PUBLIC VIVA-VOCE NOTIFICATION
Date and Time : Monday, 22 November 2021, 3.00 pm
A study of Scattering Amplitudes in the Infrared regime
Athira P V
Chennai Mathematical Institute.
In this thesis, we investigate the relationship between asymptotic symmetries of QCD and vacuum transi- tions induced during scattering. We show that the corresponding asymptotic Hilbert space is generated by a class of dressed states in which each finite energy particle is dressed by a cloud of interacting soft gluons. We identify the precise structure of the dressing using conservation laws and show that the corresponding asymptotic states are equivalent to the generalised coherent states defined by Catani et al.
We further study the classical electromagnetic/gravitational radiation in the low frequency regime. We apply the recently developed formalism by Kosower, Maybee and O’Connell (KMOC)  to analyse the soft electromagnetic and soft gravitational radiation emitted by particles without spin in D ≥ 4 dimensions. We use this formalism in conjunction with quantum soft theorems to derive radiative electro-magnetic and gravitational fields in low frequency expansion and upto next to leading order in the coupling. We show that in all dimensions, the classical limit of sub-leading soft (photon and graviton) theorems is consistent with the classical soft theorems proved by Sen et al in a series of papers. In particular in  Saha, Sahoo and Sen proved classical soft theorems for electro-magnetic and gravitational radiation in D = 4 dimensions. For the class of scattering processes that can be analyzed using KMOC formalism, we show that the classical limit of quantum soft theorems is consistent with the D = 4 classical soft theorems, paving the way for their proof from scattering amplitudes.