arXiv subjects

Avinash Tiwari

Publications and source records attributed to Avinash Tiwari.

13 recordsLinked to original sources

arXiv2026

Periodic line-of-sight velocity-driven modulations to gravitational waves emitted by compact binaries in Keplerian outer orbits

The centre of mass (CoM) of compact binary coalescences (CBCs) occurring in the vicinity of a supermassive black hole, through interaction with an arbitrary third body (e.g., of stellar mass), or in a dense stellar environment, will undergo a time-varying line-of-sight (LOS) velocity. This in turn leads to a time-varying Doppler shift and corresponding modulations in the shape of the gravitational waves (GWs). The phase and amplitude corrections arising from constant LOS acceleration and its higher-order time derivatives are already known. Specifically, these effects lead to corrections to the GW waveform at $-4n$ post-Newtonian (PN) order, where $n$ is the $n^{th}$ time derivative of the LOS velocity. In the context of a circular or eccentric outer orbit of the CoM of the CBC, these effects can be thought of as approximations to the LOS velocity in the limit: observation duration $\ll$ period of the outer orbit. However, this condition is not necessarily always satisfied. In this {\it paper}, we present phase and amplitude corrections to the GW waveforms arising from a periodic non-relativistic LOS velocity for circular and eccentric outer orbits of the CBC's CoM. Specifically, these lead to phase and amplitude modulations at 4 PN order, and reduce to the known corrections for constant kinematic parameters under appropriate limits mentioned above. We also perform a Fisher matrix analysis to forecast constraints on the environment that is sourcing the time-varying LOS velocity, for various future ground and space-based detectors. We further show that constraints acquired using GW waveforms derived in this work improve significantly in comparison to those acquired from approximate methods valid for constant kinematic parameters.

gr-qc↗

arXiv2026

Identifying and characterizing extragalactic circum-CBC exoplanets with future gravitational-wave detectors

Exoplanets are high-value targets for a variety of ground and space-based telescopes. All known exoplanets are Galactic, and a fraction of them orbit compact objects. In this work, we investigate the possibility of detecting extragalactic exoplanets orbiting stellar-mass compact binary coalescences (CBCs), such as binary neutron stars, neutron star-black holes, and binary black holes, using future gravitational wave (GW) detectors, including A+ (LIGO in O5), Einstein Telescope, and DECIGO. We use the technique of reconstructing an external potential's profile by extracting information about the centre-of-mass (CoM) kinematics of a CBC encoded in the GWs it emits. In this work, the external potential is provided by the circum-CBC exoplanet, and the resulting signature on the GW waveform comes from the ``wobble'' of the CBC's CoM around the CBC-exoplanet barycentre. As a proof of principle, we consider a few example CBCs detectable with future detectors and a range of circum-CBC exoplanet parameters in circular and eccentric orbits. We find that for a significant fraction of the range of parameters considered, we can identify the presence of a circum-CBC exoplanet by extracting its mass (up to an unknown orbital inclination angle) within a factor $\mathcal{O}(1)$ of its true value, at $68\%$ confidence.

astro-ph.HE↗

arXiv2026

Gravitational Wave Informed Inference of 21-cm Global Signal Parameters

Understanding how and when the first stars and galaxies formed remains one of the central challenges in modern cosmology. These structures emerged during the transition from the Dark Ages to the Cosmic Dawn, a period that remains observationally unconstrained despite strong theoretical progress. During this epoch, neutral hydrogen absorbed a fraction of cosmic microwave background photons through its 21-cm hyperfine transition, producing a 21-cm absorption signal whose evolution encodes the early Universe's thermal and ionization history. However, extracting the underlying astrophysical parameters from this signal is limited by severe parameter degeneracies, which cannot be resolved without independent observational probes. The next-generation gravitational wave (GW) detectors, such as Cosmic Explorer (CE), will observe binary black hole (BBH) mergers up to very large redshifts and hence will detect a fraction of them formed within the redshift range $\sim 13-25$. The merger rate of these BBHs will depend on the star formation rate density (SFRD) at these redshifts, together with the BBH formation efficiency and a time delay distribution. Therefore, the merger rate of these BBHs can work as a tracer of the SFRD in the redshift range $\sim 13-25$. In this Letter, we establish a novel multi-messenger framework and present a proof-of-principle concept of how the observations of BBH mergers form next-generation GW detectors can improve the inference of parameters generating the 21-cm cosmic hydrogen signal, and help break degeneracies between them.

