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

We consider Lovelock theories of gravity in the context of AdS/CFT. We showthat, for these theories, causality violation on a black hole background canoccur well in the interior of the geometry, thus posing more stringentconstraints than were previously found in the literature. Also, we find thatinstabilities of the geometry can appear for certain parameter values at anypoint in the geometry, as well in the bulk as close to the horizon. These newsources of causality violation and instability should be related to CFTfeatures that do not depend on the UV behavior. They solve a puzzle foundpreviously concerning unphysical negative values for the shear viscosity thatare not ruled out solely by causality restrictions. We find that, contrary toprevious expectations, causality violation is not always related to positivityof energy. Furthermore, we compute the bound for the shear viscosity to entropydensity ratio of supersymmetric conformal field theories from d=4 till d=10 -i.e., up to quartic Lovelock theory -, and find that it behaves smoothly as afunction of d. We propose an approximate formula that nicely fits these valuesand has a nice asymptotic behavior when d goes to infinity for any Lovelockgravity. We discuss in some detail the latter limit. We finally argue that itis possible to obtain increasingly lower values for the shear viscosity toentropy density ratio by the inclusion of more Lovelock terms.

Lovelock theories, holography and the fate of the viscosity bound