abstract

This study explores the elastic scattering of charged hadronic system through a new approximation scheme for the effective potential. The Phase Function Method (PFM) is employed to examine the scattering phase shifts in the \(p\)–He\(^{3}\) system, where a modified Kratzer potential is enhanced by electromagnetic interactions and spin–orbit coupling. A six-parameter potential model is developed and optimized to match the calculated scattering phase shifts, differential cross-sections, and proton analyzing power curves with experimental data for the \(p\)–He\(^{3}\) system. The results show strong consistency with experimental measurements and previous theoretical predictions, affirming the accuracy and utility of the proposed method in analyzing scattering phenomena within this system.

abstract

The evolution equation of the Szekeres metrics allows for solutions with the mass function \(M \lt 0\). They exist in both classes of the Szekeres metrics, have no Big Bang singularity and no origin. In both classes, the conditions for no shell crossings ensure that the mass density \(\rho \) of the dust source in the Einstein equations is negative at all times. Thus, these metrics do not qualify as cosmological models. In the Friedmann limit, the implication \(M \lt 0 \Longrightarrow \rho \lt 0\) is immediate. In the general Szekeres metrics, it follows by tuning conclusions from different equations.

abstract

A nonlinear Lorentz-invariant kinetic diffusion equation is introduced, which is consistent with the conservation laws of particles number, energy, and momentum. The equilibrium solution converges to the Maxwellian density in the Newtonian limit, but it is not given by the Jüttner distribution commonly employed in relativistic kinetic theory. The nonlinear kinetic diffusion equation on a general Lorentzian manifold is consistent with the contracted Bianchi identities and therefore can be coupled to the Einstein equations of general relativity.

abstract

We analyze the effect of using the Fermi–Dirac statistics, rather than its Boltzmann approximation, in numerical simulations of perfect spin hydrodynamics of particles with spin \(1/2\). The system considered is boost invariant, transversely homogeneous, with corrections to the baryon current and the energy–momentum tensor that are second order in the spin polarization tensor ω, and the spin tensor considered is first order in ω. The study shows the feasibility of this approach, as the special functions defined by integrals that appear in the coefficients in the Fermi–Dirac case can be conveniently parametrized. For sets of initial conditions used in previous works, the differences in parameter evolution between the two underlying particle statistics are about one order of magnitude smaller than corrections coming from spin feedback. We also discuss when and why the numerical solutions of the equations of perfect spin hydrodynamics break down for very large values of spin polarization in one of the geometric configurations considered.

abstract

We investigate the properties of exotic Strange Quark Matter (SQM) with spin polarization and the complex configuration of Strange Quark Stars (SQSs) using a phenomenological MIT Bag Model, enhanced by incorporating a QCD-informed running strange-quark mass dependent on the chemical potential. The effective mass using quasiparticle approach is utilized to understand the framework of SQM. The resulting Equation of State (EoS) is constructed for two distinct parameter sets, yielding an energy per baryon below the iron limit for stable configurations and thus supporting the Bodmer–Witten–Terazawa hypothesis that SQM could be the actual ground state of exotic matter. This framework is then used to address the Tolman–Oppenheimer–Volkoff (TOV) equations to study the effect of spin polarization on stellar properties. The model predicts that the maximum stellar mass increases with the degree of spin polarization, a result that diverges from previous constant-mass models. Furthermore, the model’s predictions for mass, radius, and surface redshift are in excellent agreement with observational constraints for the compact object Vela X-1. This agreement validates our theoretical approach and strengthens the candidacy of Vela X-1 as a Strange Quark Star. Overall, the model results highlight the importance of in-medium QCD effects in describing dense matter.