Thursday, February 6 2020

11:30 - 13:00

11:30 - 13:00

(LIGO) and Virgo interferometers have led to the detections of gravitational waves (GWs) from

ten binary black hole (BBH) mergers and a binary neutron star (BNS) merger. Among other

things, GWs from these compact binary mergers can be used to probe the behavior of gravity in

highly non-linear and dynamical regime and gain insights about the astrophysics associated with

the formation of these binaries. In this thesis, we explore the dynamics of the compact binary

system within the post-Newtonian (PN) framework in the context of GW astronomy and develop

tests of general relativity (GR) in the strong field regime.

We propose a new model-independent test of GR by parametrizing the gravitational waveform in

terms of the multipole moments of the compact binary using the PN framework. We derive the

parametrized multipolar GW phase evolution for compact binaries (CBs) in quasi-circular orbit

including spin effects in the inspiral dynamics at 3.5PN order and deviations to the PN coefficients

in the 3.5PN conserved energy. We assume that the companion spins are either aligned or anti-

aligned with respect to the orbital angular momentum and compute spin-orbit corrections that are

accurate up to the next-to-next-to-leading order (3.5PN order) and the quadratic-in-spin effects up

to 3PN order in the GW flux and the PN phase. We find that third generation detector such as

Cosmic Explorer (CE) and space based Laser Interferometer Space Antenna (LISA) mission have

the similar ability and can measure the first 4 leading order multipole coefficients with reasonable

accuracies.

Asymmetric emission of GWs from a compact binary can lead to a flux of linear momentum from

the system. As a result, depending on the system configuration, the center of mass (CM) of a

binary system recoils. In this thesis we compute 2PN accurate LMF from various mass and current

type multipole moments for an inspiralling, non-spinning compact binary system in quasi-elliptical

orbit. 2PN Quasi-Keplarian representation (QKR) of the parametric solution to the PN equation of

motion is employed to obtain the LMF at 2PN.

We also propose a new method to track the redshift evolution of the double neutron star mergers.

Proposed third generation detectors such as CE will have the sensitivity to observe double neutron

star (DNS) mergers up to a redshift of ~5 with good signal to noise ratios (SNRs). We argue

that the co-moving spatial distribution of DNS mergers leaves a unique imprint on the statistical

distribution of SNRs of the detected DNS mergers. Hence the SNR distribution of DNS mergers

can be used as a novel probe of their redshift evolution. We consider detections of DNS mergers

by CE and study the SNR distributions for different possible redshift evolution models of DNSs

and employ Anderson Darling p-value statistic to demonstrate the distinguishability between these

different models. We find that a few hundreds of DNS mergers in the CE era will allow us to

distinguish between different models of redshift evolution.

Done