MHz Gravitational Wave Constraints with Decameter Michelson Interferometers

TL;DR

This paper introduces the Fermilab Holometer, a novel high-frequency gravitational wave detector using 39-meter Michelson interferometers, achieving unprecedented sensitivity and setting new constraints on gravitational waves and primordial black holes in the MHz range.

Contribution

The paper presents the first high-frequency gravitational wave measurements with MHz interferometers, surpassing previous experiments in sensitivity and frequency range, and introduces new limits on primordial black holes and gravitational wave backgrounds.

Findings

Achieved strain sensitivity better than 10^{-21}/√Hz between 1-13 MHz.

Set upper limits on gravitational wave energy density at MHz frequencies.

No detectable primordial black hole binaries in the tested mass range.

Abstract

A new detector, the Fermilab Holometer, consists of separate yet identical 39-meter Michelson interferometers. Strain sensitivity achieved is better than $10^{-21} /{\sqrt{\rm{Hz}}}$ between 1 to 13 MHz from a 130-hr dataset. This measurement exceeds the sensitivity and frequency range made from previous high frequency gravitational wave experiments by many orders of magnitude. Constraints are placed on a stochastic background at 382 Hz resolution. The 3$\sigma$ upper limit on $\Omega_{\rm{GW}}$, the gravitational wave energy density normalized to the closure density, ranges from $5.6 \times 10^{12}$ at 1 MHz to $8.4 \times 10^{15}$ at 13 MHz. Another result from the same dataset is a search for nearby primordial black hole binaries (PBHB). There are no detectable monochromatic PBHBs in the mass range $0.83$ - $3.5 \times 10^{21}$g between the earth and the moon. Projections for a chirp search with the same dataset increases the mass range to $0.59 - 2.5 \times 10^{25}$g and distances out to Jupiter. This result presents a new method for placing limits on a poorly constrained mass range of primordial black holes. Additionally, solar system searches for PBHBs place limits on their contribution to the total dark matter fraction.