Research

Cosmic Inflation

Inflation is a scenario that describes a period (~10-34 seconds after the Big Bang) when the universe underwent an exponential expansion. Our most direct observations for inflation lie in the Cosmic Microwave Background (CMB). However, our best measurements of the CMB from the Planck satellite (Planck Collaboration 2018) do not have enough precision to probe the inflationary epoch. There are many different proposed models of inflation, and without very precise measurements of the CMB to probe this era of the universe, we cannot know which model is the true model of the universe. There are a number of upcoming CMB experiments, such as CMB Stage-4, Simons Observatory, and LiteBIRD, that aim to measure the CMB with extremely high precision with the goal of observing primordial gravitational waves, formed from quantum fluctuations that arose during inflation. These gravitational waves are the "smoking gun" of inflation and would be our most direct evidence for the inflationary scenario!

My research focuses on using predictions of these upcoming high-precision measurements to see if we will be able to detect and distinguish between different models of inflation. I am specifically focusing on the upcoming measurements from LiteBIRD, which aims to attain 30x the sensitivity of previous full-sky CMB experiments, including Planck, targetting large angular scales on the sky. These large angular scales are of particular interest because of an observed suppression of previous CMB measurements compared to the Standard Model of cosmology.

The Planck 2018 temperature power spectrum. The red dots are the Planck measurements and the blue line is the standard cosmological model (ΛCDM) (Planck Collaboration 2018).

The models that I'm considering are called "feature models", which take the simplest inflationary model, called single field slow roll inflation, and add small deviations at particular times. Specifically, I'm considering a "step" model (see Adams et al. 2001) and a "kink" model (see Starobinsky 1992).
Left: A single field slow roll inflation model, depicting a small field "top of hill" potential. The step and kink features are superimosed on this potential.
The deviation of the curvature power spectrum for the step and kink models from the featureless potential. (In this plot, the featureless power spectrum would be a horizontal line at zero.) These oscillatory features are what we would hope to be able to pick out of upcoming CMB measurements at large scales.

The main questions that this project aims to answer are:
  1. If the true model of the universe does not have features, are we able to rule out feature models as statistical fluctuations? Conversely, if the true model of the universe is a feature model, can we detect such a feature?
  2. If we are able to detect a feature, are we able to distinguish between different feature models?

I began working on this project as a first year grad student with my advisor Dr. Xingang Chen and collaborators Dr. Matteo Braglia and Dr. Dhiraj Hazra. I'm continuing this project into my second year of grad school and hope to continue working on similar projects in the near future! (For similar works that performed forecast analyses for Simons Observatory, CMB Stage-4, and LiteBIRD for different inflationary models, see Braglia et al. (2022) and Braglia et al. (2023).)