High Energy / Nuclear Theory / RIKEN seminars

[virtual NT/RIKEN seminar] First-principles calculation of electroweak box diagrams from lattice QCD

by Luchang Jin (U. Conn)




I will report a first, realistic lattice QCD calculation of the
\gamma W-box diagrams. The low-momentum integral for the \gamma W
loop is calculated using lattice QCD simulation and the high-momentum
part is computed using perturbation theory.  Using the pion
semileptonic decay as an example, we demonstrate the feasibility of
the methodology. By using domain wall fermion at the physical pion
mass with multiple lattice spacings and volumes, we obtain the axial
\gamma W-box contributions to the pion decay,
with the total uncertainty controlled to a level of  <1%.
This exploratory study sheds light on the first-principles computation
of the \gamma W-box contributions to the nucleon decay, which play a
decisive role in the determination of |V_{ud}|.