BITS Pilani

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Plenary/Special Talks

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IAGRG MEETING

Speakers

Plenary Talks
 
Sudipta Sarkar  (IIT Gandhinagar).
 
Title: The quest for Physics Beyond General Relativity.

Abstract: Black holes have often provided profound insights into the nature of quantum gravity and the structure of space-time. The study of the mathematical properties of black objects is a major theme of contemporary theoretical physics. In this talk, I will describe how the study of the black holes can provide constraints on the possible extensions of General Relativity.
 
 
Madhavan Varadarajan  (RRI)
 
Title: Loop Quantum Gravity

Abstract: LQG is an attempt to construct a non-perturbative quantization of General Relativity. Rather than treat the quantum gravitational field as a quantum excitation over a fixed classical space-time geometry, it seeks to construct the quantum mechanics of the gravitational field as a whole without recourse to any classical background space-time geometry. In this talk I will focus on canonical LQG. I will provide a broad overview of its key structural features and their implications, first through a discussion of its foundations and second, through an application of LQG ideas to physics near the Big Bang. 
 
  
Sukanta Bose (IUCAA)
 
Title: The long and short of gravitational waves: From a measurement of the Hubble constant to bounding the neutron star radius.

Abstract:I will summarize how within the first couple of years of direct gravitational wave (GW) observations this new information channel is already churning out some surprises and launching exciting ways of probing the cosmos. These include constraining (a) the neutron star equation of state with GW and electromagnetic observations of GW170817 as well as (b) the Hubble constant with the same observations and the GW detections of several black hole mergers.
 
Ravi Subrahmanyan  (RRI)
 
Title: Discerning evolution through Cosmic Dawn and the Epoch of Re-ionization

Abstract: As first light from the first stars transforms the universe from the dark ages into cosmic dawn, and the primordial gas transforms to galaxies and ionized intergalactic medium, the history may be traced in redshifted 21-cm from neutral hydrogen in the gas.  Efforts to build precision radiometers over the 40-200 MHz band to detect this faint signal are beginning to yield results of significance to the theory, thus constraining the starlight of the earliest galaxies. I will review the field and discuss the problems and progress.
  
Subinoy Das (IIA)
 
Title: Dark sector of our Universe.

Abstract: Inspite of extensive search, the nature of dark matter and dark energy still remains a mystery. The existence of these major components only got confirmed through their gravitational effects but the fundamental nature of this sector is unknown. In this talk,  I will discuss how near future experiments along with our present theoretical understanding will be able to shed light on this mysterious sector.  I will also discuss the status of modified theory of gravity as a substitute of real existence of dark sector. 
 
Anshuman Maharana (HRI)
 
Title: String Cosmology. 
Abstract: This talk will provide an introduction to string cosmology. We will start by discussing dimensional reduction and its implications for cosmology. We will then go on to discuss inflationay model building in string theory. Finally, we will briefly discuss more recent developments such as the swampland conjectures and their status.
  
 
 
  
 
Lekshmi Resmi (IIST)
 
Title: Astrophysics of the first binary Neutron Star merger GW170817

Abstract: The first binary Neutron Star merger and its electromagnetic counterparts have marked the beginning of multi-messenger astronomy. On 17 August 2017, AdvLIGO/VIRGO detected the gravitational wave transient GW170817 which spatially and temporally coincided with the Gamma-Ray Burst GRB170817A, triggered by FERMI gamma-ray space telescope. Soon, the Swope telescope in Chile discovered associated optical emission, to be named AT2017gfo later. This was the first direct observational confirmation of the proposed novel transient, kilonova, resulting from NS material tidally ejected during the merger. Subsequently, non-thermal afterglow of GRB170817A shone through the entire electromagnetic spectrum. These observations also confirmed that relativistic jets producing Gamma-Ray Bursts can emerge out of NS mergers. In this talk, I will review electromagnetic observations going on for the last one year across the world, including at the Giant Metrewave Radio Telescope (GMRT) in India, and the novel perceptions from joint GW-EM multi-messenger astronomy.
 
Varun Bhalerao (IITB)
 
Title - Indian eyes on gravitational wave skies.

Abstract - I will talk about India based followup of gravitational wave events with AstroSat, GMRT, and the Himalayan Chandra telescope. I will then talk about exiting prospects for the future including the GROWTH India robotic telescope and the Daksha space mission. 
 
Anuradha gupta  (Penn State)
 
Title: Compact binary mergers observed by LIGO and Virgo during their first and second observing runs.

Abstract: The first and second observing runs of advanced LIGO and Virgo detectors have led to the observation of 10 stellar-mass binary black hole mergers and one binary neutron star merger so far. With these detections, the LIGO and Virgo Scientific Collaboration has released their first catalog of gravitational wave events. In this presentation, I will talk about how the searches for these events were made, what are their properties, and what astrophysical implications they have. These detections undoubtfully have opened up new avenues for gravitational wave astronomy and astrophysics.
 
