Speaker: Silvia Gasparotto (IFAE Barcelona)
Title: Cosmic Birefringence: Insights on Axiverse and Domain Walls with CMB Polarization
Abstract: The cosmic microwave background (CMB) holds intriguing evidence of cosmic birefringence – an isotropic rotation of the polarization direction, manifesting in the CMB's parity-odd spectra. This phenomenon finds a compelling explanation within axion physics, where a light scalar field interacts with the electromagnetic field through a Chern-Simons interaction, violating parity.
I will discuss how CMB birefringence can be explained within the axiverse framework, which suggests the presence of multiple active axions post-CMB. I will show how the present and future measurements of cosmic birefringence can help constrain the probability distribution functions of the axiverse, including mass, decay constants and initial conditions.
I will also discuss the case of domain walls, topological defects enhancing the anisotropic component of the birefringence signal. I will show how the hypothesis of network annihilation post-recombination impacts the shape of the birefringence spectrum and leaves distinctive signatures on the BB spectrum of the CMB. From this contribution, new constraints on the tension of domain walls are derived within this specific parameter space.
Place: CoPS room/A5:1041 and Zoom