# Ground states and associated path measures in the renormalized Nelson model

## TL;DR

This paper establishes the existence, uniqueness, and positivity of ground states in the renormalized Nelson model, providing decay estimates, path measures, and analyzing the model's spectral properties under various conditions.

## Contribution

It offers the first comprehensive non-perturbative analysis of ground states in the massless renormalized Nelson model, including path measure construction and decay estimates.

## Key findings

- Proves existence and uniqueness of ground states under regularity conditions.
- Constructs path measures associated with ground states.
- Provides decay estimates and spectral properties of the model.

## Abstract

We prove the existence, uniqueness, and strict positivity of ground states of the possibly massless renormalized Nelson operator under an infrared regularity condition and for Kato decomposable electrostatic potentials fulfilling a binding condition. If the infrared regularity condition is violated, then we show non-existence of ground states of the massless renormalized Nelson operator with an arbitrary Kato decomposable potential. Furthermore, we prove the existence, uniqueness, and strict positivity of ground states of the massless renormalized Nelson operator in a non-Fock representation where the infrared condition is unnecessary. Exponential and superexponential estimates on the pointwise spatial decay and the decay with respect to the boson number for elements of spectral subspaces below localization thresholds are provided. Moreover, some continuity properties of ground state eigenvectors are discussed. Byproducts of our analysis are a hypercontractivity bound for the semigroup and a new remark on Nelson's operator theoretic renormalization procedure. Finally, we construct path measures associated with ground states of the renormalized Nelson operator. Their analysis entails improved boson number decay estimates for ground state eigenvectors, as well as upper and lower bounds on the Gaussian localization with respect to the field variables in the ground state. As our results on uniqueness, positivity, and path measures exploit the ergodicity of the semigroup, we restrict our attention to one matter particle. All results are non-perturbative.