Abstract
Vector bosons heavier than $10^{-22}$ eV can be viable dark matter candidates with distinctive experimental signatures. Ultralight dark matter generally requires a non-thermal origin to achieve the observed density, while still behaving like a pressureless fluid at late times. We show that such a production mechanism naturally occurs for vectors whose mass originates from a dark Higgs. If the dark Higgs has a large field value after inflation, the energy in the Higgs field can be efficiently transferred to vectors through parametric resonance. Computing the resulting abundance and spectra requires careful treatment of the transverse and longitudinal components, whose dynamics are governed by distinct differential equations. We study these equations in detail and find that the mass of the vector may be as low as $10 ^{ - 18 }$ eV, while making up the dominant dark matter abundance. This opens up a wide mass range of vector dark matter as cosmologically viable, further motivating their experimental search.
Highlights
The existence of dark matter (DM) is one of the motivations for physics beyond the Standard Model (SM)
In this work we presented a new production mechanism for vector DM in the early Universe through its coupling to a dark Higgs
The mechanism relies on the nonperturbative dynamics associated with parametric resonance, allowing the produced vectors to be ultralight while still being consistent with the stringent constraints on warm DM
Summary
The existence of dark matter (DM) is one of the motivations for physics beyond the Standard Model (SM). As the field rolls down its potential and begins to oscillate, its coupling to a vector results in a rapidly oscillating mass for the vector This leads to nonperturbative production of X particles through a parametric resonance (PR) instability (as is the case in theories of reheating [28,29,30,31], though the dynamics we consider take place solely during radiation domination). The nature of the resonance and resulting abundance of vectors and dark Higgses is different depending on the strengths of the gauge coupling e and dark Higgs quartic coupling, λ We examine both limits and find that vector DM can be produced with masses as light as mX ≳ 10−18 eV, consistent with all constraints.
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