is associated with the spontaneous breaking of the enhanced symmetry. Our previous simulation in the 2+1 dimensional spacetime confirmed that both the compensated/uncompensated strings are formed at the phase transition of the symmetry breaking. Non-trivial winding of the physical NG boson around the strings potentially causes the so-called axion domain-wall problem when the model is applied to the axion model. In this paper, we perform simulation in the 3+1 dimensional spacetime to discuss the fate of the uncompensated strings. We observe that the evolution of the string-network is highly complicated in the 3+1 dimensional simulation compared with that seen in the previous simulation. Despite such complications, we find that the number of the uncompensated strings which could cause can be highly suppressed at late times. Our observation suggests that the present setup can be applied to the axion model without suffering from the axion domain-wall problem.

   hep-phastro-ph.COhep-thJHEP(2020)·9 citations
8. 08*

   Recent developments in chiral and spin polarization effects in heavy-ion collisions

   Jian-Hua Gao🇨🇳 · Guo-Liang Ma🇨🇳 · Shi Pu🇨🇳 · Qun Wang🇨🇳

   We give a brief overview of recent theoretical and experimental results on the chiral magnetic effect and spin polarization effect in heavy-ion collisions. We present updated experimental results for the chiral magnetic effect and related phenomena. The time evolution of the magnetic fields in different models is discussed. The newly developed quantum kinetic theory for massive fermions is reviewed. We present theoretical and experimental results for the polarization of $\Lambda$ hyperons and the ${\rho }_{00}$ value of vector mesons.

   hep-phnucl-exnucl-thNucl.Sci.Tech.(2020)·132 citations
9. 09*

   Analytic model studies of polarized baryon production

   B. Boldizsár🇭🇺

   We investigate known exact solutions of hydrodynamics and derive analytic formulas for the polarization of baryons produced at freeze-out. Such polarization (observed in high energy heavy-ion experiments) carries information on the time evolution of the quark-gluon plasma (sQGP), and our results give first analytic insight into the connection between this type of measurements and dynamical properties of the sQGP (e.g. vorticity). We present results for a rotating and acceleratingly expanding solution and also give hints on how to calculate the polarization using a rotating extension of the Buda--Lund parameterization.

   hep-phnucl-thPhys.Part.Nucl.(2020)·0 citations
10. 10*

    Fluctuations of conserved charges, chiral spin symmetry and deconfinement in an SU(2)_color subgroup of SU(3)_color above T_c

    L. Ya. Glozman🇦🇹

    Above a pseudocritical temperature of chiral symmetry restoration T_c the energy and the pressure are very far from the quark-gluon-plasma limit (i.e. ideal gas of free quarks and gluons). At the same time very soon above T_c fluctuations of conserved charges behave as if quarks were free particles. Within the T_c - 3T_c interval a chiral spin symmetry emerges in QCD which is not consistent with free quarks and suggests that degrees of freedom are chirally symmetric quarks bound into the color-singlet objects by the chromoelectric field. Here we analyse temporal and spatial correlators in this interval and demonstrate that they indicate simultaneously the chiral spin symmetry as well as absence of the interquark interactions in channels constrained by a current conservation. The latter channels are responsible for both fluctuations of conserved charges and for dileptons. Assuming that a SU(2)_color subgroup of SU(3)_color is deconfined soon above T_c but confinement persits in SU(3)_color/SU(2)_color in the interval T_c - 3T_c we are able to reconcile all empirical facts listed above.

