Abstract
Dark gauge sectors and axions are well-motivated in string theory. We demonstrate that if a confining gauge sector gives rise to dark glueballs that are a fraction of the dark matter, and the associated axion has a decay constant near the string scale, then this axion is ultralight and naturally realizes the fuzzy dark matter scenario with a modest tuning of a temperature ratio. Astrophysical observations constrain the size of the glueball component relative to the axionic component, while electric dipole moments constrain mixing with the QCD axion.
Highlights
Dark gauge sectors and axions are well motivated in string theory
We demonstrate that if the dark glueball accounts for a sizable fraction of the dark matter, it is often accompanied by ultralight axionic dark matter which is a candidate for the fuzzy dark matter (FDM) scenario
We studied a scenario in which the dark matter is composed of dark glueballs and their associated axions. We found that both components may make up a nontrivial fraction of the observed dark matter relic abundance if the hidden sector confinement scale is Λ ∼ 100 eV and there is a mild preferential reheating into the visible sector
Summary
As in our previous work [11], we consider a dark pure Yang-Mills sector (as these are often present in string compactifications) with gauge group G and confinement scale Λ. The energy density in gluons is converted into glueballs These confined states are likely to persist to late times provided that (a) any portals to the Standard Model are generated only by Planck-suppressed effects, and (b) there are no light matter states (analogues to pions in the Standard Model) into which these glueball states can decay. Since ξ is assumed to be constant, and comparing to the visible sector entropy density today, the relic abundance of glueballs is [1]. Interactions have time to affect the final relic abundance In this case, assuming radiation domination at the time glueballs are formed, we find ωðΛÞ. Note that only the glueball density has a temperature dependence here
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