Nuclear Theory·nucl-th

Thursday·April 27, 2023

11 papers—4 primary·7 cross-listed

01
Neutron-proton effective mass splitting in neutron-rich matter
Sibo Wang · Hui Tong · Qiang Zhao · Chencan Wang · Peter Ring · Jie Meng
Nucleon effective masses in neutron-rich matter are studied with the relativistic Brueckner-Hartree-Fock (RBHF) theory in the full Dirac space. The neutron and proton effective masses for symmetric nuclear matter are 0.80 times rest mass, which agrees well with the empirical values. In neutron-rich matter, the effective mass of the neutron is found larger than that of the proton, and the neutron-proton effective mass splittings at the empirical saturation density are predicted as $0.187 α$ with $α$ being the isospin asymmetry parameter. The result is compared to other ab initio calculations and is consistent with the constraints from the nuclear reaction and structure measurements, such as the nucleon-nucleus scattering, the giant resonances of $^{208}$ Pb, and the Hugenholtz-Van Hove theorem with systematics of nuclear symmetry energy and its slope. The predictions of the neutron-proton effective mass splitting from the RBHF theory in the full Dirac space might be helpful to constrain the isovector parameters in phenomenological density functionals.
nucl-thnucl-exPRC(2023)·21 citations
02
Generalized time-dependent generator coordinate method for small and large amplitude collective motion
B. Li · D. Vretenar · T. Nikšić · P. W. Zhao · J. Meng
An implementation of the generalized time-dependent generator coordinated method (TD-GCM) is developed, that can be applied to the dynamics of small- and large-amplitude collective motion of atomic nuclei. Both the generator states and weight functions of the GCM correlated wave function depend on time. The initial generator states are obtained as solutions of deformation-constrained self-consistent mean-field equations, and are evolved in time by the standard mean-field equations of nuclear density functional theory (TD-DFT). The TD-DFT trajectories are used as a generally non-orthogonal and overcomplete basis in which the TD-GCM wave function is expanded. The weights, expressed in terms of a collective wave function, obey a TD-GCM (integral) equation. In this explorative paper, the generalized TD-GCM is applied to the excitation energies and spreading width of giant resonances, and to the dynamics of induced fission. The necessity of including pairing correlations in the basis of TD-DFT trajectories is demonstrated in the latter example.
nucl-thPRC(2023)·21 citations
03
Local alpha-removal strength in the mean-field approximation
Takashi Nakatsukasa · Nobuo Hinohara
The local alpha strength is proposed to quantify the possibility to form an alpha particle at a specific location inside the nucleus. It also provides the strength of ground and excited states in the residual nuclei after the removal of the alpha particle. We use the Hartree-Fock-plus-BCS (HF+BCS) method in the calculation of the local alpha strengths for Sn isotopes. The local alpha strengths are easily calculable and the results are consistent with recent experimental data for Sn isotopes.
nucl-thPRC(2023)·8 citations
04
On Sequential Single-Pion Production in Double-Pionic Fusion
M. Bashkanov🇬🇧 · H. Clement🇩🇪
Recently a two-step process has been proposed for the double-pionic fusion to deuterium $p n (I = 0) \to d π^{+} π^{-}$ . Its calculation is solely based on total cross section data for the two sequential single-pion production steps $p n (I = 0) \to pp π^{-}$ followed by $pp \to d π^{+}$ . Though this sequential process was aimed to explain the dibaryon resonance $d^{*} (2380)$ peak in double-pionic fusion, we demonstrate that this is not the case. It rather fits to a possible broad bump at 2.31 GeV in the energy dependence of the $p n \to d π^{0} π^{0}$ reaction, which was recently interpreted as a consequence of dibaryonic excitations in isoscalar single-pion production.
nucl-thhep-exhep-phnucl-exNPA(2023)·0 citations
05
Do we have enough evidence to invalidate the mean-field approximation adopted to model collective neutrino oscillations?