    hep-phhep-lathep-thnucl-thPRD(2020)·4 citations
11. 11*

    Exploring sizable triple Higgs couplings in the 2HDM

    F. Arco🇪🇸 · S. Heinemeyer🇪🇸 · M.J. Herrero🇪🇸

    An important task at future colliders is the measurement of the triple Higgs coupling. Depending on its size relative to the Standard Model (SM) value, certain collider options result in a higher experimental accuracy. Within the framework of Two Higgs Doublet Models (2HDM) type I and II we investigate the allowed ranges for all triple Higgs couplings involving at least one light, SM-like Higgs boson. We take into account theoretical constraints (unitarity, stability), experimental constraints from direct Higgs-boson searches, measurements of the SM-like Higgs-boson properties, flavor observables and electroweak precision data. We find that the SM-type triple Higgs coupling w.r.t. its SM value, ${\lambda }_{hhh}/{\lambda }_{\mathrm{SM}}$, can range between $\sim -0.5$ and $\sim 1.5$. Depending on which value is realized, the HL-LHC can compete with, or is clearly inferior to the ILC. We find the coupling ${\lambda }_{hhH}$ between $\sim -1.5$ and $\sim 1.5$. Triple Higgs couplings involving two heavy Higgs bosons, ${\lambda }_{hHH}$, ${\lambda }_{hAA}$ and ${\lambda }_{h{H}^{+}{H}^{-}}$ can reach values up to $\mathcal{O}(10)$, roughly independent of the 2HDM type. This can lead to potentially strongly enhanced production of two Higgs-bosons at the HL-LHC or high-energy $e^{+}{e}^{-}$ colliders.

    hep-phEPJC(2020)·54 citations
12. 12*

    Fat brane and seesaw mechanism in extra dimensions

    Bjorn Garbrecht🇩🇪 · Ricardo G. Landim🇩🇪

    In this paper we present a higher-dimensional seesaw mechanism. We consider a single, flat extra dimension, where a fat brane is localized and contains the standard model (SM) fields, similar to Universal Extra Dimension models. There is only one Dirac fermion in the bulk, and in four dimensions it results in two towers of Kaluza-Klein (KK) Majorana sterile neutrinos, whose mass mixing with the SM neutrinos is suppressed due to a brane-localized kinetic term. The interaction between the sterile neutrinos and the SM is through the usual coupling with the Higgs boson, where the coupling depends upon the compactification radius $R^{-1}=10^{-2}-1$ GeV and the width of the fat brane $L^{-1}=2$ TeV, where the latter value is chosen to avoid LHC constraints. Due to this suppression mechanism the mass of the lightest sterile neutrinos can be of order $\mathcal{O}(1-10)$~\text{TeV} while naturally explaining the small SM neutrino mass, which in turn is easily obtained for a large range of parameter choices. Furthermore, neutrino oscillations are not substantially influenced by the tower of sterile KK particles. Finally, leptogenesis is investigated in this setup, and it is viable for some values within the parameter space.

    hep-phhep-thPRD(2020)·4 citations
13. 13*

    Dispersive Analysis of Low Energy $\gamma N\to \pi N$ Process and Studies on the $N^{\ast }(890)$ Resonance

    Yao Ma (Peking U. and Peking U., SKLNPT)🇨🇳 · Wen-Qi Niu (Peking U. and Peking U., SKLNPT)🇨🇳 · De-Liang Yao (Hunan U.)🇨🇳 · Han-Qing Zheng (Peking U. and Peking U., SKLNPT and CICQM, Beijing)🇨🇳

    We present a dispersive representation of the $\gamma N\to \pi N$ partial-wave amplitude based on unitarity and analyticity. In this representation, the right-hand-cut contribution responsible for $\pi N$ final-state-interaction effect are taken into account via an Omnés formalism with elastic $\pi N$ phase shifts as inputs, while the left-hand-cut contribution is estimated by invoking chiral perturbation theory. Numerical fits are performed in order to pin down the involved subtraction constants. It is found that good fit quality can be achieved with only one free parameter and the experimental data of the multipole amplitude $E_0^{+}$ in the energy region below the $\Delta (1232)$ are well described. Furthermore, we extend the $\gamma N\to \pi N$ partial-wave amplitude to the second Riemann sheet so as to extract the couplings of the $N^{\ast }(890)$. The modulus of the residue of the multipole amplitude $E_0^{+}$ ($S_{11pE}$) is $2.41\mathrm{mfm}\cdot \mathrm{Ge}{\mathrm{V}}^2$ and the partial width of $N^{\ast }(890)\to \gamma N$ at the pole is about $0.369\mathrm{MeV}$, which is almost the same as the one of $N^{\ast }(1535)$, indicating that $N^{\ast }(890)$ strongly couples to $\pi N$ system.

    hep-phCPC(2021)·11 citations
14. 14*

    Jet production in Polarized DIS at NNLO

    Ignacio Borsa🇦🇷 · Daniel de Florian🇦🇷 · Iván Pedron🇦🇷

    We present the NNLO calculation for single-inclusive jet production in polarized DIS $\vec{e}\vec{p}\to \mathrm{jet}+X$. We perform the computation based on the Projection-to-Born method by combining our recent NLO result for di-jet production in polarized DIS along with the NNLO coefficients for the inclusive cross section. In this way, we achieve NNLO accuracy in a fully exclusive way for single-jet observables, the first time for a polarized cross section. We study the perturbative stability and phenomenological consequences of the QCD corrections for Electron Ion Collider kinematics.

