  Delayed radio flares of optical tidal disruption events (TDEs) indicate the
existence of non-relativistic outflows accompanying TDEs. The interaction of
TDE outflows with the surrounding circumnuclear medium creates
quasi-perpendicular shocks in the presence of toroidal magnetic fields. Because
of the large shock obliquity and large outflow velocity, we find that the shock
acceleration induced by TDE outflows generally leads to a steep particle energy
spectrum, with the power-law index significantly larger than the "universal"
index for a parallel shock. The measured synchrotron spectral indices of
recently detected TDE radio flares are consistent with our theoretical
expectation. It suggests that the particle acceleration at quasi-perpendicular
shocks can be the general acceleration mechanism accounting for the delayed
radio emission of TDEs.
