Nuclear Theory·nucl-th

Monday·January 2, 2017

10 papers—5 primary·5 cross-listed

01
Nuclear Weak Rates and Detailed Balance in Stellar Conditions
G. Wendell Misch
Detailed balance is often invoked in discussions of nuclear weak transitions in astrophysical environments. Satisfaction of detailed balance is rightly touted as a virtue of some methods of computing nuclear transition strengths, but we argue that it need not necessarily be strictly obeyed, especially when the system is far from weak equilibrium. We present the results of shell model calculations of nuclear weak strengths in both charged current and neutral current channels at astrophysical temperatures. Using these strengths to compute some reaction rates, we find that, despite some violation of detailed balance, our method is robust up to high temperature, and we comment on the relationship between detailed balance and weak equilibrium in astrophysical conditions.
nucl-thastro-ph.HEApJ(2017)·5 citations
02
Solving Dirac equations on a 3D lattice with inverse Hamiltonian and spectral methods
Z.X. Ren🇨🇳 · S.Q. Zhang🇨🇳 · J. Meng🇨🇳
A new method to solve the Dirac equation on a 3D lattice is proposed, in which the variational collapse problem is avoided by the inverse Hamiltonian method and the fermion doubling problem is avoided by performing spatial derivatives in momentum space with the help of the discrete Fourier transform, i.e., the spectral method. This method is demonstrated in solving the Dirac equation for a given spherical potential in 3D lattice space. In comparison with the results obtained by the shooting method, the differences in single particle energy are smaller than $1 0^{- 4}$ ~MeV, and the densities are almost identical, which demonstrates the high accuracy of the present method. The results obtained by applying this method without any modification to solve the Dirac equations for an axial deformed, non-axial deformed, and octupole deformed potential are provided and discussed.
nucl-thnucl-exPRC(2017)·61 citations
03
Antisymmetrized molecular dynamics studies for exotic clustering phenomena in neutron-rich nuclei
M. Kimura · T. Suhara · Y. Kanada-En'yo
We present a review of recent works on clustering phenomena in unstable nuclei studied by antisymmetrized molecular dynamics (AMD). The AMD studies in these decades have uncovered novel types of clustering phenomena brought about by the excess neutrons. Among them, this review focuses on the molecule-like structure of unstable nuclei. One of the earliest discussions on the clustering in unstable nuclei was made for neutron-rich Be and B isotopes. AMD calculations predicted that the ground state clustering is enhanced or reduced depending on the number of excess neutrons. Today, the experiments are confirming this prediction as the change of the proton radii. Behind this enhancement and reduction of the clustering, there are underlying shell effects called molecular- and atomic-orbits. These orbits form covalent and ionic bonding of the clusters analogous to the atomic molecules. It was found that this "molecular-orbit picture" reasonably explains the low-lying spectra of Be isotopes. The molecular-orbit picture is extended to other systems having parity asymmetric cluster cores and to the three cluster systems. O and Ne isotopes are the candidates of the former, while the $3 α$ linear chains in C isotopes are the latter. For both subjects, many intensive studies are now in progress. We also pay a special attention to the observables which are the fingerprint of the clustering. In particular, we focus on the monopole and dipole transitions which are recently regarded as good probe for the clustering. We discuss how they have and will reveal the exotic clustering.
nucl-thEPJA(2016)·73 citations
04
Bohr Hamiltonian for gamma=0 with Davidson Potential
I.Yigitoglu · M.Gokbulut
A gamma-rigid solution of the Bohr Hamiltonian is derived for gamma=0 utilizing the Davidson potential in the beta variable. This solution is going to be called X(3)-D. The energy eigenvalues and wave functions are obtained by using an analytic method which has been developed by Nikiforov and Uvarov. BE(2) transition rates are calculated. A variational procedure is applied to energy ratios to determine whether or not the X(3) model is located at the critical point between spherical and deformed nuclei.
nucl-thEur.Phys.J.Plus(2017)·4 citations
05
Hybrid Stars in the Framework of different NJL Models
G. A. Contrera🇦🇷 · M. Orsaria🇺🇸 · I. F. Ranea-Sandoval🇦🇷 · F. Weber🇺🇸
We compute models for the equation of state (EoS) of the matter in the cores of hybrid stars. Hadronic matter is treated in the non-linear relativistic mean-field approximation, and quark matter is modeled by three-flavor local and non-local Nambu $-$ Jona-Lasinio (NJL) models with repulsive vector interactions. The transition from hadronic to quark matter is constructed by considering either a soft phase transition (Gibbs construction) or a sharp phase transition (Maxwell construction). We find that high-mass neutron stars with masses up to $2.1 - 2.4 M_{⊙}$ may contain a mixed phase with hadrons and quarks in their cores, if global charge conservation is imposed via the Gibbs conditions. However, if the Maxwell conditions is considered, the appearance of a pure quark matter core either destabilizes the star immediately (commonly for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (generally for local NJL models).
nucl-thastro-ph.HEastro-ph.SRhep-phInt.J.Mod.Phys.Conf.Ser.(2017)·7 citations
06
Improved limits on the hadronic and semi-hadronic CP violating parameters and role of a dark force carrier in the electric dipole moment of $^{199}$ Hg
B. K. Sahoo🇮🇳
