# Criticality and Phase Diagram of Quantum Long-Range $\text{O(N)}$ models

## TL;DR

This paper analyzes the critical behavior and phase diagram of quantum long-range al models with $O(N)$ symmetry, revealing a non-trivial dependence on the decay exponent  and anisotropic correlations in space and time.

## Contribution

It provides a general theoretical framework for understanding the phases and critical behavior of quantum long-range al models in arbitrary dimensions, including a phase diagram and critical exponents.

## Key findings

- Phase diagram depends non-trivially on  and dimension d.
- Correlation functions exhibit anisotropy in space and time below a critical .
- Results for , , and comparison with numerical data are presented.

## Abstract

Several recent experiments in atomic, molecular and optical systems motivated a huge interest in the study of quantum long-range %spin systems. Our goal in this paper is to present a general description of their critical behavior and phases, devising a treatment valid in $d$ dimensions, with an exponent $d+\sigma$ for the power-law decay of the couplings in the presence of an $O(N)$ symmetry. By introducing a convenient ansatz for the effective action, we determine the phase diagram for the $N$-component quantum rotor model with long-range interactions, with $N=1$ corresponding to the Ising model. The phase diagram in the $\sigma-d$ plane shows a non trivial dependence on $\sigma$. As a consequence of the fact that the model is quantum, the correlation functions are anisotropic in the spatial and time coordinates for $\sigma$ smaller than a critical value and in this region the isotropy is not restored even at criticality. Results for the correlation length exponent $\nu$, the dynamical critical exponent $z$ and a comparison with numerical findings for them are presented.