arXiv subjects

Poulami Dutta Roy

Publications and source records attributed to Poulami Dutta Roy.

14 recordsLinked to original sources

arXiv2026

Precision Ringdown Measurements of Binary Black Hole Remnants

The ringdown gravitational wave from a binary black hole (BBH) merger is a superposition of quasi-normal modes (QNMs) of the remnant black hole. In general relativity (GR), QNMs are damped harmonic oscillations with frequencies and damping times uniquely determined by the remnant's mass and spin. The measurement of the ringdown modes and performing black hole spectroscopy provides a tool to test the validity of GR. In this work, we present RingCWB, a ringdown analysis method based on coherent WaveBurst (cWB), an unmodeled pipeline for the detection and reconstruction of gravitational-wave signals. This method yields tighter constraints on the QNM frequency and damping time than previous measurements. The improved precision results from the noise reduction achieved by the cWB reconstruction and the enhanced ringdown analysis, which probes the remnant properties at earlier times, closer to the merger. We have analysed publicly available binary black hole (BBH) detections from the third Gravitational-Wave Transient Catalog (GWTC-3). For all events considered, the measured frequency and damping time of the dominant $(l,m)=(2,2)$ mode are found to be consistent with the predictions of GR. A combined analysis further strengthens these constraints, yielding fractional deviations in frequency $δf_{220} = -0.005_{-0.028}^{+0.028}$ and damping time $δτ_{220} = 0.032_{-0.090}^{+0.108}$, consistent with zero within the quoted uncertainties.

gr-qc↗

arXiv2025

Impact of neglecting center-of-mass acceleration in parameter estimation of stellar-mass black holes

A tertiary body near a coalescing binary can imprint its influence on the gravitational waves (GWs) emitted by that binary in the form of center-of-mass (CoM) acceleration. An example of such a scenario is a binary black hole (BBH) merging near a supermassive black hole, which is touted to occur frequently. The limited low-frequency sensitivity of current GW detectors makes it challenging to detect these effects, as the associated waveform phase remains elusive. However, next-generation (3G) detectors such as Cosmic Explorer (CE) and Einstein Telescope (ET), with improved sensitivity at lower frequencies, are expected to be capable of capturing such signatures. In our study, we focus on the stellar-mass BBHs and explore the parameter space where the CoM acceleration will play a dominant role affecting parameter inference of the binary. We demonstrate that an unaccounted CoM acceleration of a low-mass binary with a total mass of $5\, \rm{M}_{\odot} $ can lead to significant systematic biases, exceeding statistical errors in the estimation of the chirp mass and symmetric mass ratio when the CoM parameter $α$ is as small as $\sim 10^{-9}$ and $10^{-10}$ $\rm{s}^{-1}$ for CE and ET, respectively. We also find that asymmetric binaries are more susceptible to systematic bias when CoM acceleration is neglected. When the effect of CoM acceleration is included in the GW phase, then $α= 10^{-7} \rm s^{-1}$ can be constrained with a bound of $10^{-9} (10^{-11})\, \rm s^{-1}$ for CE (ET). Our study thus highlights the crucial implications of considering the presence of a tertiary body in the GW emitted by a stellar-mass BBH when observed in 3G detectors.

gr-qc↗

arXiv2025

Implications of GW241011 for rotating exotic compact objects

A number of theoretical proposals have been made for horizonless compact objects with masses and spins similar to those of black holes. While gravitational wave signatures from their mergers can resemble those of black holes, features like the spin-induced quadrupole moment may reveal their distinct nature. Using the tight bounds on the spin-induced quadrupole moment of GW241011, we place gravitational wave constraints on the nature of its primary. We find that large classes of exotic compact objects (including rotating boson stars) cannot explain its nature, however, models of sufficiently large compactness of $C \gtrsim 0.24$ may still be viable contenders.

