Isospin-breaking in light-meson leptonic decays

This is a summary of the article “Isospin-breaking corrections to light-meson leptonic decays from lattice simulations at physical quark masses”. In this work we examine effects that have historically been neglected in numerical lattice calculations, but are now becoming important due to increased precision. In particular, we calculate the correction to a ratio of leptonic decay rates from two closely related effects. The first is electromagnetism (the effect of photons on the decays) and the second is the mass difference of the two light quarks (the effect on the decays from the up and down quark having different masses). One of our main focuses of the article is the role of the finite volume in the calculation, which is very important because the finite-volume effects are enhanced when photons are included.