We study the effects of quenched disorder on the first-order phase transition
in the two-dimensional three-color Ashkin-Teller model by means of large-scale
Monte Carlo simulations. We demonstrate that the first-order phase transition
is rounded by the disorder and turns into a continuous one. Using a careful
finite-size-scaling analysis, we provide strong evidence for the emerging
critical behavior of the disordered Ashkin-Teller model to be in the clean
two-dimensional Ising universality class, accompanied by universal logarithmic
corrections. This agrees with perturbative renormalization-group predictions by
Cardy. As a byproduct, we also provide support for the strong-universality
scenario for the critical behavior of the two-dimensional disordered Ising
model. We discuss consequences of our results for the classification of
disordered phase transitions as well as generalizations to other systems.Comment: 18 pages, 18 eps figures included, final version as publishe
