Nuclear Theory·nucl-th

Wednesday·June 1, 2022

9 papers—7 primary·2 cross-listed

01
Simulation of Lindblad equations for quarkonium in the quark-gluon plasma
Takahiro Miura🇯🇵 · Yukinao Akamatsu🇯🇵 · Masayuki Asakawa🇯🇵 · Yukana Kaida🇯🇵
We study the properties of the Lindbladian quantum mechanical evolution of quarkonia with non-Abelian charges (color-singlet and octet) in the quark-gluon plasma. We confirm that heavy quark recoils in the Lindblad equation correctly thermalize quarkonium colorful states within statistical errors from the simulation method. We also demonstrate that the Lindblad equation in the dipole limit can provide an efficient alternative method, which is applicable to a finite time evolution before thermalization and dramatically reduces the numerical cost. Our findings will serve as a foundation for large-scale simulation of quarkonium dynamics in the relativistic heavy-ion collisions.
nucl-thcond-mat.quant-gashep-phnucl-ex+1PRD(2022)·31 citations
02
Low-energy parameterisations of the pion-nucleon phase shifts
Evangelos Matsinos
Compared in this work are a few sets of results, obtained from the pion-nucleon ( $π N$ ) data at low energy (pion laboratory kinetic energy up to $100$ MeV) on the basis of the modelling of the $s$ - and $p$ -wave $K$ -matrix elements (or of their reciprocal) via simple polynomials. The fitted values and uncertainties of the model parameters, as well as the corresponding Hessian (covariance) matrices, for three of these parameterisations are given in tabular form for two types of joint fits: to the measurements of the two elastic-scattering processes $π^{\pm} p \to π^{\pm} p$ , and to those of the $π^{+} p$ reaction and of the $π^{-} p$ charge-exchange reaction $π^{-} p \to π^{0} n$ . From these results, reliable and (largely) data-driven (hence model-independent) predictions, accompanied by uncertainties which reflect the statistical and systematic fluctuation of the input data, can be obtained for the low-energy constants of the $π N$ interaction (scattering lengths/volumes and range parameters), for the phase shifts, for the $K$ -matrix elements, and for the partial-wave amplitudes in the (dominant at low energy) $s$ and $p$ waves. After the addition of the $d$ - and $f$ -wave contributions, and the inclusion of the electromagnetic effects, corresponding predictions can be obtained for the usual low-energy $π N$ observables, i.e., for the differential cross section and for the analysing power.
nucl-th2 citations
03
Calibration of nuclear charge density distribution by back-propagation neural networks
Zu-Xing Yang · Xiao-Hua Fan · Tomoya Naito · Zhong-Ming Niu · Zhi-Pan Li · Haozhao Liang
Based on the back-propagation neural networks and density functional theory, a supervised learning is performed firstly to generate the nuclear charge density distributions. The charge density is further calibrated to the experimental charge radii by a composite loss function. It is found that, when the parity, pairing, and shell effects are taken into account, about $96%$ of the nuclei in the validation set fall within two standard deviations of the predicted charge radii. The calibrated charge density is then mapped to the matter density, and further mapped to the binding energies according to the Hohenberg-Kohn theorem. It provides an improved description of some nuclei in both binding energies and charge radii. Moreover, the anomalous overbinding in $^{48}$ Ca implies the existence of an indispensable beyond-mean-field effect.
nucl-thPRC(2023)·27 citations
04
Spin alignment of vector mesons in heavy-ion collisions
Xin-Li Sheng🇨🇳 · Lucia Oliva🇮🇹 · Zuo-Tang Liang🇨🇳 · Qun Wang🇨🇳 · Xin-Nian Wang🇺🇸
Polarized quarks and antiquarks in high-energy heavy-ion collisions can lead to the spin alignment of vector mesons formed by quark coalescence. Using the relativistic spin Boltzmann equation for vector mesons derived from Kadanoff-Baym equations with an effective quark-meson model for strong interaction and quark coalescence model for hadronizaton, we calculate the spin density matrix element $ρ_{00}$ for $ϕ$ mesons and show that anisotropies of local field correlations or fluctuations with respect to the spin quantization direction lead to $ϕ$ meson's spin alignment. We propose that the local correlation or fluctuation of $ϕ$ fields is the dominant mechanism for the observed the $ϕ$ meson's spin alignment and its strength can be extracted from experimental data as functions of collision energies. The calculated transverse momentum dependence of $ρ_{00}$ agrees with STAR's data. We further predict the azimuthal angle dependence of $ρ_{00}$ which can be tested in future experiments.
nucl-thhep-phPRL(2023)·122 citations
05
Generalized Effective String Rope Model for the initial stages of Ultra-Relativistic Heavy Ion Collisions
Angel Reina Ramirez🇪🇸 · V.K. Magas🇪🇸 · L.P. Csernai🇳🇴 · D. Strottman🇺🇸
We present a Generalized Effective String Rope Model (GESRM) for the description of the initial state of relativistic heavy ion collisions. We start from the Effective String Rope Model (ESRM) and take into account fluctuations in the initial state following the Glauber Monte Carlo approach. Results from symmetric Au+Au collisions at different impact parameters and asymmetric A+Au head on collisions are presented at RHIC energies. The produced initial state is used as an initial condition for further hydrodynamical calculations.
nucl-thhep-phPRC(2023)·1 citation
06
Bayesian inference of signatures of hyperons inside neutron stars
Tuhin Malik🇵🇹 · Constança Providência🇵🇹
