  Recently, the first pulsating ultraluminous X-ray source M82 X-2 was reported
to be experiencing a rapid orbital decay at a rate of
$\dot{P}=-(5.69\pm0.24)\times 10^{-8}~\rm s\,s^{-1}$ based on seven years
\emph{NuSTAR} data. To account for the observed orbital-period derivative, it
requires a mass transfer rate of $\sim200\dot{M}_{\rm edd}$ ($\dot{M}_{\rm
edd}$ is the Eddington accretion rate) from the donor star to the accreting
neutron star. However, other potential models cannot be completely excluded. In
this work, we propose an anomalous magnetic braking (AMB) model to interpret
the detected orbital decay of M82 X-2. If the donor star is an Ap/Bp star with
an anomalously strong magnetic field, the magnetic coupling between strong
surface magnetic field and irradiation-driven wind from the surface of the
donor star could cause an efficient angular-momentum loss, driving a rapid
orbital decay observed in M82 X-2. The AMB mechanism of an Ap/Bp star with a
mass of $5.0-15.0~M_{\odot}$ and a surface magnetic field of $3000-4500~\rm G$
could produce the observed $\dot{P}$ of M82 X-2. We also discuss the
possibility of other alternative models including the companion star expansion
and a surrounding circumbinary disk.
