  We theoretically investigate a quasi-one-dimensional quantum wire, where the
lowest two subbands are populated, in the presence of a helical magnetic field.
We uncover a backscattering mechanism involving the helical magnetic field and
Coulomb interaction between the electrons. The combination of these ingredients
results in scattering resonances and partial gaps which give rise to
non-standard plateaus and conductance dips at certain electron densities. The
positions and values of these dips are independent of material parameters,
serving as direct transport signatures of this mechanism. Our theory applies to
generic quasi-one-dimensional systems, including a Kondo lattice and a quantum
wire subject to intrinsic or extrinsic spin-orbit coupling. Observation of the
universal conductance dips would identify a strongly correlated fermion system
hosting fractional excitations, resembling the fractional quantum Hall states.
