Nuclear Theory·nucl-th

Friday·January 15, 2016

11 papers—5 primary·6 cross-listed

01
Solitonic modulation and Lifshitz point in an external magnetic field within Nambu--Jona-Lasinio model
Gaoqing Cao🇨🇳 · Anping Huang🇨🇳
We study the inhomogeneous solitonic modulation of a chiral condensate within the effective Nambu--Jona-Lasinio model when a constant external magnetic field is present. The self-consistent Pauli-Villars regularization scheme is adopted to manipulate the ultraviolet divergence encountered in the thermodynamic quantities. In order to determine the chiral restoration lines efficiently, a new kind of Ginzburg-Landau expansion approach is proposed here. At zero temperature, we find that both the upper and lower boundaries of the solitonic modulation oscillate with the magnetic field in the $μ$ -- $B$ phase diagram which is actually the de Hass-van Alphan (dHvA) oscillation. It is very interesting to find out how the tricritical Lifshitz point $(T_{L}, μ_{L})$ evolves with the magnetic field: There are also dHvA oscillations in the $T_{L}$ -- $B$ and $μ_{L}$ -- $B$ curves, though the tricritical temperature $T_{L}$ increases monotonically with the magnetic field.
nucl-thhep-phhep-thPRD(2016)·17 citations
02
No-core configuration-interaction model for the isospin- and angular-momentum-projected states
W. Satula · P. Baczyk · J. Dobaczewski · M. Konieczka
[Background] Single-reference density functional theory is very successful in reproducing bulk nuclear properties like binding energies, radii, or quadrupole moments throughout the entire periodic table. Its extension to the multi-reference level allows for restoring symmetries and, in turn, for calculating transition rates. [Purpose] We propose a new no-core-configuration-interaction (NCCI) model treating properly isospin and rotational symmetries. The model is applicable to any nucleus irrespective of its mass and neutron- and proton-number parity. It properly includes polarization effects caused by an interplay between the long- and short-range forces acting in the atomic nucleus. [Methods] The method is based on solving the Hill-Wheeler-Griffin equation within a model space built of linearly-dependent states having good angular momentum and properly treated isobaric spin. The states are generated by means of the isospin and angular-momentum projection applied to a set of low-lying (multi)particle-(multi)hole deformed Slater determinants calculated using the self-consistent Skyrme-Hartree-Fock approach. [Results] The theory is applied to calculate energy spectra in N~Z nuclei that are relevant from the point of view of a study of superallowed Fermi beta-decays. In particular, a new set of the isospin-symmetry-breaking corrections to these decays is given. [Conclusions] It is demonstrated that the NCCI model is capable to capture main features of low-lying energy spectra in light and medium-mass nuclei using relatively small model space and without any local readjustment of its low-energy coupling constants. Its flexibility and a range of applicability makes it an interesting alternative to the conventional nuclear shell model.
nucl-thnucl-exPRC(2016)·40 citations
03
Harmonic Oscillator Trap and the Phase-Shift Approximation
H. S. Köhler
The energy-spectrum of two point-like particles interacting in a 3-D isotropic Harmonic Oscillator (H.O.) trap is related to the free scattering phase-shifts $δ$ of the particles by a formula first published by Busch et al. It is here used to find an expression for the \it shift \rm of the energy levels, caused by the interaction, rather than the perturbed spectrum itself. In the limit of high energy (large quantum number $n$ of the H.O.) this shift is shown to be given by $- 2 \frac{δ}{π}$ , also valid in the limit of infinite as well as zero scattering length at all H.O. energies. Numerical investigation shows that the shifts differ from the exact result of Busch et al, by less than $< \frac{1}{2} %$ except for $n = 0$ when it can be as large as $\approx 2.5%$ . This approximation for the energy-shift is well known from another exactly solvable model, namely that of two particles interacting in a spherical infinite square-well trap (or box) of radius $R$ in the limit $R \to \infty$ , and/or in the limit of large energy. It is in this context referred to as the \it phase-shift approximation \rm. It can be (and has been) used in (infinite) nuclear matter calculations to calculate the two-body effective interaction in situations where in-medium effects can be neglected. It has also been used in expressing the energy of free electrons in a metal.
nucl-thcond-mat.quant-gasmath-phmath.MP+1Physics(2014)·1 citation
04
Hartree-Fock Many-Body Perturbation Theory for Nuclear Ground-States
Alexander Tichai · Joachim Langhammer · Sven Binder · Robert Roth
We investigate the order-by-order convergence behavior of many-body perturbation theory (MBPT) as a simple and efficient tool to approximate the ground-state energy of closed-shell nuclei. To address the convergence properties directly, we explore perturbative corrections up to 30th order and highlight the role of the partitioning for convergence. The use of a simple Hartree-Fock solution to construct the unperturbed basis leads to a convergent MBPT series for soft interactions, in contrast to, e.g., a harmonic oscillator basis. For larger model spaces and heavier nuclei, where a direct high-order MBPT calculation in not feasible, we perform third-order calculation and compare to advanced ab initio coupled-cluster calculations for the same interactions and model spaces. We demonstrate that third-order MBPT provides ground-state energies for nuclei up into tin isotopic chain that are in excellent agreement with the best available coupled-cluster results at a fraction of the computational cost.
nucl-thPLB(2016)·92 citations
05
Sensitivity of the COSY Dibaryon Candidate to np Elastic Scattering Measurements
R.L. Workman🇺🇸 · W.J. Briscoe🇺🇸 · I.I. Strakovsky (GWU)🇺🇸
