  Certain frustrated systems, including spin ice and dimer models, exhibit a
Coulomb phase at low temperatures, with power-law correlations and
fractionalized monopole excitations. Transitions out of this phase, at which
the effective gauge theory becomes confining, provide examples of
unconventional criticality. This work studies the behavior at nonzero monopole
density near such transitions, using scaling theory to arrive at universal
expressions for the crossover phenomena. For a particular transition in spin
ice, quantitative predictions are made through a duality mapping to the XY
model, and confirmed using Monte Carlo simulations.
