arXiv subjects

Soumen Roy

Publications and source records attributed to Soumen Roy.

At least 19 recordsLinked to original sources

arXiv2026

GUEST: Gravitational Universe Exploration with Satellite Tracking. A passive satellite laser-ranging mission for the dark gravitational Universe

GUEST is a space mission concept whose central objective is the detection of gravitational waves (GWs) in the microhertz band -- a physics-rich frequency window that no other present or planned detector can reach at a significant level. The concept is simple: two dense, passive spheres, covered with cube-corner retroreflectors, deployed in {highly eccentric} Earth orbits ($e \gtrsim 0.7$, period $P \gtrsim 33$ h), tracked continuously by the global network of satellite laser-ranging stations over a minimum observation time of 10 years, with an expected total duration of 30 years. The orbits themselves act as resonant detectors of the oscillating gravitational perturbations, with the microhertz sensitivity emerging from the selected orbital parameters. From the same data stream, GUEST delivers a programme of fundamental and applied science that cuts across particle physics, gravitational-wave astronomy, cosmology, astrophysics, and geodesy: the first coherent search for GWs from supermassive black-hole binaries in the $\mu$Hz band, the exploration of primordial GW backgrounds in the unexplored energy-scale gap between pulsar-timing arrays and LISA, a dedicated probe of ultra-light dark matter in a parameter region untouched by any other experiment, a new way to search for ultra-light bosons, order-of-magnitude-improved tests of new gravitational interactions at astronomical ranges, and a step change in the absolute determination of $GM_\oplus$ that underpins the Global Geodetic Observing System and future navigation and Earth-observation missions. This white paper presents the motivation, scientific reach, and mission concept of GUEST.

astro-ph.CO↗

arXiv2026

Line-of-sight acceleration in compact binaries with higher harmonics and eccentricity

Direct detections of gravitational waves provide a unique opportunity to probe the astrophysical origin of compact binary mergers. The formation channels of these systems remain highly debated, and a fraction may originate in dynamical environments or active galactic nuclei. Binaries formed in such environments are expected to experience line-of-sight acceleration from their surroundings, which can imprint characteristic signatures on the observed gravitational-wave signal. Here, we re-derive the line-of-sight acceleration effects and implement them in state-of-the-art quasi-circular waveform models with precession and higher-order modes. We also implement the corrections in eccentric waveform models, applying them consistently to all contributing harmonics. Using this model, we investigate the impact of these effects on the inference of line-of-sight acceleration and analyze a few interesting GWTC events observed during the third observing run of LIGO and Virgo. We find no substantial evidence for line-of-sight acceleration in these events. We also show that an inconsistent treatment of line-of-sight acceleration between higher harmonics can lead to biased conclusions. Our model provides a robust framework for uncovering line-of-sight acceleration in current and future gravitational-wave observations, enabling more accurate probes of environmental signatures in compact-binary formation.

gr-qc↗

arXiv2025

Scalar fields around black hole binaries in LIGO-Virgo-KAGRA

Light scalar particles arise naturally in many extensions of the Standard Model and are compelling dark-matter candidates. Gravitational interactions near black holes can trigger the growth of dense scalar configurations that, if sustained during inspiral, alter binary dynamics and imprint signatures on gravitational-wave signals. Detecting such effects would provide a novel probe of fundamental physics and dark matter. Here we develop a semi-analytic waveform model for binaries in scalar environments, validate it against numerical relativity simulations, and apply it in a Bayesian analysis of the LIGO-Virgo-KAGRA catalog. We obtain physically meaningful upper limits on scalar densities around most compact binaries. For GW190728 and GW190814, vacuum lies outside the $95\%$ credible region. When including superradiance priors, GW190728 shows tentative evidence for a scalar environment with a Bayes factor of $\ln \mathrm{B}^{\rm env}_{\rm vac} \approx 3.5$, consistent with a light scalar of mass $\sim10^{-12}\,\mathrm{eV}$.

