Localised Horizons and Holographic Thermodynamics: Supercooling in the 1/D Expansion
In holography, four-dimensional confining gauge theories are often modelled by five-dimensional Einstein--scalar gravity by choosing a specific form of the scalar potential. In a large class of non-conformal theories, we show that a predictive structure emerges for the thermal confinement transition by generalising the gravitational dual to $D+1$ dimensions and using a $1/D$ expansion. These results are independent of the details of the scalar potential, hinting towards universality. The black brane geometry dual to the deconfined phase can be analytically constructed due to its effects being localised near the horizon at leading order. The solution does not exist below a minimal temperature $T_{\rm min}$ and the maximum possible supercooling in the transition $\epsilon_{\rm sc} = 1-T_{\rm min}/T_{\rm c}$ is generically suppressed by a factor of $1/D^2$. Remarkably, the maximum supercooling at the leading order is set by the speed of sound in the deconfined phase of the gauge theory at the critical temperature, $\epsilon_{\rm sc}=c_s^2(T_{\rm c})/2$. These predictions agree with explicit calculations in an exponential superpotential, improved holography, and the thermal transition in $\mathcal{N}=4$ super Yang--Mills on a sphere.