  We carry out a realistic simulation of Majorana nanowires in order to
understand the latest high- quality experimental data [H. Zhang et al.,
arXiv:1603.04069 (2016)] and, in the process, develop a comprehensive picture
for what physical mechanisms may be operational in realistic nanowires leading
to discrepancies between minimal theory and experimental observations (e.g.,
weakness and broadening of the zero-bias peak and breaking of particle-hole
symmetry). Our focus is on understanding specific intriguing features in the
data, and our goal is to establish matters of principle controlling the physics
of the best possible nanowires available in current experiments. We identify
dissipation, finite temperature, multi-sub-band effects, and the finite tunnel
barrier as the four most important physical mechanisms controlling the
zero-bias conductance peak. Our theoretical results including these realistic
effects agree well with the best available experimental data in ballistic
nanowires.
