  There is now experimental evidence for Higgs boson decay into a pair of
muons, and significant constraints on the Higgs boson decay into a charm
quark-antiquark pair. The data on Higgs boson decays into second generation
fermions probes various extensions of the Standard Model. We analyze the
implications for the Standard Model effective field theory (SMEFT), without and
with minimal flavor violation (MFV), for two Higgs doublet models (2HDM) with
natural flavor conservation (NFC), for models with vector-like fermions, and
for specific models that predict significant modifications of the Yukawa
couplings to the light generations.
