The LQG -- String: Loop Quantum Gravity Quantization of String Theory I. Flat Target Space

TL;DR

This paper introduces a novel, background-independent quantum string representation using Loop Quantum Gravity techniques, achieving a stable, ghost-free, anomaly-free solution in flat space that preserves Poincaré invariance without gauge fixing or divergences.

Contribution

It presents a new non-trivial representation solution for quantum strings that is background independent, ghost-free, anomaly-free, and preserves symmetries without gauge fixing or divergences.

Findings

Existence of a stable, ghost-free string representation in flat space.

Solution applies to any target space dimension and Minkowski signature.

No tachyons, anomalies, or UV divergences present.

Abstract

We combine I. background independent Loop Quantum Gravity (LQG) quantization techniques, II. the mathematically rigorous framework of Algebraic Quantum Field Theory (AQFT) and III. the theory of integrable systems resulting in the invariant Pohlmeyer Charges in order to set up the general representation theory (superselection theory) for the closed bosonic quantum string on flat target space. While we do not solve the, expectedly, rich representation theory completely, we present a, to the best of our knowledge new, non -- trivial solution to the representation problem. This solution exists 1. for any target space dimension, 2. for Minkowski signature of the target space, 3. without tachyons, 4. manifestly ghost -- free (no negative norm states), 5. without fixing a worldsheet or target space gauge, 6. without (Virasoro) anomalies (zero central charge), 7. while preserving manifest target space Poincar\'e invariance and 8. without picking up UV divergences. The existence of this stable solution is exciting because it raises the hope that among all the solutions to the representation problem (including fermionic degrees of freedom) we find stable, phenomenologically acceptable ones in lower dimensional target spaces, possibly without supersymmetry, that are much simpler than the solutions that arise via compactification of the standard Fock representation of the string. Moreover, these new representations could solve some of the major puzzles of string theory such as the cosmological constant problem. The solution presented in this paper exploits the flatness of the target space in several important ways. In a companion paper we treat the more complicated case of curved target spaces.