Thesis Defense

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Events on Thursday, May 16th, 2024

Large Blue isocurvature from a classical conformal limit
Time: 12:00 pm - 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Sai Chaitanya Tadepalli, Physics PhD Graduate Student
Abstract: When additional degrees of freedom are considered during inflation, a crucial aspect of early-universe physics emerges: the generation of isocurvature quantum fluctuations, akin to independent quantum perturbations. These fluctuations can offer valuable insights into inflation and the presence of spectator fields and their mass scales. Current data tightly constrains the cold dark matter (CDM) isocurvature amplitude on scales k&lt;0.1 h/Mpc. However, blue-tilted (spectral index &gt;1) isocurvatures can be invisible on large scales and leave a huge imprint on small scales. This thesis explores the generation and forecast of axionic blue-tilted isocurvature perturbations.

In the first part of this thesis, we study the generation of CDM uncorrelated blue-tilted isocurvature perturbations for the axions when the axionic sector is far out of equilibrium during inflation through an initial Peccei-Quinn symmetry breaking field displacement. We investigate two distinct models, where these fluctuations originate from the dynamical evolution of the radial field through the quadratic and quartic components of the effective potentials. In the quadratic case, we find that there exist parametric regions with a strong resonant spectral behavior that leads to rich isocurvature spectral shapes. A consequence of this nonlinearity-driven resonance is the chaotic nature of the map that links the underlying Lagrangian parameters to the isocurvature amplitudes. In the quartic scenario, we propose a novel method to generate the blue-tilted spectrum over a large range of scales by utilizing the classical conformal limit.

In the second part of the thesis, we present a Fisher forecast for the Euclid and MegaMapper experiments in their ability to detect blue isocurvature perturbations. We construct the theoretical predictions in the EFTofLSS and bias formalisms and report optimistic results highlighting the potential for detecting the CDM blue isocurvature amplitude in forthcoming surveys.
Host: Daniel J Chung
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