One-dimensional random field Kac's model: weak large deviations principle

Abstract

We prove a quenched weak large deviations principle for the Gibbs measures of a Random Field Kac Model (RFKM) in one dimension. The external random magnetic field is given by symmetrically distributed Bernoulli random variables. The results are valid for values of the temperature, $\beta^{-1}$, and magnitude, $\theta$, of the field in the region where the free energy of the corresponding random Curie Weiss model has only two absolute minima $m_\beta$ and $Tm_\beta$. We give an explicit representation of the rate functional which is a positive random functional determined by two distinct contributions. One is related to the free energy cost ${\cal F}^*$ to undergo a phase change (the surface tension). The ${\cal F}^*$ is the cost of one single phase change and depends on the temperature and magnitude of the field. The other is a bulk contribution due to the presence of the random magnetic field. We characterize the minimizers of this random functional. We show that they are step functions taking values $m_\beta$ and $Tm_\beta$. The points of discontinuity are described by a stationary renewal process related to the $h-$extrema for a bilateral Brownian motion studied by Neveu and Pitman, where $h$ in our context is a suitable constant depending on the temperature and on magnitude of the random field. As an outcome we have a complete characterization of the typical profiles of RFKM (the ground states) which was initiated in [14] and extended in [16].