Nuclear Theory·nucl-th

Friday·April 7, 2017

6 papers—4 primary·2 cross-listed

01
Quantum phase transitions and collective enhancement of level density in odd-A and odd-odd nuclei
S. Karampagia · A. Renzaglia · V. Zelevinsky
The nuclear shell model assumes an effective mean-field plus interaction Hamiltonian in a specific configuration space. We want to understand how various interaction matrix elements affect the observables, the collectivity in nuclei and the nuclear level density for odd-A and odd-odd nuclei. Using the sd and pf shells, we vary specific groups of matrix elements and study the evolution of energy levels, transition rates and the level density. In all cases studied, a transition between a "normal" and a collective phase is induced, accompanied by an enhancement of the level density in the collective phase. In distinction to neighboring even-even nuclei, the enhancement of the level density is observed already at the transition point. The collective phase is reached when the single-particle transfer matrix elements are dominant in the shell model Hamiltonian, providing a sign of their fundamental role.
nucl-thNPA(2017)·11 citations
02
First-principles results for electromagnetic properties of $s d$ shell nuclei
Archana Saxena · Praveen C. Srivastava
In this work we present $ab ini t i o$ shell-model calculations for electric quadrupole moments and magnetic dipole moments of $s d$ shell nuclei using valence-space Hamiltonians derived with two $ab ini t i o$ approaches: the in-medium similarity renormalization group (IM-SRG) and the coupled-cluster effective interaction (CCEI). Results are in a reasonable agreement with the available experimental data as well as with the results from the phenomenological USDB effective interaction. This work will add more information to the available $ab ini t i o$ results for the spectroscopy of $s d$ shell nuclei.
nucl-thPRC(2017)·22 citations
03
Steady state of isolated systems versus microcanonical ensemble in cell model of particle creation and annihilation
M. Gazdzicki · M. I. Gorenstein · A. Fronczak · P. Fronczak · M. Mackowiak-Pawlowska
A simple model of particle creation and annihilation in an isolated assembly of particles with conserved energy and fixed volume, the Cell Model, is formulated. With increasing time, particle number distribution, obtained by averaging over many systems, approaches a time-independent, steady state distribution. Dependence of the steady state distribution on creation and annihilation conditional reaction probabilities is studied. The results obtained for the steady state are compared with predictions of statistical mechanics within the microcanonical ensemble. In general, the predictions of both models are different. They agree only if the creation and annihilation conditional probabilities are equal. This condition also results in the detailed balance in the steady state.
nucl-thcond-mat.stat-mechIJMPE(2017)·3 citations
04
Low energy meson spectrum from a QCD approach based on many-body methods
D. A. Amor-Quiroz🇲🇽 · T. Yépez-Martínez🇦🇷 · P. O. Hess🇲🇽 · O. Civitarese🇦🇷 · A. Weber🇲🇽
The TDA and RPA many-body methods are applied to a QCD motivated Hamiltonian in the Coulomb gauge. The gluon effects in the low energy domain are accounted for by the Instantaneous color-Coulomb Interaction between color-charge densities, approximated by the sum of a Coulomb and a confining linear potentials. We use the eigenfunctions of the harmonic oscillator as a basis for the quantization of the quark fields, and discuss how suitable this basis is in various steps of the calculation. We show that the TDA results already reproduce the gross-structure of the light flavored meson states. The pion-like state in the RPA description, which is a highly collective state, is in a better agreement with the experimental value. The results are related to other nonperturbative treatments and compared to experimental data. We discuss the advantages of the present approach.
nucl-thIJMPE(2017)·14 citations
05
Interference phenomena in the decay $D_{s}^{+} \to η π^{0} π^{+}$ induced by the $a_{0}^{0} (980) - f_{0} (980)$ mixing
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
Using the data on the decay $D_{s}^{+} \to f_{0} (980) π^{+} \to K^{+} K^{-} π^{+}$ , we estimate the amplitude of the process $D_{s}^{+} \to [f_{0} (980) \to (K^{+} K^{-} + K^{0} K ˉ^{0}) \to a_{0}^{0} (980)] π^{+} \to η π^{0} π^{+}$ , caused by the mixing of $a_{0}^{0} (980)$ and $f_{0} (980)$ resonances that breaks the isotopic invariance due to the $K^{+}$ and $K^{0}$ meson mass difference. Effects of the interference of this amplitude with the amplitudes of the main mechanisms responsible for the decay $D_{s}^{+} \to η π^{0} π^{+}$ are analyzed. As such mechanisms, we examine the transition $D_{s}^{+} \to η ρ^{+} \to η π^{0} π^{+}$ , which is observed in experiment, and the possible transition $D_{s}^{+} \to (a_{0}^{0} (980) π^{+} + a_{0}^{+} (980) π^{0}) \to η π^{0} π^{+}$ . It is shown that the rapidly varying phase of the $a_{0}^{0} (980) - f_{0} (980)$ transition amplitude strongly influences on the interference curves.
↳ hep-phhep-exnucl-thPRD(2017)·21 citations
06
Evolution of a proto-neutron star with a nuclear many-body equation of state: Neutrino luminosity and gravitational wave frequencies
Giovanni Camelio🇮🇹 · Alessandro Lovato🇺🇸 · Leonardo Gualtieri🇮🇹 · Omar Benhar🇮🇹 · José A. Pons🇪🇸 · Valeria Ferrari🇮🇹
In a core-collapse supernova, a huge amount of energy is released in the Kelvin-Helmholtz phase subsequent to the explosion, when the proto-neutron star cools and deleptonizes as it loses neutrinos. Most of this energy is emitted through neutrinos, but a fraction of it can be released through gravitational waves. We model the evolution of a proto-neutron star in the Kelvin-Helmholtz phase using a general relativistic numerical code, and a recently proposed finite temperature, many-body equation of state; from this we consistently compute the diffusion coefficients driving the evolution. To include the many-body equation of state, we develop a new fitting formula for the high density baryon free energy at finite temperature and intermediate proton fraction. We estimate the emitted neutrino signal, assessing its detectability by present terrestrial detectors, and we determine the frequencies and damping times of the quasi-normal modes which would characterize the gravitational wave signal emitted in this stage.
↳ astro-ph.HEgr-qcnucl-thPRD(2017)·81 citations

Affiliations

first authorsco-authorsvia INSPIRE

Quantum phase transitions and collective enhancement of level density in odd-A and odd-odd nuclei

First-principles results for electromagnetic properties of sd shell nuclei

Steady state of isolated systems versus microcanonical ensemble in cell model of particle creation and annihilation

Low energy meson spectrum from a QCD approach based on many-body methods

Interference phenomena in the decay Ds+​→ηπ0π+ induced by the a00​(980)−f0​(980) mixing

Evolution of a proto-neutron star with a nuclear many-body equation of state: Neutrino luminosity and gravitational wave frequencies

Affiliations

First-principles results for electromagnetic properties of $s d$ shell nuclei

Interference phenomena in the decay $D_{s}^{+} \to η π^{0} π^{+}$ induced by the $a_{0}^{0} (980) - f_{0} (980)$ mixing