# New Interpretations of the Cosmological Preference for a Negative Neutrino Mass

## TL;DR

This paper explores how tensions in cosmological data regarding neutrino mass and universe expansion can be explained by new physics, such as light fields or dark sector models, predicting observable signals.

## Contribution

It proposes that current cosmological tensions can be resolved through models involving new light fields or dark sector interactions, providing testable predictions.

## Key findings

- Additional lensing signals from new light fields can be tested via temperature and polarization data.
- Dark sector models alter matter density evolution, producing signals in galaxy three-point statistics.
- Various beyond Standard Model scenarios predict observable signals that can confirm these explanations.

## Abstract

Recent observations of the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO) show some tension with a $\Lambda$CDM cosmology. For one, the cosmological parameters determined by the CMB are at odds with the expansion history determined by latest BAO measurements. In addition, the combined data has placed uncomfortably strong constraints on neutrino mass. Both effects can be interpreted as negative neutrino mass, one describing the change to the expansion history and the other one describing enhanced lensing. In this paper, we show the current tensions can be solved with a single change either to the lensing of the CMB or the expansion of the universe. We show additional lensing could arise from a variety of models with new light fields. However, these models rarely give the same signal in temperature and polarization, giving a concrete test of the scenario. Alternatively, dark sector models can explain the changes to the expansion by changing the evolution of the matter density. These models introduce new forces, giving rise to long range signals in the three-point statistics of galaxies. We discuss a range of other examples which all illustrate the pattern that additional signals should appear if these tensions are explained by beyond the Standard Model physics.