astro-ph.CO↗

arXiv2026

A pipeline to search for signatures of line-of-sight acceleration in gravitational wave signals produced by compact binary coalescences

Compact binary coalescences (CBCs), such as merging binary black holes (BBHs), binary neutron stars (BNSs), or neutron star black holes (NSBHs), hosted by dense stellar environments, could produce gravitational waves (GWs) that contain signatures of line-of-sight acceleration (LOSA) imparted by the environment's gravitational potential. We calculate the Post-Newtonian (PN) corrections to the $(2,\,2)$ mode GW phase due to a finite LOSA, starting from the leading order at -4 PN below the quadrupole order, up to 3.5 PN above the leading order correction. We do so for binaries whose component spins are aligned with the orbital angular momentum, as well as for binaries with non-zero tidal deformation. We implement these corrections into the LIGO-Virgo-Kagra (LVK) collaboration's flagship parameter estimation (PE) software Bilby_tgr. We study the systematics associated with recovering LOSAs. We find that, when the injection and recovery waveform models are identical, LOSAs are recovered as expected. We test the robustness of the pipeline against waveforms with strong higher-mode signatures or signatures of beyond-general-relativistic (beyond-GR) effects, to delimit the range of applicability of our GR-consistent quasi-circular LOSA-corrected waveforms.

astro-ph.HE↗

arXiv2026

Testing the nature of GW200105 by probing the frequency evolution of eccentricity

GW200105 is a compact binary coalescence (CBC) event, consisting of a neutron star and a black hole, observed in LIGO-Virgo-KAGRA's (LVK's) third observing run (O3). Recent reanalyses of the event using state-of-the-art waveform models have claimed observation of signatures of an eccentric orbit. It has nevertheless been pointed out in the literature that certain physical or modified gravity effects could mimic eccentricity by producing a spurious non-zero eccentricity value, at a given reference frequency, when recovered with an eccentric waveform model. We recently developed a waveform-model-independent Eccentricity Evolution Consistency Test (EECT, S. A. Bhat et al. 2025) to identify such mimickers, by comparing the measured frequency $\textit{evolution}$ of eccentricity, $e(f)$, with that expected from General Relativity (GR). In this $\textit{paper}$, we apply EECT to GW200105 and find that it satisfies EECT within 68% confidence. Our analysis therefore lends complementary support in favour of the eccentricity hypothesis, while also providing a novel test of the consistency of $e(f)$ with GR.

astro-ph.HE↗

arXiv2026

Coalescence Forensics: Weighing the Hosts of Hierarchical Binary Black Hole Mergers

We present a novel framework to infer the mass of clusters that host hierarchical binary black hole (BBH) mergers detected with gravitational-waves (GWs), on a single event basis. We show that the requirement that a second-generation (2G) remnant be retained, and subsequently undergo a dynamical encounter, places strong constraints on the mass of the cluster. Using a Plummer model as a readily interpretable baseline, we derive analytic scaling relations between the peak of the inferred host mass posterior, the GW-driven recoil velocity of the remnant, and the parameters that determine the structure of the host. We then perform exact numerical marginalization over thermal and recoil velocities, angles, and cluster structure parameters, to infer the host-mass posterior. We apply our framework to putative hierarchical mergers GW241011 and GW241110, and infer the masses of their hosts on a single-event basis. We find that these are consistent with either heavy globular clusters or nuclear star clusters, with inferred masses spanning $10^{5.7 - 7.7} M_{\odot}$ at $68\%$ confidence depending on the 2G recoil velocity distribution used.

astro-ph.HE↗

arXiv2025

Eccentricity evolution consistency test to distinguish eccentric gravitational-wave signals from eccentricity mimickers

