Evidence for parity violation in gravitational fields
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 $\cal{CP}$ 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 ($\cal C$) and space parity ($\cal P$) contributions. The measured Compton edge energy asymmetry, induced by the laser helicity flips, is as high as $(4.9\pm0.5)\cdot10^{-5}$ which corresponds to a helicity-dependent difference in the gravitational potentials of $(1.7\pm0.2)\cdot10^{-14}$. 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.