  The Kondo breakdown scenario has been claimed to allow the $T$-linear
resistivity in the vicinity of the Kondo breakdown quantum critical point, two
cornerstones of which are the dynamical exponent $z = 3$ quantum criticality
for hybridization fluctuations in three dimensions and irrelevance of vertex
corrections for transport due to the presence of localized electrons. We
revisit the issue of vertex corrections in electrical transport coefficients.
Assuming that two kinds of bosonic degrees of freedom, hybridization
excitations and gauge fluctuations, are in equilibrium, we derive coupled
quantum Boltzmann equations for two kinds of fermions, conduction electrons and
spinons. We reveal that vertex corrections play a certain role, changing the
$T$-linear behavior into $T^{5/3}$ in three dimensions. However, the $T^{5/3}$
regime turns out to be narrow, and the $T$-linear resistivity is still expected
in most temperature ranges at the Kondo breakdown quantum critical point in
spite of the presence of vertex corrections. We justify our evaluation, showing
that the Hall coefficient is not renormalized to remain as the Fermi-liquid
value at the Kondo breakdown quantum critical point.
