Abstract
Many existing and proposed experiments targeting QCD axion dark matter (DM) can also search for a broad class of axion-like particles (ALPs). We analyze the experimental sensitivities to electromagnetically-coupled ALP DM in different cosmological scenarios with the relic abundance set by the misalignment mechanism. We obtain benchmark DM targets for the standard thermal cosmology, a pre-nucleosynthesis period of early matter domination, and a period of kination. These targets are theoretically simple and assume $\mathcal{O}(1)$ misalignment angles, avoiding fine-tuning of the initial conditions. We find that some experiments will have sensitivity to these ALP DM targets before they are sensitive to the QCD axion, and others can potentially reach interesting targets below the QCD band. The ALP DM abundance also depends on the origin of the ALP mass. Temperature-dependent masses that are generated by strong dynamics (as for the QCD axion) correspond to DM candidates with smaller decay constants, resulting in even better detection prospects.
Highlights
The particle nature of dark matter (DM) is unknown
axionlike particles (ALPs) arise as pseudo-Nambu Goldstone bosons associated with the breaking of global Uð1Þ symmetries, or as zero modes of higher dimensional gauge fields that are generic in string theory [8,9,10,11]
Unlike the QCD axion, ALPs do not have to interact via the strong force and they are not associated with the strong CP problem
Summary
The particle nature of dark matter (DM) is unknown. One well-motivated DM candidate is the QCD axion, which provides a solution to the strong CP problem [1,2,3,4]. Our aim is to map cosmological models onto the ALP plane, identifying regions where the correct relic abundance is obtained from simple assumptions about the expansion history, the ALP model, and the initial conditions These regions of parameter space are compelling targets for experiments searching for electromagnetically coupled ALP DM. Since ALPs do not necessarily couple to the strong interactions, and their relic density depends on the expansion rate at early times, these targets can differ significantly from the QCD axion with a standard radiation-dominated cosmological history. Appendixes A and B contain details of the relic abundance calculations for different cosmologies and ALP mass temperature-dependence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
