No $\nu$s is Good News

Understand

The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), when combined with data from the cosmic microwave background (CMB), has placed an upper-limit on the sum of neutrino masses, $\sum m_\nu < 70$ meV (95%).

• In addition to excluding the minimum sum associated with the inverted hierarchy, the posterior is peaked at $\sum m_\nu = 0$ and is close to excluding even the minumum sum, 58 meV at 2$\sigma$.
• In this paper, we explore the implications of this data for cosmology and particle physics.
• The sum of neutrino mass is determined in cosmology from the suppression of clustering in the late universe.