The case for a dibaryon resonance, appearing in np scattering, has support from a WASA-at-COSY measurement of the polarization quantity A_y over a center-of-mass energy region suggested by structures seen earlier in two-pion production experiments. Here we compare fits with and without an associated pole in order to clarify the impact of these COSY data. We then consider what further np scattering measurements would most clearly distinguish between the pole and non-pole fit results.
nucl-thhep-exhep-phnucl-exPRC(2016)·20 citations
06
Kaon regeneration in perturbation theory
Valeriy Nazaruk🇷🇺
$K^{0} K ˉ^{0}$ transitions in a medium followed by decay and regeneration of $K_{S}^{0}$ -component are considered by means of perturbation theory. It is shown that in the previous calculations the problem different from regeneration is solved.
↳ hep-ph2 citations
07
Alpha-constrained QSE Nucleosynthesis in High-entropy and Fast-expanding Material
Sho Fujibayashi · Takashi Yoshida · Yuichiro Sekiguchi
We investigate the nucleosynthesis process in high-entropy ( $s / k_{B} ≳ 100$ ) and very fast-expanding ( $τ_{exp} \sim 1 0^{- 3} s$ ) materials. In such a material with the electron fraction near 0.5, an interesting nucleosynthesis process occurs. In this process, the abundance distribution of heavy-nuclei of $A > 100$ achieve quasi-statistical equilibrium (QSE) at high temperature and the abundances are frozen at the end of the nucleosynthesis. We explain this abundance distribution using the "alpha-constrained QSE" abundances formulated in this paper. We demonstrate that this nucleosynthesis would occur in neutrino-driven winds from massive proto-neutron stars in hypernovae, where $A \sim 140$ $p$ -nuclei are synthesized.
↳ astro-ph.HEastro-ph.SRnucl-thApJ(2016)·5 citations
08
Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation
Hector O. Silva🇺🇸 · Hajime Sotani🇯🇵 · Emanuele Berti🇵🇹
The lowest neutron star masses currently measured are in the range $1.0 - 1.1 M_{⊙}$ , but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass $M / M_{⊙} = 1.174 \pm 0.004$ by Martinez et al [Astrophys. J. 812, 143 (2015)] in a double neutron star system suggests that low-mass neutron stars may be an interesting target for gravitational-wave detectors. Furthermore, Sotani et al [PTEP 2014, 051E01 (2014)] recently found empirical formulas relating the mass and surface redshift of nonrotating neutron stars to the star's central density and to the parameter $η \equiv (K_{0} L^{2})^{1/3}$ , where $K_{0}$ is the incompressibility of symmetric nuclear matter and $L$ is the slope of the symmetry energy at saturation density. Motivated by these considerations, we extend the work by Sotani et al to slowly rotating and tidally deformed neutron stars. We compute the moment of inertia, quadrupole moment, quadrupole ellipticity, tidal and rotational Love number and apsidal constant of slowly rotating neutron stars by integrating the Hartle-Thorne equations at second order in rotation, and we fit all of these quantities as functions of $η$ and of the central density. These fits may be used to constrain $η$ , either via observations of binary pulsars in the electromagnetic spectrum, or via near-future observations of inspiralling compact binaries in the gravitational-wave spectrum.
↳ astro-ph.HEgr-qcnucl-thMNRAS(2016)·51 citations
09
Early quark production and approach to chemical equilibrium
D. Gelfand🇩🇪 · F. Hebenstreit🇨🇭 · J. Berges🇩🇪
We perform real-time lattice simulations of out-of-equilibrium quark production in non-Abelian gauge theory in 3+1-dimensions. Our simulations include the backreaction of quarks onto the dynamical gluon sector, which is particularly relevant for strongly correlated quarks. We observe fast isotropization and universal behavior of quarks and gluons at weak coupling and establish a quantitative connection to previous pure glue results. In order to understand the strongly correlated regime, we perform simulations for a large number of flavors and compare them to those obtained with two light quark flavors. By doing this we are able to provide estimates of the chemical equilibration time.
↳ hep-phhep-latnucl-thPRD(2016)·33 citations
10
An introduction to mesic nuclei
Colin Wilkin🇬🇧
There is much speculation and a modest amount of evidence that certain mesons might form quasi-bound states with nuclei to produce really exotic states of matter. For this to be a practical possibility, the interaction between the meson and nucleons at low energies must be strong and attractive and the production rates "healthy". The conditions for this are surveyed for the light mesons. How this might lead to quasi-bound states is then discussed in a few typical cases.
↳ nucl-exnucl-thActa Phys.Polon.B(2016)·22 citations
11
Event-by-event fluctuations in the medium-induced jet evolution
Miguel A. Escobedo🇫🇷 · Edmond Iancu🇫🇷
We develop the event-by-event picture of the gluon distribution produced via medium-induced gluon branching by an energetic jet which propagates through a dense QCD medium. A typical event is characterized by the production of a large number of soft gluons which propagate at large angles with respect to the jet axis and which collectively carry a substantial amount of energy. By explicitly computing 2-gluon correlations, we demonstrate the existence of large event-by-event fluctuations, which reflect the stochastic nature of the branching process. For the two quantities that we have investigated -- the energy loss at large angles and the soft gluon multiplicity --, the dispersion is parametrically as large as the respective expectation value. We identify interesting scaling laws, which suggest that the multiplicity distribution should exhibit KNO (Koba-Nielsen-Olesen) scaling. A similar scaling is known to hold for a jet branching in the vacuum, but the medium-induced distribution is found to be considerably broader. We predict that event-by-event measurements of the di-jet asymmetry in Pb+Pb collisions at the LHC should observe large fluctuations in the number of soft hadrons propagating at large angles and also in the total energy carried by these hadrons.
↳ hep-phhep-exnucl-thJHEP(2016)·26 citations

Affiliations

first authorsco-authorsvia INSPIRE