Fields in nonaffine bundles. III. Effective symmetries and conserved currents in strings and higher branes

TL;DR

This paper extends a covariant formalism for multi-scalar fields in curved target spaces to include harmonious models on strings and branes, analyzing effective symmetries and conserved currents, especially in non-Abelian and gauged contexts.

Contribution

It develops a formalism for effective symmetries and conserved currents in nonaffine, curved target space models on strings and branes, including gauged and non-Abelian cases.

Findings

Conservation conditions for internal symmetry currents are clarified.

Surface flux currents related to spacetime symmetries are analyzed.

Effective gauge adjustments can preserve current conservation despite non-invariance.

Abstract

The principles of a previously developed formalism for the covariant treatment of multi-scalar fields for which (as in a nonlinear sigma model) the relevant target space is not of affine type -- but curved -- are recapitulated. Their application is extended from ordinary harmonic models to a more general category of "harmonious" field models, with emphasis on cases in which the field is confined to a string or higher brane worldsheet, and for which the relevant internal symmetry group is non Abelian, so that the conditions for conservation of the corresponding charge currents become rather delicate, particularly when the symmetry is gauged. Attention is also given to the conditions for conservation of currents of a different kind -- representing surface fluxes of generalised momentum or energy -- associated with symmetries not of the internal target space but of the underlying spacetime background structure, including the metric and any relevant gauge field. For the corresponding current to be conserved the latter need not be manifestly invariant: preservation modulo a gauge adjustment will suffice. The simplest case is that of "strong" symmetry, meaning invariance under the action of an effective Lie derivative (an appropriately gauge adjusted modification of an ordinary Lie derivative). When the effective symmetry is of the more general "weak" kind, the kinetic part of the current is not conserved by itself but only after being supplemented by a suitable contribution from the background.