“…The hadronic matrix element for pseudoscalar‐to‐pseudoscalar meson decays is mediated by a vector current customarily factorised as:
with
. The
form factors can be obtained from LQCD calculations, [
55,93–102 ] and are transition specific. Using Equation (), the penguin contribution to the
decay amplitude, assuming flavor diagonal quarks‐ALP couplings, reads:
…”