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

Shadows of generalised Hayward spacetimes : in vacuum and with plasma

We investigate the shadow properties of a wide class of spacetimes arising from different parameter regimes of the generalized Hayward metric, characterized by two independent parameters $(σ, κ)$ (Phys. Rev. D 106, 044028). This metric extends the original Hayward regular black hole solution by introducing distinct mass functions in the $g_{tt}$ and $g_{rr}$ components, giving rise to four types of wormholes ( which include multi-peak effective potentials), a regular black hole, and a singular black hole solutions allowing for a unified treatment of black hole mimickers. We compute the shadow radii for all spacetimes in vacuum and in the presence of plasma, using both homogeneous and non-homogeneous plasma profiles. Our results show that certain wormhole solutions particularly the Hayward-Damour-Solodukhin class can exhibit multiple photon spheres, leading to shadow features that differ significantly from the Schwarzschild black hole. When these results are compared with Event Horizon Telescope observations of Sgr~$A^\star$, we find that regular black holes remain observationally viable but only within a narrow parameter space. In contrast, wormhole solutions with multi-peak effective potentials are more consistent with shadow constraints than those with single peaks. This contrasts with quasinormal mode studies, which favored single-barrier potentials, and may imply detectable late-time echoes in gravitational wave signals.

gr-qc↗

arXiv2025

Identifying intermediate mass binary black hole mergers in AGN disks using LISA

We show that Laser Interferometer Space Antenna can uniquely identify the sites of intermediate-mass binary black hole (IMBBH) mergers if they occur in Active Galactic Nuclei (AGN) disks with a gas density $ρ\geq10^{-12} \, {\rm g/cc}$ via measurement of dynamical friction effect in the gravitational waveform. We find that even a single observation of a gravitational wave source with a total mass of $10^3 M_{\odot}$ and a mass ratio of 2 at a luminosity distance of 3 Gpc is sufficient to confidently associate the merger to be in an AGN disk with a density $\sim 10^{-12} \, {\rm g/cc}$, as it allows estimation of the density with an error bar $O(100\%)$. This provides a new way of inferring AGN disk densities that complement traditional X-ray observations. Further, we find that neglecting the presence of environmental effects in the waveform models used for parameter estimation can bias the chirp mass, mass ratio and arrival time of a merger. If not corrected, this can significantly impact our ability to carry out multiband data analysis of IMBBHs that combines information from LISA and ground-based gravitational wave detectors.

astro-ph.HE↗

arXiv2024

Tests of general relativity at the fourth post-Newtonian order

The recently computed post-Newtonian (PN) gravitational-wave phasing up to 4.5PN order accounts for several novel physical effects in compact binary dynamics such as the {\it tail of the memory, tails of tails of tails and tails of mass hexadecupole and current octupole moments}. Therefore, it is instructive to assess the ability of current-generation (2G) detectors such as LIGO/Virgo, next-generation (XG) ground-based gravitational wave detectors such as Cosmic Explorer/Einstein Telescope and space-based detectors like LISA to test the predictions of PN theory at these orders. Employing Fisher information matrix, we find that the projected bounds on the deviations from the logarithmic PN phasing coefficient at 4PN is ${\cal O}(10^{-2})$ and ${\cal O}(10^{-1})$ for XG and 2G detectors, respectively. Similarly, the projected bounds on other three PN coefficients that appear at 4PN and 4.5PN are ${\cal O}(10^{-1}-10^{-2})$ for XG and ${\cal O}(1)$ for 2G detectors. LISA observations of supermassive BHs could provide the tightest constraints on these four parameters ranging from ${\cal O}(10^{-4}-10^{-2})$. The variation in these bounds are studied as a function of total mass and the mass ratio of the binaries in quasi-circular orbits. These new tests are unique probes of higher order nonlinear interactions in compact binary dynamics and their consistency with the predictions of general relativity.

gr-qc↗

arXiv2024

Impact of unmodeled eccentricity on the tidal deformability measurement and implications for gravitational wave physics inference

