High-temperature behavior of gauge theories

Using renormalization group methods, we have analysed the high-temperature behavior of gauge theories. We find that, besides the usual phenomenon of symmetry restoration at the temperature of order 300 GeV, there exist models in which symmetry is restored only at much higher temperatures of order 10¹⁶ GeV or, even more interestingly, models in which there are multiple phase transitions with at least one symmetric phase. We also discuss the physical consequences of our findings.