MHz Gravitational Wave Constraints with Decameter Michelson Interferometers

Abstract

A new detector, the Fermilab Holometer, consists of separate yet identical 39-meter Michelson interferometers. Strain sensitivity achieved is better than $10^{-21}/\sqrt{\mathrm{Hz}}$ 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$\ddot{I}ƒ$ upper limit on $\hat{I}{\text{c◯}}_{\mathrm{GW}}$, 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.