Research

My research focuses on the following aspects of Gravitational-Wave astronomy and beyond GR theories:
  • Numerical Relativity;
  • Surrogate waveform modeling of gravitational-wave sources;
  • Gravitational-wave data analysis;
  • Tests of general relativity (GR) using gravitational wave observations; and
  • Astrophysical tests for beyond GR theories.

Gravitational Wave Astrophysics

When two compact objects (e.g. binary black-holes, binary neutron stars or neutron-star and black-hole pairs) merge, they emit gravitational waves (GWs). GWs then travel through the space-time and could be detected by ground-based or space-borne fancy detectors (such as LIGO or LISA). The existence of GWs is a natural outcome in Einstein's general relativity (GR) and had finally been detected in 2015 for the first time. My research interests in GW astronomy are diverse. Below I mention some of my works.

I have contributed to the development of the following gravitational waveform models developed using reduced order surrogate techniques:

  • Minor Contributor to EMRISur1dq1e4, a surrogate waveform model for extreme-mass-ratio-inspirals. The model is available through Black-Hole Perturbation Toolkit (BHPTK) and gwsurrogate python package. The data for the model is hosted here.
  • Lead Contributor to NRSur2dq1Ecc, a numerical relativity based surrogate waveform model for eccentric non-spinning binaries with equal masses. The model would soon be available through gwsurrogate.
  • Lead Contributor to NRSur2dq1Ecc+, a customized surrogate waveform model for eccentric non-spinning binaries with comparable masses up-to mass ratio q<=3. This model too will soon be available through gwsurrogate.
  • Lead Contributor to NRSur2dq1EccRemnant, a surrogate model for the remant properties of eccentric equal mass non-spinning binaries. This model will soon be publicly available through surfinBH.

Image: LIGO-VIRGO Collaboration


Eccentric NR-Surrogate Waveform Model

Eccentric binary black hole surrogate models for the gravitational waveform andremnant properties: comparable mass, nonspinning case.
Publications: arXiv.2101.11798;

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Reanalyzing GW190412 with NRSurrogate

Improved analysis of GW190412 with aprecessing numerical relativity surrogate waveform model.
Publications: arXiv.2010.04848;

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Testing GR with higher modes

Testing the “no-hair” nature of binary black holesusing the consistency of multipolar gravitational radiation.
Publications: arXiv.1910.14259;

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GW Memory in Intermediate mass ratio inspirals (IMRIs)

Survey of gravitational wave memory in intermediate mass ratio binaries.
Publications:

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Source characterization of intermediate mass-ratio inspirals (IMRIs) black hole

Detectability and source characterization of intermediate mass-ratio black hole coalescences with gravitational waves: The importance of higher-order multipoles
Publications: arXiv.2105.04422;

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Beyond General Relativity

My secondary direction of research constitutes the exploration of beyond GR theories.

The validity of GR is well-established in solar-system neighborhood and binary pulsar systems. The detection of gravitational waves from the mergers of binary black holes (BBHs) has further allowed us to test GR in the previously unexplored highly relativistic strong field regime of gravity. So far all GW observations are consistent with GR. However, GR is plagued by an observed ‘mass-discrepancy’ in galaxies and clusters. One way to reconcile GR with observations is to invoke exotic dark matters. No-show of dark matter particles in ambitious experiments so far though has encouraged researchers to look for alternative explanation which considers the ‘mass-discrepancy’ as a signature of the breakdown of GR at galactic and cosmological scales.

Many alternative or modified gravity theories try to achieve these through replacing Einstein's GR with new laws of gravity. My research explores the ability of motivated alternative gravity theories (Weyl Conformal gravity, Chern-Simons gravity, f(R) gravity, Scalar-Tensor-Vector gravity) in providing acceptable fits to the dynamics of self gravitating objects of a wide range of masses, namely globular clusters, galaxies and clusters of galaxies.

Image: arXiv:1807.09241 (Ezquiaga & Zumalacarregui 2018)

Compact objects in beyond GR theories

White-dwarfs and Neutron stras in Scalar-Tensor-Vector Gravity and Horndeski theories.
Publications:

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NGC1052-DF2 and the fate of modified gravity

Modified Gravity Theoriesin Light of the Anomalous Velocity Dispersion of NGC1052-DF2.
Publications: arXiv.1908.07160;

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Ultre-diffuse galaxies

Enigmatic Velocity Dispersions of Ultra-Diffuse Galaxiesin Light of Modified Gravity Theories and Radial Acceleration Relation.
Publications: arXiv.1910.09726;

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Milky Way as a testing bed for gravity

Acceleration Relations in the Milky Way as Differentiators of Modified Gravity Theories.
Publications: arXiv.1911.11836;

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Globular Clusters as a probe for gravity

Globular clusters as a probe for Weyl Conformal Gravity.
Publications: arXiv.1811.00065;

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Viability of conformal gravity

Testing Weyl Gravity at Galactic and Extra-galactic Scales.
Publications: arXiv.1808.06923;

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