Equation of State and Composition of Proto-Neutron Stars and Merger Remnants with Hyperons

Finite-temperature equation of state (EoS) and the composition of dense nuclear and hypernuclear matter under conditions characteristic of neutron star binary merger remnants and supernovas are discussed. We consider both neutrino free-streaming and trapped regimes which are separated by a temperature of a few MeV. The formalism is based on covariant density functional (CDF) theory for the full baryon octet with density-dependent couplings, suitably adjusted in the hypernuclear sector. The softening of the EoS with the introduction of the hyperons is quantified under various conditions of lepton fractions and temperatures. We find that Λ, Ξ−, and Ξ0 hyperons appear in the given order with a sharp density increase at zero temperature at the threshold being replaced by an extended increment over a wide density range at high temperatures. The Λ hyperon survives in the deep subnuclear regime. The triplet of Σs is suppressed in cold hypernuclear matter up to around seven times the nuclear saturation density, but appears in significant fractions at higher temperatures, T≥20 MeV, in both supernova and merger remnant matter. We point out that a special isospin degeneracy point exists where the baryon abundances within each of the three isospin multiplets are equal to each other as a result of (approximate) isospin symmetry. At that point, the charge chemical potential of the system vanishes. We find that under the merger remnant conditions, the fractions of electron and μ-on neutrinos are close and are about 1%, whereas in the supernova case, we only find a significant fraction (∼10%) of electron neutrinos, given that in this case, the μ-on lepton number is zero.

Covariant density and velocity perturbations of the quasi-Newtonian cosmological model in f(T) gravity

We investigate classes of shear-free cosmological dust models with irrotational fluid flows within the framework of f(T) gravity. In particular, we use the $$1 + 3$$ 1 + 3 covariant formalism and present the covariant linearised evolution and constraint equations describing such models. We then derive the integrability conditions describing a consistent evolution of the linearised field equations of these quasi-Newtonian universes in the f(T) gravitational theory. Finally, we derive the evolution equations for the density and velocity perturbations of the quasi-Newtonian universe. We explore the behaviour of the matter density contrast for two models – $$f(T)= \mu T_{0}(T/T_{0})^{n}$$ f ( T ) = μ T 0 ( T / T 0 ) n and the more generalised case, where $$f(T)= T+ \mu T_{0} (T/T_{0})^{n}$$ f ( T ) = T + μ T 0 ( T / T 0 ) n , with and without the application of the quasi-static approximation. Our numerical solutions show that these f(T) theories can be suitable alternatives to study the background dynamics, whereas the growth of energy density fluctuations change dramatically from the expected $$\Lambda $$ Λ CDM behaviour even for small deviation from the general relativistic limits of the underlying f(T) theory. Moreover, applying the so-called quasi-static approximation yields exact-solution results that are orders of magnitude different from the numerically integrated solutions of the full system, suggesting that these approximations are not applicable here.

Shape evolution of Hg isotopes within the covariant density functional theory

1 The shape evolution in the neutron-deficient Hg region is investigated within the covariant density functional framework. We study in detail the chain of even–even mercury isotopes [Formula: see text]Hg using the relativistic point coupling model. The low-energy excitation spectrum and the B(E2) transitions rates of even–even nuclei are obtained as solutions of a five-dimensional collective Hamiltonian (5DCH) model, with parameters determined by constrained self-consistent mean-field calculations based on the relativistic energy density functional DD-PC1, and a finite-range pairing interaction. The calculations suggest a very interesting structure evolution with coexisting configurations for [Formula: see text]Hg, increased collectivity for the isotopes [Formula: see text]Hg and a more spherical structure for [Formula: see text]Hg.

Cranking covariant density functional theory with a shell-model-like approach for the superdeformed band of 42Ca

The superdeformed rotational band in [Formula: see text]Ca is studied with the cranking covariant density functional theory complemented by a shell-model-like approach for treating the pairing correlations. The microscopic and self-consistent description of the superdeformed rotational band is obtained. The calculated energy surfaces show local minimums at [Formula: see text] from rotational frequency [Formula: see text] [Formula: see text] to [Formula: see text][Formula: see text]MeV. The shape coexistence of spherical, normal deformation and superdeformation is found at [Formula: see text][Formula: see text]MeV. The single-particle levels and configurations are analyzed in details with the deformation. The configuration of the superdeformed band is figured out as [Formula: see text]. The single-particle Routhians indicate that the neutrons configuration plays a key role in the formation of the superdeformed band, and the change of the protons configuration at [Formula: see text][Formula: see text]MeV terminates the superdeformed band. The importance of pairing correlation to the superdeformed band is also studied in terms of the moments of inertia and the angular momentum.

Relativistic density functional theory in nuclear physics

Over the past decades, the relativistic density functional theory has been greatly developed and widely applied to investigate a variety of nuclear phenomena. In this paper, we briefly review the concept of covariant density functional theory in nuclear physics with a few latest applications in describing nuclear ground-state and excitation properties as well as nuclear dynamics. Moreover, attempts to build a microscopic and universal density functional are also discussed in terms of the successful fully self-consistent relativistic Brueckner–Hartree–Fock calculations.

Structure of 190-200Hg within the covariant density functional theory

We study in detail the chain of even - even mercury isotopes 190-200Hg using the relativistic point coupling model. A five-dimensional collective Hamiltonian (5DCH) model, with parameters determined by constrained self-consistent mean-field (SCMF) calculations based on the relativistic density-dependent pointcoupling (DD-PC1) energy density functional, and a finite-range pairing interaction is used to calculate the low-energy excitation spectrum and the B(E2) transitions rates of even-even nuclei. The calculations suggest coexisting configurations in 190Hg, increased collectivity in the isotopes 192-198Hg and a more spherical structure in 200Hg.

Relativistic Brueckner-Hartree-Fock Theory in Infinite Nuclear Matter

On the way of a microscopic derivation of covariant density functionals, the first complete solution of the relativistic Brueckner-Hartree-Fock (RBHF) equations is presented for symmetric nuclear matter. In most of the earlier investigations, the G-matrix is calculated only in the space of positive energy solutions. On the other side, for the solution of the relativistic Hartree-Fock (RHF) equations, also the elements of this matrix connecting positive and negative energy solutions are required. So far, in the literature, these matrix elements are derived in various approximations. We discuss solutions of the Thompson equation for the full Dirac space and compare the resulting equation of state with those of earlier attempts in this direction.