Disorder relevance without Harris Criterion: the case of pinning model with $γ$-stable environment

We investigate disorder relevance for the pinning of a renewal whose inter-arrival law has tail exponent $α>0$ when the law of the random environment is in the domain of attraction of a stable law with parameter $γ\in (1,2)$. We prove that in this case, the effect of disorder is not decided by the sign of the specific heat exponent as predicted by Harris criterion but that a new criterion emerges to decide disorder relevance. More precisely we show that when $α>1-γ^{-1}$ there is a shift of the critical point at every temperature whereas when $α< 1-γ^{-1}$, at high temperature the quenched and annealed critical point coincide, and the critical exponents are identical.

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