Weizmann Institute

by Nadav Outmezguine (UC Berkeley), Konstantin Springmann (TU Munich)

Wednesday 28 Jun 2023, 11:30 → 14:30 Asia/Jerusalem

Weissman Aquarium (Weizmann Institute of Science)

11:00 Coffee break

11:30 Nadav Outmezguine (UC Berkeley)

Title: The Irreducible Axion Background

Abstract: Searches for dark matter decaying into photons constrain its lifetime to be many orders of magnitude larger than the age of the Universe. A corollary statement is that the abundance of any particle that can decay into photons over cosmological timescales is constrained to be much smaller than the cold dark-matter density. We show that an irreducible freeze-in contribution to the relic density of axions is in violation of that statement in a large portion of the parameter space. This allows us to set stringent constraints on axions in the mass range 100 eV - 100 MeV. 

12:30 Lunch

13:30 Konstantin Springmann (TU Munich)

Title: How axions change stars

Abstract: Dense stars such as white dwarfs and neutron stars can trigger a phase transition for light scalars. Once the scalar obtains a non-trivial expectation value, the mass of the nucleons within the star is reduced which can lead to a new ground state of matter. The new ground state allows for dramatically heavier maximal masses and radii. Another prediction of the new ground state is a radius gap in the mass radius curve. For lighter than expected QCD axions the resulting masses and radii of white dwarfs are not compatible with existing data, allowing us to set stringent bounds on unexplored axion parameter space.