gr-qc↗

arXiv2025

Leveraging the null stream to detect strongly lensed gravitational waves

Gravitational lensing of gravitational waves is expected to be observed in current and future detectors. In view of the growing number of detections, computationally light pipelines are needed. Detection pipelines used in past LIGO-Virgo-KAGRA searches for strong lensing require parameter estimation to be performed on the gravitational wave signal or are machine learning based. Removing the need for parameter estimation in classical methods would alleviate the ever growing demand of computational resources in strong lensing searches and would make real-time analysis possible. We present a novel way of identifying strongly lensed gravitational wave signals, based on the null stream of a detector network. We lay out the basis for this detection method and show preliminary results confirming the validity of the formalism. We also discuss the next development steps, including how to make it independent of parameter estimation.

gr-qc↗

arXiv2025

Confronting general relativity with principal component analysis: Simulations and results from GWTC-3 events

We present a comprehensive assessment of multiparameter tests of general relativity (GR) in the inspiral regime of compact binary coalescences using principal component analysis (PCA). Our analysis is based on an extensive set of simulated gravitational-wave (GW) signals, including both general relativistic and non-GR sources, injected into zero-noise data colored by the noise power spectral densities of the LIGO and Virgo GW detectors at their designed sensitivities. We evaluate the performance of PCA-based methods in the context of two established frameworks: TIGER and FTI. For GR-consistent signals, we find that PCA enables stringent constraints on potential deviations from GR, even in the presence of multiple free parameters. Applying the method to simulated signals that explicitly violate GR, we demonstrate that PCA is effective at identifying such deviations. We further test the method using numerical relativity waveforms of eccentric binary black hole systems and show that missing physical effects--such as orbital eccentricity--can lead to apparent violations of GR if not properly included in the waveform models used for analysis. Finally, we apply our PCA-based test to selected real gravitational-wave events from GWTC-3, including GW190814 and GW190412. We present joint constraints from selected binary black hole events in GWTC-3, finding that the 90% credible bound on the most informative PCA parameter is $0.03^{+0.08}_{-0.08}$ in the TIGER framework and $-0.01^{+0.05}_{-0.04}$ in the FTI framework, both of which are consistent with GR. These results highlight the sensitivity and robustness of the PCA-based approach and demonstrate its readiness for application to future observational data from the fourth observing runs of LIGO, Virgo, and KAGRA.

gr-qc↗

arXiv2025

Rapid parameter estimation with the full symphony of compact binary mergers using meshfree approximation

We present a fast Bayesian inference framework to address the growing computational cost of gravitational-wave parameter estimation. The increased cost is driven by improved broadband detector sensitivity, particularly at low frequencies due to advances in detector commissioning, resulting in longer in-band signals and a higher detection rate. Waveform models now incorporate features like higher-order modes, further increasing the complexity of standard inference methods. Our framework employs meshfree likelihood interpolation with radial basis functions to accelerate Bayesian inference using the IMRPhenomXHM waveform model that incorporates higher modes of the gravitational-wave signal. In the initial start-up stage, interpolation nodes are placed within a constant-match metric ellipsoid in the intrinsic parameter space. During sampling, likelihood is evaluated directly using the precomputed interpolants, bypassing the costly steps of on-the-fly waveform generation and overlap-integral computation. We improve efficiency by sampling in a rotated parameter space aligned with the eigenbasis of the metric ellipsoid, where parameters are uncorrelated by construction. This speeds up sampler convergence. This method yields unbiased parameter recovery when applied to 100 simulated neutron-star-black-hole signals (NSBH) in LIGO-Virgo data, while reducing computational cost by up to an order of magnitude for the longest-duration signal. The meshfree framework equally applies to symmetric compact binary systems dominated by the quadrupole mode, supporting parameter estimation across a broad range of sources. Applied to a simulated NSBH signal in Einstein Telescope data, where the effects of Earth's rotation are neglected for simplicity, our method achieves an O(10^4) speed-up, demonstrating its potential use in the third-generation (3G) era.

