Effects of neutron-rich nuclei masses on symmetry energy

We explore the impact of neutron-rich nuclei masses on the symmetry energy properties using the mass table evaluated by the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) model. First, using the semi-empirical mass formula with the DRHBc mass table, we investigate the symmetry energy at saturation density $\rho_0$, denoted as $S_0$, and the ratio of surface to volume contributions to the symmetry energy, $\kappa$. As a result, we obtain $S_0=27.85\,{\rm MeV}$ ($\kappa=1.38$) for $a_{\rm sym}(A) =S_0 (1 - \kappa A^{-1/3})$ (Type I) and $S_0=32.66\,{\rm MeV}$ ($\kappa=3.15$) for $a_{\rm sym}(A) = S_0 (1 + \kappa A^{-1/3} )^{-1}$ (Type II), which are lower than those obtained using the AME2020 mass table, $S_0=28.54\,{\rm MeV}$ ($\kappa=1.29$) for Type I and $S_0=33.81\,{\rm MeV}$ ($\kappa=3.04$) for Type II. Second, we further investigate the effect of these changes in $a_{\rm sym}(A)$ on the density-dependent symmetry energy by employing the empirical model of $S(\rho) = C_k(\rho/\rho_0)^{2/3} + C_1(\rho/\rho_0) + C_2(\rho/\rho_0)^{\gamma}$ and universal relation of $a_{\rm sym}(A=208) = S(\rho=0.1\,{\rm fm}^{-3})$. Compared to the experimental constraints, we find that $S_0$ and slope parameter $L$, determined by the DRHBc mass table with Type II, are more suitable to explain the constraints by heavy ion collisions and isobaric analog states than AME2020. We also discuss the neutron skin thickness derived from the $L$, comparing it with experimental measurements

An exact solution of the higher-order gravity in standard radiation-dominated era

We report that the standard evolution of radiation-dominated era (RDE) universe $a \propto t^{1/2}$ is a sufficient condition for solving a sixth order gravitational field equation derived from the Lagrangian containing $B R^{ab}R_{ab} + C R {R^{;c}}_{c}$ as well as a polynomial $f(R)$ for a spatially flat radiation FLRW universe. By virtue of the similarity between $R^{ab}R_{ab}$ and $R^2$ models up to the background order and of the vanishing property of ${R^{;c}}_{c}$ for $H = 1/(2t)$, the analytical solution can be obtained from a special case to general one. This proves that the standard cosmic evolution is valid even within modified gravitational theory involving higher-order terms. An application of this background solution to the tensor-type perturbation reduces the complicated equation to the standard second order equation of gravitational wave. We discuss the possible ways to discriminate the modified gravity model on the observations such as the gravitational wave from the disturbed universe and primordial abundances

Effects of electromagnetic fluctuations in plasmas on solar neutrino fluxes

We explore the effects of electromagnetic (EM) fluctuations in plasmas on solar neutrino fluxes exploiting the fluctuation-dissipation theorem. We find that the EM spectrum in the solar core is enhanced by the EM fluctuations due to the high density of the Sun, which increases the radiation energy density and pressure. By the EM fluctuations involving the modified radiation formula, the central temperature decreases when the central pressure of the Sun is fixed. With a help of the empirical relation between central temperature and neutrino fluxes deduced from the numerical solar models, we present the change in each of the solar neutrino fluxes by the EM fluctuations. We also discuss the enhanced radiation pressure and energy density by the EM fluctuations for other astronomical objects