With the expected large number of binary neutron star (BNS) observations through gravitational waves (GWs), third-generation GW detectors, Cosmic Explorer (CE) and Einstein Telescope (ET), will be able to constrain the tidal deformability, and hence the equation of state (EoS) of neutron star (NS) with exquisite precision. A subset of the detected BNS systems can retain residual eccentricity in the detector frequency band. We study the systematic errors due to unmodeled eccentricity in the tidal deformability measurement and its implications for NS EoS and redshift measurement via the Love siren method. We find that the systematic errors in the tidal deformability parameter exceed the statistical errors at an eccentricity of $\sim 10^{-3}$ ($\sim 3\times 10^{-4}$) at $10$Hz reference GW frequency for CE (ET). We show that these biases on tidal deformability parameter can significantly bias the NS EoS inference. Furthermore, the error on tidal deformability propagates to the source frame NS mass, which in turn biases the redshift inference. For CE, the redshift inference is significantly biased at an eccentricity of $\sim 10^{-3}$ (at a reference frequency of $10$Hz). We also study the implications of biased tidal deformability in testing the Kerr nature of black holes. Systematic error on the tidal deformability parameter leads to a non-zero value of tidal deformability for binary black holes, indicating a false deviation from the Kerr nature. Finally, we show that including eccentricity in the waveform model increases the statistical errors in tidal deformability measurement by a factor of $\lesssim 2$. Our study, therefore, highlights the importance of using accurate eccentric waveform models for GW parameter inference.

astro-ph.HE↗

arXiv2024

Black holes in degenerate Einstein Gauss-Bonnet gravity: Can QNMs distinguish them from GR?

In this study, for the first time, we analyse the quasinormal modes of black holes occurring within the framework of degenerate gravity. We investigate the properties of the asymptotically flat spacetimes introduced recently in [JCAP 02(2022)02] that satisfy degenerate Einstein Gauss-Bonnet(dEGB) action and belong to a much larger class of solutions which include cosmological constant. This solution has two distinct branches akin to Einstein Gauss-Bonnet(EBG) gravity. However, unlike the EBG solutions, both the branches of dEGB are well-defined asymptotically. The negative branches from both theories can be identified for the asymptotically flat case. We observe black holes for specific ranges of the Gauss-Bonnet coupling parameter and perform a stability analysis by calculating the quasinormal modes (QNMs) under scalar wave propagation. Finally, the ringdown spectrums of our black holes are compared with their GR counterparts.

gr-qc↗

arXiv2022

Generalised Hayward spacetimes: Geometry, matter and scalar quasinormal modes

Bardeen's 1968 idea of a regular black hole spacetime was revived by Hayward in 2006 through the construction of a new example of such a geometry. Later it was realised by Neves and Saa, that a wider, two-parameter class exists, with Bardeen and Hayward spacetimes as special cases. In this article, we revisit and generalise the Hayward spacetime by applying the Damour-Solodukhin (DS) prescription. Recalling the DS suggestion of a deformed Schwarzschild spacetime where $g_{tt} = -\left (1-\frac{2M_1}{r}\right )$, $g_{rr} = \left (1-\frac{2M_2}{r}\right )^{-1}$ and $M_1\neq M_2$, we propose a similar deformation of the Hayward geometry. The $g_{tt}$ and $g_{rr}$ in the original Hayward line element remain functionally the same, {\em albeit} mutations introduced via differently valued metric parameters, following the DS idea. This results in a plethora of spacetime geometries, known as well as new, and including singular black holes, wormholes or regular black holes. We first study the geometric features and matter content of each of such spacetimes in some detail. Subsequently, we find the scalar quasinormal modes corresponding to scalar wave propagation in these geometries. We investigate how the real and imaginary parts of the quasinormal modes depend on the values and ranges of the metric parameters used to classify the geometries. Finally, we argue how our results on this family of spacetimes suggest their utility as black hole mimickers.

gr-qc↗

arXiv2022

Novel triple barrier potential for axial gravitational perturbations of a family of Lorentzian wormholes