Shashank Shalgar🇩🇰 · Irene Tamborra🇩🇰
Recent body of work points out that the mean-field approximation, widely employed to mimic the neutrino field within a neutrino-dense source, might give different results in terms of flavor evolution with respect to the correspondent many-body treatment. In this paper, we investigate whether such conclusions derived within a constrained framework should hold in an astrophysical context. We show that the plane waves, commonly adopted in the many-body literature to model the neutrino field, provide results that are crucially different with respect to the ones obtained using wavepackets of finite size streaming with a non-zero velocity. The many-body approach intrinsically includes coherent and incoherent scatterings. The mean-field approximation, on the other hand, only takes into account the coherent scattering in the absence of the collision term. Even if incoherent scatterings are included in the mean-field approach, the nature of the collision term is different from that in the many-body approach. Because of this, if only a finite number of neutrinos is considered, as often assumed, the two approaches naturally lead to different flavor outcomes. These differences are further exacerbated by vacuum mixing. We conclude that existing many-body literature, based on closed neutrino systems with a finite number of particles, is neither able to rule out nor assess the validity of the mean-field approach adopted to simulate the evolution of the neutrino field in dense astrophysical sources, which are open systems.
↳ astro-ph.HEhep-phnucl-thPRD(2023)·35 citations
06
Novel phase transition at the Unruh temperature
Georgy Yu. Prokhorov🇷🇺 · Oleg V. Teryaev🇷🇺 · Valentin I. Zakharov🇷🇺
We consider gas of massless fermions at certain temperature T and acceleration a. We find a second order phase transition at temperature T approaching the Unruh temperature TU. The implications for hadronization of the quark-gluon plasma produced in heavy-ion collisions (HIC) and for black-hole physics are discussed. In particular, this novel phase transition may be associated with thermalization in HIC, indicating its analogy with falling into a black hole.
↳ hep-thgr-qcnucl-th14 citations
07
The chiral limit of a fermion-scalar $(1/2)^{+}$ system in covariant gauges
A. Noronha🇧🇷 · W. de Paula🇧🇷 · J.H. de Alvarenga Nogueira🇧🇷 · T. Frederico🇧🇷 · E. Pace🇮🇹 · G. Salmè🇮🇹
The homogeneous Bethe-Salpeter equation (BSE) of a (1/2) $^{+}$ bound system, that has both fermionic and bosonic degrees of freedom, that we call a {\em mock nucleon}, is studied in Minkowski space, in order to analyse the chiral limit in covariant gauges. After adopting an interaction kernel built with a one-particle exchange, the $χ$ -BSE is numerically solved by means of the Nakanishi integral representation and light-front projection. Noteworthy, the chiral limit induces a scale-invariance of the model and consequently generates a wealth of striking features: i) it reduces the number of non trivial Nakanishi weight functions to only one; ii) the form of the surviving weight function has a factorized dependence on the two relevant variables, compact and non-compact one; iii) the coupling constant becomes an explicit function of the real exponent governing the power-law fall-off of the non trivial Nakanishi weight function. The thorough investigation at large transverse-momentum of light-front Bethe-Salpeter amplitudes, obtained with massive constituents, provides a confirmation of the expected universal power-law fall-off, with exponents predicted by our non-perturbative framework. Finally, one can shed light on the exponents that govern the approach to the upper extremum of the longitudinal-momentum fraction distribution function of the {\em mock nucleon}, when the coupling constant varies.
↳ hep-phhep-thnucl-thPRD(2023)·2 citations
08
Two-proton emission and related phenomena
Marek Pfützner · Ivan Mukha · Simin Wang
One of characteristic phenomena for nuclei beyond the proton dripline is the simultaneous emission of two protons (2\emph{p}). The current status of our knowledge of this most recently observed and the least known decay mode is presented. First, different approaches to theoretical description of this process, ranging from effective approximations to advanced three-body models are overviewed. Then, after a brief survey of main experimental methods to produce 2\emph{p}-emitting nuclei and techniques to study their decays, experimental findings in this research field are presented and discussed. This review covers decays of short-lived resonances and excited states of unbound nuclei as well as longer-lived, ground-state radioactive decays. In addition, more exotic decays like three- and four-proton emission are addressed. Finally, related few-body topics, like two-neutron and four-neutron radioactivity, and the problem of the tetraneutron are shortly discussed.
