Modern Physics Letters A

We review the origins, motivations, and implications for cosmology and black holes, of our proposal that “dark energy” is not a quantum vacuum energy, but rather arises from a Weyl scaling invariant nonderivative component of the gravitational action.

The main aim of this work is to give a suitable explanation of present accelerating universe through an acceptable interactive dynamical cosmological model. A three-fluid cosmological model is introduced in the background of Friedmann–Lemaître–Robertson-Walker asymptotically flat spacetime. This model consists of interactive dark matter and dark energy with baryonic matter, taken as perfect fluid, satisfying barotropic equation of state. We consider dust as the candidate of dark matter. A scalar field $\varphi$ represents dark energy with potential $V(\varphi )$. Einstein’s field equations are utilized to construct a three-dimensional interactive autonomous system by choosing suitable interaction between dark energy and dark matter. We take the interaction kernel as $Q=3{\beta }^{2}H{\rho }_d$, where ${\rho }_d$ indicates the density of dark energy, $\beta$ is the interacting constant and $H$ is Hubble parameter. In order to explain the stability of this system, we obtain some suitable critical points. We analyze stability of obtained critical points to show the different phases of universe and cosmological implications. Surprisingly, we find some stable critical points which represent late-time dark energy-dominated era when a model parameter $\alpha$ is equal to $-5.05$. We introduce a two-dimensional interactive autonomous system and after phase portrait analysis of it, we get several stable points which represent dark energy-dominated era and late-time cosmic acceleration simultaneously. Here, we also demonstrate the variation in interaction at vicinity of phantom barrier $({\omega }_{\mathrm{\text{eff}}}=-1)$. From our work, we can also predict the future phase evolution of the universe.

In this paper, a new model using a general expression of the radiation energy and explaining the dynamics of the afterglows is proposed. It is shown that this model is suitable for the ultra-relativistic and non-relativistic phases as well as the study of radiative and adiabatic fireballs.

In this work, we analyze the Joule–Thomson expansion in an AdS Reissner–Nordström black hole, surrounded by an average cosmological fluid, in Rainbow Gravity. We plot the graphs corresponding to the inversion temperature curves and numerically calculate the ratio between the minimum of the inversion temperature and the critical temperature, with the aim of investigating how Rainbow Gravity alters such behaviors compared to General Relativity.

In this work, we study static spherically symmetric solutions representing wormhole configurations in Poincarè gauge theory (PGT). The gravitational sector of the Lagrangian is chosen as a subclass of PGT Lagrangians for which the spin-$0^{+}$ is the only propagating torsion mode. The spacetime torsion in PGT has a dynamical nature even in the absence of intrinsic angular momentum (spin) of matter, hence torsion can play a principal role in the case of usual spin-less gravitating systems. We therefore consider a spin-less matter distribution with an anisotropic energy–momentum tensor (EMT) as the supporting source for wormhole structure to obtain a class of zero tidal force wormhole solutions. It is seen that the matter distribution obeys the physical reasonability conditions, i.e. the weak (WEC) and null (NEC) energy conditions either at the throat and throughout the spacetime. We further consider varying equations of state in radial and tangential directions via definitions $w_r(r)=p_r(r)/\rho (r)$ and $w_t(r)=p_t(r)/\rho (r)$ and investigate the behavior of state parameters at the throat of wormhole. We observe that our solutions allow for wormhole configurations without the need of exotic matter. Observational features of the wormhole solutions are also discussed utilizing gravitational lensing effects. It is found that the light deflection angle diverges at the throat (which indeed, effectively acts as a photon sphere) and can get zero and negative values depending on the model parameters.

In classical mechanics, in the case of gravitational and electromagnetic interactions, the force on a particle is usually proportional to its acceleration: The force acts locally on the particle. However, there are situations possible-if the particle moves through a suitable medium, for example, in which the force depends also on the first-time derivative of its acceleration, the jerk, and on its second-time derivative, the snap, and possibly also on higher-time derivatives. Such forces are called nonlocal, and this work investigates such nonlocal forces, mainly those depending on the jerk. In particular, we implement jerk and acceleration in geodesics by means of the nonlocal-in-time kinetic energy approach to spacetime physics. We describe a framework that can be used to estimate the quantum nonlocal time parameter by studying the deflection of light around the Sun. Comparing our results with long baseline interferometry (VLBI) observations, we concluded that the nonlocal time parameter $\tau <1.415\times 10^{-10}$ s.

In this study, we investigate the Pauli oscillator in a noncommutative space. In other words, we derive wave function and energy spectrum of a spin half non-relativistic charged particle that is moving under a constant magnetic field with an oscillator potential in noncommutative space. We obtain critical values of the deformation parameter and the magnetic field, which they counteract the normal and anomalous Zeeman effects. Moreover, we find that the deformation parameter has to be smaller than $2.57\times 10^{-26}{\mathrm{\text{m}}}^2$. Then, we derive the Helmholtz free energy, internal energy, specific heat and entropy functions of the Pauli oscillator in the non commutative space. With graphical methods, at first, we compare these functions with the ordinary ones, and then, we demonstrate the effects of magnetic field on these thermodynamic functions in the commutative and noncommutative space, respectively.