Charged polymers in the attractive regime: a first order transition from Brownian scaling to four points localization

TL;DR

This paper analyzes a charged-polymer model, revealing a first-order transition from delocalized Brownian behavior to localized folding, with discontinuous changes at critical temperatures and insights into phase transition nature.

Contribution

It provides rigorous proofs of phase transition behaviors in a quenched charged-polymer model, including delocalization, localization, and collapse phenomena, and characterizes the nature of these transitions.

Findings

Polymer is delocalized below critical temperature, converging to Brownian motion.

At critical temperature, the polymer's maximum point occupation jumps discontinuously.

For large critical temperatures, the polymer collapses onto four positions with logarithmic diameter growth.

Abstract

We study a quenched charged-polymer model, introduced by Garel and Orland in 1988, that reproduces the folding/unfolding transition of biopolymers. We prove that, below the critical inverse temperature, the polymer is delocalized in the sense that: (1) The rescaled trajectory of the polymer converges to the Brownian path; and (2) The partition function remains bounded. At the critical inverse temperature, we show that the maximum time spent at points jumps discontinuously from 0 to a positive fraction of the number of monomers, in the limit as the number of monomers tends to infinity. Finally, when the critical inverse temperature is large, we prove that the polymer collapses in the sense that a large fraction of its monomers live on four adjacent positions, and its diameter grows only logarithmically with the number of the monomers. Our methods also provide some insight into the annealed phase transition and at the transition due to a pulling force; both phase transitions are shown to be discontinuous.