Eccentric compact binary coalescences (CBCs) are expected to be observed in current and future gravitational-wave (GW) detector networks. However, it has been recently pointed out that a number of other physical and beyond-GR effects, could imitate, or be mimicked by, eccentric CBCs. In this work, we propose a conceptually simple but powerful method to directly confirm or reject the eccentric hypothesis, without needing to compare the hypothesis with the plethora of other possible hypotheses. The key idea is that while spurious non-zero values of eccentricity, at some reference frequency, could be acquired when a non-eccentric CBC with additional physical/beyond-GR effects is recovered with an eccentric CBC waveform model, the {\itshape evolution} of eccentricity with frequency will in general not be mimicked. We accordingly formulate an eccentricity evolution consistency test (EECT). The method compares the eccentricity recovered at some low frequency value (e.g, $10$ Hz), evolved to higher frequencies assuming GR, with eccentricities recovered at those same higher frequencies. Discrepancy between the two eccentricities at any reference frequency would violate EECT and indicate the presence of a mimicker. As a proof of concept, assuming a few eccentric CBC systems, quasi-circular CBCs with additional physics mimicking eccentricity, and an O4-like three-detector-network configuration, we demonstrate that our proposed method is indeed able to reject mimickers at $\geq 68\%$ confidence, while ensuring that truly eccentric CBCs satisfy EECT.

gr-qc↗

arXiv2025

Profiling stellar environments of gravitational wave sources

Gravitational waves (GWs) have enabled direct detections of compact binary coalescences (CBCs). However, their poor sky localisation and the typical lack of observable electromagnetic (EM) counterparts make it difficult to confidently identify their hosts, and study the environments that nurture their evolution. In this work, we show that $\textit{detailed}$ information of the host environment (e.g. the mass and steepness of the host potential) can be directly inferred by measuring the kinematic parameters (acceleration and its time-derivatives) of the binary's center of mass using GWs alone, without requiring an EM counterpart. We consider CBCs in various realistic environments such as globular clusters, nuclear star clusters, and active galactic nuclei disks to demonstrate how orbit and environment parameters can be extracted for CBCs detectable by ground- and space-based observatories, including the LIGO detector at A+ sensitivity, Einstein Telescope of the XG network, LISA, and DECIGO, $\textit{on a single-event basis}$. These constraints on host stellar environments promise to shed light on our understanding of how CBCs form, evolve, and merge.

astro-ph.HE↗

arXiv2025

Profiling Dark Matter Spikes with Gravitational Waves from Accelerated Binaries

Dark matter halos can develop a density spike, e.g., around a galactic supermassive black hole, with the profile $ρ\propto r^{-γ_{\rm sp}}$ determined both by the galaxy's formation history and the microphysics of dark matter. We show that future LISA/DECIGO observations, of intermediate/stellar-mass binary mergers inside the spike around the supermassive black hole, can measure $γ_{\rm sp}$ at a few-percent--level precision. The spike induces a distinctive time-dependent acceleration along the non-circular orbit taken by the binary's center of mass, which is observable as a secular modulation of the gravitational wave signal. This method -- insensitive to confounding astrophysical effects (dynamical friction, tidal effects, etc.) and not reliant on unknown dark matter particle physics -- provides a clean diagnostic of density spikes and a new probe of dark matter.

hep-ph↗

arXiv2024

Accelerated binary black holes in globular clusters: forecasts and detectability in the era of space-based gravitational-wave detectors

