Constraints on non-minimally coupled curved space electrodynamics from astrophysical observations

TL;DR

This paper investigates how electromagnetic fields coupled to spacetime curvature affect photon behavior, using astrophysical data to constrain the coupling strength, and finds the tightest bounds from pulsar timing measurements.

Contribution

It introduces constraints on non-minimally coupled electrodynamics with curvature, using astrophysical observations to limit the coupling constant.

Findings

Pulsar timing provides the most stringent constraint on the coupling constant.

Coupling does not cause photon dispersion but leads to birefringence.

The upper bound on the coupling constant is $oxed{ ext{}oxed{ ext{}} ext{}} ext{10}^{11} ext{cm}^2$ from pulsar data.

Abstract

We study interactions of electro-magnetic fields with the curvature tensor of the form $\lambda R_{\mu \nu \alpha \beta}F^{\mu \nu}F^{\alpha \beta}$. Such coupling terms though are invariant under general coordinate transformation and CPT, however violate the Einstein equivalence principle. These couplings do not cause any energy dependent dispersion of photons but they exhibit birefringence. We put constraints on the coupling constant $\lambda$ using results from solar system radar ranging experiments and millisecond-pulsar observations. We find that the most stringent constraint comes from pulsar observations and is given by $ \lambda < 10^{11} cm^2 $ obtained from the timing of binary pulsar PSR B1534+12.