Nuclear Theory·nucl-th

Wednesday·February 16, 2022

8 papers—4 primary·4 cross-listed

01
Application of complex transition density to nuclear reaction and effect of phase factor
T. Furumoto
Complex transition density can be constructed by a nuclear structure model with a complex basis and/or complex coefficient. In general, the complex transition density is converted to the real one with phase factor. In this study, we apply the complex transition density directly to the microscopic reaction model. We compare with scattering cross sections calculated with the real and complex transition densities in the frameworks of the optical model, the distorted wave Born approximation, and the coupled-channel (CC) calculation, respectively. In addition, we investigate the dependence of the phase factor for the transition density in the elastic and inelastic cross sections. The effect of the phase factor on the elastic and inelastic cross sections can be seen in the CC calculation. Finally, we found an important role of the phase factor in the nuclear elastic and inelastic scatterings.
nucl-thnucl-ex0 citations
02
In-medium $Λ$ isospin impurity from charge symmetry breaking in the $_{Λ}^{4} H -_{Λ}^{4} He$ mirror hypernuclei
M. Schäfer🇮🇱 · N. Barnea🇮🇱 · A. Gal🇮🇱
The $Λ$ separation energies in the mirror hypernuclei $_{Λ}^{4} H -_{Λ}^{4} He$ exhibit large charge symmetry breaking (CSB). Analyzing this CSB within pionless effective field theory while using partially conserved baryon-baryon SU(3) flavor symmetry, we deduce a $Λ - Σ^{0}$ induced in-medium admixture amplitude $A_{I = 1} \approx 1.5%$ in the dominantly isospin $I = 0$ $Λ$ hyperon. Our results confirm the free-space value $A_{I = 1}^{(0)}$ inferred directly within the SU(3) baryon octet by Dalitz and von-Hippel in 1964 and reaffirmed in a recent QCD+QED lattice calculation. Furthermore, exploring the consequences of SU(3) flavor symmetry on the $Λ$ -nucleon interaction, we find that CSB is expected to impact the $S = 1$ and $S = 0$ spin channels in opposite directions, with the latter dominating by an order of magnitude. These observations explain a recent deduction of $Λ$ -nucleon CSB strengths.
nucl-thhep-phnucl-exPRC(2022)·13 citations
03
Many-body approximations to the superfluid gap and critical temperature in pure neutron matter
M. Drissi · A. Rios
We compute singlet pairing gaps and critical temperatures in pure neutron matter with different many-body approximations. Medium effects tend to reduce gaps and critical temperatures compared to the standard BCS ansatz. In the mean-field approximation, the ratio of these two quantities remains constant across a wide range of densities. This constant ratio is close to the universal prediction of BCS theory, whether three-neutron interactions are included or not. Using a more sophisticated many-body approach that incorporates the effect of short-range correlations in pairing properties, we find that the gap to critical temperature ratio in the low-density regime is substantially larger than the BCS prediction, independently of the interaction. In this region, our results are relatively close to experiments and theoretical calculations from the unitary Fermi gas. We also find evidence for a different density dependence of zero-temperature gaps and critical temperatures in neutron matter.
nucl-thEPJA(2022)·12 citations
04
Theoretical description of pygmy (dipole) resonances
Edoardo G. Lanza · Andrea Vitturi
Stable and unstable nuclei with neutron excess ( $N > Z$ ) show - in the isovector dipole transition strength distribution - a small hump around the neutron emission threshold energy known as Pygmy Dipole Resonance (PDR). One of its main features is the isospin mixing allowing the experimental studies with both isovector and isoscalar probes. Different theoretical approaches and methodologies are used to deduce the characteristics of the PDR. In this Chapter, the various mean-field theories and their extensions, devoted to understand and reproduce the strength distribution of these low-lying dipole states, are summarised. Special attention is dedicated to the calculations of the inelastic cross section, aspect that is particularly important in the investigation with isoscalar probes, such as $α$ -particles or $^{17}$ O. The relevance of the radial form factors is presented in relation to the inelastic cross-section calculations.
nucl-thnucl-ex1 citation
05
Landau quantization and spin polarization of cold magnetized quark matter
Zhen-Yan Lu🇨🇳 · Jian-Feng Xu🇨🇳 · Xin-Jian Wen🇨🇳 · Guang-Xiong Peng🇨🇳 · Marco Ruggieri🇨🇳