Combining the recently reported electric dipole moment (EDM) of $^{199}$ Hg atom due to breaking of parity and time-reversal symmetries with the improved relativistic atomic calculations, precise limits on the tensor-pseudotensor (T-PT) electron-nucleus (e-N) coupling coefficient and the nuclear Schiff moment (NSM) interactions are determined. Using these limits with the nuclear calculations, we infer limits on the EDMs of neutron and proton as $d_{n} < 2.2 \times 1 0^{- 26} ∣ e ∣ cm$ and $d_{p} < 2.1 \times 1 0^{- 25} ∣ e ∣ cm$ , respectively, and on the quantum chromodynamics (QCD) parameter and the combined up- and down- quark chromo-EDMs as $∣ θ ˉ ∣ < 1.1 \times 1 0^{- 10}$ and $∣ d ~_{u} - d ~_{d} ∣ < 5.5 \times 1 0^{- 27} ∣ e ∣ cm$ , respectively. These are the best limits till date to probe new sources of CP violation beyond the standard model (SM) from a diamagnetic atom. Role of considering a capable many-body method to account the electron correlation effects to all orders for inferring the above limits has been highlighted. From this analysis, constraints on the T-PT e-N coupling coefficient with a large range of mass of a possible dark matter carrier $χ$ between the atomic electrons and nucleus are given.
↳ hep-phnucl-thphysics.atom-phPRD(2017)·48 citations
07
Semirelativistic approximation to the $γ^{*} N \to N (1520)$ and $γ^{*} N \to N (1535)$ transition form factors
G. Ramalho🇧🇷
The representation of the wave functions of the nucleon resonances within a relativistic framework is a complex task. In a nonrelativistic framework the orthogonality between states can be imposed naturally. In a relativistic generalization, however, the derivation of the orthogonality condition between states can be problematic, particularly when the states have different masses. In this work we study the $N (1520)$ and $N (1535)$ states using a relativistic framework. We considered wave functions derived in previous works, but impose the orthogonality between the nucleon and resonance states using the properties of the nucleon, ignoring the difference of masses between the states (semirelativistic approximation). The $N (1520)$ and $N (1535)$ wave functions are then defined without any adjustable parameters and are used to make predictions for the valence quark contributions to the transition form factors. The predictions compare well with the data particularly for high momentum transfer, where the dominance of the quark degrees of freedom is expected.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2017)·30 citations
08
Generalized Beth-Uhlenbeck approach to the equation of state for quark-hadron matter
D. Blaschke🇷🇺 · A. Dubinin🇵🇱 · L. Turko🇵🇱
A unified equation of state for quark-hadron matter is presented in the generalized Beth-Uhlenbeck form. It follows from a $Φ -$ derivable approach to the thermodynamic potential where the ansatz for the $Φ$ functional contains all 2PI diagrams at two-loop order formed with quark cluster Green's functions for quark, diquark, meson and baryon propagators. We present numerical results using an effective model for the generic behaviour of hadron masses and phase shifts at finite temperature which shares basic features with recent developments within the PNJL model for correlations in quark matter. We obtain the transition between a hadron resonance gas phase and the quark gluon plasma where the Mott dissociation of hadrons is encoded in the hadronic phase shifts. The resulting thermodynamics is in very good agreement with recent lattice QCD simulations.
↳ hep-phnucl-thActa Phys.Polon.Supp.(2017)·14 citations
09
Fine-tuning the Color-Glass Condensate with the nuclear configurational entropy
Gayane Karapetyan🇧🇷
The dipole-nucleus forward scattering amplitude rules the onset of the gluon anomalous dimension, in the Color-Glass Condensate regime. In this model, the onset of quantum regime is here derived as a critical stable point in the nuclear configurational entropy, matching the fitted experimental data in the literature with accuracy of 1%. It corroborates with the informational entropy paradigm in high energy nuclear physics.
↳ hep-phhep-thnucl-thEPL(2017)·38 citations
10
Liquid-Gas Phase Transitions and $C K$ Symmetry in Quantum Field Theories
Hiromichi Nishimura🇺🇸 · Michael C. Ogilvie🇺🇸 · Kamal Pangeni🇺🇸
A general field-theoretic framework for the treatment of liquid-gas phase transitions is developed. Starting from a fundamental four-dimensional field theory at nonzero temperature and density, an effective three-dimensional field theory with a sign problem is derived. Although charge conjugation $C$ is broken at finite density, there remains a symmetry under $C K$ , where $K$ is complex conjugation. We consider four models: relativistic fermions, nonrelativistic fermions, static fermions and classical particles. The thermodynamic behavior is extracted from $C K$ -symmetric complex saddle points of the effective field theory at tree level. The relativistic and static fermions show a liquid-gas transition, manifesting as a first-order line at low temperature and high density, terminated by a critical end point. In the cases of nonrelativistic fermions and classical particles, we find no first-order liquid-gas transitions at tree level. The mass matrix controlling the behavior of correlation functions is obtained from fluctuations around the saddle points. Due to the $C K$ symmetry of the models, the eigenvalues of the mass matrix can be complex. This leads to the existence of disorder lines, which mark the boundaries where the eigenvalues go from purely real to complex. The regions where the mass matrix eigenvalues are complex are associated with the critical line. In the case of static fermions, a powerful duality between particles and holes allows for the analytic determination of both the critical line and the disorder lines. Depending on the values of the parameters, either zero, one or two disorder lines are found. Numerical results for relativistic fermions give a very similar picture.
↳ hep-thhep-lathep-phnucl-thPRD(2017)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE