Nuclear Theory·nucl-th

Friday·June 19, 2015

9 papers—5 primary·4 cross-listed

01
Equation of state for neutron stars with hyperons and quarks in relativistic Hartree-Fock approximation
Tsuyoshi Miyatsu🇰🇷 · Myung-Ki Cheoun🇰🇷 · Koichi Saito🇯🇵
We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark-meson coupling model with relativistic Hartree-Fock approximation, the EoS for hadronic matter is derived by taking into account the strange ( $σ^{*}$ and $ϕ$ ) mesons as well as the light non-strange ( $σ$ , $ω$ , $π$ and $ρ$ ) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector ( $ϕ$ ) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark-hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron star data.
nucl-thastro-ph.HEhep-phApJ(2015)·62 citations
02
Precise determination of lattice phase shifts and mixing angles
Bing-Nan Lu🇩🇪 · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Ulf-G. Meißner🇩🇪
We introduce a general and accurate method for determining lattice phase shifts and mixing angles, which is applicable to arbitrary, non-cubic lattices. Our method combines angular momentum projection, spherical wall boundaries and an adjustable auxiliary potential. This allows us to construct radial lattice wave functions and to determine phase shifts at arbitrary energies. For coupled partial waves, we use a complex-valued auxiliary potential that breaks time-reversal invariance. We benchmark our method using a system of two spin-1/2 particles interacting through a finite-range potential with a strong tensor component. We are able to extract phase shifts and mixing angles for all angular momenta and energies, with precision greater than that of extant methods. We discuss a wide range of applications from nuclear lattice simulations to optical lattice experiments.
nucl-thhep-lathep-phPLB(2016)·44 citations
03
Structure of Lambda(1405) and construction of KbarN local potential based on chiral SU(3) dynamics
Kenta Miyahara🇯🇵 · Tetsuo Hyodo🇯🇵
We develop the single-channel local potential for the KbarN system, which is applicable to quantitative studies of Kbar bound states in nuclei. Because the high precision measurement of the kaonic hydrogen by SIDDHARTA reduces the uncertainty of the KbarN amplitude below the KbarN threshold, the local potential should be calibrated in a wide energy region. We establish a new method to construct the local potential focusing on the behavior of the scattering amplitude in the complex energy plane. Applying this method, we construct the KbarN potential based on the chiral coupled-channel approach with the SIDDHARTA constraint. The wave function from the new potential indicates the KbarN molecular structure of Lambda(1405).
nucl-thhep-phPRC(2016)·61 citations
04
Scaled variance, skewness, and kurtosis near the critical point of nuclear matter
V. Vovchenko · D. V. Anchishkin · M. I. Gorenstein · R. V. Poberezhnyuk
The van der Waals (VDW) equation of state predicts the existence of a first-order liquid-gas phase transition and contains a critical point. The VDW equation with Fermi statistics is applied to a description of the nuclear matter. The nucleon number fluctuations near the critical point of nuclear matter are studied. The scaled variance, skewness, and kurtosis diverge at the critical point. It is found that the crossover region of the phase diagram is characterized by the large values of the scaled variance, the almost zero skewness, and the significantly negative kurtosis. The rich structures of the skewness and kurtosis are observed in the phase diagram in the wide region around the critical point, namely, they both may attain large positive or negative values.
nucl-thPRC(2015)·96 citations
05
Conjunction of $γ$ -rigid and $γ$ -stable collective motion in the critical point of the phase transition from spherical to deformed nuclear shapes
R. Budaca · A. I. Budaca
Based on the competition between $γ$ -stable and $γ$ -rigid collective motions mediated by a rigidity parameter, a two-parameter exactly separable version of the Bohr Hamiltonian is proposed. The $γ$ -stable part of the Hamiltonian is restricted to stiff oscillations around the $γ$ value of the rigid motion. The separated potential for $β$ and $γ$ shape variables is chosen such that in the lower limit of this parameter, the model recovers exactly the ES- $X (5)$ model, while in the upper limit it tends to the prolate $γ$ -rigid solution $X (3)$ . The combined effect of the rigidity and stiffness parameters on the energy spectrum and wave function is duly investigated. Numerical results are given for few nuclei showing such ambiguous behaviour.
nucl-thJ.Phys.G(2015)·16 citations
06
Unitary fermions and Luscher's formula on a crystal
Manuel Valiente · Nikolaj Thomas Zinner
We consider the low-energy particle-particle scattering properties in a periodic simple cubic crystal. In particular, we investigate the relation between the two-body scattering length and the energy shift experienced by the lowest-lying unbound state when this is placed in a periodic finite box. We introduce a continuum model for s-wave contact interactions that respects the symmetry of the Brillouin zone in its regularisation and renormalisation procedures, and corresponds to the naïve continuum limit of the Hubbard model. The energy shifts are found to be identical to those obtained in the usual spherically symmetric renormalisation scheme upon resolving an important subtlety regarding the cutoff procedure. We then particularize to the Hubbard model, and find that for large finite lattices the results are identical to those obtained in the continuum limit. The results reported here are valid in the weak, intermediate and unitary limits, and can be used for the extraction of scattering information ,via exact diagonalisation or Monte Carlo methods, of two-body systems in realistic periodic lattices.
↳ cond-mat.quant-gasnucl-thquant-phSCPMA(2016)·5 citations
07
Kinetic theory of a longitudinally expanding system of scalar particles
Thomas Epelbaum🇨🇦 · Francois Gelis🇫🇷 · Sangyong Jeon🇨🇦 · Guy Moore🇩🇪 · Bin Wu🇫🇷
A simple kinematical argument suggests that the classical approximation may be inadequate to describe the evolution of a system with an anisotropic particle distribution. In order to verify this quantitatively, we study the Boltzmann equation for a longitudinally expanding system of scalar particles interacting with a $ϕ^{4}$ coupling, that mimics the kinematics of a heavy ion collision at very high energy. We consider only elastic $2 \to 2$ scatterings, and we allow the formation of a Bose-Einstein condensate in overpopulated situations by solving the coupled equations for the particle distribution and the particle density in the zero mode. For generic CGC-like initial conditions with a large occupation number and a moderate coupling, the solutions of the full Boltzmann equation do not follow a classical attractor behavior.
↳ hep-phnucl-thJHEP(2015)·24 citations
08
New analysis of the low-energy $π^{\pm} p$ differential cross sections of the CHAOS Collaboration
Evangelos Matsinos🇨🇭 · Günther Rasche🇨🇭
In a previous paper, we reported the results of a partial-wave analysis of the pion-nucleon ( $π N$ ) differential cross sections (DCSs) of the CHAOS Collaboration and came to the conclusion that the angular distribution of their $π^{+} p$ data sets is incompatible with the rest of the modern (meson-factory) database. The present work, re-addressing this issue, has been instigated by a number of recent improvements in our analysis, namely regarding the inclusion of the theoretical uncertainties when investigating the reproduction of experimental data sets on the basis of a given `theoretical' solution, modifications in the parameterisation of the form factors of the proton and of the pion entering the electromagnetic part of the $π N$ amplitude, and the inclusion of the effects of the variation of the $σ$ -meson mass when fitting the ETH model of the $π N$ interaction to the experimental data. The new analysis of the CHAOS DCSs confirms our earlier conclusions and casts doubt on the value for the $π N$ $Σ$ term, which Stahov, Clement, and Wagner have extracted from these data.
↳ hep-phnucl-thIJMPE(2015)·5 citations
09
The pion quasiparticle in the low-temperature phase of QCD
Bastian B. Brandt🇩🇪 · Anthony Francis🇨🇦 · Harvey B. Meyer🇩🇪 · Daniel Robaina🇩🇪
We investigate the properties of the pion quasiparticle in the low-temperature phase of two-flavor QCD on the lattice with support from chiral effective theory. We find that the pion quasiparticle mass is significantly reduced compared to its value in the vacuum, by contrast with the static screening mass, which increases with temperature. By a simple argument, near the chiral limit the two masses are expected to determine the quasiparticle dispersion relation. Analyzing two-point functions of the axial charge density at non-vanishing spatial momentum, we find that the predicted dispersion relation and the residue of the pion pole are simultaneously consistent with the lattice data at low momentum. The test, based on fits to the correlation functions, is confirmed by a second analysis using the Backus-Gilbert method.
↳ hep-lathep-phnucl-thPRD(2015)·69 citations

Affiliations

first authorsco-authorsvia INSPIRE