Conveners
Axion II
- Michael Fedderke (Johns Hopkins University)
Axion-like particles (ALPs) coupled to photons are produced inside stars via the Primakoff process and photon coalescence. They spontaneously decay into two gamma-ray photons that escape from the stellar interior only if decays occur outside the photosphere. Owing to their hot and dense plasma and small radius of the photosphere, horizontal branch stars are promising astrophysical objects to...
Recent studies reveal that more than a dozen of white dwarfs displaying near-perfect blackbody spectra in the optical range have been lurking in the Sloan Digital Sky Survey catalog. We point out that, in a way analogous to the Cosmic Microwave Background, these stars serve as excellent testbeds for new physics. Specifically, we show how their observed lack of spectral distortions translate...
We study the cosmological signatures of a completely secluded dark sector consisting of axion-like particles (ALPs) with anomalous coupling to a dark Abelian gauge boson. The lighter ALP starts rolling during matter domination and produces dark photons through tachyonic instabilities. The resulting exponential growth in dark photon quanta sources tensor and scalar perturbations which are...
We studied the non-equilibrium dynamics of an axion-like particle (ALP) weakly coupled to a thermal bath and misaligned initial conditions. The ALP’s evolution is studied to leading order in the ALP coupling to the bath but to all orders in couplings among the bath’s degrees of freedom. Results are obtained using both Langevin equation derived from in-in formalism and quantum master equation,...
In this talk I will first discuss how rotation-dominated galaxies can be used to constrain the size of solitons inside galaxy dark matter halos. I will discuss how this confronts the theoretical expectation, which leads to a robust constraint on the fraction of ultralight dark matter in a wide mass range from 10^{-24} eV to 10^{-20} eV. I will then discuss how this bound is affected by the...
There exists a whole landscape of QCD axion models. However, if this particle is to make up the dark matter, the absence of catastrophic domain walls and exotic strongly interacting relics singles out two minimal versions of hadronic axions as the only viable possibilities. I argue that these models generically predict sizeable flavor-violating axion couplings to quarks that can be probed at...
