AdS braneworld with Backreaction

We review the tachyon model derived from the dynamics of a 3-brane moving in the AdS5 bulk. The bulk geometry is based on the Randall-Sundrum II model extended to include the radion. The effective tachyon Lagrangian is modified due to the back-reaction of the brane on the bulk geometry.Comment: 21 pages, 5 figures, typos corrected, a refference added, based on the talk of NB presented at BW2013 - Beyond the standard models, April 2013, Vrnjacka Banja, Serbia, to appear in CEJ

Cosmological k-essence condensation

We consider a model of dark energy/matter unification based on a k-essence type of theory similar to tachyon condensate models. Using an extension of the general relativistic spherical model which incorporates the effects of both pressure and the acoustic horizon we show that an initially perturbative k-essence fluid evolves into a mixed system containing cold dark matter like gravitational condensate in significant quantities.Comment: 8 pages, 2 figures, presented by NB at the conference Beyond 2010, Cape Town, 1-6 February 201