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arXiv:2112.05562math.PR

On the variational method for Euclidean quantum fields in infinite volume

Nikolay Barashkov, Massimiliano Gubinelli

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Abstract

We investigate the infinite volume limit of the variational description of Euclidean quantum fields introduced in a previous work. Focussing on two dimensional theories for simplicity, we prove in details how to use the variational approach to obtain tightness of $\varphi^4_2$ without cutoffs and a corresponding large deviation principle for any infinite volume limit. Any infinite volume measure is described via a forward--backwards stochastic differential equation in weak form (wFBSDE). Similar considerations apply to more general $P (\varphi)_2$ theories. We consider also the $\exp (β\varphi)_2$ model for $β^2 < 8 π$ (the so called full $L^1$ regime) and prove uniqueness of the infinite volume limit and a variational characterization of the unique infinite volume measure. The corresponding characterization for $P (\varphi)_2$ theories is lacking due to the difficulty of studying the stability of the wFBSDE against local perturbations.

arXiv comments
39 pages, some corrections and remarks on the FBSDE formulation
Journal reference
Prob. Math. Phys. 4 (2023) 761-801
DOI
doi:10.2140/pmp.2023.4.761
Subjects
math.PRProbability math-phMathematical Physics

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