<mods:mods xmlns:mods="http://www.loc.gov/mods/v3" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-7.xsd"><mods:titleInfo><mods:title>Aspects of Cosmological, Celestial and String Amplitudes</mods:title></mods:titleInfo><mods:typeOfResource authority="primo">dissertations</mods:typeOfResource><mods:name type="personal"><mods:namePart>De, Shounak</mods:namePart><mods:role><mods:roleTerm type="text">creator</mods:roleTerm></mods:role></mods:name><mods:name type="personal"><mods:namePart>Volovich, Anastasia</mods:namePart><mods:role><mods:roleTerm type="text">Advisor</mods:roleTerm></mods:role></mods:name><mods:name type="personal"><mods:namePart>Alexander, Stephon</mods:namePart><mods:role><mods:roleTerm type="text">Reader</mods:roleTerm></mods:role></mods:name><mods:name type="personal"><mods:namePart>Fan, JiJi</mods:namePart><mods:role><mods:roleTerm type="text">Reader</mods:roleTerm></mods:role></mods:name><mods:name type="corporate"><mods:namePart>Brown University. Department of Physics</mods:namePart><mods:role><mods:roleTerm type="text">sponsor</mods:roleTerm></mods:role></mods:name><mods:originInfo><mods:copyrightDate>2025</mods:copyrightDate></mods:originInfo><mods:physicalDescription><mods:extent>xxiii, 220 p.</mods:extent><mods:digitalOrigin>born digital</mods:digitalOrigin></mods:physicalDescription><mods:note type="thesis">Thesis (Ph. D.)--Brown University, 2025</mods:note><mods:genre authority="aat">theses</mods:genre><mods:abstract>In this thesis, we present novel perspectives on the explicit evaluation and analytic structure of correlation functions and scattering amplitudes in flat and expanding spacetimes. Specifically, we analyze wavefunction coefficients in a toy model theory of conformally coupled scalars within power-law FRW cosmologies, examine unitarity constraints on dual resonant string amplitudes, and further our understanding of the flat-space S-matrix using the framework of celestial amplitudes.
First, we explore intriguing connections between positive geometries, on-shell methods, and bootstrap principles studied within the modern scattering amplitudes program to the Bunch-Davies wavefunction in toy models of FRW cosmologies. Leveraging recent advances in twisted cohomology and generalized unitarity from the Feynman integral literature, we develop an algorithm to construct a physical basis that simplifies the computation of differential equations for all tree and loop-level wavefunction contributions. Furthermore, we unravel the existence of hidden zeros in the cosmological wavefunction and demonstrate a universal factorization behavior associated with the kinematics of near-zero configurations for all tree and loop graphs.
Second, we investigate the constraints of partial wave unitarity on dual resonant amplitudes from the viewpoint of the modern S-matrix bootstrap. Focusing on the Coon amplitude - a one-parameter deformation of the Veneziano amplitude with logarithmic Regge trajectories - we establish manifest positivity on certain Regge trajectories while identifying regions of unitarity violation in parameter space using tools from q-calculus and numerical methods.
Finally, we make substantial advances in the study of celestial amplitudes by investigating the dual celestial conformal field theory (CCFT) and the role of light-ray operators, which are increasingly recognized as fundamental components of the CCFT spectrum. We present new computations of tree-level correlation functions for these operators, demonstrating their appearance in the operator product expansion of gluon primaries. Additionally, we examine the treatment of distributional low-point correlators by introducing a background that breaks bulk translation invariance, yielding correlators that more closely resemble those found in traditional two-dimensional CFTs.</mods:abstract><mods:subject authority="fast" authorityURI="http://id.worldcat.org/fast" valueURI="http://id.worldcat.org/fast/00880600"><mods:topic>Cosmology</mods:topic></mods:subject><mods:subject><mods:topic>scattering amplitudes</mods:topic></mods:subject><mods:subject authority="fast" authorityURI="http://id.worldcat.org/fast" valueURI="http://id.worldcat.org/fast/01085105"><mods:topic>Quantum field theory</mods:topic></mods:subject><mods:subject><mods:topic>string theory</mods:topic></mods:subject><mods:subject><mods:topic>conformal field theory</mods:topic></mods:subject><mods:language><mods:languageTerm authority="iso639-2b">English</mods:languageTerm></mods:language><mods:recordInfo><mods:recordContentSource authority="marcorg">RPB</mods:recordContentSource><mods:recordCreationDate encoding="iso8601">20250707</mods:recordCreationDate></mods:recordInfo></mods:mods>