Alok Laddha (CMI)
 
Title: Classical Limit of Soft Graviton Theorem and the memory effect. 

Abstract: In this talk we will show how Soft Graviton Theorem in Quantum Gravity can be used for analysing low frequency gravitational radiation in classical scattering processes in arbitrary dimensions. In Four dimensional this analysis yields an interesting observable effect.  Namely, a late time component in Gravitational field that falls off as inverse power of time, which can be interpreted as a tail term to the Linear Memory effect.
 
  
Kandaswamy Subramanian  (IUCAA)
 
Title: Origins of cosmic magnetism
 
Abstract: The universe is magnetised from stars to the large-scale coherent magnetic fields detected in galaxies and galaxy clusters, and even perhaps the intergalactic medium in voids. The standard picture for the origin of fields in all astrophysical systems involves turbulent dynamo amplification of a weak seed magnetic field. In such dynamos the kinetic energy of motions get converted to magnetic energy. We review the basic idea behind such dynamos and the main challenges they encounter. While it is relatively easy for magnetic energy to grow, explaining the observed degree of coherence of cosmic magnetic fields generated by turbulent dynamos, remains challenging. We outline potential resolution of these challenges, and a new paradigm for rapid unified growth of both large and small scale fields in galaxies. We end with a possible model of inflationary magnetogenesis which addresses several difficulties of such scenarios, and could explain the magnetic field in voids providing also a seed magnetic field for the dynamo. 
 
R. Loganayagam  (ICTS)

Title: Fluid/Gravity correspondence

Abstract: Will be updated. 
 
 
  
 Special Talks:
 
Daksh Lohiya (Hawking Memorial Lecture)
 
Title: Working with Stephen Hawking.

Abstract: I recount memories of my association with Stephen Hawking spanning more than four decades. I would try and describe what made Stephen so famous. I would recount the behind the scenes action on several discoveries Stephen made: (a) As the primary irritant for Fred Hoyle's efforts on the Steady State Cosmology; (b) As the primary damper for the misdirected Soviet School of Cosmology; and finally (c) As the cause of the most intense debate on aspects of black hole  radiation and information paradox. The talk is for a general audience.
  
Jayant V Narlikar (Vaidya Centenary Lecture)
 
Title: Spectral shifts in General Relativity.
                            
Abstract - Through this lecture the speaker will pay his homage to the late Professor P.C. Vaidya during his birth centenary year. This work will describe a unified way of looking at different types of spectral shifts (Doppler, gravitational and cosmological) in such a way that the basic approach is the same for all. Explicit examples are given to show how this calculation works.  This topic will be of interest to general relativists because of the use made of parallel transport.  It is argued that although different types of redshifts are usually discussed separately, they should be looked at in a unified way.
 
 
Pratik Majumdar (SNIP) 
 
Title : Multi-messenger Astrophysics with high energy gamma rays and neutrinos.

Abstract: Recent detection of a very high energy neutrino above several hundred TeV coincident with a high energy gamma-ray flare (from few hundred MeV to few hundred GeV) from a "blazar" source (TXS 0506+056) has generated a lot of excitement because of its implications for the long standing problem of the origin of high energy cosmic rays. Follow-up observations were also conducted in other wavelengths (X-rays and optical). We will briefly review the different observations that led to this new detection and also discuss their implications for the mechanisms of production of high energy gamma-rays and neutrinos in this source in particular, and the origin of high energy cosmic rays in general.
 P Ajith (ICTS-TIFR)

Title: Gravitational-waves from binary black holes: The interplay of theory and observation 

Abstract - Coalescing binary black holes are among the strongest sources of gravitational waves. Binary black hole observations by LIGO and Virgo are now providing interesting probes of strong gravity and astrophysics. This talk will trace some recent developments in the theoretical modeling of the expected signals from binary black holes and their application in LIGO’s data analysis pipelines that aided these detections and the extraction of source parameters. The talk will also discuss some of the ongoing probes of strong gravity and astrophysics from these observations and will give a flavor of the future prospects.
 
 N D Hari Dass (ICTS-TIFR)

Title: Low energy theorems for electromagnetic and gravitational radiation.

Abstract: After explaining the spirit behind the so called low energy theorems, LETs (more accurately, low momentum transfer theorems), I will first demonstrate their great powers in delivering many important results in particle physics. I will then show how Francis Low applied this to electromagnetic radiation. After describing some of Weinberg’s pioneering works in applications to gravitation, I will describe my own work on gravitational radiation using LET’s, reproducing Einstein’s quadrupole formula. I shall bring out various nuances and discuss future prospects.
 
 

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