Neutron Lifetime from Lattice QCD

Measurements of the neutron lifetime and CKM matrix elements have evolved to become high-precisions tests of the existence of new physics.
Thanks to the Standard Model relation between the neutron lifetime, the axial coupling $g_A$ of the neutron, and the CKM matrix element $V_{ud}$, we can use a QCD calculation of $g_A$ and $V_{ud}$ to learn about neutron decay from first-principles.
Lattice QCD provides a robust framework to numerically compute inherently non-perturbative quantities from first principles. Starting only from the Lagrangian of QCD and owing to new improved numerical algorithms, we calculate the axial coupling of the neutron with unprecedented precision and thus obtain input about the neutron lifetime.
This calculation is challenging and the outcome is very promising: it paves the way to understanding nuclear observables directly from QCD degrees of freedom with high accuracy.