Cosmological constraints on the neutron lifetime

TL;DR

This paper uses Planck 2015 CMB data and primordial Helium measurements to derive cosmological constraints on the neutron lifetime, finding some tension with laboratory measurements and projecting future survey improvements.

Contribution

It provides new cosmological bounds on the neutron lifetime using CMB and primordial element data, highlighting potential tensions with particle physics measurements.

Findings

Planck data constrains neutron lifetime to 907 ± 69 s.

Including Helium data tightens constraints to 875 ± 19 s and 921 ± 11 s.

Future surveys could measure neutron lifetime with ~6 s precision.

Abstract

We derive new constraints on the neutron lifetime based on the recent Planck 2015 observations of temperature and polarization anisotropies of the CMB. Under the assumption of standard Big Bang Nucleosynthesis, we show that Planck data constrains the neutron lifetime to $\tau_n=(907 \pm 69) \, [\text{s}]$ at $68 \%$ c.l.. Moreover, by including the direct measurements of primordial Helium abundance of Aver et al. (2015) and Izotov et al. (2014), we show that cosmological data provide the stringent constraints $\tau_n=(875 \pm 19) \, [\text{s}]$ and $\tau_n=(921 \pm 11) \, [\text{s}]$ respectively. The latter appears to be in tension with neutron lifetime value quoted by the Particle Data Group ($\tau_n=(880.3 \pm 1.1) \, [\text{s}]$). Future CMB surveys as COrE+, in combination with a weak lensing survey as EUCLID, could constrain the neutron lifetime up to a $\sim 6 \, [\text{s}]$ precision.