  We propose a new, generic mechanism of inflation mediated by a balance
between potential forces and a Chern-Simons interaction. Such quasi-topological
interactions are ubiquitous in string theory. In the minisuperspace
approximation, their effect on the dynamics can be mapped onto the problem of a
charged particle in an electromagnetic field together with an external
potential; slow roll arises when the motion is dominated by the analogue of
`magnetic drift'. This mechanism is robust against radiative corrections. We
suggest a possible experimental signature which, if observed, might be
considered strong evidence for string theory.
