A Global Network for the Search for High Frequency Gravitational Waves

Introduction

The overarching goal of the GravNet project is to develop, test, and deploy a novel experimental platform that could enable the first detection of gravitational waves (GWs) in the frequency range of MHz to GHz. This would provide a new and unique window into astrophysical processes that have so far eluded observation.

Background

The first detection of gravitational waves by LIGO in 2015 ushered in a new era of fundamental physics. Since then, a network of ground-based GW interferometers has probed the frequency range from 10 Hz to 10 kHz, detecting nearly a hundred mergers of black-hole and neutron-star binaries.

In 2023, a signal at much lower frequency, in the nHz band, was detected by timing radio signals from pulsars. The race is now on to explore other bands. Of particular interest in this context is access to the MHz-GHz range, as signals may be generated copiously by events such as:

• Primordial-black-hole mergers
• The dynamics of ultra-light dark matter overdensities
• Violent phenomena in primordial cosmological times

These processes are related to some of the most pressing open questions about our Universe.

Methodology

The use of cavities in strong magnetic fields has been identified as one of the most promising techniques to search for high-frequency gravitational waves. So far, efforts have focused on cavities with small volumes that are tuned to search for axion-like particles.

By contrast, the GravNet scheme is based on combining different technologies and methodological approaches to measure synchronously cavity signals from multiple devices in magnetic fields operated as a network across Europe. This approach increases the sensitivity to high-frequency GWs (HFGWs) by several orders of magnitude compared to current methods.

Conclusion

In this way, GravNet will open up a new, vast parameter space for gravitational-wave searches and might be the enabling step towards the first detection of HFGWs, with the potential to revolutionize our understanding of the Universe.