Talk presented by Paolo Provero

Parallel Session: Spin Models I

Thursday July 1st, 15.30 - 15.50, Room B

Nonperturbative states in the 3D $\phi^4$ theory

Abstract: We show that the spectrum of the three dimensional $\phi^4$ theory in the broken symmetry phase contains non-perturbative states. We determine the spectrum using a new variational technique based on the introduction of operators corresponding to different length scales. The presence of non-perturbative states accounts for the discrepancy between MonteCarlo and perturbative results for the universal ratio $\xi/\xi_{2nd}$. We introduce and study some universal amplitude ratios related to the overlap of the spin operator with the states of the spectrum. The analysis is performed for the $\phi^4$ theory regularized on a lattice and for the Ising model.

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