  Using the Feynman-Kac formula, a work fluctuation theorem for a Brownian
particle in a nonconfining potential, e.g., a potential well with finite depth,
is derived. The theorem yields aninequality that puts a lower bound on the
average work needed to change the potential in time.In comparison to the
Jarzynski equality, which holds for confining potentials, an additional
termdescribing a form of energy related to the never ending diffusive expansion
appears.
