Nuclear Theory·nucl-th

Monday·January 11, 2021

10 papers—7 primary·3 cross-listed

01
Neutrinoless $β β$ -Decay in DCEQTDA
C. De Conti (1)🇧🇷 · V. dos S. Ferreira (2)🇧🇷 · A.R. Samana (3)🇧🇷 · C.A. Barbero (4)🇮🇹 · F. Krmpotić (4) ((1) UNESP, Rosana, SP, Brazil, (2) UERJ, Rio de Janeiro, Brazil, (3) UESC, Ilhéus, Brazil, (4) IFLP-CONICET, La Plata, Argentina)🇮🇹
We have recently developed a nuclear model, which is a natural extension of the $p n$ -QRPA model, specially designed to describe double charge exchange (DCE) processes generated by two-body DCE transition operators. It is based on the Quasiparticle Tamm-Dancoff Approximation (QTDA) for $p n$ and $2 p 2 n$ excitations in intermediate and final nuclei, respectively, and will be called DCEQTDA. As such, this model, having the same number of free parameters as the $p n$ -QRPA, also brings into play the excitations of four quasiparticles to build up the final nuclear states, which are then used to evaluate the nuclear matrix elements (NMEs) for all $0^{+}$ and $2^{+}$ final states, including resonances, and not just for the ground state as in $p n$ -QRPA. In addition, it allows us to evaluate: (a) the values of $Q_{β β}$ , (b) the excitation energies in final nuclei, and (c) the DCE sum rules, which are fulfilled in the DCEQTDA. So far, this model has been used mainly to calculate double beta decays with the emission of two neutrinos ( $2 ν β β$ -decay). Here, we extend it to the study of these processes when no neutrinos are emitted ( $0 ν β β$ -decay), evaluating them in a series of nuclei, but paying special attention to (i) $^{76}$ Se, which have been measured recently in the GERDA and MAJORANA experiments, and (ii) $^{124}$ Te, for which the first direct observation of the double electron capture $2 ν$ has been performed with the XENON1T dark matter detector. We obtain good agreement with the data for both the ground state and the excited states. The validity of the DCEQTDA model is checked by comparing the calculation with the experimental data for the $2 ν β β$ NMEs, and for the $Q_{β β}$ , in a series of nuclei.
nucl-thEPJA(2025)·0 citations
02
Cumulants and factorial cumulants in the 3-dimensional Ising universality class
Xue Pan🇨🇳 · Mingmei Xu🇨🇳 · Yuanfang Wu🇨🇳
The high-order cumulants and factorial cumulants of conserved charges are suggested to study the critical dynamics in heavy ion collisions. In this paper, using parametric representation of the 3-dimensional Ising model, the sign distribution on the phase diagram and temperature dependence of the cumulants and factorial cumulants is studied and compared. In the vicinity of the critical point, the cumulants and factorial cumulants can not be distinguished. Far away from the critical point, sign changes occur in the factorial cumulants comparing with the same order cumulants. The cause of these sign changes is analysed. They may be used to measure the distance to the critical point.
nucl-thhep-phIJMPE(2021)·3 citations
03
Anisotropic fluid dynamical simulations of heavy-ion collisions
M. McNelis🇺🇸 · D. Bazow🇺🇸 · U. Heinz🇺🇸
We present VAH, a (3+1)-dimensional simulation that evolves the far-from-equilibrium quark-gluon plasma produced in ultrarelativistic heavy-ion collisions with anisotropic fluid dynamics. We solve the hydrodynamic equations on an Eulerian grid using the Kurganov-Tadmor algorithm in combination with a new adaptive Runge-Kutta method. Our numerical scheme allows us to start the simulation soon after the nuclear collision, largely avoiding the need to integrate it with a separate pre-equilibrium dynamics module. We test the code's performance by simulating on the Eulerian grid conformal and non-conformal Bjorken flow as well as conformal Gubser flow, whose (0+1)-dimensional solutions are precisely known. Finally, we compare non-conformal anisotropic hydrodynamics to second-order viscous hydrodynamics in central Pb+Pb collisions and find that the former's longitudinal flow profile responds more consistently to the fluid's gradients along the spacetime rapidity direction.
nucl-thhep-phComput.Phys.Commun.(2021)·32 citations
04
A unified description of the structure and electromagnetic breakup of $^{11}$ Be
M. Dan (IITR) · R. Chatterjee (IITR) · M. Kimura (Uni Hokkaido)🇯🇵
We study both the static properties of $^{11}$ Be and its reaction dynamics during electromagnetic breakup under a unified framework. A many-body approach - the antisymmetrized molecular dynamics (AMD) is used to describe the structure of the neutron-halo nucleus, $^{11}$ Be. The same AMD wave function is then adapted as an input to the fully quantum theory of Coulomb breakup under the aegis of the finite range distorted wave Born approximation theory. The calculated observables are also compared with those obtained with a phenomenological Woods-Saxon potential model wave function. The experimental core-valence neutron relative energy spectrum and dipole response along with other observables are well described by our calculations.
