arXiv subjects

Hardik Jitendra Kuralkar

Publications and source records attributed to Hardik Jitendra Kuralkar.

3 recordsLinked to original sources

arXiv2026

A New Framework to Detect Multi-Messenger Signals from Bright Sporadic Stochastic Gravitational Wave Background

The temporal dependence of the astrophysical stochastic gravitational-wave (GW) background (SGWB) in the hecto-hertz band brings a unique avenue to identify multi-messenger signals to these sources by using coincident detection in both GW and multi-band EM signals. We developed a new analysis pipeline, \textit{Multi-messenger Cross-Correlation} (MC$^2$) that can search for EM counterparts to the SGWB signal originating from both modeled and unmodeled sources by harnessing the nearly full-sky gamma-ray sky map. We provide an observation strategy that can be followed by current and future missions to discover EM counterparts to the weak GW signal hidden in the SGWB. We demonstrate the ability of this technique to drastically reduce the false alarm rates when involving EM multi-band analysis. This formalism aims towards advancing the multi-messenger observation frontier and improving our understanding of the population of bright SGWB sources present in the high-redshift universe and can also be applied to other messengers such as neutrinos in the future.

astro-ph.HE↗

arXiv2025

Eff-ACT-ive Starobinsky pre-inflation

We consider quantum corrections to a recently obtained perturbative form of Starobinsky model to extract information about the initial conditions of the universe leading to cosmological inflation. Integrating out graviton modes, we find higher-derivative instabilities that are shown to decay into scalarons, causing an effective kinetic-domination stage which is shown to lead naturally to inflation without the need for fine-tuning of initial inflaton amplitude. We find a perturbative upper bound on scalaron magnitude that matches Planck constraints on inflaton energy density near the pivot scale. This modified history also affects observables and resolves other anomalies such as the low-$\ell$ power deficit in the TT spectrum as well as the disfavorment of Starobinsky model based on updated predictions of scalar spectral index accounting for data from Atacama Cosmology Telescope (ACT).

gr-qc↗

arXiv2025

Observable Primordial Gravitational Waves from Non-minimally Coupled $R^2$ Palatini Modified Gravity

We probe the spectrum of primordial gravitational waves (GWs) produced during the eras of hyperkination, kination, and reheating in a non-minimally coupled, $\mathcal{L} \propto (1+ ξχ/M_{\text{Pl}})^t (R+αR^2)$, modified gravity using the Palatini formulation. We consider a runaway potential, which gives an era of kinetic domination after the end of inflation. The coupling order $t$ is varied to examine a large class of theories up to $χ^2 R^2$. For models with $t>0$, reheating is not achieved naturally; hence, we supplement such theories with a reheating mechanism based on the interaction of inflaton and radiation produced at the end of inflation due to cosmological expansion. We demonstrate that the energy density of the GWs is enhanced as a function of the coupling during kination for all considered theories, and a short-lived phase of hyperkination truncates the boost and avoids the over-production of GWs. Hyperkination, and thus the $R^2$ term, should be deemed necessary in all theories with a runaway potential as it prevents the GW enhancement during kination from destabilizing the Big Bang Nucleosynthesis. The spectrum remains flat for the period of hyperkination and reheating. We examine the available parameter space for which the theories remain valid and place bounds on the Hubble parameter ($H$) and radiation energy density ($Ω_r^{\text{end}}$) at the end of inflation. We find that as we decrease the order of the coupling, the spectra shift towards a more observable regime of future GW experiments. The observation of the plateau during reheating will constrain the $H$ and $Ω_r^{\text{end}}$ values, while the spectral shape of the boost obtained during kination will confirm the nature of the theory. The bounds from hyperkination lie in the kHz-GHz frequency range.

astro-ph.CO↗