    hep-phPRL(2020)·27 citations
15. 15*

    $WW\gamma$ production at hadron colliders with NLO QCD+EW corrections and parton shower effects

    Jian-Wen Zhu🇨🇳 · Ren-You Zhang🇨🇳 · Wen-Gan Ma🇨🇳 · Qiang Yang🇨🇳 · Yi Jiang🇨🇳

    $W^{+}{W}^{-}\gamma$ production in proton-proton collision provides a window to the mechanism of electroweak symmetry breaking and a direct accessment to triple and quartic gauge couplings. Precision study of gauge boson self-interactions may also provide evidence of existence of new physics beyond the Standard Model. In this paper, we study the $W^{+}{W}^{-}\gamma$ production at the LHC and future higher energy proton-proton colliders at the QCD+EW NLO including parton shower effects. We find that the contributions from the photon-induced (i.e., $q\gamma$- and $\gamma \gamma$-initiated) channels are non-negligible since the photon luminosity can be enhanced significantly with the increment of colliding energy, and the large real jet emission QCD and EW corrections can be depressed sufficiently by applying the jet veto event selection scheme. Moreover, we also investigate the theoretical errors arising from the PDF uncertainty and the factorization/renormalization scale dependence.

    hep-phJ.Phys.G(2020)·11 citations
16. 16*

    LISA Sensitivity to Gravitational Waves from Sound Waves

    Kai Schmitz🇨🇭

    Gravitational waves (GWs) produced by sound waves in the primordial plasma during a strong first-order phase transition in the early Universe are going to be a main target of the upcoming Laser Interferometer Space Antenna (LISA) experiment. In this short note, I draw a global picture of LISA's expected sensitivity to this type of GW signal, based on the concept of peak-integrated sensitivity curves (PISCs) recently introduced in [1909.11356, 2002.04615]. In particular, I use LISA's PISC to perform a systematic comparison of several thousands of benchmark points in ten different particle physics models in a compact fashion. The presented analysis (i) retains the complete information on the optimal signal-to-noise ratio, (ii) allows for different power-law indices describing the spectral shape of the signal, (iii) accounts for galactic confusion noise from compact binaries, and (iv) exhibits the dependence of the expected sensitivity on the collected amount of data. An important outcome of this analysis is that, for the considered set of models, galactic confusion noise typically reduces the number of observable scenarios by roughly a factor two, more or less independent of the observing time. The numerical results presented in this paper are also available on Zenodo [http://doi.org/10.5281/zenodo.3837877].

    hep-phastro-ph.COgr-qcSymmetry(2020)·48 citations
17. 17*

    Exploring $J/\psi$ production mechanism at the future Electron-Ion Collider

    Jian-Wei Qiu🇺🇸 · Xiang-Peng Wang🇺🇸 · Hongxi Xing🇨🇳

    We propose to use transverse momentum $p_T$ distribution of $J/\psi$ production at the future Electron Ion Collider (EIC) to explore the production mechanism of heavy quarkonia in high energy collisions. We apply QCD and QED collinear factorization to the production of a $c\bar{c}$ pair at high $p_T$, and non-relativistic QCD factorization to the hadronization of the pair to a $J/\psi$. We evaluate $J/\psi$ $p_T$-distribution at both leading and next-to-leading order in strong coupling, and show that production rates for various color-spin channels of a $c\bar{c}$ pair in electron-hadron collisions are very different from that in hadron-hadron collisions, which provides a strong discriminative power to determine various transition rates for the pair to become a $J/\psi$. We predict that the $J/\psi$ produced in electron-hadron collisions is likely unpolarized, and the production is an ideal probe for gluon distribution of colliding hadron (or nucleus). We find that the $J/\psi$ production is dominated by the color-octet channel, providing an excellent probe to explore the gluon medium in large nuclei at the EIC.

    hep-phhep-exnucl-exnucl-thChin.Phys.Lett.(2021)·21 citations
18. 18*

    Enhancing Sensitivities to Long-lived Particles with High Granularity Calorimeters at the LHC

