Running with Rugby Balls: Bulk Renormalization of Codimension-2 Branes

TL;DR

This paper calculates how quantum bulk effects influence the effective interactions and cosmological constant in models with codimension-two branes, using explicit one-loop computations in a 6D setup with general applicability.

Contribution

It provides explicit one-loop renormalization formulas for bulk and brane interactions in codimension-two brane models, applicable to various geometries and dimensions.

Findings

Bulk renormalization is independent of boundary conditions at branes.

Boundary conditions affect local brane renormalization but not distant branes.

Results help understand UV sensitivity of vacuum energy and cosmological constant.

Abstract

We compute how one-loop bulk effects renormalize both bulk and brane effective interactions for geometries sourced by codimension-two branes. We do so by explicitly integrating out spin-zero, -half and -one particles in 6-dimensional Einstein-Maxwell-Scalar theories compactified to 4 dimensions on a flux-stabilized 2D geometry. (Our methods apply equally well for D dimensions compactified to D-2 dimensions, although our explicit formulae do not capture all divergences when D>6.) The renormalization of bulk interactions are independent of the boundary conditions assumed at the brane locations, and reproduce standard heat-kernel calculations. Boundary conditions at any particular brane do affect how bulk loops renormalize this brane's effective action, but not the renormalization of other distant branes. Although we explicitly compute our loops using a rugby ball geometry, because we follow only UV effects our results apply more generally to any geometry containing codimension-two sources with conical singularities. Our results have a variety of uses, including calculating the UV sensitivity of one-loop vacuum energy seen by observers localized on the brane. We show how these one-loop effects combine in a surprising way with bulk back-reaction to give the complete low-energy effective cosmological constant, and comment on the relevance of this calculation to proposed applications of codimension-two 6D models to solutions of the hierarchy and cosmological constant problems.