arXiv subjects

Tamanna Jain

Publications and source records attributed to Tamanna Jain.

11 recordsLinked to original sources

arXiv2026

Black-Hole Scattering in Einstein-scalar-Gauss-Bonnet: Numerical Relativity Meets Analytics

The study of hyperbolic binary black hole encounters yields an effective probe of the strong field regime of black holes, thus providing an additional channel to test General Relativity. We study the scattering of two black holes in Einstein-scalar-Gauss-Bonnet gravity, a well-motivated effective field theory of gravity, by comparing the scattering angle obtained from the first fully nonlinear black hole scattering simulations with its effective-one-body analytic description. We obtain excellent agreement between analytics and numerics, exhibiting accurate capturing of strong-field scalar-gravitational dynamics. Our work paves the way towards semi-analytical waveform templates of compact object binaries in modified theories of gravity.

gr-qc↗

arXiv2026

Lessons from binary dynamics of inspiralling equal-mass boson-star mergers

We explore the gravitational-wave phenomenology of equal-mass inspiralling boson-star binaries using numerical relativity simulations. In particular, we characterise the waveform differences between binary boson-star and black-hole systems across (i) the early inspiral, by matching our waveforms to post-Newtonian expressions, (ii) merger, and (iii) late ringdown, by extracting the quasi-normal mode frequencies of the remnants. We find that boson-star binaries exhibit the largest deviations from comparable binary black-hole systems during the late inspiral and merger phases. Remarkably, for a subset of these equal-mass boson-star binaries (with certain phase offsets in the scalar-field profiles) we identify the excitation of subdominant odd $m$-multipoles in the gravitational-wave emission, absent in equal-mass nonspinning black-hole binaries. Despite differences in the phenomenology of binary boson-star and black-hole signals, injections of some boson-star signals into detector noise exhibit degeneracy with current waveform approximants. Building on these results, we demonstrate how inspiral-merger-ringdown consistency tests can overcome these degeneracies.

gr-qc↗

arXiv2026

Scattering angle at 3PM in scalar-tensor theories using the PM-EFT formalism

In this work, we derive the conservative dynamics of non-spinning binaries in the massless scalar-tensor theories using the post-Minkowskian Effective Field Theory (EFT) approach. Our main result is an analytic expression of the scattering angle, computed up to third Post-Minkowskian order via two-loop Feynman diagrams. Our results are in perfect agreement with previous literature, in particular within the post-Newtonian limit.

hep-th↗

arXiv2025

Radiation reaction force for scalar-tensor theories in effective-one-body formalism

Whilst most of the binary configurations in modified theories of gravity are studied under quasi-circular orbit limit, eccentricity effects could play a significant role in future gravitational wave detections. We derive the gravitational radiation-reaction force for nonspinning eccentric orbits within the effective-one-body (EOB) description for the massless scalar-tensor theories up to 1.5 post-Newtonian (PN) order. The effects in such theories start at $1/c^3$ and interestingly, the 1.5PN order effect is due to the radiation reaction square effects which is a conservative effect. The results derived here can be implemented in the quasi-circular EOB-based waveform models to construct waveform templates for generic orbit binaries within massless scalar-tensor theories of gravity.

gr-qc↗

arXiv2025

Gravitational scattering of solitonic boson stars: Analytics vs Numerics

We study the scattering of boson-star binaries, taking into account three effects: point-mass gravitational, tidal, and short-range scalar-field interactions. We compare analytic results to the scattering angle extracted from four sequences of numerical-relativity simulations at fixed energy and varying impact parameter. The very good agreement exhibits the attractive (repulsive) effect of in-phase (out-of-phase) binaries, wich dominates at small impact parameters. We thus obtain the first effective-one-body potential, central for the construction of analytic gravitational-wave templates.

gr-qc↗

arXiv2025

A Non-linear Massive Gravity Theory of Geometric Origin

We study the number of propagating degrees of freedom, at non-linear order, in torsion gravity theories, a class of modified theories of gravity that include a propagating torsion in addition to the metric. We focus on a three-parameter subfamily of theories (``torsion bigravity") that contains, at linear order, only two physical excitations: a massless spin-2 one (with two degrees of freedom) and a massive spin-2 one (with five degrees of freedom). We study the dynamics of the massive spin-2 field in the limit where the torsion field decouples from the metric. The number of degrees of freedom of the torsion field is found to {\it change, at non-linear order, from five to nine}.

