  The need for a cutoff in the Lamb shift calculation suggests that high-energy
virtual photons do not interact with the real particles. In this study, we
assume that the creation of high-energy virtual particles is suppressed by a
Boltzmann factor $e^{-\beta E}$ and apply this Boltzmann factor to the
effective potential of the $\phi^4$ theory. Consequently, the effective
potential is transformed into $V(\phi) = 1/4!\phi^4 + \beta^{-4} \left \{
\phi^3 K_3(\phi) -\phi^2 K_2 (\phi) \right\}$. $K_n(x)$ is the modified Bessel
function of the second kind of order $n$. We demonstrate that the minimum of
the effective potential occurs for $\phi \ne 0$.