gr-qc↗

arXiv2025

Probing missing physics from inspiralling compact binaries via time-frequency tracks

The orbital evolution of binary black hole (BBH) systems is determined by the component masses and spins of the black holes and the governing gravity theory. Gravitational wave (GW) signals from the evolution of BBH orbits offer an unparalleled opportunity for examining the predictions of General Relativity (GR) and for searching for missing physics in the current waveform models. We present a method of stacking up the time-frequency pixel energies through the orbital frequency evolution with the flexibility of gradually shifting the orbital frequency curve along the frequency axis. We observe a distinct energy peak corresponding to the GW signal's quadrupole mode. If an alternative theory of gravity is considered and the analysis of the BBH orbital evolution is executed following GR, the energy distribution on the time-frequency plane will be significantly different. We propose a new consistency test to check whether our theoretical waveform explains the BBH orbital evolution. Through the numerical simulation of beyond-GR theory of gravity and utilizing the framework of second-generation interferometers, we demonstrate the efficiency of this new method in detecting any possible departure from GR. Finally, when applied to an eccentric BBH system and GW190814, which shows the signatures of higher-order multipoles, our method provides an exquisite probe of missing physics in the GR waveform models.

gr-qc↗

arXiv2025

Testing modified gravity with the eccentric neutron star--black hole merger GW200105

Direct detections of gravitational waves offer a unique opportunity to test gravity in the highly dynamical and strong field regime. Current tests are typically performed assuming signals from quasicircular binaries. However, the complex waveform morphology induced by orbital eccentricity can enhance our ability to probe gravity with greater precision. A recent analysis of the neutron star-black hole event GW200105 identified strong evidence for orbital eccentricity. We extend an eccentric-precessing waveform model to test alternative models with this signal by incorporating eccentric corrections induced by Brans-Dicke, Einstein-dilaton-Gauss-Bonnet, and dynamical Chern-Simons gravity at leading post-Newtonian order. We show that analyzing this event with a quasi-circular model leads to a false deviation from general relativity, while the inclusion of eccentricity improves the bounds on the models. Our analysis of GW200105 places tight constraints on Einstein-dilaton-Gauss-Bonnet gravity, $\alpha^{1/2}_{\rm{EdGB}} \lesssim 2.38\,\text{km}$, and Brans-Dicke gravity, $\omega_{\rm{BD}} \gtrsim 3.5$, while dynamical Chern-Simons gravity remains unconstrained due to the low spin content.

gr-qc↗

arXiv2025

Probing gravitational waves using GNSS constellations

The detection of gravitational waves opened up a new window to look into the Universe by probing phenomena invisible through electromagnetic observations. As gravitational waves interact very weakly with matter, their detection is challenging and expensive. So far, they have been observed in the nHz frequency and audible ranges. Future detectors are expected to cover the mHz frequency, leaving the $\mu$Hz regime largely unexplored. With on-board atomic clocks and orbits determined to the cm, Global Navigation Satellite System constellations (GNSS), like GPS or Galileo, offer free access to more than 30 years of clock and orbit data for tests of general relativity. We develop a framework for calculating the deviation in the evolution of GNSS orbits induced by gravitational wave signals. We show that when a gravitational wave interacts in resonance with a satellite's orbit, effects amplify, which can be used to bridge the gap in the $\mu$Hz regime. Finally, we demonstrate that the orbital deviations induced by gravitational waves are coherent across the entire constellation, enabling a satellite network to disentangle GW effects from satellite systematics.

gr-qc↗

arXiv2025

Improved parametrized test of general relativity using the IMRPhenomX waveform family: Including higher harmonics and precession

