Nuclear Theory·nucl-th

Tuesday·May 24, 2022

11 papers—5 primary·6 cross-listed

01
Magnetic dipole moments as a strong signature for $α$ -clustering in even-even self-conjugate nuclei
Gianluca Stellin · Karl-Heinz Speidel · Ulf-G. Meißner
We investigate the magnetic dipole moments in even-even self-conjugate nuclei from $^{12} C$ to $^{44} Ti$ . For the latter, the measured gyromagnetic factors of excited states turn out to assume the same value of $g \approx + 0.5$ within statistical errors. This peculiar feature can be interpreted on the basis of collective excitations of $α$ -clusters. Analogously, the behaviour of the same observable is studied for all isotopes obtained by adding one or two neutrons to the considered self-conjugate nuclei. It is found that for the $N = Z + 1$ isotopes the $α$ -cluster structure hardly contributes to the observed negative g- factor value, corroborating molecular $α$ -cluster models. The addition of a further neutron, however, restores the original $α$ -cluster g-factors, except for the semi-magic isotopes, in which the deviations from $g \approx + 0.5$ can be associated with the relevant shell closures. Secondly, we analyze the same observable in the framework of a macroscopic $α$ -cluster model on a finite lattice of side length $L$ . We focus on the discretization effects induced in the magnetic dipole moments of the $2_{1}^{+}$ and the $3_{1}^{-}$ states of $^{12} C$ at different values of the lattice spacing $a$ .
nucl-thEPJA(2022)·5 citations
02
Effects of pairing gap and band gap on superfluid density in the inner crust of neutron stars
Yuki Minami · Gentaro Watanabe
Calculations of the superfluid density in the inner crust of neutron stars by different approaches are in strong disagreement, which causes a debate on the accountability of pulsar glitches based on superfluidity. Taking a simple unified model, we study the dependence on approximation of the superfluid density in a periodic potential. In comparison with the Hartree-Fock-Bogoliubov (HF-Bogoliubov) theory which treats the effects of the band gap and the pairing gap on equal footing, we examine the HF-BCS-type approximation in which the former is incorporated in priority, and another approximation in which the latter is incorporated in priority. We find that, when the pairing gap and the band gap are comparable as in the inner crust of neutron stars, they need to be treated on equal footing, and the HF-BCS approximation can considerably underestimate the superfluid density even if the pairing gap is much smaller than the Fermi energy. Our result suggests that the validity of the HF-BCS approximation for evaluating the superfluid density in neutron star crusts is questionable.
nucl-thastro-ph.HEcond-mat.quant-gasPRResearch(2022)·15 citations
03
Spinodal Enhancement of Light Nuclei Yield Ratio in Relativistic Heavy Ion Collisions
Kai-Jia Sun🇺🇸 · Wen-Hao Zhou🇨🇳 · Lie-Wen Chen🇨🇳 · Che Ming Ko🇺🇸 · Feng Li🇨🇳 · Rui Wang🇨🇳 · Jun Xu🇨🇳
Using a relativistic transport model to describe the evolution of the quantum chromodynamic matter produced in Au+Au collisions at $s_{N N} = 3 - 200$ GeV, we study the effect of a first-order phase transition in the equation of state of this matter on the yield ratio $N_{t} N_{p} / N_{d}^{2}$ ( $tp / d^{2}$ ) of produced proton ( $p$ ), deuteron ( $d$ ), and triton ( $t$ ). We find that the large density inhomogeneities generated by the spinodal instability during the first-order phase transition can survive the fast expansion of the subsequent hadronic matter and lead to an enhanced $tp / d^{2}$ in central collisions at $s_{N N} = 3 - 5$ GeV as seen in the experiments by the STAR Collaboration and the E864 Collaboration. However, this enhancement subsides with increasing collision centrality, and the resulting almost flat centrality dependence of $tp / d^{2}$ at $s_{N N} = 3$ GeV can also be used as a signal for the first-order phase transition.
