  In a recent high-quality experimental work on normal metal--superconducting
nanowire junctions arXiv:1807.01940 (2018), strong anisotropic suppression of
induced superconductivity has been observed in tunnel conductance measurements
in the presence of applied magnetic field with variable orientation. Following
this finding, we investigate theoretically the dependence of tunnel conductance
on the direction of the Zeeman field in order to understand the operational
mechanisms and to extract effective system parameters. Second, motivated by a
generic discrepancy between experiment and theory, i.e., many in-gap and
above-gap conductance features predicted by theory are barely observed in
experiments, we study several mechanisms possibly responsible for the
suppression of the theoretically predicted conductance features (e.g., length
of the nanowire, self-energy effect due to the proximity effect, finite
temperature, finite dissipation, and multiband effect). One essential finding
in the current work is that only by a combined understanding of both
suppression mechanisms can we extract effective system parameters from the
experimental data (e.g., the effective nanowire-superconductor coupling, the
effective Land\'e $g$ factor, and the chemical potential of the semiconducting
nanowire). In addition, we consider topologically trivial Andreev bound states
in hybrid nanowires in the presence of potential inhomogeneities, such as
external quantum dots or potential inhomogeneities inside the nanowire. We
compare the anisotropic, field-dependent features induced by these
nontopological Andreev bound states with the corresponding features produced by
topological Majorana zero modes in pristine nanostructures, so that we can
provide guidance to differentiate between the topologically trivial and
nontrivial cases.