When testing general relativity (GR) with gravitational wave observations, parametrized tests of deviations from the expected strong-field source dynamics are one of the most widely used techniques. We present an updated version of the parametrized framework with the state-of-art IMRPhenomX waveform family. Our new framework incorporates deviations in the dominant mode as well as in the higher-order modes of the waveform. We demonstrate that the missing physics of either higher-order modes or precession in the parametrized model can lead to a biased conclusion of false deviation from GR. Our new implementation mitigates this issue and enables us to perform the tests for highly asymmetric and precessing binaries without being subject to systematic biases due to missing physics. Finally, we apply the improved test to analyze events observed during the second half of the third observing run of LIGO and Virgo (O3b). We provide constraints on GR deviations by combining O3b results with those from previous observation runs. Our findings show no evidence for violations of GR.

gr-qc↗

arXiv2025

General Concurrence Percolation on Quantum Networks

A quantum network is a network of entangled states, which can be used to transmit quantum information. Nonmaximally entangled states are not really effective in establishing quantum communication across vast distances. Creating and maintaining a maximally entangled state over which quantum information can be transferred more effectively is difficult in experiments, as nonmaximally entangled states are typically produced there. Therefore, we usually construct a network of nonmaximally entangled states and use the underlying network structure to establish maximal entanglement between distant nodes. Various protocols leveraging interesting aspects of quantum and statistical physics are designed to achieve long-range maximally entangled states. Here, we consider two-dimensional lattices as quantum networks where edges represent nonmaximally entangled pure states. We introduce a general protocol based on bond percolation -- general concurrence percolation (GCP) -- to create a network of maximally entangled states. The associated network obtained through GCP ought to enable the achievement of long-range quantum communication. Our observations indicate that, similar to other existing protocols, GCP falls within the percolation universality class, as determined through finite-size scaling analysis performed on two-dimensional lattices. We find that the associated percolation threshold value is smaller than that of the existing protocols. We introduce and analytically solve a minimal model that renders insight into the origin of the fundamentally lower percolation threshold achieved by GCP.

quant-ph↗

arXiv2024

Compact Binary Coalescences in Dense Gaseous Environments Can Pose as ones in Vacuum

The gravitational-wave events observed by the LIGO-Virgo-KAGRA collaboration are attributed to compact binary coalescences happening in vacuum. However, several studies suggest that gaseous environments may play a significant role in the formation and evolution of compact binaries. Why have we not seen environmental effects in LVK signals? While matched-filtering remains the most effective technique for gravitational-wave searches, it comes with a burden: we might only observe signals that align with our (vacuum) expectations, potentially missing unexpected or unknown phenomena. Even more concerning is the possibility that environmental effects could mimic vacuum waveforms, introducing biases in parameter estimation and impacting population studies. Here, we use numerical relativity simulations of binary black hole mergers inside stellar envelopes to show that: (i) a $\texttt{GW150914}$-like event would be detected (with a false alarm rate smaller than $10^{-4}\, \mathrm{yr^{-1}}$) using a template bank of vacuum waveforms, even when immersed in a stellar envelope of density larger than $10^{7}\,\mathrm{g/cm^3}$; (ii) environmental effects can pass routinely performed tests of vacuum General Relativity, while leading to considerable biases in parameter estimation; but (iii) phenomenological environment waveforms are effectual in detecting environmental effects and can resolve systematics.

gr-qc↗

arXiv2024

What is the nature of GW230529? An exploration of the gravitational lensing hypothesis

