Resonant to broadband searches for cold dark matter consisting of weakly interacting slim particles

Dark matter may consist of light, very weakly interacting bosons, produced nonthermally in the early Universe. Prominent examples of such very weakly interacting slim particles are axions and hidden photons. Direct detection experiments for such particles are based on the conversion of these particles into photons. This can be done in resonant cavities, featuring a resonant enhancement, or by using suitably shaped reflecting surfaces that allow for broadband searches. In this paper we want to elucidate the relation between the two setups and study the transition from resonant to broadband searches. This then allows us to determine the sensitivity of off-resonance cavity searches for cavities much larger than the wavelength of the generated photons.

Figure 1

Parameter space where HP dark matter is allowed by cosmological constraints (red region), together with laboratory, cosmological, and astrophysical constraints that hold independently of the dark matter hypothesis (colored regions). See 9, 10, 18 for references.

Figure 2

Sketch of the various ingoing, reflected and transmitted hidden photon waves (dashed) and the transmitted and reflected photon waves (wavy) at the transition between two media.

Figure 3

Simplified scheme for the photon wave created by the passing of a HP through a dielectric mirror of low reflectivity surfaces.

Figure 4

Power output for a cubic cavity with length $L$ as a function of frequency. The blue curve corresponds to $Q_0=8$, the red one for $Q_0=4$. On the left side we clearly see resonant enhancement by a factor $\sim Q$ of the mode. The thin blue and red lines denote the peak value expected for the lowest mode from Eq. (3.8). The black line is the expectation in the $\omega \to \infty$ limit.