Cosmological constraints on the neutron lifetime

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.