Is graviton shot noise detectable?
Viktor T. Toth
TL;DR
Direct detection of gravitons is unlikely, so the paper proposes testing quantum gravity by searching for graviton shot noise (or its absence) in LIGO data. Using a semiclassical framework, it computes gravitational-wave opacity and the expected graviton-shot-noise level, obtaining $N \approx 145$ per sample and $\mathrm{SNR} \approx 12$, with a shot-noise strain and spectrum close to the LIGO noise floor. A non-detection of such a shot-noise signature would challenge gravity as a conventional low-energy quantum field theory, offering a powerful constraint on quantum gravity models using existing GW observations. Overall, the work connects classical GW absorption calculations to quantum-gravity phenomenology and provides a quantitative, falsifiable target for current detectors.
Abstract
Direct detection of gravitons in gravitational experiments, including gravitational wave observatories, has been all but ruled out given the weak coupling between the gravitational field and matter. Here we propose an alternative: looking not for the presence but for the absence of graviton shot noise in gravitational wave data. Gravitational wave experiments detect very weak signals that correspond to a surprisingly small number of gravitons even at the relatively low frequencies that characterize signals from gravitational wave events. A detailed calculation, which also yields results that are consistent with the existing literature, demonstrates that graviton shot noise may be present at detectable levels in gravitational wave observations. The absence of elevated noise levels due to graviton shot noise, in turn, would indicate that gravity is not a quantum field theory with a conventional perturbative expansion at low energies.