It's All ${\tt Ok}$: Curvature in Light of BAO from DESI DR2

TL;DR

This paper explores the implications of a small negative spatial curvature as a solution to the tension between BAO measurements from DESI and CMB data, highlighting its effects on cosmological parameters and inflationary models.

Contribution

It analyzes the role of negative curvature in cosmological distance measures and its potential to resolve tensions between DESI BAO data and CMB observations.

Findings

DESI data suggests a small negative curvature at 2σ

Allowing curvature relaxes neutrino mass constraints to < 0.10 eV

Future surveys can distinguish curvature from dark energy solutions

Abstract

Recent measurements of baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI) show hints of tension with data from the cosmic microwave background (CMB) when interpreted within the standard model of cosmology. In this short note we discuss the consequences of one solution to this tension, a small but negative spatial curvature with $R_k = 21 H_0^{-1}$, which DESI measures at $2\sigma$ when combined with CMB data. We describe the physical role of curvature in cosmological distance measures tied to recombination, i.e. the CMB and BAO, and the relation to neutrino mass constraints which are relaxed to $\sum m_\nu < 0.10$ eV at $95\%$ confidence when curvature is allowed to deviate from zero. A robust detection of negative curvature would have significant implications for inflationary models: improved BAO measurements, particularly from future high-redshift spectroscopic surveys, will be able to distinguish curvature from other solutions to the DESI-CMB tension like phantom dark energy at high significance.