Cosmic optical activity in the spacetime of a scalar-tensor screwed cosmic string

TL;DR

This paper proposes that optical activity observed in light from distant galaxies can be explained by electromagnetic interactions with a scalar-tensor screwed cosmic string via a Chern-Simons coupling, supported by astronomical data.

Contribution

It introduces a novel explanation for cosmic optical activity involving scalar-tensor gravity and Chern-Simons interactions with cosmic strings, and constrains the coupling constant using observational data.

Findings

The coupling constant is approximately 10^{-26} eV.

The coupling is two orders of magnitude larger than in string-inspired theories.

The model explains polarization excess in radio galaxies and quasars.

Abstract

Measurements of radio emission from distant galaxies and quasars verify that the polarization vectors of these radiations are not randomly oriented as naturally expected. This peculiar phenomenon suggests that the spacetime intervening between the source and observer may be exhibiting some sort of optical activity, the origin of which is not known. In the present paper we provide a plausible explanation to this phenomenon by investigating the r\^ole played by a Chern-Simons-like term in the background of an ordinary or superconducting screwed cosmic string in a scalar-tensor gravity. We discuss the possibility that the excess in polarization of the light from radio-galaxies and quasars can be understood as if the electromagnetic waves emitted by these cosmic objects interact with a scalar-tensor screwed cosmic string through a Chern-Simons coupling. We use current astronomical data to constrain possible values for the coupling constant of this theory, and show that it turns out to be: $\lambda \sim 10^{-26}$ eV, which is two orders of magnitude larger than in string-inspired theories.