Thermal Fluctuations and Validity of the 1-loop Effective Potential

We examine the validity of the 1-loop approximation to the effective potential at finite temperatures and present a simple test for its reliability. As an application we study the standard electroweak potential, showing that for a Higgs mass above 70 GeV, and fairly independently of the top mass (with mt ≥ 90 GeV), the 1-loop approximation is no longer valid for temperatures in the neighborhood of the critical temperature. [email protected] [email protected]