Exact scaling form for the collapsed 2D polymer phase

Abstract

It has been recently argued that interacting self-avoiding walks (ISAW) of length $ \ell , $ in their low temperature phase (i.e. below the $ Θ$-point) should have a partition function of the form: $$ Q_{\ell} \sim μ^{ \ell}_ 0μ^{ \ell^ σ}_ 1\ell^{ γ-1}\ , \eqno $$ where $ μ_ 0(T) $ and $ μ_ 1(T) $ are respectively bulk and perimeter monomer fugacities, both depending on the temperature $ T. $ In $ d $ dimensions the exponent $ σ$ could be close to $ (d-1)/d, $ corresponding to a $ (d-1) $-dimensional interface, while the configuration exponent $ γ$ should be universal in the whole collapsed phase. This was supported by a numerical study of 2D partially {\sl directed\/} SAWs for which $ σ\simeq 1/2 $ was found. I point out here that formula (1) already appeared at several places in the two-dimensional case for which $ σ=1/2, $ and for which one can even conjecture the exact value of $ γ. $