= Critical dimension
{disambiguate=phase transition}
{wiki=Critical_dimension}
In the analysis of a <phase transition>, a critical dimension is a spatial dimension at which the character of fluctuations and critical behavior changes. Below a lower critical dimension the relevant ordered phase cannot persist; above an upper critical dimension mean-field critical exponents apply. This is distinct from the <critical dimension of string theory>, where cancellation of quantum anomalies selects a target-spacetime dimension.
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