    Jia Liu🇺🇸 · Zhen Liu🇺🇸 · Lian-Tao Wang🇺🇸 · Xiao-Ping Wang🇺🇸

    The search for long-lived particles (LLP) is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. In this paper, we focus on a new search strategy of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the high granularity of the calorimeter with this upgrade, which allows us to see "shower tracks" in the calorimeter, can play a crucial role in identifying the signal and suppressing the background. We study the potential reach of the HGCAL using a signal model in which the Standard Model Higgs boson decays into a pair of LLPs, $h\to XX$. After carefully estimating the Standard Model QCD and the misreconstructed fake-track backgrounds, we give the projected reach for both a more conservative vector boson fusion trigger and a novel displaced-track-based trigger. Our results show that the best reach for the Higgs decay branching ratio, BR$(h\to XX)$, in the vector boson fusion channel is about $\mathcal{O}(10^{-4})$ with lifetime $c{\tau }_X\sim 0.1$--$1$ meters, while for the gluon gluon fusion channel it is about $\mathcal{O}(10^{-5}\text{–}10^{-6})$ for similar lifetimes. Alternatively, for an LLP with $c{\tau }_X\sim 10^3$ meters, the HGCAL based search should be able to probe BR$(h\to XX)$ down to a few $\times 10^{-4}$($10^{-2}$) in the gluon gluon fusion (vector boson fusion) channels, respectively. In comparison with these previous searches, our new search shows enhanced sensitivity in complementary regions of the LLP parameter space.

    hep-phhep-exJHEP(2020)·35 citations
19. 19*

    Synthetic Gravitational Waves from a Rolling Axion Monodromy

    Ogan Özsoy🇵🇱

    In string theory inspired models of axion-like fields, sub-leading non-perturbative effects, if sufficiently large, can introduce steep cliffs and gentle plateaus onto the underlying scalar potential. During inflation, the motion of a spectator axion $\sigma$ on this potential becomes temporarily fast, leading to localized amplification of one helicity state of gauge fields. In this model, the tensor and scalar correlators sourced by the vector fields exhibit localized peak(s) in momentum space corresponding to the modes that exit the horizon while the roll of $\sigma$ is fast. Thanks to the gravitational coupling of gauge fields with the visible sector and the localized nature of particle production, this model can generate observable gravitational waves (GWs) at CMB scales while satisfying the current limits on scalar perturbations. The resulting GW signal breaks parity and exhibit sizeable non-Gaussianity that can be probed by future CMB B-mode missions. Depending on the initial conditions and model parameters, the roll of the spectator axion can also generate an observably large GW signature at interferometer scales while respecting the bounds on the scalar fluctuations from primordial black hole limits. In our analysis, we carefully investigate bounds on the model parameters that arise through back-reaction and perturbativity considerations to show that these limits are satisfied by the implementations of the model that generate GW signals at CMB and sub-CMB scales.

    ↳ astro-ph.COhep-phhep-thJCAP(2021)·63 citations
20. 20*

    Quark spin and orbital angular momentum from proton GPDs

    Adam Freese🇺🇸 · Ian C. Cloët🇺🇸

    We calculate the leading-twist helicity-dependent generalized parton distributions (GPDs) of the proton at finite skewness in the Nambu--Jona-Lasinio (NJL) model of quantum chromodynamics (QCD). From these (and previously calculated helicity-independent GPDs) we obtain the spin decomposition of the proton, including predictions for quark intrinsic spin and orbital angular momentum. The inclusion of multiple species of diquarks is found to have a significant effect on the flavor decomposition, and resolving the internal structure of these dynamical diquark correlations proves essential for the mechanical stability of the proton. At a scale of $Q^2=4$GeV${}^2$ we find that the up and down quarks carry an intrinsic spin and orbital angular momentum of $S_u=0.534$, $S_d=-0.214$, $L_u=-0.189$, and $L_d=0.210$, whereas the gluons have a total angular momentum of $J_g=0.151$. The down quark is therefore found to carry almost no total angular momentum due to cancellations between spin and orbital contributions. Comparisons are made between these spin decomposition results and lattice QCD calculations.

