Ghosts and Tachyons in the Fifth Dimension

Abstract

We present several solutions for the five dimensional gravity models in the presence of bulk ghosts and tachyons to argue that these "troublesome" fields can be a useful modelbuilding tool. The ghost-like signature of the kinetic term for a bulk scalar creates a minimum in the scale factor, removing the necessity for a negative tension brane in models with the compactified fifth dimension. It is shown that the model with the positive tension branes and a ghost field in the bulk leads to the radion stabilization. The bulk scalar with the variable sign kinetic term can be used to model both positive and negative tension branes of a finite width in the compact dimension. Finally, we present several ghost and tachyon field configurations in the bulk that lead to the localization of gravity in four dimensions, including one solution with the Gaussian profile for the metric, g µν (y) = η µν exp{−αy 2 }, which leads to a stronger localization of gravity than the Randall-Sundrum model.

Anti-De Sitter Island-Universes From 5d Standing Waves

“…Further it was shown that a bulk scalar field whose sign can vary between regular (positive) and ghost (negative) can be used to model both positive and negative tension branes. Also, there are certain configurations of the bulk ghost fields of reference [51] which lead to stronger localization of gravity than the original brane models. In references [52,53] it is shown that the two brane model of [1,2,3,4] is stabilized by a ghost/tachyon bulk field, while for a regular bulk scalar field the two brane model is unstable.…”

Localization Problem in the 5d Standing Wave Braneworld

“…5D standing wave braneworld [13][14][15] is generated by gravity coupled to a non-self-interacting scalar phantom-like field (different brane models with phantom fields can be found in [38][39][40][41][42][43]), which depends on time and propagates in the bulk. The action of the model has the form:…”

Localization of matter fields in the 5D standing wave braneworld

“…Note that, as a consequence of (4.17) and (4.21), in our setup the right fermionic modes are absent on the brane: ρ(r)| r→±0 = 0 . In the second limited region -far away from the brane, 23) and the equation (4.18) takes the asymptotic form:…”