Research projects

• Coherent data analysis strategies for the search for transient, unmodelled GW bursts using a network of detectors:  Given the time-series data from multiple gravitational wave (GW) detectors, one can find a particular linear combination of the data streams such that all GW signals are canceled.  The idea of this null-stream was proposed by G\"ursel and Tinto in the late-1980's.  The null-stream can be used to distinguish between real GW triggers and spurious noise transients in a triggered search for GW bursts using a network of detectors. We formulate and demonstrate a 'veto' strategy which can be used to separate real and spurious triggers in the search for transient, unmodelled GW bursts using  a network of ground-based interferometric GW detectors. 

• Instrumental vetoes for GW burst triggers:  The search for signatures of GW bursts in the data of ground-based interferometric detectors typically uses `excess-power' search methods. One of the most challenging problems in the burst-data-analysis is to distinguish between actual GW bursts and spurious noise transients that trigger the detection algorithms. We have formulated a unique and robust strategy to `veto' the instrumental glitches. This method makes use of the phenomenological understanding of the coupling of different detector sub-systems to the main detector output. The main idea behind this method is that the noise at the detector output (channel H) can be projected into two orthogonal directions in the Fourier space - along, and orthogonal to, the direction in which the noise in an instrumental channel X would couple into H. If a noise transient in the detector output originates from channel X, it leaves the statistics of the noise-component of H  orthogonal to X unchanged.

• Post-Newtonian theory and data-analysis from inspiralling compact binaries: Post-Newtonian expansions of the binding energy and gravitational wave flux truncated at the same relative post-Newtonian order form the basis of the standard adiabatic approximation to the  phasing of GWs from inspiralling compact binaries. Viewed in terms of the dynamics of the binary, the  standard approximation is equivalent to neglecting certain conservative post-Newtonian terms in the acceleration. We have proposed a new complete adiabatic approximant constructed from the energy and flux functions. At the leading order it employs the 2PN energy function rather than the 0PN one in the standard approximation, so that, effectively the approximation corresponds to the dynamics where there are no missing post-Newtonian terms in the acceleration. We have compared the overlaps of the standard and complete adiabatic templates with the exact waveform in the adiabatic approximation of a test-mass motion in the Schwarzschild spacetime.  The complete adiabatic approximants lead to a remarkable improvement in the effectualness at lower PN (< 3PN) orders, while standard approximants of order >= 3PN provide a good lower-bound to the complete approximants for the construction of effectual templates.  Faithfulness of complete approximants is better than that of standard approximants except for a few post-Newtonian orders.

• Application of numerical relativity into gravitational-wave data analysis: Coalescing binary black-hole systems are among the most promising sources of gravitational waves for ground-based interferometers. While the inspiral and ring-down stages of the binary black-hole coalescence are well-modelled by analytical approximation methods in general relativity, the recent progress in numerical relativity has enabled us to compute accurate waveforms from the merger stage also. This has important impacts in the search for gravitational waves from binary black holes. In particular, while the current gravitational-wave searches look for each stage of the coalescence separately, combining the results from analytical and numerical relativity enables us to coherently search for all three stages using a single template family. This coherent search is significantly more sensitive than the current searches, potentially bringing remarkable improvement in the event rate for ground-based detectors.