  In search for a composite Higgs boson (techni-dilaton) in the walking
technicolor, we present our preliminary results on the first observation of a
light flavor-singlet scalar in a candidate theory for the walking technicolor,
the Nf=8 QCD, which was found in our previous paper to have spontaneous chiral
symmetry breaking together with remnants of the conformality. Based on
simulations with the HISQ-type action on several lattice sizes with various
fermion masses, we find evidence of a flavor-singlet scalar meson with mass
comparable to that of the Nambu-Goldstone pion in both the small fermion-mass
region, where chiral perturbation theory works, and the intermediate
fermion-mass region where the hyperscaling relation holds. We further discuss
its chiral limit extrapolation in comparison with other states studied in our
previous paper: the scalar has a mass much smaller than that of the vector
meson, which is compared to the Nambu-Goldstone pion having a vanishing mass in
that limit.