nucl-thnucl-exEPJA(2021)·10 citations
05
Fermi polaron in low-density spin-polarized neutron matter
Isaac Vidana🇮🇹
We study the properties of a spin-down neutron impurity immersed in a low-density free Fermi gas of spin-up neutrons. In particular, we analyze its energy ( $E_{↓}$ ), effective mass ( $m_{↓}^{*}$ ) and quasiparticle residue ( $Z_{↓}$ ). Results are compared with those of state-of-the-art quantum Monte Carlo calculations of the attractive Fermi polaron realized in ultracold atomic gases experiments, and with those of previous studies of the neutron polaron. Calculations are performed within the Brueckner--Hartree--Fock approach using the chiral two-body nucleon-nucleon interaction of Entem and Machleidt at N $^{3}$ LO with a 500 MeV cut-off and the Argonne V18 phenomenological potential. Only contributions from the $^{1} S_{0}$ partial wave, which is the dominant one in the low-density region considered, are included. Contributions from three-nucleon forces are expected to be irrelevant at these densities and, therefore, are neglected in the calculation. Our results show that for Fermi momenta between $\sim 0.25$ and $\sim 0.45$ fm $^{- 1}$ the energy, effective mass and quasiparticle residue of the impurity vary only slightly, respectively, in the ranges $- 0.604 E_{F} < E_{↓} < - 0.635 E_{F}$ , $1.300 m < m_{↓}^{*} < 1.085 m$ and $0.741 < Z_{↓} < 0.836$ in the case of the chiral interaction, and $- 0.621 E_{F} < E_{↓} < - 0.643 E_{F}$ , $1.310 m < m_{↓}^{*} < 1.089 m$ and $0.739 < Z_{↓} < 0.832$ when using the Argonne V18 potential. These results are compatible with those derived from ultracold atoms and show that a spin-down neutron impurity in a free Fermi gas of spin-up neutrons with a Fermi momentum in the range $0.25 ≲ k_{F} ≲ 0.45$ fm $^{- 1}$ exhibits properties very similar to those of an attractive Fermi polaron in the unitary limit.
nucl-thcond-mat.quant-gasPRC(2021)·12 citations
06
Microscopic description of octupole collective excitations near $N = 56$ and $N = 88$
K. Nomura🇭🇷 · L. Lotina🇭🇷 · T. Nikšić🇭🇷 · D. Vretenar🇭🇷
Octupole deformations and related collective excitations are analyzed using the framework of nuclear density functional theory. Axially-symmetric quadrupole-octupole constrained self-consistent mean-field (SCMF) calculations with a choice of universal energy density functional and a pairing interaction are performed for Xe, Ba, and Ce isotopes from proton-rich to neutron-rich regions, and neutron-rich Se, Kr, and Sr isotopes, in which enhanced octupole correlations are expected to occur. Low-energy positive- and negative-parity spectra and transition strengths are computed by solving the quadrupole-octupole collective Hamiltonian, with the inertia parameters and collective potential determined by the constrained SCMF calculations. Octupole-deformed equilibrium states are found in the potential energy surfaces of the Ba and Ce isotopes with $N \approx 56$ and 88. The evolution of spectroscopic properties indicates enhanced octupole correlations in the regions corresponding to $N \approx Z \approx 56$ , $Z \approx 88$ and $Z \approx 56$ , and $N \approx 56$ and $Z \approx 34$ . The average $β_{30}$ deformation parameter and its fluctuation exhibit signatures of octupole shape phase transition around $N = 56$ and 88.
nucl-thnucl-exPRC(2021)·25 citations
07
Second-forbidden nonunique $β^{-}$ decays of $^{59, 60}$ Fe: Possible candidates for $g_{A}$ sensitive electron spectral-shape measurements
Anil Kumar · Praveen C. Srivastava · Jouni Suhonen
In this work, we present a theoretical study of the electron spectral shapes for the second-forbidden nonunique $β^{-}$ -decay transitions $^{59} Fe (3/ 2^{-}) \to^{59} Co (7/ 2^{-})$ and $^{60} Fe (0^{+}) \to^{60} Co (2^{+})$ in the framework of the nuclear shell model. We have computed the involved wave functions by carrying out a complete $0ℏ ω$ calculation in the full $f p$ model space using the KB3G and GXPF1A effective interactions. When compared with the available data, these interactions predict the low-energy spectra and electromagnetic properties of the involved nuclei quite successfully. This success paves the way for the computations of the $β$ -decay properties, and comparison with the available data. We have computed the electron spectral shapes of the mentioned decay transitions as functions of the value of the weak axial coupling $g_{A}$ . By comparing these computed shapes with the measured spectral shapes allows then to extract the effective value of $g_{A}$ for these decay transitions. This procedure, coined the spectrum-shape method (SSM) in several earlier studies, complements the method of determining the value of $g_{A}$ by reproducing the (partial) half-lives of decay transitions. Here we have enhanced the original SSM by constraining the value of the relativistic vector matrix element, $^{V} M_{K K - 11}^{(0)}$ , using the conserved vector-current hypothesis (CVC) as a starting point. We hope that this finding would be a strong incentive to measure the spectral shapes in the future.
