Apurba Samanta | Searcharxiv

arXiv2026

Constraining inflationary models via de-Sitterization of Bianchi Cosmologies

Our Universe is isotropic and homogeneous when we observe it on $\gtrsim$ Mpc length scales. It is desirable that present state of the Universe has no dependence on its initial geometry. In case of Bianchi Universes, i.e., anisotropic but homogeneous Universe, this has already been demonstrated via cosmological constant in a process that we call \textit{de Sitterization}. In this letter, we show that for Bianchi Universe, the same state can be achieved by a homogeneous inflaton field with a general potential and satisfying a criterion without the need of a cosmological constant. More importantly, we show that the same condition can constrain models of inflation and explain our idea with examples.

gr-qc↗

arXiv2026

Constraining Scale-Dependent Growth in $f(R)$ Gravity with Future 21 cm Surveys

Recent observations, particularly from DESI, have provided intriguing hints of dynamical behaviour in late-time dark energy. Modified gravity theories offer a compelling framework for interpreting such phenomena, with $f(R)$ gravity emerging as one of the most extensively studied examples. A central challenge in these models, however, lies in determining the precise functional form of $f(R)$. Nevertheless, several viable models have been proposed that successfully reproduce the standard $\Lambda$CDM cosmology at high red shifts while generating late-time cosmic acceleration without an explicit dark energy component. Within this framework, the evolution of the linear matter density contrast becomes scale dependent, leading to a growth index that varies with both scale and redshift. In this work, we explore the capability of forthcoming 21 cm observations to constrain the growth index, as well as the combined neutral hydrogen (HI) bias and growth-rate parameter. Our results indicate that future 21 cm surveys can provide meaningful, though moderate, support for these modified gravity scenarios.

astro-ph.CO↗