Proposal to Search for the CP Violating Electromagnetic Vacuum Angle at the Event Horizon Telescope

TL;DR

This paper explores the potential to detect CP violation in electromagnetic interactions near black holes using Event Horizon Telescope data, proposing methods to distinguish universal signals from plasma effects.

Contribution

It introduces a novel approach to identify CP-violating effects in black hole environments through polarization analysis of EHT observations.

Findings

Evidence for polarization flips suggests strong plasma effects.

Proposed data averaging could reveal residual CP-violating signals.

Current data is insufficient for definitive tests.

Abstract

We examine the possibility that evidence for a non-zero value of the CP violating $ \frac{e^2 }{32\pi^2}\theta_{EM} \int d^4 x {\vec E}\cdot {\vec B}$ coupling might be extracted from Event Horizon Telescope observations of the black holes SgA* and M87*. The Fischler-Kundu\cite{FK} effect predicts a universal Hall current in the relaxation of charge falling onto the black hole horizon. We argue that this leads to a non-zero value of a certain CP-violating observable ${\cal C}$, defined below. The effect can be masked by parity violating plasma currents. In particular, evidence for polarization flips \cite{flip} in the signals from M87* indicate strong plasma effects in the data. We suggest that time averaging the data over periods including the flip might leave over a residual that would be an indicator of the FK signal. In addition, similarities in the polarization patterns between the two very different black holes, and a part of the signal that is uniform in frequency, might enable us to distinguish the universal topological signal from source and frequency dependent plasma effects. Current data does not appear to be sufficient to perform such a test.