  We study AC conductivities in high-Tc cuprates, which offer us significant
information to reveal the true electronic ground states. Based on the
fluctuation-exchange (FLEX) approximation, current vertex corrections (CVC's)
are correctly taken into account to satisfy the conservation laws. We find the
significant role of the CVC's on the optical Hall conductivity in the presence
of strong antiferromagnetic (AF) fluctuations. This fact leads to the failure
of the relaxation time approximation (RTA). As a result, experimental highly
unusual behaviors, (i) prominent frequency and temperature dependences of the
optical Hall coefficient, and (ii) simple Drude form of the optical Hall andge
for wide range of frequencies, are satisfactorily reproduced. In conclusion,
both DC and AC transport phenomena in (slightly under-doped) high-Tc cuprates
can be explained comprehensively in terms of nearly AF Fermi liquid, if one
take the CVC's into account.
