Probing dark photons with plasma haloscopes

Abstract

Dark photons (DPs) produced in the early Universe are well-motivated dark matter (DM) candidates. We show that the recently proposed tunable plasma haloscopes are particularly advantageous for DP searches. While in-medium effects suppress the DP signal in conventional searches, plasma haloscopes make use of metamaterials that enable resonant absorption of the DP by matching its mass to a tunable plasma frequency and thus enable efficient plasmon production. Using thermal field theory, we confirm the in-medium DP absorption rate within the detector. This scheme allows us to competitively explore a significant part of the DP DM parameter space in the DP mass range of 6-400 μeV. If a signal is observed, the observation of a daily or annual modulation of the signal would be crucial to clearly identify the signal as due to DP DM and could shed light on the production mechanism.

Search for dark photons using a multilayer dielectric haloscope equipped with a single-photon avalanche diode

“…For a more detailed treatment, see for example Ref. [13]. Since the propagation and interaction basis are distinct, a propagating dark photon state is a mixture of the dark photon and the SM photon interaction states.…”

“…Refs. [13,16]), but for the sake of simplicity, we shall consider the DP at a given point in time in the detector to be described by a plane wave with zero momentum, and solve for the propagating eigenstates. As we are concerned with dielectric media, we can rewrite the bound charges contained in J µ into the refractive index n of the material, and following the prescription in Ref.…”

“…While a propagating DP may excite a small E-field in an infinite medium, due to conservation of momentum, a non-relativistic DP-like state cannot convert into an ultra-relativistic photon-like state. One interesting exception to this is when m X matches the plasma frequency of a material, as in plasma haloscopes [13,20]. Alternatively, one can mix the photon with a quasi-particle axion to provide a massive photon-like state [21,22].…”

Scalar Direct Detection: In-Medium Effects

“…Here, we follow the discussion of Refs. [31,36] of the absorption of axions and dark photons in a detector, respectively 1 . The emission and absorption rates of a boson by a medium are directly related to the self-energy Π of the particle in the medium itself as [38,39] Im Π = −ωΓ .…”

“…Detection proposals based on materials with a small band-gap O(meV) envision having good sensitivity to halo DM particles with mass larger than the gap, through the efficient excitation of quasiparticles, such as phonons, magnons, and plasmons. Proposed target materials include superconductors [20,21], graphene [22], Dirac materials [13,23], superfluid helium [24][25][26][27][28] and polar materials [29], as well as plasma haloscopes [30,31]. Proposals based on molecular targets have also been advanced [32].…”