nucl-thhep-ph13 citations
04
Modeling Neutron Star Matter in the Age of Multimessenger Astrophysics
Omar Benhar · Alessandro Lovato · Giovanni Camelio
The interpretation of the available and forthcoming data obtained from multimessenger astrophysical observations -- potentially providing unprecedented access to neutron star properties -- will require the development of novel, accurate theoretical models of dense matter. Of great importance, in this context, will be the capability to devise a description of thermal effects applicable to the study of quantities other than the equation of state, such as the transport coefficients and the neutrino mean free path in the nuclear medium. The formalism based on correlated basis states and the cluster expansion technique has been previously employed to derive a well-behaved effective interaction -- suitable for use in standard perturbation theory -- from a state-of-the-art nuclear Hamiltonian, including phenomenological two- and three-nucleon potentials. Here, we provide a comprehensive and self-contained account of the extension of this approach to the treatment of finite-temperature effects, and report the results of numerical calculations of a number of properties of nuclear matter with arbitrary neutron excess and temperature up to 50 MeV.
nucl-thApJ(2022)·8 citations
05
Systematic shell model study for $N = 82$ and $N = 126$ isotones and nuclear isomers
Bharti Bhoy · Praveen C. Srivastava
In the present work, we have done a systematic shell model study of $N = 82$ and $N = 126$ isotones. For the $N = 82$ isotones, we have performed calculations using SN100PN interaction, while for $N = 126$ isotones, we have used KHPE interaction. Similarities between these two isotonic chains have been reported, using the strong resemblance between the high- $j$ orbitals. Apart from the nuclear spectroscopic properties, we have also explained different isomeric states in these two regions. In the $N$ =82 region, we have mainly discussed the properties of the $6^{+}$ and $17/ 2^{+}$ isomers, while in the $N = 126$ region for $8^{+}$ , $1 1^{-}$ , $21/ 2^{-}$ and $29/ 2^{+}$ isomers. We have reported $B (E 2)$ , $B (E 3)$ , $g$ -factor, and quadrupole moments of the isomeric states for comparison in these two isotonic chains.
nucl-thnucl-exJ.Phys.G(2022)·14 citations
06
Distinguishing (Dirac or Majorana) neutrinos in purely leptonic decays of leptons
Yao Yu🇨🇳 · Bai-Cian Ke🇨🇳
We investigate purely leptonic decays of leptons $\l^{' -} \to l^{-} ν ˉ_{l} ν_{l^{'}}$ to distinguish Dirac or Majorana neutrinos. We derive the differences of the decay width (and associated quantities) between the two neutrino hypotheses by the effect of identical particles. Evidence from experimental data makes the hypothesis of Majorana neutrinos very unlikely and our results strongly favor the hypothesis of Dirac neutrinos (in the standard three-neutrino theory). Moreover, our exploration for decay widths can be extended to the polarization angles of leptons, which will inspire new information for experimental and theoretical studies.
↳ hep-phhep-exhep-thnucl-th0 citations
07
Attractive $N$ - $ϕ$ Interaction and Two-Pion Tail from Lattice QCD near Physical Point
Yan Lyu🇨🇳 · Takumi Doi🇯🇵 · Tetsuo Hatsuda🇯🇵 · Yoichi Ikeda🇯🇵 · Jie Meng🇨🇳 · Kenji Sasaki🇯🇵 · Takuya Sugiura🇯🇵
First results on the interaction between the $ϕ$ -meson and the nucleon ( $N$ ) are presented based on the ( $2 + 1$ )-flavor lattice QCD simulations with nearly physical quark masses. Using the HAL QCD method, the spacetime correlation of the $N$ - $ϕ$ system in the spin 3/2 channel is converted into the $N$ - $ϕ$ scattering phase shift through the interaction potential. The $N$ - $ϕ$ potential appears to be a combination of a short-range attractive core and a long-range attractive tail. The latter is found to be consistent with the two-pion exchange (TPE) obtained from the interaction between a color-dipole and the nucleon. The resultant scattering length and effective range for $m_{π} =$ 146.4 MeV are $a_{0}^{(3/2)} = - 1.43 (23)_{stat.} (_{- 06}^{+ 36})_{syst.} fm$ and $r_{eff}^{(3/2)} = 2.36 (10)_{stat.} (_{- 48}^{+ 02})_{syst.} fm$ , respectively. The magnitude of the scattering length is shown to have nontrivial dependence of $m_{π}$ and is sensitive to the existence of the long-range tail from TPE.
