Nuclear Theory·nucl-th

Tuesday·May 4, 2021

12 papers—5 primary·7 cross-listed

01
Constraining free parameters of a color superconducting non-local Nambu-Jona-Lasinio model using Bayesian analysis of neutron stars mass and radius measurements
Mahboubeh Shahrbaf🇵🇱 · Sofija Antić🇵🇱 · A. Ayriyan🇷🇺 · David Blaschke🇵🇱 · Ana Gabriela Grunfeld🇦🇷
We provide a systematic study of hybrid neutron star equations of state (EoS) consisting of a relativistic density functional for the hadronic phase and a covariant nonlocal Nambu--Jona-Lasinio (nlNJL) model to describe the color superconducting quark matter phase. Changing the values of the two free parameters, the dimensionless vector and diquark coupling strengths $η_{V}$ and $η_{D}$ results in a set of EoS with varying stiffness and deconfinement onset. The favorable parameters are obtained from a systematic Bayesian analysis for which the multi-messenger constraint on the neutron star radius at $1.4$ M $_{⊙}$ and the combined mass-radius constraint for PSR J0740+6620 from NICER experiment are used as the constraints. Additionally, the transition from hadronic matter to deconfined quark matter is constrained to occur above nuclear saturation density. Hybrid stars modeled with these favorable parameters are compatible with the NICER results for the radius of the highest known mass neutron star, PSR J0740+6620. Three new observations interesting for neutron star phenomenology are reported: 1) We show that the constant sound speed (CSS) EoS provides an excellent fit to that of the nlNJL model which implies the squared speed of sound at high densities to be about $0.5$ for the optimized parameters; 2) we give a simple functional form for the mapping between the parameter spaces of these two models valid for the whole range of relevant chemical potentials and 3) we observe that the special point property of hybrid EoS based on CSS quark matter generalizes to a set of lines consisting of special points when two EoS parameters are varied instead of one. A lower limit for the maximum mass of hybrid stars as a function of the vector coupling strength is obtained.
nucl-thastro-ph.HEhep-phPRD(2023)·34 citations
02
Scaling of factorial moments in cumulative variables
Subhasis Samanta🇵🇱 · Tobiasz Czopowicz🇵🇱 · Marek Gazdzicki🇵🇱
A search for power-law fluctuations within the framework of the intermittency method is ongoing to locate the critical point of the strongly interacting matter. In particular, experimental data on proton and pion production in heavy-ion collisions are analyzed in transverse-momentum, $p_{T}$ , space. In this regard, we have studied the dependence of the second scaled factorial moment $F_{2}$ of particle multiplicity distribution on the number of subdivisions of transverse momentum-interval used in the analysis. The study is performed using a simple model with a power-law two-particle correlation function in $p_{T}$ . We observe that $F_{2}$ values depend on the size and position of the $p_{T}$ interval. However, when we convert the non-uniform transverse-momentum distribution to uniform one using cumulative transformation, $F_{2}$ calculated in subdivisions of the cumulative $p_{T}$ becomes independent of the cumulative- $p_{T}$ interval. The scaling behaviour of $F_{2}$ for the cumulative variable is observed. Moreover, $F_{2}$ follows a power law with the number of subdivisions of the cumulative- $p_{T}$ interval with the intermittency index close to the correlation function's exponent.
nucl-thNPA(2021)·11 citations
03
QCD equation of state and the structure of neutron stars in NJL model
Shu-Sheng Xu🇨🇳
The chiral and pion superfluidity phase transitions are studied within NJL model. The model parameters are fitted by pion mass and decay constant together with recent isospin density from lattice QCD. The dense and cold QCD matter suffered the first order chiral phase transition during the quark chemical potential increase. Based on the studies of phase structures, the equation of states~(EoS) of dense QCD matter are calculated with the conditions of $β$ equilibrium and electric charge neutrality. Take the EoS as input, the mass-radius relation of neutron stars are predicted, which is consistent with recent observations of heaviest mass and radius of $1.4 M_{⊙}$ .
nucl-thNPB(2021)·11 citations
04
On the structure in the $Λ N$ cross section at the $Σ N$ threshold
J. Haidenbauer🇩🇪 · U.-G. Meißner🇩🇪
The complexity of threshold phenomena is exemplified on a prominent and long-known case - the structure in the $Λ p$ cross section (invariant mass spectrum) at the opening of the $Σ N$ channel. The mass splitting between the $Σ$ baryons together with the angular momentum coupling in the $^{3} S_{1}$ - $^{3} D_{1}$ partial wave imply that, in principle, up to six channels are involved. Utilizing hyperon-nucleon potentials that provide an excellent description of the available low-energy $Λ p$ and $Σ N$ scattering data, the shape of the resulting $Λ p$ cross section is discussed and the poles near the $Σ N$ threshold are determined. Evidence for a strangeness $S = - 1$ dibaryon is provided, in the form of a deuteron-like (unstable) $Σ N$ bound state. Predictions for level shifts and widths of $Σ^{-} p$ atomic states are given.
nucl-thCPC(2021)·15 citations
05
Transient Relativistic Fluid Dynamics in a General Hydrodynamic Frame
Jorge Noronha🇺🇸 · Michał Spaliński🇵🇱 · Enrico Speranza🇺🇸
We propose a new theory of second-order viscous relativistic hydrodynamics which does not impose any frame conditions on the choice of the hydrodynamic variables. It differs from Mueller-Israel-Stewart theory by including additional transient degrees of freedom, and its first-order truncation reduces to Bemfica-Disconzi-Noronha-Kovtun theory. Conditions for causality and stability are explicitly given in the conformal regime. As an illustrative example, we consider Bjorken flow solutions to our equations and identify variables which make a hydrodynamic attractor manifest.
nucl-thgr-qchep-thPRL(2022)·61 citations
06
Analysis of the differential cross section and photon beam asymmetry data for $γ p \to η^{'} p$
Yu Zhang🇨🇳 · Ai-Chao Wang🇨🇳 · Neng-Chang Wei🇨🇳 · Fei Huang🇨🇳
The photoproduction reaction of $γ p \to η^{'} p$ is investigated based on an effective Lagrangian approach in the tree-level approximation, with the purpose being to understand the reaction mechanisms and to extract the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$ -channel $ρ$ and $ω$ exchanges, $s$ - and $u$ -channel nucleon exchanges, and generalized contact term, the exchanges of a minimum number of nucleon resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that a satisfactory description of the available data on both differential cross sections and photon beam asymmetries can be obtained by including in the $s$ channel the exchanges of the $N (1875) 3/ 2^{-}$ and $N (2040) 3/ 2^{+}$ resonances. The reaction mechanisms of $γ p \to η^{'} p$ are discussed and a prediction for the target nucleon asymmetries is presented.
↳ hep-phnucl-thPRD(2021)·7 citations
07
Coulomb effects in the decays $Υ (4 S) \to B B ˉ$
A.I. Milstein🇷🇺 · S.G. Salnikov🇷🇺
A simple exactly solvable model is proposed for describing the decays $Υ (4 S) \to B^{0} B ˉ^{0}$ and $Υ (4 S) \to B^{+} B^{-}$ . Our predictions agree with available experimental data. Using this model, we analyze the Coulomb effects in the spectra of these decays. It is shown that the frequently used assumption of factorization of Coulomb effects is not fulfilled. The Coulomb interaction leads to the difference in the positions and heights of the peaks corresponding to the charged and neutral modes. As a result, the ratio of probability of $Υ (4 S) \to B^{+} B^{-}$ decay and $Υ (4 S) \to B^{0} B ˉ^{0}$ decay is a nontrivial function of energy.
↳ hep-phnucl-thPRD(2021)·13 citations
08
Constraints on the kinetic mixing parameter $ϵ^{2}$ for the light dark photons from dilepton production in heavy-ion collisions in the few-GeV energy range
Ida Schmidt (Frankfurt Uni.)🇩🇪 · Elena Bratkovskaya (GSI, Darmstadt, Frankfurt Uni.)🇩🇪 · Malgorzata Gumberidze (GSI, Darmstadt)🇩🇪 · Romain Holzmann (GSI, Darmstadt)🇩🇪
The vector $U$ -bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. They are supposed to interact with the standard matter via a 'vector portal' due to the $U (1) - U (1)^{'}$ symmetry group mixing which might make them visible in particle and heavy-ion experiments. While there is no confirmed observation of dark photons, the detailed analysis of different experimental data allows to estimate the upper limit for the kinetic mixing parameter $ϵ^{2}$ depending on the mass $M_{U}$ of $U$ -bosons which is also unknown. In this study we present theoretical constraints on the upper limit of $ϵ^{2} (M_{U})$ in the mass range $M_{U} \leq 0.6$ GeV from the comparison of the calculated dilepton spectra with the experimental data from the HADES Collaboration at SIS18 energies where the dark photons are not observed. Our analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces well the measured dilepton spectra in $p + p$ , $p + A$ and $A + A$ collisions. Additionally to the different dilepton channels originating from interactions and decays of ordinary matter particles (mesons and baryons), we incorporate the decay of hypothetical $U$ -bosons to dileptons, $U \to e^{+} e^{-}$ , where the $U$ -bosons themselves are produced by the Dalitz decay of pions $π^{0} \to γ U$ , $η$ -mesons $η \to γ U$ and Delta resonances $Δ \to N U$ . Our analysis can help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.
↳ hep-phhep-exnucl-thPRD(2021)·10 citations
09
The proton charge radius
Haiyan Gao🇺🇸 · Marc Vanderhaeghen🇩🇪
Nucleons (protons and neutrons) are the building blocks of atomic nuclei, and are responsible for more than 99\% of the visible matter in the universe. Despite decades of efforts in studying its internal structure, there are still a number of puzzles surrounding the proton such as its spin, and charge radius. Accurate knowledge about the proton charge radius is not only essential for understanding how quantum chromodynamics (QCD) works in the non-perturbative region, but also important for bound state quantum electrodynamics (QED) calculations of atomic energy levels. It also has an impact on the Rydberg constant, one of the most precisely measured fundamental constants in nature. This article reviews the latest situation concerning the proton charge radius in light of the new experimental results from both atomic hydrogen spectroscopy and electron scattering measurements, with particular focus on the latter. We also present the related theoretical developments and backgrounds concerning the determination of the proton charge radius using different experimental techniques. We discuss upcoming experiments, and briefly mention the deuteron charge radius puzzle at the end.
↳ hep-phnucl-exnucl-thRMP(2022)·162 citations
10
Quark model analysis of the Weinberg operator contribution to the nucleon EDM
Nodoka Yamanaka🇺🇸 · Emiko Hiyama🇯🇵
The Weinberg operator (chromo-electric dipole moment of gluon) is a CP violating quantity generated in many candidates of new physics beyond the standard model, and it contributes to observables such as the electric dipole moments (EDM) of the neutron or atoms which are currently measured in experiments. In this proceedings contribution, we report on our result of the evaluation of the Weinberg operator contribution to the nucleon EDM in the nonrelativistic quark model using the Gaussian expansion method.
↳ hep-phnucl-thFew Body Syst.(2021)·0 citations
11
The I-Love-Q Relations for Superfluid Neutron Stars
Cheung-Hei Yeung🇨🇳 · Lap-Ming Lin🇨🇳 · Nils Andersson🇬🇧 · Greg Comer🇺🇸
The I-Love-Q relations are approximate equation-of-state independent relations that connect the moment of inertia, the spin-induced quadrupole moment, and the tidal deformability of neutron stars. In this paper, we study the I-Love-Q relations for superfluid neutron stars for a general relativistic two-fluid model: one fluid being the neutron superfluid and the other a conglomerate of all charged components. We study to what extent the two-fluid dynamics might affect the robustness of the I-Love-Q relations by using a simple two-component polytropic model and a relativistic mean field model with entrainment for the equation-of-state. Our results depend crucially on the spin ratio $Ω_{n} / Ω_{p}$ between the angular velocities of the neutron superfluid and the normal component. We find that the I-Love-Q relations can still be satisfied to high accuracy for superfluid neutron stars as long as the two fluids are nearly co-rotating $Ω_{n} / Ω_{p} \approx 1$ . However, the deviations from the I-Love-Q relations increase as the spin ratio deviates from unity. In particular, the deviation of the Q-Love relation can be as large as $O (10%)$ if $Ω_{n} / Ω_{p}$ differ from unity by a few tens of percent. As $Ω_{n} / Ω_{p} \approx 1$ is expected for realistic neutron stars, our results suggest that the two-fluid dynamics should not affect the accuracy of any gravitational waveform models for neutron star binaries that employ the relation to connect the spin-induced quadrupole moment and the tidal deformability.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thUniverse(2021)·22 citations
12
Vector and Axial-Vector Mesons in Nuclear Matter
Ralf-Arno Tripolt🇩🇪 · Christopher Jung🇩🇪 · Lorenz von Smekal🇩🇪 · Jochen Wambach🇩🇪
As a first step towards a realistic phenomenological description of vector and axial-vector mesons in nuclear matter, we calculate the spectral functions of the $ρ$ and the $a_{1}$ meson in a chiral baryon-meson model as a low-energy effective realization of QCD, taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the Functional Renormalization Group (FRG) approach. The phase diagram of the effective hadronic theory exhibits a nuclear liquid-gas phase transition as well as a chiral phase transition at a higher baryon-chemical potential. The in-medium $ρ$ and $a_{1}$ spectral functions are calculated by using the previously introduced analytically-continued FRG (aFRG) method. Our results show strong modifications of the spectral functions in particular near the critical endpoints of both phase transitions which may well be of relevance for electromagnetic rates in heavy-ion collisions or neutrino emissivities in neutron-star merger events.
↳ hep-phnucl-thPRD(2021)·42 citations

Affiliations

first authorsco-authorsvia INSPIRE