  Charge density waves with unconventional order parameters, for instance, with
d-wave symmetry (DDW), may be relevant in the underdoped regime of high-T_c
cuprates or other quasi-one or two dimensional metals. A DDW state is
characterized by two branches of low-lying electronic excitations. The
resulting quantum mechanical current has an inter-branch component which leads
to an additional mass term in the expression for the Hall conductivity. This
extra mass term is parametrically enhanced near the ``hot spots'' of fermionic
dispersion and is non-neglegible as is shown by numerical calculations of the
Hall number in the DDW state.