↳ hep-lathep-exhep-phnucl-ex+1PRD(2022)·73 citations
08
Astrophysical implications on hyperon couplings and hyperon star properties with relativistic equations of states
Xiangdong Sun🇨🇳 · Zhiqiang Miao🇨🇳 · Baoyuan Sun🇨🇳 · Ang Li🇨🇳
Hyperons are essential constituents in the neutron star interior. The poorly-known hyperonic interaction is a source of uncertainty for studying laboratory hypernuclei and neutron star observations. In this work, we perform Bayesian inference of phenomenological hyperon-nucleon interactions using the tidal-deformability measurement of the GW170817 binary neutron star merger as detected by LIGO/Virgo and the mass-radius measurements of PSR J0030+0541 and PSR J0740+6620 as detected by NICER. The analysis is based on a set of stiff relativistic neutron-star-matter equation of states with hyperons from the relativistic mean-field theory, naturally fulfilling the causality requirement and empirical nuclear matter properties. We specifically utilize the strong correlation recently deduced between the scalar and vector meson hyperon couplings, imposed by the measured $Λ$ separation energy in single- $Λ$ hypernuclei, and perform four different tests with or without the strong correlation. We find that the laboratory hypernuclear constraint ensures a large enough $Λ$ -scalar-meson coupling to match the large vector coupling in hyperon star matter. When adopting the current most probable intervals of hyperon couplings from the joint analysis of laboratory and astrophysical data, we find the maximum mass of hyperon stars is at most $2.17 6_{- 0.202}^{+ 0.085} M_{⊙}$ ( $68%$ credible interval) from the chosen set of stiff equation of states. The reduction of the stellar radius due to hyperons is quantified based on our analysis and various hyperon star properties are provided.
↳ astro-ph.HEastro-ph.SRnucl-thApJ(2023)·52 citations
09
Strangeness enhancement across collision systems without a plasma
Christian Bierlich🇸🇪 · Smita Chakraborty🇸🇪 · Gösta Gustafson🇸🇪 · Leif Lönnblad🇸🇪
We present novel rope hadronization results for strange hadron enhancement in pp, pPb, and PbPb collisions using PYTHIA/Angantyr at LHC energies. With the rope model for string fragmentation, we find that the strangeness and baryon enhancement has a coherent increase across all collision systems as a function of average charged central multiplicity, in qualitative agreement with LHC data. In AA collisions, we find that the baryonic yields overshoot data at high multiplicities, and we discuss how a combination of rope hadronization with other string interactions may tame this rise.
↳ hep-phnucl-thPLB(2022)·25 citations
10
Resonance form factors from finite-volume correlation functions with the external field method
Jonathan Lozano🇩🇪 · Ulf-G. Meißner🇩🇪 · Fernando Romero-López🇺🇸 · Akaki Rusetsky🇩🇪 · Gerrit Schierholz🇩🇪
A novel method for the extraction of form factors of unstable particles on the lattice is proposed. The approach is based on the study of two-particle scattering in a static, spatially periodic external field by using a generalization of the Lüscher method in the presence of such a field. It is shown that the resonance form factor is given by the derivative of the resonance pole position in the complex plane with respect to the coupling constant to the external field. Unlike the standard approach, this proposal does not suffer from problems caused by the presence of the triangle diagram.
↳ hep-lathep-phnucl-thJHEP(2022)·11 citations
11
Pion damping width and pion spectral function in hot pion gas
D. Goderidze🇷🇺 · A. Friesen🇷🇺 · Yu. Kalinovsky🇷🇺
The temperature behaviour of the pion width in the hadronic phase is investigated in the framework of the NJL model. The contribution to the width from the pion-pion collision is considered with a scalar sigma-meson as an intermediate state. It is shown that the pion width significantly broadens at $T > 0.1$ GeV. Using the two-step iteration method, suggested by Kadanoff and Baym, the pion spectral function in a hot pion gas is calculated at different temperatures.
↳ hep-phnucl-thInt.J.Mod.Phys.A(2022)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE