  We followed the Shastry--Shraiman formulation of Raman scattering in Hubbard
systems and considered the Raman intensity profile in the spin-1/2 "perfect"
kagome lattice herbertsmithite ZnCu_3(OH)_6Cl_2, assuming the ground state is
well-described by the U(1) Dirac spin-liquid state. In the derivation of the
Raman T-matrix, we found that the spin chirality term appears in the A_{2g}
channel in the kagome lattice at the t^4/(\omega_i-U)^3 order, but (contrary to
the claims by Shastry and Shraiman) vanishes in the square lattice to that
order. In the ensuing calculations on the spin-1/2 kagome lattice, we found
that the Raman intensity profile in the E_g channel is invariant under an
arbitrary rotation in the kagome plane, and that in all (A_{1g}, E_g, and
A_{2g}) symmetry channels the Raman intensity profile contains broad continua
that display power-law behaviors at low energy, with exponent approximately
equal to 1 in the A_{2g} channel and exponent approximately equal to 3 in the
E_g and the A_{1g} channels. For the A_{2g} channel, the Raman profile also
contains a characteristic 1/\omega singularity, which arose in our model from
an excitation of the emergent U(1) gauge field.
