Lorentz violating backgrounds from quadratic, shift-symmetric, ultralight dark matter

TL;DR

This paper explores how ultralight, shift-symmetric scalar fields coupled via dimension-8 operators could lead to Lorentz violation and variations in fundamental constants, with implications for dark matter detection.

Contribution

It introduces a theoretical framework for ultralight dark matter with quadratic, shift-symmetric couplings and analyzes their effects on Lorentz violation and experimental bounds.

Findings

Dimension-8 operators induce weak bounds on Lorentz violation.

UV cutoff scale for these effects is around keV.

Operators could influence experiments searching for fundamental constant oscillations.

Abstract

We consider an effective theory for a shift-symmetric, quadratically-coupled, ultralight spin-0 field. The leading CP-conserving interactions with Standard Model fields in the effective theory arise at dimension 8. We discuss the renormalization group evolution and positivity bounds on these operators, as well as their possible UV origins. Assuming that the spin-0 field is associated with an ultralight dark matter candidate, we discuss the effects of the dimension-8 operators on experiments searching for the oscillation of fundamental constants and Lorentz violation. We find that the direct bounds on these two effects are of similar strength but rather weak, corresponding to a UV cutoff scale of keV order, as they are mediated by dimension-8 operators.