International Journal of Modern Physics D

Understanding how massive stars die as supernovae (SNe) is a crucial question in modern astrophysics. SNe are powerful stellar explosions and key drivers in the cosmic baryonic cycles by injecting their explosion energy and heavy elements to the interstellar medium that forms new stars. After decades of effort, astrophysicists have built up a stand model for the explosion mechanism of massive stars. However, this model is challenged by new kinds of stellar explosions discovered in the recent transit surveys. In particular, the new population called superluminous SNe, which are a hundred times brighter than typical SNe, is revolutionizing our understanding of SNe. New studies suggest the superluminous SNe are associated with the unusual demise of very massive stars and their extreme SNe powered by the radioactive isotopes or compact objects formed after the explosion. Studying these SNe fills a gap of knowledge between the death of massive stars and their explosions; furthermore, we may apply their intense luminosity to light up the distant universe. This paper aims to provide a timely review of superluminous SNe physics, focusing on the latest development of their theoretical models.

The general potential of power-law inflation is as $V(\varphi )\propto {\varphi }^n$ with scalar field $\varphi$. The behavior of inflation is often known as power-law expansion like $S(\eta )\propto {\eta }^{1+\beta }$ with $1+\beta <0$. In this paper, the theoretical spectra of relic gravitational waves are compared with the measured strain sensitivity of Advanced LIGO and VIRGO, corresponding to the latest detected events of gravitational waves. The results show tight constraints on $\beta$ and $n$. Also, the obtained constraints indicate that special types of the potential of inflation, prototype, and KKLTI models, which are originated from string theory, may be good candidates for potential of inflation. Also these results may emphasize the evidence of stochastic GWs that originated from inflation based on 12:5-year pulsar timing data set of North American Nanohertz Observatory for GWs.

We extend Verlinde gravity formalism to nonspherically symmetric case and apply it to calculate the gravitational acceleration near, but above the surface of Earth. We predict the violation of equivalence principle, and obtain $\eta =3.4\times 10^{-12}$ for gold and aluminum, which agrees with $\eta (\mathrm{\text{Au, Al}})=(1.3\pm 1.0)\times 10^{-11}$ obtained by an experiment conducted in 1964. We also obtained $\eta =-1.2\times 10^{-13}$ for beryllium and titanium, which agrees with $\eta (\mathrm{\text{Be, Ti}})=(0.3\pm 1.8)\times 10^{-13}$ obtained by an experiment conducted in 2007. Finally, we suggest that this experiment in 2007 be repeated with beryllium or titanium replaced by silver or gold, which would make $\eta$ enough big to confirm the violation of the equivalence principle.

Within the framework of a derivable construction of QED, a formulation of nonlinear axion-electrodynamics is investigated. This approach is intended to predict possible strong-QED processes with a discussion of the role of axion-like particles that might be significant in nonlinear electrodynamics (NLED). We introduce a nonlinear model of axion-electrodynamics with remaining questions to be further explored.

We study the shadows of four-dimensional black holes in M-theory inspired models. We first inspect the influence of M2-branes on such optical aspects for nonrotating solutions. In particular, we show that the M2-brane number can control the circular shadow size. This geometrical behavior is distorted for rotating solutions exhibiting cardioid shapes in certain moduli space regions. Implementing a rotation parameter, we analyze the geometrical shadow deformations. Among others, we recover the circular behaviors for a large M2-brane number. Investigating the energy emission rate at high energies, we find, in a well-defined approximation, that the associated peak decreases with the M2-brane number. Moreover, we investigate a possible connection with observations (from Event Horizon Telescope or future devices) from a particular M-theory compactification by deriving certain constraints on the M$2$-brane number in the light of the $M87^{\star }$ observational parameters.

In this work, the evolution of spherically symmetric charged anisotropic viscous fluids is discussed in framework of $f(R,T)$ gravity. In order to conduct the analysis, modified Einstein Maxwell field equations are constructed. Nonzero divergence of modified energy momentum tensor is taken that implicates dynamical equations. The perturbation scheme is applied to dynamical equations for stability analysis. The stability analysis is carried out in Newtonian and post-Newtonian limits. It is observed that charge, fluid distribution, electromagnetic field, viscosity and mass of the celestial objects greatly affect the collapsing process as well as stability of stars.

In this work, we obtain the black hole solutions in the dilaton $f(R)$-gravity (R is not considered as a constant here) and investigate their thermodynamics especially phase transition and critical behavior in the anti-de Sitter (AdS) extended phase-space. We obtain the exact Banados, Teitelboim and Zanelli (BTZ) counterpart solutions in dilaton $f(R)$-gravity which is the basis of our work. We also obtain the exact form of $f(R)$ model for some solutions. In the thermodynamical analysis, we calculate the thermodynamical quantities like the temperature and entropy for these solutions and we compare them with the BTZ corresponding quantities. After that, we investigate the stability (local and global) for these obtained solutions. In the critical behavior analysis, we find that there is no evidence to show the existence of P–V criticality (like the ordinary BTZ case) in this modified gravity model except some unusual P–V behavior in the corresponding diagrams.

We have computed the properties of compact objects like neutron stars based on equation of state (EOS) deduced from a core–envelope model of superdense stars. Such superdense stars have been studied by solving Einstein’s equation based on pseudo-spheroidal and spherically symmetric spacetime geometry. The computed star properties are compared with those obtained based on nuclear matter EOSs. From the mass–radius ($M$–$R$) relationship obtained here, we are able to classify compact stars in three categories: (i) highly compact self-bound stars that represents exotic matter compositions with radius lying below 9km; (ii) normal neutron stars with radius between 9 to 12km and (iii) soft matter neutron stars having radius lying between 12 to 20km. Other properties such as Keplerian frequency, surface gravity and surface gravitational redshift are also computed for all the three types. This work would be useful for the study of highly compact neutron like stars having exotic matter compositions.

In a recent publication, a procedure was developed which can be used to derive completely gauge invariant models from general Lagrangian densities with $N$ order of derivatives and $M$ rank of tensor potential. This procedure was then used to show that unique models follow for each order, namely classical electrodynamics for $N=M=1$ and linearized Gauss–Bonnet gravity for $N=M=2$. In this paper, the nature of the connection between these two well-explored physical models is further investigated by means of an additional common property; a complete dual formulation. First, we give a review of Gauss–Bonnet gravity and the dual formulation of classical electrodynamics. The dual formulation of linearized Gauss–Bonnet gravity is then developed. It is shown that the dual formulation of linearized Gauss–Bonnet gravity is analogous to the homogenous half of Maxwell’s theory; both have equations of motion corresponding to the (second) Bianchi identity, built from the dual form of their respective field strength tensors. In order to have a dually symmetric counterpart analogous to the nonhomogenous half of Maxwell’s theory, the first invariant derived from the procedure in $N=M=2$ can be introduced. The complete gauge invariance of a model with respect to Noether’s first theorem, and not just the equation of motion, is a necessary condition for this dual formulation. We show that this result can be generalized to the higher spin gauge theories, where the spin-$n$ curvature tensors for all $N=M=n$ are the field strength tensors for each $n$. These completely gauge invariant models correspond to the Maxwell-like higher spin gauge theories whose equations of motion have been well explored in the literature.