  Proton decay is a major prediction of Grand-Unified Theories (GUT) and its
observation would indicate baryon number violation that is required for
baryogenesis. Many decades of searching for proton decay have constrained its
rate and ruled out some of the simplest GUT models. Apart from the baryon
number-violating interactions, this rate also depends on transition amplitudes
between the proton and mesons or leptons produced in the decay, which are
matrix elements of three-quark operators. We report nonperturbative calculation
of these matrix elements for the most studied two-body decay channels into a
meson and antilepton done on a lattice with physical light and strange quark
masses and lattice spacings $a\approx0.14$ and 0.20 fm. We perform
nonperturbative renormalization and excited state analysis to control
associated systematic effects. Our results largely agree with previous lattice
calculations done with heavier quark masses and thus remove ambiguity in ruling
out some simple GUT theories due to quark mass dependence of hadron structure.