Comprehensive Analyses of the Neutrino-Process in the Core-collapsing Supernova

We investigate the neutrino flavor change effects due to neutrino self-interaction, shock wave propagation as well as matter effect on the neutrino process of the core-collapsing supernova. For the hydrodynamics, we use two models: a simple thermal bomb model and a specified hydrodynamic model for SN1987A. As a pre-supernova model, we take an updated model adjusted to explain the SN1987A employing recent development of the $(n,\gamma)$ reaction rates for nuclei near the stability line $(A \sim 100)$. As for the neutrino luminosity, we adopt two different models: equivalent neutrino luminosity and non-equivalent luminosity models. The latter is taken from the synthetic analyses of the CCSN simulation data which involved quantitatively the results obtained by various neutrino transport models. Relevant neutrino-induced reaction rates are calculated by a shell model for light nuclei and a quasi-particle random phase approximation model for heavy nuclei. For each model, we present abundances of the light nuclei ($^7$Li, $^7$Be, $^{11}$B and $^{11}$C) and heavy nuclei ($^{92}$Nb, $^{98}$Tc, $^{138}$La and $^{180}$Ta) produced by the neutrino-process. The light nuclei abundances turn out to be sensitive to the Mikheyev-Smirnov-Wolfenstein region around ONeMg region while the heavy nuclei are mainly produced prior to the MSW region. Through the detailed analyses of the numerical abundances, we find that neutrino self-interaction becomes a key ingredient in addition to the MSW effect for understanding the neutrino process and the relevant nuclear abundances. However, the whole results are shown to depend on the adopted neutrino luminosity scheme. Detailed evaluations of the nuclear abundances for the two possible neutrino mass hierarchies are performed with the comparison to the available meteorite analyses data. The normal mass hierarchy is shown to be more compatible with the meteoritic data

Oscillating cosmic evolution and constraints on big bang nucleosynthesis in the extended Starobinsky model

We investigate the cosmic evolutions in the extended Starobinsky model (eSM) obtained by adding one RabRab term to the Starobinsky model. We discuss the possibility of various cosmic evolutions with a special focus on the radiation-dominated era (RDE). Using simple assumptions, a second-order non-linear differential equation describing the various cosmic evolutions in the eSM is introduced. By solving this non-linear equation numerically, we show that the various cosmic evolutions, such as the standard cosmic evolution (a ∝ t 1/2) and a unique oscillating cosmic evolution, are feasible due to the effects of higher-order terms introduced beyond Einstein's gravity. Furthermore, we consider big bang nucleosynthesis (BBN), which is the most important observational result in the RDE, to constrain the free parameters of the eSM. The primordial abundances of the light elements, such as 4He, D, 3He, 7Li, and 6Li by the cosmic evolutions are compared with the most recent observational data. It turns out that most non-standard cosmic evolutions can not easily satisfy these BBN constraints, but a free parameter of the viable models with the oscillating cosmic evolution is shown to have an upper limit by the constraints. In particular, we find that the free parameter is most sensitive to deuterium and 4He abundances, which are being precisely measured among other elements. Therefore, more accurate measurements in the near future may enable us to distinguish the eSM from the standard model as well as other models. © 2023 IOP Publishing Ltd and Sissa Medialab.11Nsciescopu

Reinvestigating the Gamow Factor of Reactions on Light Nuclei

We present a modified Gamow factor by reinvestigating the conventional assumptions used in its derivation. The conventional Gamow factor, factorized from the total cross section, effectively describes the penetration probabilities (PPs) in low-energy nuclear reactions under the assumption of particle energies significantly lower than the Coulomb barrier. However, we find that the assumption is invalid for light nuclei, resulting in PPs that depend on the nuclear potential depth for such nuclei. By adopting a potential depth fitted to experimental fusion cross sections, we demonstrate that PPs for light nuclei (D+D, D+T, D+ ^3 He, p+D, p+ ^6 Li, and p+ ^7 Li) become higher than those predicted by the conventional form near the Coulomb barrier. This reduces the Gamow peak energy by a factor of 5.3 maximally compared to the conventional form. Furthermore, we show that the enhancement factor due to the Debye screening effects in the solar core can be reduced by approximately 5%–10% due to the modified PP. Our findings hold implications for evaluating the available energy region in low-energy reaction experiments based on the Gamow peak energy region and for understanding electron screening effects in typical astrophysical environments

Dynamical Screening Effects on Big Bang Nucleosynthesis

A moving ion in plasma creates a deformed electric potential depending on the ion velocity, which leads to the distinct screening effect compared to the standard static Salpeter formula. In this paper, adopting the test charge method, we explore the dynamical screening effects on big bang nucleosynthesis (BBN). We find that the high temperature in the early universe causes the ion velocity to be faster than the solar condition so that the electric potential is effectively polarized. However, the low density of background plasma components significantly suppresses the dynamical screening effects on thermonuclear reaction rates during the BBN epoch. We compare our results with several thermonuclear reaction rates for solar fusion considering the dynamical screening effects. Also, we discuss the additional plasma properties in other astrophysical sites for the possible expansion from the present calculation in the future