E-Thesis 380 views 256 downloads
Gravitational Waves from Inflation / MARIA MYLOVA
Swansea University Author: MARIA MYLOVA
DOI (Published version): 10.23889/SUthesis.56907
Abstract
The focus of this work is on the topic of gravitational wave cosmology. We look for new observational signatures for primordial gravitational waves and especially for frameworks that can produce an enhanced tensor spectrum. In such cases, the gravitational wave energy density can enter within the se...
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Swansea
2020
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Tasinato, Gianmassimo |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa56907 |
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| Abstract: |
The focus of this work is on the topic of gravitational wave cosmology. We look for new observational signatures for primordial gravitational waves and especially for frameworks that can produce an enhanced tensor spectrum. In such cases, the gravitational wave energy density can enter within the sensitivity curves of gravi-tational wave detectors or it could leave a measurable imprint in the polarization pattern of the Cosmic Microwave Background radiation. This is very important as more sensitive, next generation experiments are expected to make indirect and direct measurements of the primordial stochastic gravitational wave background.Our investigation showed that an enhanced tensor amplitude can be achieved, within the framework of the Horndeski theory, if there is a short period where slow-roll inflation is violated. We considered a model of kinetically driven inflation where for a short time the scalar field velocity is heavily time-dependent. During that time the would-be decaying tensor mode becomes a growing mode. Analysis of the bispectrum showed that this can lead to sizeable tensor non-Gaussianities.We also considered possible realizations of the effective field theory of Scalar-Tensor gravity. In particular, we looked for a setup up of operators that could lead to the enhancement of parity violating effects for tensors. We introduced modifications to gravity which enabled us to parametrically approach the scale at which maximal parity violation occurs. Using the mathematical machinery for effective field theories we showed that sub-leading quadratic operators can become important signalling the presence of the Chern Simons instability. This inevitably implies the existence of non-trivial cubic interactions which could stand the theory strongly coupled at energies not far above the energy scale of inflation. Consequently, this can lead to large parity violation in tensor non-Gaussianity. |
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| Item Description: |
ORCiD identifier https://orcid.org/0000-0003-1772-7014 |
| Keywords: |
gravitational waves, inflation, parity violation, non-attractor, non-Gaussianity |
| College: |
Faculty of Science and Engineering |