New perspective in searching for axion-like particles from flavor
  physics
  We propose new perspective in searching for axion-like particles (ALPs) from
quark and lepton flavor physics: measurements of the time-dependent CP
asymmetry in $B^0 \to K_S^0 \pi^0 \gamma$ and the branching ratio of $B_s \to
e^\pm \mu^\mp$ decay possess, along with the anomalous magnetic moment of muon.
In the mass range of sub-GeV, accessible by the flavorful ALPs search, the
experimental sensitivity for these flavor observables reaches the maximum at
around the pion mass scale (called the {\it sweetest} spots), where a couple of
loopholes (unexplored regions) for the ALP parameter space have heretofore been
present, because of an unavoidable contamination with pion background events.
The proposed complementary probes can precisely determine the ALP coupling to
photon at these {\it sweetest} spots/loopholes, and will significantly help
cover whole parameter spaces in the ALP search including the present loopholes
in the future.
