Speaker: Dr. Jan Tristram Acuña (NTHU)
Talk title: Phenomenology of compact objects from a first order phase transition in the dark sector
Time: 2024/09/30 (Mon.) 12:30 
Place: R517, New Physics Building

Abstract:
The recent observation of stochastic gravitational waves by NANOGrav has provided impetus to rekindle the interest in studying first order phase transitions (FOPT) in the context of early Universe cosmology. FOPT dynamics may be realized in certain extensions of the Standard Model, which accommodate particle species that reside in the dark sector. In this seminar, I will discuss the scenario of trapped dark matter particles in the false vacuum, leading to the formation of Fermi balls that subsequently collapse into primordial black holes (PBHs). PBHs of masses 10^{-8} to 10 solar masses may induce a Doppler phase shift in the pulsar timing signal, at a level comparable to the sensitivity of SKA-like pulsar timing measurements. By taking stochastic GWs as a complementary probe, we found that critical temperatures of interest lie in the 0.1-10 keV range. This further imposes constraints on the class of quartic scalar potentials that could lead to FOPTs, which can be probed by pulsar timing and GW searches. Finally, motivated by the result that black holes are characterized by their mass and spin, I will present some preliminary results on the spins of false vacuum bubbles, induced by cosmological perturbations during the FOPT. This may serve as a first step in determining the initial spins of PBHs produced from this mechanism.