Astrophysics Seminar

The cosmic microwave background (CMB) is one of our most powerful probes of fundamental physics, encoding information about the early universe in its temperature and polarization. As CMB photons travel to us, they are deflected by the intervening large-scale structure, a phenomenon known as gravitational lensing, which both carries rich cosmological information and acts as a contaminant for primordial signals. In this talk, I will present a series of results connecting CMB lensing, delensing, and searches for new physics.

I will begin with an overview of CMB lensing and present forecasts for its full-sky measurement with the upcoming satellite mission LiteBIRD. I will then discuss delensing, the method of using a reconstructed lensing map to partially remove the lensing-induced B-mode polarization, and show how it improves LiteBIRD's sensitivity to inflationary gravitational waves. A central part of the talk focuses on cosmic birefringence, the rotation of the CMB polarization plane due to parity-violating new physics such as axion-like particles coupled to photons. I will introduce both isotropic and anisotropic birefringence and present the first study demonstrating how delensing enhances cosmic birefringence constraints: for isotropic birefringence, delensing reduces the lensing-induced variance in the EB power spectrum, while for anisotropic birefringence, it mitigates the dominant reconstruction bias and tightens amplitude constraints. Finally, I will present a complementary approach to measure anisotropic cosmic birefringence through its imprint on CMB B-mode polarization and constraint leading observational bounds using combined data from SPTpol, ACT, POLARBEAR, and BICEP, illustrating the promise of next-generation experiments in the search for parity-violating physics beyond the Standard Model.