We study the behavior of a specific Lorentzian wormhole family under gravitational perturbations. In earlier work [EPJC 80, 850 (2020)], we have proved the stability of a test scalar field in the background of the wormhole family, where the effective potential was that of a double barrier. Continuing with the stability analysis, here we focus on the more physically relevant scenario, that of axial gravitational perturbations. Interestingly, we find that the effective potential is a triple barrier for lower angular momentum modes. This raises important questions on the ringdown of the corresponding wormhole geometry as well as the gravitational wave echo profile that we try to answer through our work. We study in detail how the geometry of each member wormhole affects the quasinormal modes, the time evolution of the signal as well as echoes which are, in general, very feeble in comparison to the main signal. Different `cleaning' techniques have been used to obtain the echo profile in the time evolution of the signal. Lastly, we dwell on the possibility of our wormhole family as a candidate black hole mimicker, as long as its stability is proven under all kinds of perturbations. We briefly present a comparison of the ringdown characteristics of these wormholes with that of a black hole, in support of this speculation.

gr-qc↗

arXiv2021

A new model with solitary waves: solution, stability and quasinormal modes

We construct solitary wave solutions in a $1+1$ dimensional massless scalar ($ϕ$) field theory with a specially chosen potential $V(ϕ)$. The equation governing perturbations about this solitary wave has an effective potential which is a simple harmonic well over a region, and a constant beyond. This feature allows us to ensure the stability of the solitary wave through the existence of bound states in the well, which can be found by semi-analytical methods. A further check on stability is performed through our search for quasi-normal modes (QNM) which are defined for purely outgoing boundary conditions. The time-domain profiles of the perturbations and the parametric variation of the QNM values are presented and discussed in some detail. Expectedly, a damped oscillatory temporal behaviour (ringdown) of the fluctuations is clearly seen through our analysis of the quasi-normal modes.

hep-th↗

arXiv2020

Revisiting a family of wormholes: geometry, matter, scalar quasinormal modes and echoes

We revisit a family of ultra-static Lorentzian wormholes which includes Ellis-Bronnikov spacetime as a special case. We first show how the required total matter stress energy (which violates the local energy conditions) may be split into a part due to a phantom scalar and another extra piece (which vanishes for Ellis--Bronnikov) satisfying the Averaged Null Energy Condition (ANEC) along radial null geodesics. Thereafter,we examine the effective potential for scalar wave propagation in a general setting. Conditions on the metric function, for which the effective potential may have double barrier features are written down and illustrated (using this class of wormholes). Subsequently, using numerous methods, we obtain the scalar quasinormal modes (QNMs). We note the behaviour of the QNMs as a function of $n$ (the metric parameter) and $b_0$ (the wormhole throat radius). Thus, the shapes and sizes of the wormholes, governed by the metric parameter $n$ and the throat radius $b_0$ are linked to the variation and the values of the QNMs. Finally, we demonstrate how, for large $n$, the time domain profiles exhibit, expectedly, the occurence of echoes. In summary, our results suggest that this family of wormholes may indeed be used as a template for further studies on the gravitational wave physics of exotic compact objects.

gr-qc↗

arXiv2019

Quasi-normal modes in a symmetric triangular barrier

Quasi-normal modes (QNMs) of the massless scalar wave in $1+1$ dimensions are obtained for a symmetric, finite, triangular barrier potential. This problem is exactly solvable, with Airy functions involved in the solutions. Before obtaining the QNMs, we demonstrate how such a triangular barrier may arise in the context of scalar wave propagation in a tailor-made wormhole geometry. Thereafter, the Ferrari-Mashhoon idea is used to show how bound states in a well potential may be used to find the QNMs in a corresponding barrier potential. The bound state condition in the exactly solvable triangular well and the transformed condition for finding the QNMs are written down. Real bound state energies and complex QNMs are found by solving the respective transcendental equations. Numerical integration of the wave equation yields the time domain profiles for scalar waves propagating in this wormhole geometry which illustrate the quasinormal ringing. Estimates relating the size of the wormhole throat (in units of solar mass) with the QNM frequencies are stated and discussed. Finally, we show how the effective potential and the QNMs for scalar perturbations of the Ellis--Bronnikov wormhole spacetime can be reasonably well--approximated using a properly parametrised triangular barrier.

gr-qc↗