arXiv subjects

Soham Bhattacharyya

Publications and source records attributed to Soham Bhattacharyya.

13 recordsLinked to original sources

arXiv2026

Impact of the Host Galaxy on the Search for Gravitational-Wave Microlensing by Compact Objects

Gravitational-wave (GW) microlensing occurs when an intervening compact object causes diffraction of the GW, imprinting characteristic frequency-dependent modulations on the observed signal. Current searches for microlensing signatures in the detected GW events, including those used to constrain the fraction of dark matter in the form of compact objects, assume an isolated point mass lens (PML) model. However, astrophysical compact objects are typically embedded within larger structures, such as galaxies, whose potentials introduce additional convergence and tidal shear, thereby perturbing the lensed signal. In this work, we study the impact of the background galaxy in the search for microlensing by compact objects using a PML model. We distribute the compact objects inside a galaxy following the Navarro-Frenk-White density profile. We model the microlensing effects using the potential of a PML embedded in a constant convergence and shear, which are, in turn, calculated from a singular isothermal sphere model of the galaxy lens. We demonstrate that neglecting the galaxy's effects can systematically reduce sensitivity in microlensing searches, particularly for high microlens masses. Thus, future searches may need to incorporate the additional effect of the lens galaxy, particularly those aimed at placing robust constraints on the abundance of compact dark matter.

gr-qc↗

arXiv2026

Spin precession effects in the phasing formula of eccentric compact binary inspirals up to the second post-Newtonian order

Compact binary systems emitting gravitational waves (GWs) can exhibit orbital eccentricity, along with generic spin orientations, leading to the precession of the orbital angular momentum, individual spins, and the orbital plane. While eccentric binaries with aligned spins are well studied, closed form post Newtonian (PN) expressions that simultaneously include eccentricity and precessing spin effects have remained unavailable. Eccentricity complicates orbital evolution because solving the coupled differential equations typically requires numerical integration, which slows down the generation of waveforms. We exploit the separation of timescales between orbital motion, spin precession, and radiation reaction, applying the precession averaging method of Morras et al. (2025) to remove explicit time dependence from the spin orbit and spin spin dynamics through the second PN order. Using this framework, we derive analytic phasing formulae from the evolution equations for orbital frequency and eccentricity, treating eccentricity as a small parameter. Closed form solutions for the eccentricity evolution and GW phase are obtained up to eighth order in the initial eccentricity. We also generalize the TaylorT2 approximant to include spin precession effects and compute the orbital phase in both time and frequency domains. To improve accuracy for moderate to high initial eccentricities, we perform a resummation of the TaylorT2 phasing. These results offer efficient, closed form phasing expressions that capture the coupled dynamics of eccentricity and precession, enabling more accurate and computationally tractable GW waveform modeling for data analysis.

gr-qc↗

arXiv2026

Thermal description of braneworld effective theories

Low-energy effective theories provide the natural description of four-dimensional physics in higher-dimensional geometries, where the imprint of the bulk appears as parameters of the lower dimensional theory. Motivated by the recent progress in the first-order thermodynamic formulation of modified gravity theories, we investigate the thermodynamics of effective theories in braneworld scenarios and thereby the attractor mechanism towards general relativity in such theories. We consider the two-brane Randall-Sundrum model where the low-energy theory on either brane is of scalar-tensor nature with the extra-dimensional radion playing the role of the scalar. We study the thermodynamic implications of a non-vanishing gravitational contribution to the radion potential, and further explore the dynamics in the presence of a bulk stabilizing field.

hep-th↗

arXiv2025

Analyzing the general conditions for modulus stabilization in a warped braneworld

