Browsing by Author "Toporensky, A."

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Aspects of scalar field dynamics in Gauss-Bonnet Brane Worlds
    (2011-07-06) Sami, M.; Savchenko, N.; Toporensky, A.
    The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to a complicated Friedmann equation which simplifies to H2 ∼ ρq in the asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to q = 2 whereas q = 2/3 & q = 1 give rise to high energy Gauss-Bonnet (GB) regime and the standard GR respectively. Amazingly, while evolving from RS regime to high energy GB limit, one passes through a GR like region which has important implications for brane world inflation. For tachyon GB inflation with potentials V (φ) ∼ φp investigated in this paper, the scalar to tensor ratio of perturbations R is maximum around the RS region and is generally suppressed in the high energy regime for the positive values of p. The ratio is very low for p > 0 at all energy scales relative to GB inflation with ordinary scalar field. The models based upon tachyon inflation with polynomial type of potentials with generic positive values of p turn out to be in the 1σ observational contour bound at all energy scales varying from GR to high energy GB limit. The spectral index nS improves for the lower values of p and approaches its scale invariant limit for p = −2 in the high energy GB regime. The ratio R also remains small for large negative values of p, however, difference arises for models close to scale invariance limit. In this case, the tensor to scale ratio is large in the GB regime whereas it is suppressed in the intermediate region between RS and GB. Within the frame work of patch cosmologies governed by H2 ∼ ρq , the behavior of ordinary scalar field near cosmological singularity and the nature of scaling solutions are distinguished for the values of q < 1 and q > 1. The tachyon dynamics, on the other hand, exhibits stable scaling solutions ∀q if the adiabatic
  • No Thumbnail Available
    Item
    Phantom field and the fate of the Universe
    (2011-07-06) Sami, M.; Toporensky, A.
    In this paper we analyze the cosmological dynamics of phantom field in a variety of potentials unbounded from above. We demonstrate that the nature of future evolution generically depends upon the steepness of the phantom potential and discuss the fate of Universe accordingly.
  • No Thumbnail Available
    Item
    Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology
    (2006-03-24) Tretjakov, P. V.; Toporensky, A.; Shtanov, Yuri; et al.