International Journal of Modern Physics D

The interaction of massless minimally coupled scalar field and spinor field $(\mathrm{\Psi }+{\mathrm{\Phi }}_m\to \mathrm{\Psi }+{\mathrm{\Phi }}_m)$ is investigated and the behavior of interaction and scattering matrix in Minkowski limit is studied. It is seen that the massless minimally coupled scalar field operator, the interaction Lagrangian and the scattering matrix become zero. Also, the incoming and outgoing spinor fields, which in de Sitter spacetime are different and are interacted with massless minimally coupled scalar field, in null curvature limit are the same and no interaction seen. In other words, the massless minimally coupled scalar field is dependent on curvature and can be considered as a part of a gravitational field.

The detection of an unexpected $\sim 2.5M_{\odot }$ component in the gravitational wave event GW190814 has puzzled the community of high-energy astrophysicists, since in the absence of further information it is not clear whether this is the heaviest “neutron star” ever detected or either the lightest black hole known, of a kind absent in the local neighborhood. We show in this work a few possibilities for a model of the former, in the framework of three different quark matter models with and without anisotropy in the interior pressure. As representatives of classes of “exotic” solutions, we show that even though the stellar sequences may reach this ballpark, it is difficult to fulfill simultaneously the constraint of the radius as measured by the NICER team for the pulsar PSR J0030+0451. Thus, and assuming both measurements stand, compact neutron stars cannot be all made of self-bound quark matter, even within anisotropic solutions which boost the maximum mass well above the $\sim 2.5M_{\odot }$ figure. We also point out that a very massive compact star will limit the absolute maximum matter density in the present universe to be less than 6 times the nuclear saturation value.

This work is the continuation of the investigation of aspects of wave turbulence in preheating we started in [J. A. Crespo and H. P. de Oliveira, J. Cosmol. Astropart. Phys. 12 (2019) 045; (2014) 006] but considering several classes of inflationary two-field models. We exhibit the main elements of the wave turbulence phase imprinted in the power spectra of relevant quantities in the time and space domains. As a general feature, the power spectra resemble in their structure to those obtained using the single nonminimally coupled scalar field of the previous work. As a consequence, we obtained an estimate of the temperature corresponding to the thermalized phase from the power spectrum of the total energy density. Another feature allowed by the simulations was the determination of the effective equation of state after taking into account the backreaction of the produced particles.

We consider a model of exponential electrodynamics as a source of gravitational field and worked for the solution describing magnetic black hole surrounded by a quintessence and cloud of strings. In this set up, a new family of Lovelock black hole solutions of the gravitational field equations are constructed. The thermodynamics of these black holes is also studied and the mass as well as the other associated thermodynamic quantities such as Hawking temperature and heat capacity in terms of horizon radius are computed. These quantities are dependent on the parameters of exponential electrodynamics, cloud of strings and quintessential dark energy, which have been used for the identification of the regions corresponding to thermal phase transitions and thermodynamic stability of black holes. Furthermore, the effects of thermal fluctuations are also discussed and modified thermodynamic quantities associated to logarithmic correction in entropy are calculated. The Hawking radiations corresponding to these black holes are briefly discussed as well.

The motion and acceleration of an electrically charged and magnetized particle around a cylindrical black hole in the presence of an external asymptotically uniform magnetic field parallel to the $z$-axis are investigated. We look at circular orbits around a central object and study the dependence of the most internal stable circular orbits (ISCO) on the so-called magnetic coupling parameters, which are responsible for the interaction between the external magnetic field and magnetized and charged particles. It is shown that the ISCO radius decreases with increasing magnetized interaction parameter. Therefore, we also studied collisions of magnetized particles around a cylindrical black hole immersed in an external magnetic field, and showed that the magnetic field can act as a particle accelerator near nonrotating cylindrical black holes.

We determine the scalar field evolution of a braneworld localized black hole with both dark matter and dark energy components, obtained within a dynamical and continuous embedding formalism by use of Nash’s theorem. We further extract the associated quasinormal modes for both de Sitter–Schwarzschild-Dark matter and anti-de Sitter–Schwarzschild-Dark matter solutions, for the different causal structures (one, two or three horizon spacetimes) given by the space of parameters. By comparison with standard solutions within stand alone general relativity, we conclude with comments on possible observable astrophysical differences via quasinormal spectra, and remark on the interpretations of previous AdS/CFT correspondence scenarios.

In this work, we propose a new dark energy (DE) model by applying the Barrow entropy and the holographic principle, with a time scale as IR cut-off. Analyzing the conformal time as well as universe’s age as infrared cut-offs, we explore the cosmological importance of the suggested DE models and examine the universe evolution filled with the proposed DE applicants and a pressure-less matter. We observe that the equation of state, deceleration, the density parameters can present adequate nature, and these models may also explain the late-time acceleration though the proposed models are unstable except for some values of Barrow exponent $\mathrm{\Delta }$. Furthermore, we mention the consequences of the presence of interaction among the universe sectors.

In this paper, we study the gravitational collapse of a spherical symmetric star constituted of matter interacting with vacuum energy density $\mathrm{\Lambda }$ in the background of spacetime curvature. We consider the gravitational collapse for closed, flat, and hyperbolic spacetime geometry $(k=1,0,-1)$. We take the process of gravitational collapse for an anisotropic fluid interacting with a growing vacuum energy density by taking a complete physically general-relativistic approach in the background of spacetime curvature. Here, we achieved analytic solutions with some assumptions of physical significance. We executed and interpreted the solutions for several cases of the equation of state parameters, $(l,\omega )$. In all physical cases, we investigate the formation of a black hole and the naked singularity.