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Title: Asymptotic-freedom growth of the O(N) correlation length
Plain: Perturbation theory predicts exactly how fast the distance over which arrows stay aligned grows as the temperature goes to zero, an exponential in the inverse temperature. Proving this formula would confirm asymptotic freedom in a lattice model.
Precise: For the $O(N)$ model on $Z^2$ with $N \ge 3$, prove $\xi(\beta) = C_N \beta^{-1/(N-2)} \exp(2 \pi \beta/(N-2)) (1 + o(1))$ as $\beta \to \infty$, with $\xi = 1/m$ the exponential correlation length; the constant C_N was predicted by Hasenfratz, Maggiore and Niedermayer (1990) from the Bethe ansatz. Answer: a proof of the leading asymptotics, with or without the constant.
Settled by: Matching upper and lower bounds on $\xi(\beta)$ with the two-loop exponential and power-law factors.
Kind: well-posed
Answer type: proof
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)