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Nuclear Theory·nucl-th

Wednesday·September 13, 2017

10 papers—7 primary·3 cross-listed

All10Primary7Cross-lists3
  1. 01

    A quasiparticle equation of state with a phenomenological critical point

    Hong-Hao Ma🇧🇷 · Wei-Liang Qian🇧🇷

    We propose a hybrid parameterization of a quasiparticle equation of state, where a critical point is implemented phenomenologically. In this approach, a quasiparticle model with finite chemical potential is used to describe the quark-gluon plasma phase by fitting to the lattice quantum chromodynamics data at high temperature. On the other hand, the hadronic resonance gas model with excluded volume correction is employed for the hadronic phase. An interpolation scheme is implemented so that the phase transition is a smooth crossover when the chemical potential is smaller than a critical value, or otherwise approximately of first order according to Ehrenfest's classification. Also, the thermodynamic consistency is guaranteed for the equation of state related to both the quasiparticle model and the implementation of the critical point.

    nucl-thBraz.J.Phys.(2018)·8 citations
  2. 02

    Quantum Monte Carlo calculations of weak transitions in =6--10 nuclei

    S. Pastore · A. Baroni · J. Carlson · S. Gandolfi · Steven C. Pieper · R. Schiavilla · R.B. Wiringa

    Ab initio calculations of the Gamow-Teller (GT) matrix elements in the decays of He and C and electron captures in Be are carried out using both variational and Green's function Monte Carlo wave functions obtained from the Argonne two-nucleon and Illinois-7 three-nucleon interactions, and axial many-body currents derived from either meson-exchange phenomenology or chiral effective field theory. The agreement with experimental data is excellent for the electron captures in Be, while theory overestimates the He and C data by and , respectively. We show that for these systems correlations in the nuclear wave functions are crucial to explain the data, while many-body currents increase by -- the one-body GT contributions. These findings suggest that the longstanding -problem, i.e., the systematic overprediction ( in nuclei) of GT matrix elements in shell-model calculations, may be resolved, at least partially, by correlation effects.

    nucl-thPRC(2018)·98 citations
  3. 03

    Photon emission from quark-gluon plasma out of equilibrium

    Sigtryggur Hauksson🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

    The photon emission from a non-equilibrium quark-gluon plasma (QGP) is analyzed. We derive an integral equation that describes photon production through quark-antiquark annihilation and quark bremsstrahlung. It includes coherence between different scattering sites, also known as the Landau-Pomeranchuk-Migdal effect. These leading-order processes are studied for the first time together in an out-of-equilibrium field theoretical treatment that enables the inclusion of viscous corrections to the calculation of electromagnetic emission rates. In the special case of an isotropic, viscous, plasma the integral equation only depends on three constants which capture the non-equilibrium nature of the medium.

    nucl-thhep-phPRC(2018)·33 citations
  4. 04

    Quasiparticle-vibration coupling effects on nuclear transitions of astrophysical interest

    Caroline Robin · Elena Litvinova

    The relativistic quasiparticle time-blocking approximation (RQTBA) is applied to the description of nuclear excitation modes of astrophysical interest. This method is based on the meson-nucleon Lagrangian and goes beyond the standard relativistic quasiparticle random-phase approximation (RQRPA) by treating the coupling between single quasiparticles and collective vibrations of the nucleus. We calculate electric dipole transitions and Gamow-Teller modes in the (p,n) direction in a few Sn isotopes and obtain the rates of (n,) reaction and -decay processes, which govern the r-process nucleosynthesis, in a unified RQTBA framework. Gamow-Teller transitions in the (n,p) branch, which in principle can serve for the modeling of stellar evolution, are also investigated, and Zr is taken as a study case.

    nucl-thnucl-exAIP Conf.Proc.(2017)·3 citations
  5. 05

    Statistical errors in Weizsaecker-Skyrme mass model

    Min Liu · Yu Gao · Ning Wang

    The statistical uncertainties of 13 model parameters in the Weizsäcker-Skyrme (WS*) mass model are investigated for the first time with an efficient approach, and the propagated errors in the predicted masses are estimated. The discrepancies between the predicted masses and the experimental data, including the new data in AME2016, are almost all smaller than the model errors. For neutron-rich heavy nuclei, the model errors increase considerably, and go up to a few MeV when the nucleus approaches the neutron drip line. The most sensitive model parameter which causes the largest statistical error is analyzed for all bound nuclei. We find that the two coefficients of symmetry energy term significantly influence the mass predictions of extremely neutron-rich nuclei, and the deformation energy coefficients play a key role for well-deformed nuclei around the -stability line.

    nucl-thastro-ph.SRCPC(2017)·7 citations
  6. 06

    Charge-exchange quasi-elastic process under in the frame of elastic scattering to

    R. A. Shindin · D. K. Guriev · A. N. Livanov · I. P. Yudin

    It is considered the problem of spin physics related with the difference of representation of the elastic interaction between the neutron and proton. In the first case the charge-exchange reaction under the angle is supposed, in the second --- the simple elastic scattering of , when the neutron is going in opposite direction . The transition from one representation to another is provided by the Majorana operator. In the framework of impulse approximation it is twice calculated the quasi-elastic charge-exchange reaction of a neutron on a deuteron. In the frame of scattering of proton to the angle it gives the well-known Dean formula. Using other representation as a neutron elastic scattering under the angle (together with neutron-spectator in -pair) the alternative formula is presented.

    nucl-thnucl-ex0 citations
  7. 07

    Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

    J.-B. Rose🇩🇪 · J. M. Torres-Rincon🇩🇪 · A. Schäfer🇩🇪 · D. R. Oliinychenko🇩🇪 · H. Petersen🇩🇪

    We address a discrepancy between different computations of (shear viscosity over entropy density) of hadronic matter. Substantial deviations of this coefficient are found between transport approaches mainly based on resonance propagation with finite lifetime and other (semi-analytical) approaches with energy-dependent cross-sections, where interactions do not introduce a timescale. We provide an independent extraction of this coefficient by using the newly-developed SMASH (Simulating Many Accelerated Strongly interacting Hadrons) transport code, which is an example of a mainly resonance-based approach. We compare the results from SMASH with numerical solutions of the Boltzmann equation for simple systems using the Chapman-Enskog expansion, as well as previous results in the literature. Our conclusion is that the hadron interaction via resonance formation/decay strongly affects the transport properties of the system, resulting in significant differences in with respect to other approaches where binary collisions dominate. We argue that the relaxation time of the system ---which characterizes the shear viscosity--- is determined by the interplay between the mean-free time and the lifetime of resonances. We show how an artificial shortening of the resonance lifetimes, or the addition of a background elastic cross section nicely interpolate between the two discrepant results.

    nucl-thhep-phPRC(2018)·97 citations

Affiliations

first authorsco-authorsvia INSPIRE