arXiv subjects

Ramin Hassannejad

Publications and source records attributed to Ramin Hassannejad.

5 recordsLinked to original sources

arXiv2026

Gravitational Landscapes: black holes with linear equations of state in asymptotically safe gravity

We study black holes with linear equation of state within the framework of asymptotically safe gravity. This study extends previous work on gravitational collapse in asymptotically safe gravity (that has been done for a dust fluid) by considering into account the pressure of stellar matter. We derive modified field equations containing the running gravitational coupling and the cosmological constant as functions of energy density. The interior space-time of collapsing star is modeled by the Friedmann-Lemaître-Robertson-Walker metric, while the exterior is described by a static spherically symmetric space-time. Different equations of state from ordinary matter to exotic phantom energy are considered to investigate their impact on black hole structure and horizon formation. Our results illustrate that asymptotically safe gravity can introduce non-singular black hole solutions under specific conditions. These results provide new insights into black hole physics and the avoidance of singularities within the asymptotically safe gravity framework.

gr-qc↗

arXiv2025

Mori-Zwanzig formalism for early cosmic inflation

The existence of fluctuations at the early stage of the universe provides enough confidence to rely on averaging methods. However, the nonlinearity of general relativity makes this process extremely difficult. Several methods have been proposed to study inhomogeneous cosmology and address the averaging problem, such as Buchert's spatial averaging. In this work, early cosmic inflation is investigated using the Buchert equations and the Mori-Zwanzig projection operator formalism. The coarse-grained description derived from these approaches acts as a geometrical source of early cosmic inflation through higher-order differential equations. The theoretical results, while not an exact match, exhibit close agreement with observational data, demonstrating the robustness of the model and its potential for further cosmological applications.

gr-qc↗

arXiv2025

Gravitational Collapse in Scale-Dependent Gravity

In this paper we study an Oppenheimer-Snyder (OS)-like gravitational collapse in the general framework of scale-dependent gravity. We explore the collapse in spherically symmetric solutions suggested both by asymptotically safe gravity (characterized by a positive $\om$-parameter) and by scale-dependent gravity (negative $\om$-parameter), when a singularity at a finite positive radial coordinate is developed. The inner geometry of the collapsing star is described, as usual, by a spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) metric, and matter is uniformly distributed without any assumptions about its equation of state. The outer asymptotically-safe/scale-dependent black hole metric is smoothly matched to the inner geometry, and this yields the equation of motion of the star surface, the energy density, pressure, and equation of state of the collapsing matter. We study in detail the proper-time evolution of the event and apparent horizons. Finally, the constraints of the energy conditions on the equation of state, and its properties, are considered and discussed.

gr-qc↗

arXiv2020

Deriving Einstein's Field Equation(EFE) and Modified Gravity by Statistical Mechanics and Quantization of Non-Commuting Space

In this paper, we derive the Einstein's field equation (EFE) by considering an non-commuting two dimensional quantized space, which can be excited by absorbing energy. Any variation of the energy level of space quantas, will result in a change in the quanta's area state. This means, that the geometry of space depends on the energy which exists in it. Using Holographic principle and Unruh effect, without any further assumptions like equipartition theorem, our model leads to Newton's law of gravity in the limit $\hbar \to 0$.

gr-qc↗

arXiv2019

Repulsive gravity regime in the early Universe as a consequence of quantized space

In this paper, we showed that gravity might have been repulsive in the first moments of the Universe! To find this, we used quantization of the anti-commuting space and derived a gravitational equation in the limit $T \gg T_p$, which shows interesting behaviors. We saw that gravity is repulsive in the distances less than $\mathcal{R} = 4.37 \times 10^{-32} \times \sqrt{M}$, where $M$ is the mass of the object which gives rise to the gravitational field. Also, we calculated an acceleration of the order $\simeq - 3.494 \times 10^{52}$ for the first moment of the Universe ($r = 0$), where the temperature is $T \gg T_p$. Our results can explain the inflation in the first stages of the Universe and do not have any singularity at $r = 0$.

gr-qc↗