arXiv subjects

Raj Kumar Das

Publications and source records attributed to Raj Kumar Das.

3 recordsLinked to original sources

arXiv2025

Parametrizing the Hubble function instead of dark energy: Many possibilities

In the present article, we propose a very simple parametrization of the Hubble function without parametrizing the dark components of the Universe. One of the novelties of the parametrization is that it may include a wide variety of the cosmological models, such as dark energy (both noninteracting and interacting fluids), modified gravity, cosmological matter creation and other known scenarios. The model is constrained with the latest astronomical probes from Hubble parameter measurements, three distinct versions of Type Ia Supernovae (Pantheon+, DESY5, Union3) and baryon acoustic oscillations from Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument data releases 1 and 2. Our results suggest a mild deviation from the standard $\Lambda$CDM cosmological model for most of the combined datasets. We also find that our model is thermodynamically consistent and performs well in the model comparison tests.

astro-ph.CO↗

arXiv2025

Non-Commutative fluid: an alternative source of cosmic acceleration

We present a novel formulation for the Hubble parameter derived from Newtonian cosmology, incorporating non-commutative fluid dynamics through a deformed Poisson bracket structure. This approach introduces a new cosmological parameter, denoted by $\sigma$, which emerges naturally from the underlying non-commutative framework. It gives rise to a source term in the background fluid continuity equation, thereby leading to an apparent type of matter creation picture through the resulting non-conservation. Remarkably, the resulting Hubble function accounts for the observed accelerated expansion of the universe without invoking any external dark energy component or cosmological constant. Instead, the parameter $\sigma$ effectively serves as the driver of acceleration. We further examine the observational constraints on $\sigma$ using current cosmological data, including the recent Dark Energy Spectroscopic Instrument(DESI) dataset, demonstrating its viability as an alternative explanation for late-time cosmic acceleration within a non-commutative cosmological model.

gr-qc↗

arXiv2024

Cosmology in $R^2$-gravity: Effects of a Higher Derivative Scalar Condensate Background

A well known extension of Einstein General Relativity is the addition of an $R^2$-term, which is free of ghost excitations and in the linearized framework, reduces Einstein General Relativity and an additional higher derivative scalar. According to \cite{Chakraborty:2020ktp}, the above scalar sector can sustain a Time Crystal-like minimum energy state, with non-trivial time dependence. Exploiting previous result that the scalar can sustain modes with periodic time dependence in its lowest energy, we consider this condensate as a source and study the Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology in this background. The effect of the $R^2$-term is interpreted as a back reaction. A remarkable consequence of the condensate is that, irrespective of open or close geometry of the Universe, for an appropriate choice of parameter window, the condensate can induce a decelerating phase before the accelerated expansion starts and again, in some cases, it can help to avoid the singularity in the deceleration parameter (that is present in conventional FLRW Cosmology).

gr-qc↗