Maximal free energy of the log-gamma polymer
摘要
We prove a phase transition for the law of large numbers and fluctuations of FN, the maximum of the free energy of the log-gamma directed polymer with parameter θ, maximized over all possible starting and ending points in an N × N square. In particular, we find an explicit critical value θc = 2Ψ−1(0) > 0 (Ψ is the digamma function) such that: For θ < θc, FN+ 2Ψ(θ/2)N has order N1/3 GUE Tracy–Widom fluctuations. For θ = θc, FN = Θ(N1/3(log N)2/3). For θ > θc, FN = Θ(log N).
Using the same techniques for analyzing FN, we also show that an analogous phase transition occurs in a certain free start/end-point polymer measure with inverse gamma weights. By exploiting a connection between the log-gamma polymer and a certain random operator on the honeycomb lattice, recently found by Kotowski and Virág (Comm. Math. Phys. 370, 2019), we also deduce a similar phase transition for the asymptotic behavior of the smallest positive eigenvalue of the aforementioned random operator.