gr-qc↗

arXiv2024

Angular Momentum Flux in Scalar-Tensor Theories up to 1.5 post-Newtonian Order

We compute the angular momentum flux from a non-circular nonspinning binary system of compact objects in massless scalar-tensor theories up to one and a half post-Newtonian (1.5PN) order using multipole moments. The angular momentum flux in scalar-tensor theories involves both a tensorial and a scalar contribution which can be further decomposed as instantaneous, tail and non-linear memory effects up to 1.5PN order. We compute the explicit expressions of tail effects using the Fourier decomposition of tensorial and scalar multipole moments, and non-linear memory effects using the Newtonian order quasi-Keplerian representation of elliptic orbits in scalar-tensor theories. This work is important to construct the radiation-reaction force and hence the waveform templates for eccentric binaries in scalar-tensor theories of gravity.

gr-qc↗

arXiv2024

Improving inference on neutron star properties using information from binary merger remnants

The gravitational-wave signal GW170817 is a result of a binary neutron star coalescence event. The observations of electromagnetic counterparts suggest that the event didn't led to the prompt formation of a black-hole. In this work, we first classify the GW170817 LIGO-Virgo data sample into prompt collapse to a black-hole using the $q$-dependent threshold mass fits and then remove these cases from the data sample. We find that the cases without a prompt black-hole formation do not support radii $ <$ 10 km unlike the LIGO-Virgo data sample. This is consistent with the maximum mass constraint, based on the binary pulsar J0348+0432, imposed LIGO-Virgo data sample. Additionally, we find that the cases without the prompt collapse to a black-hole improve the uncertainty range of neutron star radii from 3.3 km to 2.6 km for the data sample without the mass constraint and from 2.8 km to 2.5 km for the data sample with the mass constraint, implying improved constraints on the neutron star radii and hence the equation-of-state.

gr-qc↗

arXiv2023

Gravitational scattering upto third post-Newtonian approximation for conservative dynamics: Scalar-Tensor theories

We compute the scattering angle $χ$ for hyperboliclike encounters in massless Scalar-Tensor (ST) theories up to third post-Newtonian (PN) order for the conservative part of the dynamics. To calculate the gauge-invariant scattering angle as a function of energy and orbital angular momentum, we use the approach of Effective-One-Body formalism as introduced in [Phys.Rev.D 96 (2017) 6, 064021]. We then compute the nonlocal-in-time contribution to the scattering angle by using the strategy of order-reduction of nonlocal dynamics introduced for small-eccentricity orbits.

gr-qc↗

arXiv2023

Nonlocal-in-time effective one body Hamiltonian in scalar-tensor gravity at third post-Newtonian order

We complete the nonlocal-in-time effective-one-body (EOB) formalism of conservative dynamics for massless Scalar-Tensor (ST) theories at third post-Newtonian (PN) order. The nonlocal-in-time EOB Hamiltonian is obtained by mapping the order-reduced Hamiltonian corresponding to the nonlocal-in-time Lagrangian derived in [Phys. Rev. D 99, 044047 (2019)]. To transcribe the dynamics within EOB formalism, we use a strategy of order-reduction of nonlocal dynamics to local ordinary action-angle Hamiltonian. We then map this onto the EOB Hamiltonian to determine the nonlocal-in-time ST corrections to the EOB potentials $(A,B,Q_e)$ at 3PN order.

gr-qc↗

arXiv2022

Effective one body Hamiltonian in scalar-tensor gravity at third post-Newtonian order

We determine the general local-in-time effective-one-body (EOB) Hamiltonian for massless Scalar-Tensor (ST) theories at third post-Newtonian (PN) order. Starting from the Lagrangian derived in [Phys. Rev. D 99, 044047 (2019)], we map it to the corresponding ordinary Hamiltonian describing the two-body interaction in ST theories at 3PN level. Using a canonical transformation, we then map this onto an EOB Hamiltonian so as to determine the ST corrections to the 3PN-accurate EOB potentials $(A,B,Q_e)$ at 3PN. We then focus on circular orbits and compare the effect of the newly computed 3PN terms, also completed with finite-size and nonlocal-in-time contributions, on predictions for the frequency at the innermost stable circular orbit. Our results will be useful to build high-accuracy waveform models in ST theory, which could be used to perform precise tests against General Relativity using gravitational wave data from coalescing compact binaries.

gr-qc↗