From Dark Matter to Deficit Angles: Effective Field Theory in Cosmology and AdS/CFT
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The Standard Model (SM) of particle physics, despite its accurate and thoroughly tested description of nature, is an incomplete theory. Astrophysical observations indicate an abundance of matter beyond that of the SM, which currently can only be observed through indirect gravitational effects. The Cosmic Microwave Background (CMB) provides a means to constrain both the abundance of this dark matter and the presence of additional light particle species. The SM also fails to provide a full description of gravity, with many open questions as to the quantum nature of gravitational phenomena. In this thesis, we consider three distinct but complementary means of extending this modern framework. Conventional attempts to determine the nature of dark matter are insensitive to models with mass below about a GeV. We consider newly proposed technology which would allow for the detection of dark matter as light as an MeV in mass, through the observation of single electron events in semiconductor materials with significantly lowered thresholds. We find that such detectors would be particularly sensitive to dark matter with electric and magnetic dipole moments, with a reach many orders of magnitude beyond current bounds. We then consider the effects of new light species on the CMB. We perform a thorough survey of natural, minimal models containing new light species and numerically calculate the precise contribution of each of these models to the CMB. We provide a map between the parameters of any particular theory and the results of observational experiments. Using this map, we present new constraints placed by the Planck experiment on the parameter space of several models containing new light species. Finally, we study the universal behavior of long-distance gravitational interactions in AdS3 from the perspective of conformal field theory (CFT). To do so, we compute the structure of Virasoro conformal blocks in a semi-classical, large central charge approximation. Using this result, we then prove the existence of large spin operators with fixed ‘anomalous dimensions’ indicative of the presence of deficit angles in AdS3. As we approach the threshold for the BTZ black hole, interpreted as a CFT2 scaling dimension, the twist spectrum of large spin operators becomes dense. We derive the BTZ quasi-normal modes and show that primary states above the BTZ threshold mimic a thermal background for light operators through exchange of the Virasoro identity block.