Journal Articleshttps://repository.iitgn.ac.in/handle/123456789/6122019-12-06T17:15:22Z2019-12-06T17:15:22ZConstraints on higher curvature gravity from time delay between GW170817 and GRB 170817AGhosh, AvirupJana, SoumyaMishra, Akash K.Sarkar, Sudiptahttps://repository.iitgn.ac.in/handle/123456789/49622019-11-19T11:29:03Z2019-10-01T00:00:00ZConstraints on higher curvature gravity from time delay between GW170817 and GRB 170817A
Ghosh, Avirup; Jana, Soumya; Mishra, Akash K.; Sarkar, Sudipta
General relativity may be an effective theory with higher curvature correction terms in the action. Inclusion of these terms leads to exciting new possibilities, e.g., gravitational and electromagnetic perturbations following different geodesics, leading to a time delay. Such a time delay was observed between the gravitational wave event GW170817 and its electromagnetic counterpart GRB 170817A. We describe how this effect can be used to constrain the coupling of the higher curvature term. Our method is sufficiently general and applicable to any higher curvature theory.
2019-10-01T00:00:00ZA subset selection based approach to structural reducibility of complex networksTripathi, RichaReza, Amithttps://repository.iitgn.ac.in/handle/123456789/49642019-11-19T11:29:03Z2019-10-01T00:00:00ZA subset selection based approach to structural reducibility of complex networks
Tripathi, Richa; Reza, Amit
Most of the real world networks such as the internet network, collaboration networks, brain networks, citation networks, powerline and airline networks are very large and to study their structure and dynamics one often requires working with large connectivity (adjacency) matrices. However, it is almost always true that a few or sometimes most of the nodes and their connections are not very crucial for network functioning or that the network is robust to a failure of certain nodes and their connections to the rest of the network. In the present work, we aim to extract the size reduced representation of complex networks such that new representation has the most relevant network nodes and connections and retains its spectral properties. To achieve this, we use the Subset Selection (SS) procedure. The SS method, in general, is used to retrieve maximum information (based on Frobenius norm) from a matrix in terms of its most informative columns. The retrieved matrix, typically known as subset has columns of an original matrix that have the least linear dependency. We present the application of SS procedure to many adjacency matrices of real-world networks and model network types to extract their subset. The subset owing to its small size can play a crucial role in analyzing spectral properties of large complex networks where space and time complexity of analyzing full adjacency matrices are too expensive. The adjacency matrix constructed from the obtained subset has a smaller size and represents the most important network structure. We observed that the subset network which is almost half the size of the original network has better information flow efficiency than the original network. Also, we found that the contribution to the Inverse Participation ratio of the network comes almost entirely from nodes that are there in the subset. This implies that the SS procedure can extract the top most influential nodes without the need for analyzing the full adjacency matrix.
2019-10-01T00:00:00ZSearch for eccentric binary black hole mergers with advanced LIGO and advanced Virgo during their first and second observing runsSengupta, Anand S.https://repository.iitgn.ac.in/handle/123456789/49382019-11-19T11:29:01Z2019-09-01T00:00:00ZSearch for eccentric binary black hole mergers with advanced LIGO and advanced Virgo during their first and second observing runs
Sengupta, Anand S.
When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates gsim100 Gpc?3 yr?1 for e > 0.1, assuming a black hole mass spectrum with a power-law index lesssim2.
2019-09-01T00:00:00ZSearch for sub-solar mass ultracompact binaries in advanced LIGO's second observing runSengupta, Anand S.https://repository.iitgn.ac.in/handle/123456789/49392019-11-19T11:29:01Z2019-10-01T00:00:00ZSearch for sub-solar mass ultracompact binaries in advanced LIGO's second observing run
Sengupta, Anand S.
Dark matter; Gravitational wave sources; Gravitational waves; Massive compact halo objects; Astronomical black holes; Gravitational wave detection
2019-10-01T00:00:00Z