The possible signatures of the presence of hyperons inside neutron stars are discussed within a Bayesian inference framework applied to a set of models based on a density-dependent relativistic mean-field description of hadronic matter. Nuclear matter properties, hypernuclei properties, and observational information are used to constrain the models. General properties of neutron stars such as the maximum mass, radius, tidal deformability, proton fraction, hyperon fraction, and speed of sound are discussed. It is shown that the two solar mass constraint imposes that neutron stars described by equations of state that include hyperons have on average a larger radius, $≳ 0.5$ km, and a larger tidal deformability, $≳ 150$ , than the stars determined from a nucleonic equation of state, while the speed of sound at the center of the star is more than 25\% smaller. If a 1.4 M $_{⊙}$ star with a radius $≲ 12.5$ km is measured it is quite improbable that a massive star described by the same model contains hyperons. A similar conclusion is drawn if a two solar mass star with a radius $≲ 11.5$ km or a neutron star with a mass above 2.2 M $_{⊙}$ is observed: the possible hyperon content of these stars is ruled out or very reduced. The hyperon presence inside neutron stars is compatible with the present NICER mass-radius observations of the pulsars PSR J0030+0451 and PSR J0740+6620 and the gravitational wave detection GW170817. {It is shown that if the polytropic index $γ = \partial ln p / \partial ln ϵ$ takes values of the order of 1.75 at not too large densities, it may indicate the onset of some kind of exotic matter, but not necessarily of deconfined quark matter.
nucl-thgr-qchep-phPRD(2022)·48 citations
07
Effective operators for valence space calculations from the {\itshape ab initio} No-Core Shell Mode
Zhen Li🇫🇷 · N. A. Smirnova🇫🇷 · A. M. Shirokov🇷🇺 · I. J. Shin🇰🇷 · B. R. Barrett🇺🇸 · P. Maris🇺🇸 · J. P. Vary🇺🇸
In recent years, remarkable progress has been achieved in developing novel non-perturbative techniques for constructing valence space shell model Hamiltonians from realistic internucleon interactions. One of these methods is based on the Okubo--Lee--Suzuki (OLS) unitary transformation applied to no-core shell model (NCSM) solutions. In the present work, we implement the corresponding approach to solve for valence space effective electromagnetic operators. To this end, we use the NCSM results for $A = 16 - 18$ , obtained at $N_{max} = 4$ , to derive a charge-dependent version of the effective interaction for the $s d$ shell, which allows us to exactly reproduce selected NCSM spectra of $^{18}$ O, $^{18}$ F and $^{18}$ Ne within the two valence nucleon space. We then deduce effective single-particle matrix elements of electric quadrupole ( $E 2$ ) and magnetic dipole ( $M 1$ ) operators by matching them to the electromagnetic transitions and moments for $^{17}$ O and $^{17}$ F from the NCSM at $N_{max} = 4$ . Thus, effective $E 2$ and $M 1$ operators are obtained as sets of single-particle matrix elements for the valence space ( $s d$ shell) which allow us to reproduce the NCSM results for $A = 17$ exactly. Systematic comparison of a large set of $s d$ shell results on quadrupole and magnetic dipole moments and transitions for $A = 18$ using effective $E 2$ and $M 1$ operators that we derive from the full NCSM calculations demonstrates a remarkable agreement.
nucl-th2 citations
08
Fresh look at experimental evidence for odderon exchange
Zhu-Fang Cui🇨🇳 · Daniele Binosi🇮🇹 · Craig D. Roberts🇨🇳 · Sebastian M. Schmidt🇩🇪 · D. N. Triantafyllopoulos🇮🇹
Theory suggests that in high-energy elastic hadron+hadron scattering, $t$ -channel exchange of a family of colourless crossing-odd states -- the odderon -- may generate differences between $p p ˉ$ and $pp$ cross-sections in the neighbourhood of the diffractive minimum. Using a mathematical approach based on interpolation via continued fractions enhanced by statistical sampling, we develop robust comparisons between $p p ˉ$ elastic differential cross-sections measured at $\sqrt s = 1.96$ TeV by the D0 Collaboration at the Tevatron and function-form-unbiased extrapolations to this energy of kindred $pp$ measurements at $\sqrt s / TeV = 2.76, 7, 8, 13$ by the TOTEM Collaboration at the LHC and a combination of these data with earlier cross-section measurements at $\sqrt s / GeV = 23.5, 30.7, 44.7, 52.8, 62.5$ made at the internal storage rings. Focusing on a domain that straddles the diffractive minimum in the $p p ˉ$ and $pp$ cross-sections, we find that these two cross-sections differ at the $(2.2 - 2.6) σ$ level; hence, supply evidence with this level of significance for the existence of the odderon. If combined with evidence obtained through different experiment-theory comparisons, whose significance is reported to lie in the range $(3.4 - 4.6) σ$ , one arrives at a $(4.0 - 5.2) σ$ signal for the odderon.
↳ hep-phhep-exhep-latnucl-ex+1PLB(2023)·11 citations
09
Propagation of spin channel waves
Jin Hu🇨🇳 · Zhe Xu🇨🇳
A mutilated model is constructed to approximate the collision term of spin Boltzmann equation that incorporates newly appearing collisional invariants i.e, the total angular momentum. With recourse to degenerate perturbation theory, the dispersion relations of hydrodynamic modes are formulated, among which spin modes are responsible for spin equilibration. We find that the non-locality does not change the sound speed but slows down the propagation of spin channel waves. The damping rates of spin modes are close to those of spinless modes over a reasonable parameter value range. The results reveal that both spin and momentum should be treated simultaneously in a unified transport framework. In the nonrelativistic limit, the short-wavelength behavior for normal modes is also explored and there exists a critical point for every distinct discrete mode over which only quasiparticle modes contribute.
↳ hep-phnucl-thPRD(2023)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE