Magnetic field driven enhancement of the weak decay width of charged pions

Abstract

We study the effect of a uniform magnetic field B^→ on the decays π⁻ → l⁻ ν⁻_l, where l⁻ = e⁻, μ⁻, carrying out a general analysis that includes four π⁻ decay constants. Taking the values of these constants from a chiral effective Nambu-Jona-Lasinio (NJL) model, it is seen that the total decay rate gets strongly increased with respect to the B = 0 case, with an enhancement factor ranging from ∼ 10 for eB = 0.1 GeV² up to ∼ 10³ for eB = 1 GeV². The ratio between electronic and muonic decays gets also enhanced, reaching a value of about 1 : 2 for eB = 1 GeV². In addition, we find that for large B the angular distribution of outgoing antineutrinos shows a significant suppression in the direction of the magnetic field.