# Upper limits on the amplitude of ultra-high-frequency gravitational waves from graviton-photon mixing

## TL;DR

This paper establishes the first experimental upper limits on stochastic ultra-high-frequency gravitational waves using existing WISP detection facilities, demonstrating their potential to constrain or detect signals from primordial black holes.

## Contribution

It introduces a novel method of using graviton-photon conversion in magnetic fields to set upper limits on ultra-high-frequency gravitational waves with existing experimental setups.

## Key findings

- Excluded gravitational wave amplitudes down to 6×10^{-26} and 5×10^{-28} at specific high frequencies.
- Demonstrated that WISP detection facilities are also sensitive to gravitational waves.
- Provided a new approach to constrain early universe phenomena like primordial black hole evaporation.

## Abstract

In this work, we present the first experimental upper limits on the presence of stochastic ultra-high-frequency gravitational waves. We exclude gravitational waves in the frequency bands from $(2.7 - 14)\times10^{14}~$Hz and $(5 - 12)\times10^{18}~$Hz down to a characteristic amplitude of $h_c^{\rm min}\approx6\times 10^{-26}$ and $h_c^{\rm min}\approx 5\times 10^{-28}$ at $95~$% confidence level, respectively. To obtain these results, we used data from existing facilities that have been constructed and operated with the aim of detecting WISPs (Weakly Interacting Slim Particles), pointing out that these facilities are also sensitive to gravitational waves by graviton to photon conversion in the presence of a magnetic field. The principle applies to all experiments of this kind, with prospects of constraining (or detecting), for example, gravitational waves from light primordial black hole evaporation in the early universe.