Coarse-Grained Fluctuation Probabilities in the Standard Model and Subcritical Bubbles

We compute systematically the probability for fluctuations of the Higgs field, averaged over a given spatial scale, to exceed a specified value, in the Standard Model. For the particular case of interest of averages over one coherence volume we show that, even in the worst possible case of taking the one-loop improved effective potential parameters, the probability for the field to fluctuate from the symmetric to the asymmetric minimum before the latter becomes stable is very small for Higgs masses of the order of those of the $W$ and $Z$ bosons, whereas the converse is more likely. As such, metastability should be satisfied dynamically at the Electroweak phase transition and its dynamics should therefore proceed by the usual mechanism of bubble nucleation with subcritical fluctuations playing no particularly relevant role in it.