Abstract
Dark matter axion condensates may experience stimulated decays into photon pairs. This effect has been often interpreted as a parametric resonance of photons from the axion-photon coupling, leading to an exponential growth of the photon occupation number in a narrow instability band. Most of the previous literature does not consider the possible evolution of the axion field due to the photon growth. We revisit this effect presenting a mean field solution of the axion-photon kinetic equations, in terms of number of photons and pair correlations. We study the limit of no axion depletion, recovering the known instability. Moreover, we extend the results including a possible depletion of the axion field. In this case we find that the axion condensate exhibits the behaviour of an inverted pendulum. We discuss the relevance of these effects for two different cases: an homogeneous axion field at recombination and a localized axion clump and discuss constraints that could result from the induced photon background.
Highlights
Axions emerge in relation to the strong CP problem of the strong interactions
Dark matter axion condensates may experience stimulated decays into photon pairs. This effect has been often interpreted as a parametric resonance of photons from the axion-photon coupling, leading to an exponential growth of the photon occupation number in a narrow instability band
In this work we revisited the stimulated decay of dark matter axion condensates into photon pairs
Summary
Axions emerge in relation to the strong CP problem of the strong interactions. the most elegant solution to this puzzle is based on the Peccei-Quinn (PQ) mechanism [1,2,3,4], in which the Standard Model is enlarged with an additional global Uð1ÞA symmetry, known as the PQ symmetry. A new variation of this scheme is the dielectric haloscope approach, where the conversion of dark matter axions to microwave photons is enabled by immersing one or more dielectric layers in a strong laboratory field. This has recently been proposed through the MADMAX [19] project. 1.1 × 10−24 s−1ma; eV ð3Þ where the first term at the right-hand side is valid for generic axionlike-particles, while the second uses the relation between gaγ and Fa for QCD axions Comparing this decay rate with the lifetime of the Universe 4.3 × 1017 s, one would realize that for typical masses of axion dark matter these particles would be stable on cosmological scales.
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