↳ nucl-exnucl-thPPNP(2023)·51 citations
09
Heavy- and light-flavor symmetry partners of the $T_{cc}^{+} (3875)$ , the $X (3872)$ and the $X (3960)$ from light-meson exchange saturation
Fang-Zheng Peng🇨🇳 · Mao-Jun Yan🇨🇳 · Manuel Pavon Valderrama🇨🇳
The spectrum of the charmed meson-(anti)meson system is a fundamental tool for disentangling the nature of a few exotic hadrons, including the recently discovered $T_{cc}^{+} (3875)$ tetraquark, the $X (3960)$ , or the $X (3872)$ , the nature of which is still not clear after almost two decades of its discovery. Here we consider that the charmed meson-(anti)meson short-range interaction is described by the exchange of light-mesons ( $σ$ , $ρ$ , $ω$ ). The effects of light-meson exchanges are recast into a simple contact-range theory by means of a saturation procedure, resulting in a compact description of the two-hadron interaction. From this, if the $T_{cc}^{+}$ were to be an isoscalar $D^{*} D$ molecule, then there should exist an isoscalar $J = 1$ $D^{*} D^{*}$ partner, as constrained by heavy-quark spin symmetry. Yet, within our model, the most attractive two charmed meson configurations are the isovector $J = 0$ $D^{*} D^{*}$ molecule and its sextet $D_{s}^{*} D^{*}$ and $D_{s}^{*} D_{s}^{*}$ flavor partners. Finally, we find a tension between the molecular descriptions of the $T_{cc}^{+}$ and that of the $X (3872)$ and $X (3960)$ , where most parameter choices suggest that if the $T_{cc}^{+}$ is purely molecular then the $X (3872)$ overbinds (or conversely, if the $X (3872)$ is a molecule the $T_{cc}^{+}$ does not bind). This might be consequential for determining the nature of these states.
↳ hep-phhep-exnucl-thPRD(2023)·31 citations
10
Determination of the moments of the proton charge density
M. Atoui🇫🇷 · M.B. Barbaro🇮🇹 · M. Hoballah🇫🇷 · C. Keyrouz🇫🇷 · M. Lassaut🇫🇷 · D. Marchand🇫🇷 · G. Quéméner🇫🇷 · E. Voutier🇫🇷
A global analysis of proton electric form factor experimental data from Rosenbluth separation and low squared four-momentum transfer experiments is discussed for the evaluation of the spatial moments of the proton charge density based on the recently published integral method. Specific attention is paid to the evaluation of the systematic errors of the method, particularly the sensitivity to the choice of the mathematical expression of the form factor fitting function. Within this comprehensive analysis of proton electric form factor data, the moments of the proton charge density are determined for integer order moments, particularly: $⟨ r^{2} ⟩$ =0.694(09) $_{S t a .}$ (16) $_{S y s .}$ ~fm $^{2}$ , $⟨ r^{3} ⟩$ =0.870(46) $_{S t a .}$ (80) $_{S y s .}$ ~fm $^{3}$ , and $⟨ r^{4} ⟩$ =1.47(25) $_{S t a .}$ (45) $_{S y s .}$ ~fm $^{4}$ .
↳ nucl-exnucl-thPRC(2024)·5 citations
11
Determination of meson fragmentation functions in the Field-Feynman model
Qiaomu Peng🇨🇳 · Bo-Qiang Ma🇨🇳
We study the fragmentation functions of both pions and kaons in the Field-Feynman recursive model with the extended SU(2) flavor symmetry relations of fragmentation functions and fitting parameters. Parametrizations are determined from a leading-order (LO) analysis of HERMES experimental multiplicity data of meson production in semi-inclusive deep inelastic scattering, and uncertainties are estimated with the Hessian method. We compare our results with the experimental data and the analysis results of other parametrizations. The SU(2) flavor symmetry breaking effect of meson fragmentation functions of $u d$ quarks is also discussed, and we show that the fragmentation functions of kaons have a bigger SU(2) flavor symmetry breaking effect of $u d$ quarks than these of pions.
↳ hep-phnucl-thPRC(2023)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE