Mass generation for the two dimensional O(N) Linear Sigma Model in the large N limit
Matías G. Delgadino, Scott A. Smith
TL;DR
The paper addresses mass generation in the two-dimensional $O(N)$ Linear Sigma Model under a $1/N$ expansion, proving exponential decay of correlations and that each component converges to a massive Gaussian Free Field in the large-$N$ limit. The authors combine the Feyel/Üstünel extension of Talagrand's inequality with classical Euclidean QFT tools, including Wick renormalization and Moshe–Kupiainen-type gap equations, to obtain uniform-in-$N$ ultraviolet stability and quantitative Wasserstein-distance convergence to a massive GFF. A key result is that the plane model admits a mass $m_*$ given by a gap equation, and the marginals converge to $\mu_{m_*}^{\otimes N}$ with rate $O(N^{-1/2})$ in an appropriate Sobolev-based Wasserstein metric; in a double scaling limit, the mass scales as $m_* = e^{-2\pi\beta}$, matching Polyakov-type predictions. The work thus provides a rigorous large-$N$ mass-generation mechanism in 2D sigma models, supports continuum-limit behavior, and offers quantitative transport-entropy tools that may influence rigorous QFT analyses and 1/N expansions.
Abstract
This work studies the $O(N)$ Linear Sigma Model on $\mathbb{R}^{2}$ under a scaling dictated by the formal $1/N$ expansion. We show that in the large $N$ limit, correlations decay exponentially fast, where the acquired mass decays exponentially in the inverse temperature. In fact, each marginal converges to a massive Gaussian Free Field (GFF) on $\mathbb{R}^{2}$, quantified in the $2$-Wasserstein distance with a weighted $H^{1}(\mathbb{R}^{2})$ cost function. In contrast to prior work on the torus via parabolic stochastic quantization, our results hold without restrictions on the coupling constants, allowing us to also obtain a massive GFF in a suitable double scaling limit. Our proof combines the Feyel/Üstünel extension of Talagrand's inequality with some classical tools in Euclidean Quantum Field Theory.
