English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Spin foams are candidate state-sum models for transition amplitudes inquantum gravity. An active research subject is to identify the possibledivergences of spin foam models, or alternatively to show that models arefinite. We will discuss in detail the (non--occurrence of) divergences in theBarrett-Crane model, formulated as an integral of delta function weights only.We will furthermore present a simple method to estimate the divergence degreeof the so-called bubbles for general spin foam models. Divergences in spinfoams are expected to be related to the existence of gauge symmetries(diffeomorphisms). Thus we have to conclude that such gauge symmetries are not(fully) present in the model we consider. But we will identify a class of gaugesymmetries which occur at special solutions of the equations imposed by thedelta function weights. This situation is surprisingly similar to the case ofbroken diffeomorphism symmetries in discrete gravity, which are present aroundflat solutions. We introduce a method to derive (Ward-identity-like) equationsfor the vertex amplitude of the model in the case of broken gauge symmetries.

Bubble divergences and gauge symmetries in spin foams