In braneworld scenarios with compact extra dimensions, the modulus field typically remains undetermined without an appropriate stabilization mechanism. A common approach introduces a bulk scalar field that generates an effective potential for the modulus with a stable minimum. In this work, we explore some novel aspects of such stabilization mechanisms. We study how the bulk scalar profile influences the stabilization procedure. Following the approach of Chacko et al. [1], we analyze several representative cases using methods of singular perturbation theory. We identify a consistent relationship between the structure of the bulk potential and the emergence of a stabilized modulus, and outline the general conditions that any bulk potential must satisfy to enable stabilization. In this context, we also examine a potential connection between geometric consistency conditions - specifically, the "brane world sum rules" - and the stabilized value of the modulus. In some scenarios where stabilization occurs, we find that these sum rules can offer additional constraints on the modulus, providing a complementary perspective on its determination. Taken together, these results offer a broader perspective on the mechanisms that govern modulus stabilization in higher-dimensional warped geometries.

hep-ph↗

arXiv2025

Worldline EFT treatment of quadratic and cubic gravity theories

This paper explores modifications to General Relativity (GR) by considering higher-order curvature terms in the gravitational action, specifically focusing on the quadratic Ricci scalar and a particular cubic contraction of the Riemann tensor. These modifications introduce new interactions at short distances, potentially altering the dynamics of compact objects. We calculate the effective two-body binding potential energy for these modified theories to quantify these effects using the worldline effective field theory (WEFT) formalism. This approach allows us to systematically integrate out short-distance gravitational effects, capturing the modifications to the binding potential. Our results demonstrate how the quadratic Ricci scalar and cubic Riemann tensor terms contribute to the two-body interaction at the leading order, highlighting deviations from classical GR predictions. These findings offer insight into the potential observational signatures of modified gravity theories in binary systems and other astrophysical settings.

gr-qc↗

arXiv2025

Spin effects in the phasing formula of eccentric compact binary inspirals up to the third post-Newtonian order

Compact binary sources that emit gravitational waves (GW) are expected to be both spinning and on eccentric orbits. No closed-form expression for the phasing of GWs are available to date that contain information from both spin and eccentricity. The introduction of eccentricity can slow waveform generation, often requiring slower numerical methods governing its evolution. However, closed-form expressions for the waveform phase can be obtained when eccentricity is treated as a small parameter, enabling quick waveform generation. In this paper, closed-form expressions for the GW phasing in the form of Taylor approximants up to the eighth power in initial eccentricity $(e_0)$ are obtained while also including aligned spins up to the third post-Newtonian order. The phasing is obtained in both time and frequency domains. The fully analytical approximant (TaylorT2) is also resummed for usage in scenarios where initial eccentricities are as high as 0.5. The frequency domain approximant (TaylorF2) based on Stationary Phase approximation is compared with an existing model (TaylorF2Ecc) to assess the importance of the newly computed eccentric/spinning terms. The findings indicate that for eccentricities $\gtrsim 0.15$ (defined at 10 Hz) and small spins $(\sim 0.2)$, the mismatches can be higher than 1%. This leads to an overall loss in signal-to-noise ratio and lower detection efficiency of GWs coming from eccentric spinning compact binary inspirals if the combined effects of eccentricity and aligned spins are neglected in the waveforms.

gr-qc↗

arXiv2025

Upper Bounding Hilbert Space Dimensions which can Realize all the Quantum Correlations

We introduce novel upper bounds on the Hilbert space dimensions required to realize quantum correlations in Bell scenarios. We start by considering bipartite cases wherein one of the two parties has two settings and two outcomes. Regardless of the number of measurements and outcomes of the other party, the Hilbert space dimension of the first party can be limited to two while still achieving all convexly extremal quantum correlations. We then leverage Schmidt decomposition to show that the remaining party can losslessly also be restricted to a qubit Hilbert space. We then extend this idea to multipartite scenarios. We also adapt our results to provide upper bounds of local Hilbert space dimensions to achieve any quantum correlation, including convexly non-extremal correlations, by utilizing Caratheodory's theorem. Finally, we generalize our results to nonstandard Bell scenarios with communication. Taken together, our results fill in several previously unresolved aspects of the problem of determining sufficient Hilbert space dimensionality, expanding the collection of scenarios for which finite-dimensional quantum systems are known to be sufficient to reproduce any quantum correlation.

