Continuum-Mediated Dark Matter-Baryon Scattering

TL;DR

This paper explores how a continuum of light mediator states, possibly from a conformal sector, affects dark matter-baryon scattering, providing a new framework for interpreting direct detection signals.

Contribution

It introduces a novel theoretical framework for continuum-mediated dark matter interactions and analyzes specific models, expanding beyond contact or single-mediator scenarios.

Findings

Continuum mediators modify the scattering amplitude with a power-law function of momentum transfer.

Scalar mediator models are highly constrained by existing data.

Tensor operator mediators have a viable parameter space for direct detection signals.

Abstract

Many models of dark matter scattering with baryons may be treated either as a simple contact interaction or as the exchange of a light mediator particle. We study an alternative, in which a continuum of light mediator states may be exchanged. This could arise, for instance, from coupling to a sector which is approximately conformal at the relevant momentum transfer scale. In the non-relativistic effective theory of dark matter-baryon scattering, which is useful for parametrizing direct detection signals, the effect of such continuum mediators is to multiply the amplitude by a function of the momentum transfer q, which in the simplest case is just a power law. We develop the basic framework and study two examples: the case where the mediator is a scalar operator coupling to the Higgs portal (which turns out to be highly constrained) and the case of an antisymmetric tensor operator ${\cal O}_{\mu \nu}$ that mixes with the hypercharge field strength and couples to dark matter tensor currents, which has an interesting viable parameter space. We describe the effect of such mediators on the cross sections and recoil energy spectra that could be observed in direct detection.