On the 29th of May 2023, the LIGO-Virgo-KAGRA Collaboration observed a compact binary coalescence event consistent with a neutron star-black hole merger, though the heavier object of mass 2.5-4.5 $M_\odot$ would fall into the purported lower mass gap. An alternative explanation for apparent observations of events in this mass range has been suggested as strongly gravitationally lensed binary neutron stars. In this scenario, magnification would lead to the source appearing closer and heavier than it really is. Here, we investigate the chances and possible consequences for the GW230529 event to be gravitationally lensed. We find this would require high magnifications and we obtain low rates for observing such an event, with a relative fraction of lensed versus unlensed observed events of $2 \times 10^{-3}$ at most. When comparing the lensed and unlensed hypotheses accounting for the latest rates and population model, we find a 1/58 chance of lensing, disfavoring this option. Moreover, when the magnification is assumed to be strong enough to bring the mass of the heavier binary component below the standard limits on neutron star masses, we find high probability for the lighter object to have a sub-solar mass, making the binary even more exotic than a mass-gap neutron star-black hole system. Even when the secondary is not sub-solar, its tidal deformability would likely be measurable, which is not the case for GW230529. Finally, we do not find evidence for extra lensing signatures such as the arrival of additional lensed images, type-II image dephasing, or microlensing. Therefore, we conclude it is unlikely for GW230529 to be a strongly gravitationally lensed binary neutron star signal.

gr-qc↗

arXiv2024

Tests of General Relativity with GW230529: a neutron star merging with a lower mass-gap compact object

On May 29, 2023, the LIGO Livingston observatory detected the gravitational-wave signal GW230529_181500 from the merger of a neutron star with a lower mass-gap compact object. Its long inspiral signal provides a unique opportunity to test general relativity (GR) in a parameter space previously unexplored by strong-field tests. In this work, we performed parameterized inspiral tests of GR with GW230529_181500. Specifically, we search for deviations in the frequency-domain GW phase by allowing for agnostic corrections to the post-Newtonian coefficients. We performed tests with the Flexible Theory Independent and Test Infrastructure For General Relativity frameworks using several quasicircular waveform models that capture different physical effects (higher modes, spins, tides). We find that the signal is consistent with GR for all deviation parameters. Assuming the primary object is a black hole, we obtain particularly tight constraints on the dipole radiation at $-1$PN order of $|\delta\hat{\varphi}_{-2}| \lesssim 8 \times 10^{-5}$, which is a factor $\sim17$ times more stringent than previous bounds from the neutron star--black hole merger GW200115_042309, as well as on the 0.5PN and 1PN deviation parameters. We discuss some challenges that arise when analyzing this signal, namely biases due to correlations with tidal effects and the degeneracy between the 0PN deviation parameter and the chirp mass. To illustrate the importance of GW230529_181500 for tests of GR, we mapped the agnostic $-1$PN results to a class of Einstein-scalar-Gauss-Bonnet (ESGB) theories of gravity. We also conducted an analysis probing the specific phase deviation expected in ESGB theory and obtain an upper bound on the Gauss-Bonnet coupling of $\ell_{\rm GB} \lesssim 0.51~\rm{M}_\odot$ ($\sqrt{\alpha_{\rm GB}} \lesssim 0.28$ km), which is better than any previously reported constraint.

gr-qc↗

arXiv2023

Template bank to search for exotic gravitational wave signals from astrophysical compact binaries

Modeled searches of gravitational wave signals from compact binary mergers rely on template waveforms determined by the theory of general relativity (GR). Once a signal is detected, one generally performs the model agnostic test of GR, either looking for consistency between the GR waveform and data or introducing phenomenological deviations to detect the departure from GR. The non-trivial presence of beyond-GR physics can alter the waveform and could be missed by the GR template-based searches. A recent study [Phys. Rev. D 107, 024017 (2023)] targeted the binary black hole merger, assuming the parametrized deviation in lower post-Newtonian terms and demonstrated a mild effect on the search sensitivity. Surprisingly, for the search space of binary neutron star (BNS) systems where component masses range from 1 to $2.4\:\rm{M}_\odot$ and parametrized deviations span $1\sigma$ width of the deviation parameters measured from the GW170817 event, the GR template bank is highly ineffectual for detecting the non-GR signals. Here, we present a new hybrid method to construct a non-GR template bank for the BNS search space. The hybrid method uses the geometric approach of three-dimensional lattice placement to cover most of the parameter space volume, followed by the random method to cover the boundary regions of parameter space. We find that the non-GR bank size is $\sim$15 times larger than the conventional GR bank and is effectual towards detecting non-GR signals in the target search space.

