Conveners
Axions & ALPs II
- Brooks Thomas (Lafayette College)
The QCD axion provides an elegant solution to the Strong CP Problem. While the minimal realization is vulnerable to the so-called “Axion Quality Problem”, I will consider a more robust realization in the presence of a mirror sector related to the Standard Model by a (softly broken) $Z_2$ symmetry. Interestingly, the resulting “heavy” axion has a large and uncharted parameter space where it...
I show that the upper bound of the classical QCD axion window can be significantly relaxed with low-scale inflation. If the Gibbons-Hawking temperature during inflation is lower than the QCD scale and the inflation lasts long enough, the initial QCD axion misalignment angle follows an equilibrium distribution. The distribution is peaked at the strong CP conserving minimum and the variance is...
I will present the results of our study of the non-adiabatic cosmological production of ultra light dark matter (ULDM) under a minimal set of assumptions: a free ultra light real scalar as a spectator field in its Bunch-Davies vacuum state during inflation and instantaneous reheating into a radiation dominated era. For (ULDM) fields minimally coupled to gravity, non-adiabatic particle...
Many axion models in the literature strive to generate phenomenologically advantageous features, such as hierarchies between axion couplings to different gauge fields and/or large effective field ranges. Because these features are strongly constrained by periodicity of the axion coupling to gauge fields for models with only a single axion, many models use mixing of multiple axion fields to try...
We present a new mechanism to relax the initial misalignment angle of the QCD axion and raise the cosmological bound on the axion decay constant. The QCD axion receives a contribution from small UV instantons during inflation, which raises its mass to the inflationary Hubble scale. This makes the axion start rolling down its potential early on. In the scenario, the standard model Yukawa...
To address five fundamental shortcomings of the Standard Model (SM) of particle physics and cosmology, we propose a SMART U(1)$_X$ model which is a $U(1)_X \times U(1)_{PQ}$ extension of the SM, where the $U(1)_X$ gauge symmetry is a generalization of the well-known $U(1)_{B-L}$ symmetry and $U(1)_{PQ}$ is the global Peccie-Quinn (PQ) symmetry. Three right handed neutrinos required to cancel...
I will discuss a production scenario for QCD axion dark matter where the Peccei-Quinn phase transition occurs at a temperature far below the symmetry breaking scale. Both early cosmic string network dynamics and parametric resonance contribute to the axion population. The observed dark matter abundance is reproduced even if the decay constant is much lower than 10^11 GeV. I will also discuss...