The magnetic field and density behaviors of various thermodynamic quantities of strange quark matter under compact star conditions are investigated in the framework of the thermodynamically self-consistent quasiparticle model. For individual species, a larger number density $n_{i}$ leads to a larger magnetic field strength threshold that align all particles parallel or antiparallel to the magnetic field. Accordingly, in contrast to the finite baryon density effect which reduces the spin polarization of magnetized strange quark matter, the magnetic field effect leads to an enhancement of it. We also compute the sound velocity as a function of the baryon density and find the sound velocity shows an obvious oscillation with increasing density. Except for the oscillation, similar to the zero-magnetic field case that the sound velocity grows with increasing density and approaches the conformal limit $V_{s}^{2} = 1/3$ at high densities from below.
↳ hep-phnucl-thCPC(2022)·7 citations
06
Linear mode analysis from spin transport equation
Jin Hu🇨🇳
We provide a linear analysis on normal modes of the spin Boltzmann equation proposed in \cite{Weickgenannt:2021cuo}, where the non-diagonal or polarized part of the transition rate is neglected to ensure the Hermitian property of linearized collision operator. As an instrumental element of spin kinetic theory, the conservation of total angular momentum is explicitly considered, thus our analysis is relevant to the recent investigation on the issue of local spin polarization. By treating the linearized collision operator as an evolution operator, solving the normal modes turns out a degenerate perturbation problem in quantum mechanics. The dispersion relations of spinless modes are in accordance with well-known calculations, while the frequencies of spin modes are also determined up to second-order in wave vector and the second order expressions are only formal solutions to be further determined. Moreover, the relaxation of spin density is related to our linear mode analysis, which shall play a big role in investigating the issues of the local spin polarization in the relativistic heavy-ion collisions.
↳ hep-phnucl-thPRD(2022)·29 citations
07
Fundamental limitations of the eigenvalue continuation approach
Tomasz Sowiński🇵🇱 · Miguel A. Garcia-March🇪🇸
In this work, we show that the eigenvalue continuation approach introduced recently in [Phys. Rev. Lett. {\bf 121}, 032501 (2018)], despite its many advantages, has some fundamental limitations which cannot be overcome when strongly correlated many-body systems are considered. Taking as a working example a very simple system of several fermionic particles confined in a harmonic trap we show that the eigenvector continuation is not able to go beyond the accuracy of the sampling states. We support this observation within a very simple three-level model capturing directly this obstacle. Since mentioned inaccuracy cannot be determined self-consistently within the eigenvalue continuation approach, support from other complementary methods is needed.
↳ cond-mat.quant-gasnucl-thquant-phPRC(2022)·4 citations
08
Tau longitudinal and transverse polarizations from visible kinematics in (anti-)neutrino nucleus scattering
E. Hernández🇪🇸 · J. Nieves🇪🇸 · F. Sánchez🇨🇭 · J. E. Sobczyk🇩🇪
Since the $ν_{τ} (ν ˉ_{τ}) A_{Z} \to τ^{\mp} X$ reaction is notoriously difficult to be directly measured, the information on the dynamics of this nuclear process should be extracted from the analysis of the energy and angular distributions of the tau decay visible products. These distributions depend on the components of the tau-polarization vector. We give, for the first time, the general expression for the outgoing hadron (pion or rho meson) energy and angular differential cross section for the sequential $ν_{τ} A_{Z} \to τ^{-} (π^{-} ν_{τ}, ρ^{-} ν_{τ}) X$ and $ν ˉ_{τ} A_{Z} \to τ^{+} (π^{+} ν ˉ_{τ}, ρ^{+} ν ˉ_{τ}) X$ reactions. Though all possible nuclear reaction mechanisms contribute to the distribution, it may be possible to isolate/enhance one of them by implementing appropriate selection criteria. For the case of the quasi-elastic reaction off oxygen and neutrino energies below 6 GeV, we show that the pion distributions are sensitive to the details of the tau-polarization components. We find significant differences between the full calculation, where the longitudinal and transverse components of the tau polarization vector vary with the energy and the scattering angle of the produced tau, and the simplified scheme in which the polarizations are set to one and zero (respective asymptotic values in the high energy regime). In addition to its potential impact on neutrino oscillation analyses, this result can be used to further test different nuclear models, since these observables provide complementary information to that obtained by means of the inclusive nuclear weak charged-current differential cross section. We also study the effects on the cross section of the $W_{4}$ , $W_{5}$ nuclear structure functions, which contributions are proportional to the charged lepton mass, and therefore difficult to constrain in muon and electron neutrino experiments.
↳ hep-phnucl-thPLB(2022)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE