Photon and Graviton Mass Limits

TL;DR

This paper reviews the progress and current status of limits on the masses of photons and gravitons, highlighting recent astronomical observations and theoretical debates about their possible nonzero masses and implications for fundamental physics.

Contribution

It provides a comprehensive summary of historical and recent experimental and observational limits on photon and graviton masses, including discussions on their theoretical implications and cosmological relevance.

Findings

Photon Compton wavelength lower limit has improved to about one astronomical unit.

Astronomical observations challenge Einstein gravity, suggesting alternative explanations like dark matter and dark energy.

Debates continue on the concept of graviton rest mass and its role in cosmology.

Abstract

Efforts to place limits on deviations from canonical formulations of electromagnetism and gravity have probed length scales increasing dramatically over time.Historically, these studies have passed through three stages: (1) Testing the power in the inverse-square laws of Newton and Coulomb, (2) Seeking a nonzero value for the rest mass of photon or graviton, (3) Considering more degrees of freedom, allowing mass while preserving explicit gauge or general-coordinate invariance. Since our previous review the lower limit on the photon Compton wavelength has improved by four orders of magnitude, to about one astronomical unit, and rapid current progress in astronomy makes further advance likely. For gravity there have been vigorous debates about even the concept of graviton rest mass. Meanwhile there are striking observations of astronomical motions that do not fit Einstein gravity with visible sources. "Cold dark matter" (slow, invisible classical particles) fits well at large scales. "Modified Newtonian dynamics" provides the best phenomenology at galactic scales. Satisfying this phenomenology is a requirement if dark matter, perhaps as invisible classical fields, could be correct here too. "Dark energy" {\it might} be explained by a graviton-mass-like effect, with associated Compton wavelength comparable to the radius of the visible universe. We summarize significant mass limits in a table.