Measuring cosmic expansion with diffractive gravitational scintillation of nanoHertz gravitational waves

TL;DR

This paper proposes using diffractive gravitational scintillation of nanoHertz gravitational waves, observed via pulsar timing arrays, as a novel method to measure cosmic expansion with high precision.

Contribution

It introduces the concept that wave lensing-induced scintillation patterns in PTA data can be used to determine cosmic distances and expansion rates.

Findings

Modulations in strain due to wave lensing are detectable with PTAs.

Hundreds of redshift-distance pairs could be measured from a single PTA source.

Diffractive lensing effects can provide new cosmological measurements.

Abstract

The recent discovery of ultra-long wavelength gravitational waves through the advent of pulsar timing arrays (PTA) has opened up new avenues for fundamental science. Here we show that every PTA source will be diffractively lensed by potentially hundreds of galactic disks transverse to its line of sight, leading to modest modulations in the strain, $\Delta h / h \sim 10^{-3} \lambda^{-1}_{1 \rm pc.}$, due to wave lensing effects. The induced interference, or scintillation, pattern will be resolvable by coherent PTAs and may be leveraged, alongside fore-ground redshift information, to make precise measurements of cosmic expansion. If future PTA experiments can achieve enough signal-to-noise to detect these small modulations, hundreds of redshift-distance pairs may be inferred from the diffractive lensing of an individual PTA source.