quant-ph↗

arXiv2023

On the equivalence between $ f\left(R\right) $ theories and Einstein gravity

In this brief note we present a somewhat trivial result. Namely, we show that perturbative off-shell $f(R)$-theory is equivalent to Einstein gravity, as well as to the Brans-Dicke theory and the Einstein scalar field model. We also discuss possible generalisation of this result to higher-order gravitational field models.

gr-qc↗

arXiv2022

The Equivalence and/or the Effacing principle in $ f\left(R\right) $ theories of gravity

The Einstein-Hilbert action of general theory of relativity (GR) is the integral of the scalar curvature $R$. It is a theory that is drawn from the Equivalence principle, and has predictions that come out as a consequence of the principle, in observables. Testing such observables to find confirmation/infirmation of the principle have formed a significant chunk of tests of GR itself. It is expected that quantum corrections to GR may add additional higher powers of $R$ to the Einstein-Hilbert action, or more generally, modifying the action into a generic class of functions of the Ricci scalar. Testing the fate of the prized equivalence principle, in such modified theories of gravity, hence become important in order to obtain a more generic theory of gravitation, and consequently, of gravitating objects. In this study, it is shown that a Post-Newtonian (PN) expansion of a class of $ f\left(R\right) $ theories lead to a sequence of solutions to the two-body problem, which follows the equivalence principle (EP) at the Newtonian order, and generalizes to the 'effacing principle' at a higher PN order.

gr-qc↗

arXiv2021

Two body dynamics in a quadratic modification of general relativity

It is shown in this study that deviations from the Einstein-Hilbert action at the quadratic level using a proper analyses and suitable dynamical variables lead to a tiny modification to the post-Newtonian equations of motion, and non-GR-like behavior at very short length scales.

gr-qc↗

arXiv2019

Distinguishing general relativity from Chern-Simons gravity using gravitational wave polarizations

Quasi-normal modes (QNMs) uniquely characterize the final black-hole. Till now, only the QNM frequency and damping time are used to test General relativity. In this work, we show explicitly that another property of the QNMs --- their polarization --- can be a reliable tool for probing gravity. We provide a consistent test for General relativity by considering Chern-Simons gravity. Distinguishing Chern-Simons gravity from General relativity using only template matching is highly challenging. Thus a parameter that can differentiate between Chern-Simons gravity and GR will be a suitable candidate for any modified theories of gravity. We discuss the implications of our result for the future gravitational wave detectors.

gr-qc↗

arXiv2018

Quasinormal modes as a distinguisher between general relativity and f(R) gravity: Charged black-holes

The ring-down phase of black-hole perturbations is governed by the Quasi-Normal modes (QNM) and offer valuable insight into the nature of the objects emitting them. In General relativity, we identify a dimensionless parameter that can estimate the charge of a black-hole from the energetics of quasi-normal modes. We then extend the analysis for f(R) theories of gravity. Using Isaacson's prescription to modified theories of gravity, we obtain an accurate and robust method to estimate the difference in the radiated energies in the scalar and vector modes due to modifications to general relativity. We then discuss how to quantify the deviation from general relativity.

gr-qc↗

arXiv2017

Quasinormal modes as a distinguisher between general relativity and f(R) gravity

Quasi-Normal Modes (QNM) or ringdown phase of gravitational waves provide critical information about the structure of compact objects like Black Holes. Thus, QNMs can be a tool to test General Relativity (GR) and possible deviations from it. In the case of GR, it is known for a long time that a relation between two types of Black Hole perturbations: scalar (Zerilli) and vector (Regge-Wheeler), leads to an equal share of emitted gravitational energy. With the direct detection of Gravitational waves, it is now natural to ask: whether the same relation (between scalar and vector perturbations) holds for modified gravity theories? If not, whether one can use this as a way to probe deviations from General Relativity. As a first step, we show explicitly that the above relation between Regge-Wheeler and Zerilli breaks down for a general f (R) model, and hence the two perturbations do not share equal amounts of emitted gravitational energy. We discuss the implication of this imbalance on observations and the no-hair conjecture.

gr-qc↗