  It is shown in previous works that the coupling between two Majorana end
states in superconducting quantum wires leads to fractional Josephson effect.
However, in realistic experimental conditions, multiple bands of the wires are
occupied and the Majorana end states are accompanied by other fermionic end
states. This raises the question concerning the robustness of fractional
Josephson effect in these situations. In this work, we show that the absence of
the avoided energy crossing which gives rise to the fractional Josephson effect
is robust, even when the Majorana fermions are coupled with arbitrary strengths
to other fermions. Moreover, we calculate the temperature dependence of the
fractional Josephson current and show that it is suppressed by thermal
excitations to the other fermion bound states.