gr-qc↗

arXiv2023

First constraints on compact binary environments from LIGO-Virgo data

The LIGO-Virgo analyses of signals from compact binary mergers observed so far have assumed isolated binary systems in a vacuum, neglecting the potential presence of astrophysical environments. We present here the first investigation of environmental effects on each of the events of GWTC-1 and two low-mass events from GWTC-2. We find no evidence for the presence of environmental effects. Most of the events decisively exclude the scenario of dynamical fragmentation of massive stars as their formation channel. GW170817 results in the most stringent upper bound on the medium density ($\lesssim 21\,\mathrm{g/cm^3}$). We find that environmental effects can substantially bias the recovered parameters in the vacuum model, even when these effects are not detectable. We forecast that the Einstein Telescope and B-DECIGO will be able to probe the environmental effects of accretion disks and superradiant boson clouds on compact binaries.

gr-qc↗

arXiv2023

Low-latency gravitational wave alert products and their performance at the time of the fourth LIGO-Virgo-KAGRA observing run

Multi-messenger searches for BNS and NSBH mergers are currently one of the most exciting areas of astronomy. The search for joint electromagnetic and neutrino counterparts to GWs has resumed with O4. To support this effort, public semi-automated data products are sent in near real-time and include localization and source properties to guide complementary observations. In preparation for O4, we have conducted a study using a simulated population of compact binaries and a MDC in the form of a real-time replay to optimize and profile the software infrastructure and scientific deliverables. End-to-end performance was tested, including data ingestion, running online search pipelines, performing annotations, and issuing alerts to the astrophysics community. We present an overview of the low-latency infrastructure and the performance of the data products that are now being released during O4 based on the MDC. We report the expected median latency for the preliminary alert of full bandwidth searches (29.5s) and show consistency and accuracy of released data products using the MDC. For the first time, we report the expected median latency for triggers from early warning searches (-3.1s), which are new in O4 and target neutron star mergers during inspiral phase. This paper provides a performance overview for LVK low-latency alert infrastructure and data products using the MDC and serves as a useful reference for the interpretation of O4 detections.

astro-ph.HE↗

arXiv2022

Unraveling information about supranuclear-dense matter from the complete binary neutron star coalescence process using future gravitational-wave detector networks

Gravitational waves provide us with an extraordinary tool to study the matter inside neutron stars. In particular, the postmerger signal probes an extreme temperature and density regime and will help reveal information about the equation of state of supranuclear-dense matter. Although current detectors are most sensitive to the signal emitted by binary neutron stars before the merger, the upgrades of existing detectors and the construction of the next generation of detectors will make postmerger detections feasible. For this purpose, we present a new analytical, frequency-domain model for the inspiral-merger-postmerger signal emitted by binary neutron stars systems. The inspiral and merger part of the signals are modeled with IMRPhenomD_NRTidalv2, and we describe the main emission peak of postmerger with a three-parameter Lorentzian, using two different approaches: one in which the Lorentzian parameters are kept free, and one in which we model them via quasi-universal relations. We test the performance of our new complete waveform model in parameter estimation analyses, studying simulated signals obtained from both our developed model and by injecting numerical relativity waveforms. We investigate the performance of different detector networks to determine the improvement that future detectors will bring to our analysis. We consider Advanced LIGO+ and Advanced Virgo+, KAGRA, and LIGO-India. We also study the possible impact of a detector with high sensitivity in the kilohertz band like NEMO, and finally we compare these results to the ones we obtain with third-generation detectors, the Einstein Telescope and the Cosmic Explorer.

gr-qc↗