Conveners
Axions & ALPs
- Raymond Co (University of Michigan)
We consider a generic framework for axion-like particles (ALPs) by introducing a complex scalar singlet field. The breaking of the corresponding global U(1) symmetry at some high scale leads to a (pseudo) Goldstone boson that is identified as the ALP. We show that if the complex scalar field is coupled to the Standard Model Higgs boson, there exists a large parameter space for which the U(1)...
Axion-like particles (ALPs) produced in the core of a neutron star can convert to photons in the magnetosphere, leading to possible signatures in the soft and hard X-ray emission from these sources. We study these signatures taking the magnetar SGR 1806-20 as an example. In particular, assuming ALP emission rates from the core that are just subdominant to neutrino emission, the parameter...
White dwarf (WD) stars may radiate keV-energy axions produced in their stellar cores. This has been extensively studied as an extra channel by which WDs may cool, with some analyses even suggesting that axions can help explain the observed WD luminosity function. We show that the radiated axions may convert into X-rays in the strong magnetic fields surrounding the WDs, leading to observable...
Axions, which can solve the Strong CP problem, and axion-like particles (ALPs), which arise naturally in many models of high-scale physics, provide theoretically compelling dark matter candidates. Axions and ALPs which couple to photons have been shown to produce observable radio emission through their conversion to photons in the magnetospheres of neutron stars, providing a means of indirect...
Ultracompact dark matter (DM) minihalos at characteristic masses at and below $10^{-10}$ solar masses are expected to arise in axion DM models where the Peccei-Quinn (PQ) symmetry is broken after inflation. The minihalos arise from density perturbations that are generated through the collapse of the axion-string and domain-wall network during the quantum chromodynamics (QCD) phase-transition,...
The QCD axion is a viable dark matter candidate as the misalignment mechanism can furnish the observed dark matter abundance. Although a wide range of axion decay constants $f_a$ are compatible with astrophysical bounds, very large $f_a \sim\mathcal{O}(10^{17}-10^{18}$) GeV (and small $f_a\sim \mathcal{O}(10^9-10^{10})$ GeV) values require a misalignment angle $\theta_\text{mis} \ll 1$ $(\pi -...
We consider a partially composite axion which results from a linear mixing between an elementary scalar and a composite operator of dimension four. Non-perturbative effects generate a mass for the partially composite axion and mix it with the heavier axion states. This causes the misalignment mechanism to produce multiple axions with different abundances and leads to new interesting...
