Massive neutrinos and interacting dark matter look alike through the lens of lensing

TL;DR

This paper shows that effects of massive neutrinos on CMB lensing can be confused with dark matter-baryon interactions, potentially complicating neutrino mass measurements.

Contribution

It reveals a degeneracy between neutrino mass effects and dark matter-baryon interactions in CMB lensing data, highlighting a challenge for future precision measurements.

Findings

Neutrino-induced suppression of CMB lensing can be mimicked by dark matter-baryon interactions.

Degeneracy occurs for a dark matter-proton cross section proportional to v^{-4}.

Next-generation CMB experiments may not distinguish between these effects.

Abstract

We demonstrate that the suppression in the lensing power spectrum of the cosmic microwave background (CMB) caused by massive neutrinos can be mimicked by dark matter-baryon interactions at the precision of next-generation CMB experiments. Thus, a determination of neutrino masses from the CMB lensing power spectrum may be compromised. We illustrate the degeneracy for a dark matter-proton cross section $\propto v^{-4}$, which arises in the $t$-channel exchange of an ultralight mediator in the nonrelativistic limit.