The motion of the center of mass of a coalescing binary black hole (BBH) in a gravitational potential imprints a line-of-sight acceleration (LOSA) onto the emitted gravitational wave (GW) signal. The acceleration could be sufficiently large in dense stellar environments, such as globular clusters (GCs), to be detectable with next-generation space-based detectors. In this work, we use outputs of the \textsc{cluster monte carlo (cmc)} simulations of dense star clusters to forecast the distribution of detectable LOSAs in DECIGO and LISA eras. We study the effect of cluster properties -- metallicity, virial and galactocentric radii -- on the distribution of detectable accelerations, account for cosmologically-motivated distributions of cluster formation times, masses, and metallicities, and also incorporate the delay time between the formation of BBHs and their merger in our analysis. We find that larger metallicities provide a larger fraction of detectable accelerations by virtue of a greater abundance of relatively lighter BBHs, which allow a higher number of GW cycles in the detectable frequency band. Conversely, smaller metallicities result in fewer detections, most of which come from relatively more massive BBHs with fewer cycles but larger LOSAs. We similarly find correlations between the virial radii of the clusters and the fractions of detectable accelerations. Our work, therefore, provides an important science case for space-based GW detectors in the context of probing GC properties via the detection of LOSAs of merging BBHs.

astro-ph.HE↗

arXiv2023

Waltzing binaries: Probing line-of-sight acceleration of merging compact objects with gravitational waves

Line-of-sight acceleration of a compact binary coalescence (CBC) event would modulate the shape of the gravitational waves (GWs) it produces with respect to the corresponding non-accelerated CBC. Such modulations could be indicative of its astrophysical environment. We investigate the prospects of detecting this acceleration in future observing runs of the LIGO-Virgo-KAGRA network, as well as in next-generation (XG) detectors and the proposed DECIGO. We place the first observational constraints on this acceleration, for putative binary neutron star mergers GW170817 and GW190425. We find no evidence of line-of-sight acceleration in these events at $90\%$ confidence. Prospective constraints for the fifth observing run of the LIGO at A+ sensitivity suggest that accelerations for typical BNSs could be constrained with a precision of $a/c \sim 10^{-7}~[\mathrm{s}^{-1}]$, assuming a signal-to-noise ratio of $10$. These improve to $a/c \sim 10^{-9}~[\mathrm{s}^{-1}]$ in XG detectors, and $a/c \sim 10^{-16}~[\mathrm{s}^{-1}]$ in DECIGO. We also interpret these constraints in the context of mergers around supermassive black holes.

astro-ph.HE↗

arXiv2020

Dependency of Sliding Friction for Two Dimensional Systems on Electronegativity

We study the role of electronegativity in sliding friction for five different two dimensional (2D) monolayer systems using density functional theory (DFT) with van der Waals (vdW) corrections. We show that the friction between the commensurate 2D layered systems depends strongly on the electronegativity difference of the involved atoms. All the 2D layered structures exhibit almost the same magnitude of friction force when sliding along the nonpolar path, independent of the material and the surface structures. In contrast, for sliding friction along the polar path, the friction force obeys a universal linear scaling law as a function of the electronegativity difference of its constituent atoms. Further analyses demonstrate that atomic dipoles in the 2D monolayers induced by the electronegativity difference enhance the corrugation of charge distribution and increase the sliding barrier accordingly. Our studies reveal that electronegativity plays an important role in friction of low dimensional systems, and will provide a strategy for designing nanoscale devices further.

cond-mat.mtrl-sci↗

arXiv2017

Thermomechanical properties of zirconium tungstate/hydrogenated nitrile butadiene rubber (HNBR) composites for low-temperature applications

Rubber compounds for pressure sealing application typically have inferior dimensional stability with temperature fluctuations compared with their steel counterparts. This effect may result in seal leakage failures when subjected to decreases in temperature. Composites of hydrogenated nitrile butadiene rubber (HNBR) and zirconium tungstate as a negative thermal expansion filler were prepared in order to control the thermal expansivity of the material. The amount of zirconium tungstate (ZrW2O8) was varied in the range of 0 to about 40 vol%. The coefficient of thermal expansion (CTE), bulk modulus, uniaxial extension and compression set properties were measured. The CTE of the ZrW2O8-filled HNBR decreases with the filler content and it is reduced by a factor of 2 at the highest filler concentration used. The filler effect on CTE is found to be stronger when HNBR is below the glass transition temperature. The experimental thermal expansion data of the composites are compared with the theoretical estimates and predictions given by FEA. The effect of ZrW2O8 on the mechanical characteristics and compression set of these materials is also discussed.

cond-mat.mtrl-sci↗