l in combatting systematic noise sources that are encountered in searching for a time independent moment.

We begin by briefly reviewing the physics of the axion in section \[Sec:Overview\]. In this section, we discuss the theoretical origins of axions and ALPs, their parameter space, the current constraints on this parameter space and the region where they can be dark matter. We also review the salient features of axion (and ALP) dark matter. Following this review, we discuss current bounds on such moments and estimate the reach of the precision magnetometry experiments discussed above to probe this parameter space.

Axions and Axion-like-Particles (ALPs) {#Sec:Overview}
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Axions and ALPs are generically expected in many models of physics beyond the standard model [@Svrcek:2006yi]. They are the Goldstone bosons of global symmetries that are broken at some scale $f_a$. The Goldstone nature of their origin is manifest in the fact that all their interactions are suppressed by the scale $f_a$ and they are coupled derivatively in these interactions (for example, the operators in ). If they were pure Goldstone bosons, they would be completely massless and would not be the dark matter. However, their pure Goldstone nature could be broken leading to a generation of a mass for them.

This mass generation can occur if the associated global symmetry is anomalous. For example, when this global symmetry has an anomaly with QCD, non-perturbative dynamics at the QCD scale can generate a mass $m_a \sim \frac{\Lambda_{\text{QCD}}^2}{f_a}$ or more precisely $$\label{eqn: axion mass}
m_a \approx 6 \times 10^{-10} \text{ eV} \, \left(\frac{10^{16} \text{ GeV}}{f_a}\right)$$ for the Goldstone boson with about a 10% uncertainty due to QCD [@Cadamuro:2010cz]. This Goldstone boson is called the axion. While it was initially introduced to dynamically solve the strong CP problem [@Peccei:1977hh; @Peccei:1977ur], the underlying mechanism responsible for its dynamics is very general. For example, if th