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 Tools annual

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 monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

We review some interrelated aspects of thick brane worlds constructed withinthe framework of 5D gravity coupled to a scalar field depending on the extradimension. It turns out that when analyzing localization of 4D gravity in thissmooth version of the Randall-Sundrum model, a kind of dichotomy emerges. Inthe first case the geometry is completely smooth and the spectrum of metricfluctuations shows a single massless bound state, corresponding to the 4Dgraviton, and a tower of massive states described by a continuous spectrum ofKaluza-Klein excitations starting from zero mass, indicating the lack of a massgap. In the second case, there are two bound states, a massless 4D graviton anda massive excitation, separated by a mass gap from a continuous spectrum ofmassive modes; nevertheless, the presence of a mass gap in the gravitonspectrum of the theory is responsible for a naked singularity at the boundaries(or spatial infinity) of the Riemannian manifold. However, the imposition ofunitary boundary conditions, which is equivalent to eliminating the continuousspectrum of gravitational massive modes, renders these singularities harmlessfrom the physical point of view, providing the viability of the model.

Aspects of thick brane worlds: 4D gravity localization, smoothness, and mass gap