Simulating rare kaon decays K + → π + ℓ + ℓ − using domain wall lattice QCD with physical light quark masses

We report the first calculation using physical light-quark masses of the electromagnetic form factor V(z) describing the long-distance contributions to the K+→π+ℓ+ℓ- decay amplitude. The calculation is performed on a 2+1 flavor domain wall fermion ensemble with inverse lattice spacing a-1=1.730(4)GeV. We implement a Glashow-Iliopoulos-Maiani cancellation by extrapolating to the physical charm-quark mass from three below-charm masses. We obtain V(z=0.013(2))=-0.87(4.44), achieving a bound for the value. The large statistical error arises from stochastically estimated quark loops.