On a semi-classical limit of loop space quantum mechanics

TL;DR

This paper develops a semi-classical framework for loop space quantum mechanics derived from non-linear sigma models, showing how effective dynamics localize on the target manifold and reproducing tachyon equations up to Ricci scalar divergences.

Contribution

It introduces a finite-dimensional analogue of loop space quantum mechanics with a tubular expansion, enabling semi-classical analysis and deriving effective equations at leading order in '.

Findings

Reproduces the linearized tachyon effective equation with Ricci scalar divergences

Develops a tubular expansion framework for loop space quantum mechanics

Constructs a tubular neighborhood in loop space using exponential maps

Abstract

Following earlier work, we view two dimensional non-linear sigma model with target space $\cM$ as a single particle relativistic quantum mechanics in the corresponding free loop space $\cLM$. In a natural semi-classical limit ($\hbar=\alpha' \to 0$) of this model the wavefunction localizes on the submanifold of vanishing loops which is isomorphic to $\cM$. One would expect that the relevant semi-classical expansion should be related to the tubular expansion of the theory around the submanifold and an effective dynamics on the submanifold is obtainable using Born-Oppenheimer approximation. In this work we develop a framework to carry out such an analysis at the leading order in $\alpha'$-expansion. In particular, we show that the linearized tachyon effective equation is correctly reproduced up to divergent terms all proportional to the Ricci scalar of $\cM$. The steps leading to this result are as follows: first we define a finite dimensional analogue of the loop space quantum mechanics (LSQM) where we discuss its tubular expansion and how that is related to a semi-classical expansion of the Hamiltonian. Then we study an explicit construction of the relevant tubular neighborhood in $\cLM$ using exponential maps. Such a tubular geometry is obtained from a Riemannian structure on the tangent bundle of $\cM$ which views the zero-section as a submanifold admitting a tubular neighborhood. Using this result and exploiting an analogy with the toy model we arrive at the final result for LSQM.