    ↳ nucl-thhep-phPRC(2021)·24 citations
21. 21*

    A novel method of measuring cosmological distances using broad-line regions of quasars

    Hong Li🇨🇳 · Xin Zhang🇨🇳

    The absolute distance scale measurements in cosmology have always been an important mission. In particular, in recent years, the Hubble constant tension between the measurements from early and late universe has become a new crisis for cosmology, which calls for new, independent absolute cosmological distance measurements. Recently, a result of measuring the parallax distance to 3C 273 through spectroastrometry and reverberation mapping was reported. We comment on this novel method in this News & Views paper.

    ↳ astro-ph.COgr-qchep-phSci.Bull.(2020)·15 citations
22. 22*

    Neutron stars with large quark cores

    Márcio Ferreira🇵🇹 · Renan Câmara Pereira🇵🇹 · Constança Providência🇵🇹

    We describe charge-neutral neutron star matter in $\beta -$equilibrium using hybrid equations of state, where a first-order phase transition from hadronic to quark matter is realized. The hadronic matter is described in a model-independent way by a Taylor expansion around saturation density $n_0$, while the three-flavor NJL model is used for the quark matter. Exploring the present uncertainty on the empirical parameters of nuclear matter and the parameter space of the NJL model, we construct two datasets of thermodynamically consistent and causal hybrid EoSs, compatible with astrophysical observations. We conclude that, to sustain a considerable quark core size, the intensity of the phase transition from hadron to quark matter cannot be strong, having a energy density gap below $200$ MeV/fm${}^3$, and must occur at baryon densities not above four times the saturation density. A non zero but not too strong quark vector-isoscalar term and a weak vector isovector quark term are required. Large quark cores carrying almost half of the star mass are possible inside neutron stars with a maximum mass $\approx 2.2M_{\odot }$. To get a considerable number of hybrid EoS predicting quark matter already inside neutron stars with a mass $\sim 1.4M_{\odot }$, we require that the onset of quarks occurs in the range $1.3n_0$ and $2.5n_0$. Neutron stars with large quark cores corresponding to more than one fourth of the total star mass, are possible if the energy density gap and the pressure at transition are below 100 MeV/fm${}^3$. However, under these constraints, the maximum neutron star mass is limited to $\lesssim 2.06M_{\odot }$. No strong signatures from quark matter were found on the radius and the tidal deformability for neutron star masses below $1.8M_{\odot }$.

    ↳ nucl-thastro-ph.HEhep-phPRD(2020)·53 citations
23. 23*

    Chiral symmetry and taste symmetry from the eigenvalue spectrum of staggered Dirac operators

    Hwancheol Jeong🇰🇷 · Chulwoo Jung🇺🇸 · Seungyeob Jwa🇰🇷 · Jangho Kim🇩🇪 · Jeehun Kim🇰🇷 · Nam Soo Kim🇰🇷 · Sunghee Kim🇰🇷 · Sunkyu Lee🇰🇷 · Weonjong Lee🇰🇷 · Youngjo Lee🇰🇷 · Jeonghwan Pak (SWME Collaboration)🇰🇷

    We investigate general properties of the eigenvalue spectrum for improved staggered quarks. We introduce a new chirality operator $[{\gamma }_5\otimes 1]$ and a new shift operator $[1\otimes {\xi }_5]$, which respect the same recursion relation as the ${\gamma }_5$ operator in the continuum. Then we show that matrix elements of the chirality operator sandwiched between two eigenstates of the staggered Dirac operator are related to those of the shift operator by the Ward identity of the conserved $U(1{)}_A$ symmetry of staggered fermion actions. We perform a numerical study in quenched QCD using HYP staggered quarks to demonstrate the Ward identity. We introduce a new concept of leakage patterns which collectively represent the matrix elements of the chirality operator and the shift operator sandwiched between two eigenstates of the staggered Dirac operator. The leakage pattern provides a new method to identify zero modes and non-zero modes in the Dirac eigenvalue spectrum. This method is as robust as the spectral flow method but requires much less computing power. Analysis using a machine learning technique confirms that the leakage pattern is universal, since the staggered Dirac eigenmodes on normal gauge configurations respect it. In addition, the leakage pattern can be used to determine a ratio of renormalization factors as a by-product. We conclude that it might be possible and realistic to measure the topological charge $Q$ using the Atiya-Singer index theorem and the leakage pattern of the chirality operator in the staggered fermion formalism.

    ↳ hep-lathep-phPRD(2021)·3 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.