### Localization transition for a polymer near an interface

Erwin Bolthausen and Frank den Hollander
Source: Ann. Probab. Volume 25, Number 3 (1997), 1334-1366.

#### Abstract

Consider the directed process $(i, S_i)$ where the second component is simple random walk on $\mathbb{Z} (S_0 = 0)$. Define a transformed path measure by weighting each $n$-step path with a factor $\exp [\lambda \sum_{1 \leq i \leq n}(\omega_i + h)\sign (S_i)]$. Here, $(\omega_i)_{i \geq 1}$ is an i.i.d. sequence of random variables taking values $\pm 1$ with probability 1/2 (acting as a random medium) , while $\lambda \in [0, \infty)$ and $h \in [0, 1)$ are parameters. The weight factor has a tendency to pull the path towards the horizontal, because it favors the combinations $S_i > 0, \omega_i = +1$ and $S_i < 0, \omega_i = -1$. The transformed path measure describes a heteropolymer, consisting of hydrophylic and hydrophobic monomers, near an oil-water interface.

We study the free energy of this model as $n \to \infty$ and show that there is a critical curve $\lambda \to h_c (\lambda)$ where a phase transition occurs between localized and delocalized behavior (in the vertical direction). We derive several properties of this curve, in particular, its behavior for $\lambda \downarrow 0$. To obtain this behavior, we prove that as $\lambda, h \downarrow 0$ the free energy scales to its Brownian motion analogue.

First Page:
Primary Subjects: 60F10, 60J15, 82B26
Full-text: Open access

Permanent link to this document: http://projecteuclid.org/euclid.aop/1024404516
Mathematical Reviews number (MathSciNet): MR1457622
Digital Object Identifier: doi:10.1214/aop/1024404516
Zentralblatt MATH identifier: 0885.60022

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