U(N) tools for Loop Quantum Gravity: The Return of the Spinor

TL;DR

This paper develops a classical and quantum framework for SU(2) intertwiners in loop quantum gravity using spinors, enabling new insights into spin network states and their dynamics.

Contribution

It introduces a classical spinor phase space for U(N) intertwiners, connects it to the standard quantum Hilbert space, and proposes a dynamical action principle for spin networks.

Findings

Classical spinor phase space reproduces standard intertwiner Hilbert space.

Framework allows construction of spin network states from intertwiners.

Application to 2-vertex graph illustrates the approach and Hamiltonian properties.

Abstract

We explore the classical setting for the U(N) framework for SU(2) intertwiners for loop quantum gravity (LQG) and describe the corresponding phase space in terms of spinors with appropriate constraints. We show how its quantization leads back to the standard Hilbert space of intertwiner states defined as holomorphic functionals. We then explain how to glue these intertwiners states in order to construct spin network states as wave-functions on the spinor phase space. In particular, we translate the usual loop gravity holonomy observables to our classical framework. Finally, we propose how to derive our phase space structure from an action principle which induces non-trivial dynamics for the spin network states. We conclude by applying explicitly our framework to states living on the simple 2-vertex graph and discuss the properties of the resulting Hamiltonian.