Evidence for parity violation in gravitational fields

Abstract

Discrete symmetries in gravity have only been tested for low energy, non-relativistic matter, confirming the perfectly symmetric general relativity. A hint for high energy $\mathcal{C}\mathcal{P}$ violation in gravitational fields has recently been found in the HERA Compton polarimeter's two spectra, measured with electron and positron beams. Here we report results of the analysis of the same polarimeter's 314896 spectra, acquired during 2004--2007 and tagged by laser polarization states allowing the separation of charge ($\mathcal{C}$) and space parity ($\mathcal{P}$) contributions. The measured Compton edge energy asymmetry, induced by the laser helicity flips, is as high as $(4.9\pm 0.5)\cdot 10^{-5}$ which corresponds to a helicity-dependent difference in the gravitational potentials of $(1.7\pm 0.2)\cdot 10^{-14}$. In the case of the observed anomalous coupling's energy independence, the spin asymmetric gravity will contribute to the galactic rotational curves. Further analysis and calculations can determine whether the observed magnitude of the gravitational parity violation is sufficient for detaching this famous phenomena from the dark matter theory.

June 2021 revised version of DESY 18-171, following peer review at an APS journal. 9 pages, 5 figures