Modern Physics Letters A

We analyze the universe as a thermodynamic system, homogeneously filled up by exotic matters popularly named as dark energies. Different dark energy models are chosen. We start with the equation of continuity and derive the time and scale factor relations for different EoSs of different dark energy models. To do the time-scale factor relation analysis, nature of dependences on different dark energy modeling parameters have been studied. For this, the help of different plots are used. In general, different dark energies show different properties while occurrences of future singularities are considered. Those properties can be supported by the graphical analysis of their cosmic time-scale factor studies.

Methods of Hamiltonian dynamics are applied to study the geodesic flow on the resolved conifolds (rcs) over Sasaki–Einstein space $T^{1,1}$. We construct explicitly the constants of motion and prove complete integrability of geodesics in the five-dimensional Sasaki–Einstein space $T^{1,1}$ and its Calabi–Yau metric cone. The singularity at the apex of the metric cone can be smoothed out in two different ways. Using the small resolution, the geodesic motion on the rc remains completely integrable. Instead, in the case of the deformation of the conifold, the complete integrability is lost.

Recently, some authors showed that a classical collapse scenario ignores this richness of information in the resulting spectrum and a consistent quantum treatment of the entire collapse process might allow us to retrieve much more information from the spectrum of the final radiation. We confirm these results and show that by considering the quantum entanglement between metrics, we can uncover information of black holes. In our model, a density matrix is defined for the spaces, both inside and outside of the event horizon. These inside and outside spaces of black holes are obtained by tracing from a bigger space. An observer that lives in this big space can recover total information regarding the inside and outside of black hole.

This paper studies the gravitational collapse of charged anisotropic spherical stellar objects in $f({𝒢})$ gravity. For this purpose, we derive dynamical equations by considering Misner–Sharp mechanism and explore physical impact of charge, anisotropy and effective pressure on the rate of collapse. We establish the relationship between matter variables, Weyl tensor and the Gauss–Bonnet (GB) terms. For constant value of $f({𝒢})$, it turns out that conformal flatness condition is no longer valid due to the effect of anisotropic factor in the present scenario. To obtain conformally flat metric, we impose the condition of isotropic matter distribution which provides energy density homogeneity and conformal flatness of the metric. We conclude that GB terms lead to decrease in the collapse rate due to their anti-gravitational effects.

Solar System tests of a brane world, which is called DMPR model, were studied in recent works. The correction of DMPR model to the general relativity (GR) in the four-dimensional curved spacetime can be parametrized by a “tidal charge” parameter $Q$. The parameter $Q$ in this model was obtained and improved as $\left|Q\right|\lesssim 6.7{\mathrm{\text{m}}}^2$ by the Earth–Mercury ranging. A new test of the DMPR model based on gravitational time advancement is proposed and investigated in this work. The advancement is a gravitational consequence on round-trip proper time duration of a photon. For ranging a distant spacecraft, it is shown that (1) the “tidal charge” parameter can make the advancement larger or smaller than the one of GR, depending on the sign of $Q$; (2) the superior conjunction (SC) and the inferior conjunction (IC) are all suitable for detecting the advancement; (3) the advancement can be complementary to the classical test of Shapiro time delay for detecting the brane world; and (4) the implementation of optical clocks and planetary laser ranging will provide more insights on the brane world model in the future.