Prospects in classical and quantum gravity : from theory to phenomenology

Mohapatra, Sonali (2019) Prospects in classical and quantum gravity : from theory to phenomenology. Doctoral thesis (PhD), University of Sussex.

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Abstract

General Relativity (GR) is a highly successful theory whose predictions are still being confirmed a hundred years later. However, despite its significant success, there still remain questions beyond the realm of its validity. The reconciliation of Standard Model (SM) and GR or Quantum Mechanics (QM) and GR point towards the need for a potential modification of GR or a consistent theory of quantum gravity (QG). The purpose of this thesis is to explore classical and quantum gravity in order to improve our understanding of different aspects of gravity, such as black holes (BHs), exotic compact objects (ECOs) like Boson Stars (BS) and gravitational waves (GW). We follow recent advancements in the field of Effective Quantum Gravity (EQG) by noticing that gravity naturally lends itself to an effective framework. The cut off of this effective theory is set to be the Planck mass since this is where UV effects are expected to take over. We focus on finding low energy quantum corrections to General Relativity by using the effective 1PI action and the modified gravity propagator. These include predictions of two new gravitational wave modes in addition to the usual classical GW mode predicted by GR. We investigate and make comments on whether these modes could have been produced by the events observed by LIGO and the energy scales in which these could be possibly produced. In the next project, we investigated whether there exists a correction to the quadrupole moment formula in GR to calculate the energy carried away by gravitational radiation. We apply the corrected formula to calculate the gravitational radiation produced in a binary black hole system in the effective quantum gravity formalism. We make comments regarding its regime of validity. While working in the field of gravitational waves, an interesting aside was modelling of Exotic Compact Objects such as Boson Stars which could also potentially act as black hole mimickers. We calculated analytically the gravitational radiation background produced by binary BS systems. We also commented on and put constraints on their possible detectability by LISA. Last but not the least, an important area in QG is the study of black hole thermodynamics. Corrections to the Bekenstein-Hawking area theorem have been calculated in various quantum gravity approaches and have been found to have a logarithmic form. In the last paper of this thesis, combining insights from Effective Quantum Gravity and Black Hole Thermodynamics, we motivate a generalised Area-Entropy law for black holes building upon the idea of an adiabatic invariant. This allows us to find interesting constraints on the number of fields in a consistent theory of quantum gravity. This work is particularly interesting because of its potential consequences in finding minimal extensions to the standard model and combining the standard model with a consistent theory of gravity.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics > QC0170 Atomic physics. Constitution and properties of matter Including molecular physics, relativity, quantum theory, and solid state physics > QC0178 Theories of gravitation
Depositing User: Library Cataloguing
Date Deposited: 02 Jan 2020 09:39
Last Modified: 02 Jan 2020 09:39
URI: http://sro.sussex.ac.uk/id/eprint/88758

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