# Standard-Model Extension Constraints on Lorentz and CPT Violation From Optical Polarimetry of Active Galactic Nuclei

## TL;DR

This study uses ground-based optical polarimetry of active galactic nuclei to set new constraints on Lorentz and CPT violation parameters in the Standard-Model Extension, demonstrating the effectiveness of a cost-efficient, automated observational approach.

## Contribution

It introduces a pilot polarimetry system that provides competitive constraints on Standard-Model Extension parameters using smaller telescopes and broader passbands.

## Key findings

- Constraints on $d=5$ operators are within a factor of 1-10 of larger telescope bounds.
- Ground-based polarimetry can effectively constrain Lorentz and CPT violation.
- A future dedicated survey could improve constraints on higher $d$ coefficients.

## Abstract

Vacuum birefringence from Lorentz and CPT violation in the Standard-Model Extension can be constrained using ground-based optical polarimetry of extragalactic sources. We describe results from a pilot program with an automated system that can perform simultaneous optical polarimetry in multiple passbands on different telescopes with an effective 0.45 m aperture. Despite the limited collecting area, our polarization measurements of AGN using a wider effective optical passband than previous studies yielded individual line-of-sight constraints for Standard-Model Extension mass dimension $d = 5$ operators within a factor of about one to ten of comparable broadband polarimetric bounds obtained using data from a 3.6 m telescope with roughly 64 times the collecting area. Constraining more general anisotropic Standard-Model Extension coefficients at higher $d$ would require more AGN along different lines of sight. This motivates a future dedicated ground-based, multi-band, optical polarimetry AGN survey with $\gtrsim 1$ m-class telescopes, to obtain state-of-the-art anisotropic Standard-Model Extension $d = 4, 5, 6$ constraints, while also using complementary archival polarimetry. This could happen more quickly and cost-effectively than via spectropolarimetry and long before more competitive constraints from space- or balloon-based x-ray/$\gamma$-ray polarization measurements.