nucl-thEPJA(2021)·24 citations
08
Mass ejection in failed supernovae: equation of state and neutrino loss dependence
Mario Ivanov🇨🇦 · Rodrigo Fernández🇨🇦
A failed core-collapse supernova from a non-rotating progenitor can eject mass due to a weakening of gravity associated to neutrino emission by the protoneutron star. This mechanism yields observable transients and sets an upper limit to the mass of the black hole (BH) remnant. Previous global simulations of this mechanism have included neutrino losses parametrically, however, with direct implications for the ejecta mass and energy. Here we evolve the inner supernova core with a spherically-symmetric, general-relativistic neutrino radiation-hydrodynamic code until BH formation. We then use the result in a Newtonian code that follows the response of the outer layers of the star to the change in gravity and resolves the surface pressure scale height. We find that the dense-matter equation of state (EOS) can introduce a factor $\sim 2$ variation in gravitational mass lost to neutrinos, with a stiff EOS matching previous parametric results, and a soft EOS yielding lower ejecta masses and energies by a factor of several. This difference is caused primarily by the longer time to BH formation in stiffer EOSs. With a soft EOS, our red and yellow supergiant progenitors fail to unbind mass if hydrogen recombination energy is not included. Using a linear ramp in time for mass-energy lost to neutrinos (with suitable parameters) yields a stellar response within $\sim 10%$ of that obtained using the detailed history of neutrino losses. Our results imply quantitative but not qualitative modifications to previous predictions for shock breakout, plateau emission, and final BH masses from these events.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thApJ(2021)·41 citations
09
Broad excitations in a 2+1D overoccupied gluon plasma
K. Boguslavski🇦🇹 · A. Kurkela🇳🇴 · T. Lappi🇫🇮 · J. Peuron🇸🇪
Motivated by the initial stages of high-energy heavy-ion collisions, we study excitations of far-from-equilibrium 2+1 dimensional gauge theories using classical-statistical lattice simulations. We evolve field perturbations over a strongly overoccupied background undergoing self-similar evolution. While in 3+1D the excitations are described by hard-thermal loop theory, their structure in 2+1D is nontrivial and nonperturbative. These nonperturbative interactions lead to broad excitation peaks in spectral and statistical correlation functions. Their width is comparable to the frequency of soft excitations, demonstrating the absence of soft quasiparticles in these theories. Our results also suggest that excitations at higher momenta are sufficiently long-lived, such that an effective kinetic theory description for 2+1 dimensional Glasma-like systems may exist, but its collision kernel must be nonperturbatively determined.
↳ hep-phhep-latnucl-thJHEP(2021)·21 citations
10
The relevance of nuclear reactions for Standard Solar Models construction
Francesco L. Villante🇮🇹 · Aldo Serenelli🇪🇸
The fundamental processes by which nuclear energy is generated in the Sun have been known for many years. However, continuous progress in areas such as neutrino experiments, stellar spectroscopy and helioseismic data and techniques requires ever more accurate and precise determination of nuclear reaction cross sections, a fundamental physical input for solar models. In this work, we review the current status of (standard) solar models and present a detailed discussion on the relevance of nuclear reactions for detailed predictions of solar properties. In addition, we also provide an analytical model that helps understanding the relation between nuclear cross sections, neutrino fluxes and the possibility they offer for determining physical characteristics of the solar interior. The latter is of particular relevance in the context of the conundrum posed by the solar composition, the solar abundance problem, and in the light of the first ever direct detection of solar CN neutrinos recently obtained by the Borexino collaboration. Finally, we present a short list of wishes about the precision with which nuclear reaction rates should be determined to allow for further progress in our understanding of the Sun.
↳ astro-ph.SRnucl-exnucl-thFront.Astron.Space Sci.(2021)·21 citations

Affiliations

first authorsco-authorsvia INSPIRE