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Gauge fixing in constrained systems

Published online by Cambridge University Press:  05 November 2011

J.M. Pons
Affiliation:
Universitat de Barcelona
L.C. Shepley
Affiliation:
The University of Texas
John M. Charap
Affiliation:
Queen Mary University of London
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Summary

Abstract

In this paper we show how to eliminate nonphysical degrees of freedom in both the Lagrangian and Hamiltonian formulations of a constrained system. The use of gauge fixing procedures is different in the two cases, but the final result is that the number of degrees of freedom in the two formulations agrees. The two key steps in our method are to use gauge fixing to eliminate ambiguities in the dynamics and to determine the inequivalent initial data. Applications to reparameterization invariant theories are briefly discussed.

Introduction

The degrees of freedom in either the Lagrangian or the Hamiltonian formulation of a singular system are reduced in two stages: reduction from using the natural constraints (with consistency requirements) and reduction through a gauge fixing procedure. In general the number of natural constraints in the Lagrangian formulation differs from the number in the Hamiltonian formulation [1]. In this paper we show how to determine the dynamics and fix the gauge in both formalisms. We believe the Lagrangian discussion is new and useful. The result includes a proof that the final number of degrees of freedom in the two formalisms is the same. Important parts of our methods are the two steps of determining the dynamics and determining the independent initial data.

In section 2 we develop a detailed version of the Hamiltonian gauge fixing procedure. In section 3 we study the Lagrangian gauge fixing procedure and show that the number of degrees of freedom in the Hamiltonian and Lagrangian formalisms are equal.

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Publisher: Cambridge University Press
Print publication year: 1995

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