Renormalization group improvement of the effective potential in massive {phi}{sup 4} theory

Using the method of the renormalization group, we improve the two-loop effective potential of the massive {phi}{sup 4} theory to obtain the next-next-to-leading logarithm correction in the {ovr MS} scheme. Our result reproduces well the next-next-to-leading logarithm parts of the ordinary loop expansion result known up to four-loop order. {copyright} {ital 1999} {ital The American Physical Society}