Generalized Randall Sundrum Research Articles

Inflation in anisotropic brane universe using tachyon field

Cosmological solution to the gravitational field equations in the generalized Randall–Sundrum model for an anisotropic brane with Bianchi-I geometry and perfect fluid as matter sources has been considered. The matter on the brane is described by a tachyonic field. The solution admits inflationary era and at a later epoch the anisotropy of the universe washes out. We obtain two classes of cosmological scenario: in the first case, universe evolves from singularity and in the second case, universe expands without singularity.

Brane cosmological constant in two-brane warped geometry model

In the backdrop of generalized Randall–Sundrum braneworld scenario, we look for the possible origin of an effective four-dimensional cosmological constant (Ω vis ) on the visible three-brane due to the effects of bulk curvature and the modulus field that can either be a constant or a time-dependent quantity. In case of constant modulus field, the induced Ω vis leads to an exponentially expanding universe and the presence of vacuum energy densities on either of the three-branes as well as a nonvanishing bulk curvature [Formula: see text] are essential to generate an effective Ω vis . The Hubble constant turns out to be equal to the visible brane cosmological constant which agrees with the present result. In an alternative scenario, a time-dependent modulus field is found to be capable of decelerating the universe. The Hubble parameter, in this case is determined for a slowly time-varying modulus field.

Generalized Randall–Sundrum model with a single thick brane

A generalized version of the Randall-Sundrum model-2 with different cosmological constants on each side of a brane has been discussed. A possibility of replacing the singular brane by a configuration of a scalar field has been also considered, the Einstein equations for this setup were solved and stability of the solution discussed. It has been shown that under mild assumptions the relation between cosmological constants and the brane tension obtained in the brane limit does not depend on the particular choice of the regularizing profile of the scalar field.

Antisymmetric tensor fields in a generalized Randall–Sundrum scenario

Bulk antisymmetric tensor fields of different ranks have been studied in the context of a generalized Randall–Sundrum model with a non-vanishing induced cosmological constant on the visible brane. It is shown that instead of the usual exponential suppression of the couplings of the zero modes of these bulk fields with the brane fermions in the original Randall–Sundrum model, here the couplings are proportional to the brane cosmological constant. Thus in an era of large cosmological constant these fields have significant role in physical phenomena because of their enhanced couplings with the visible brane fermions.

Kaluza–Klein modes of bulk fields in a generalized Randall–Sundrum scenario

We consider a generalised two brane Randall–Sundrum model with non-zero cosmological constant on the visible TeV brane. Massive Kaluza–Klein modes for various bulk fields namely graviton, gauge field and antisymmetric second rank Kalb–Ramond field in a such generalized Randall–Sundrum scenario are determined. The masses for the Kaluza–Klein excitations of different bulk fields are found to depend on the brane cosmological constant indicating interesting consequences in warped brane particle phenomenology.

Second-order light deflection by tidal charged black holes on the brane

We derive the deflection angle of light rays passing near a black hole with mass m and tidal charge q, confined to a generalized Randall–Sundrum brane with co-dimension 1. We employ the weak lensing approach, up to the second order in perturbation theory by two distinct methods. First we adopt a Lagrangian approach and derive the deflection angle from the analysis of the geodesic equations. Then we adopt a Hamiltonian approach and we recover the same result from the analysis of the eikonal. With this we re-establish the unicity of the result as given by the two methods. Our results in turn implies a more rigorous constraint on the tidal charge from solar system measurements, than derived before.

Cosmic acceleration from asymmetric branes

We consider a single 3-brane sitting in between two different five-dimensional spacetimes. On each side of the brane, the bulk is a solution to Gauss–Bonnet gravity, although the bare cosmological constant, fundamental Planck scale and Gauss–Bonnet coupling can differ. This asymmetry leads to weighted junction conditions across the brane and interesting brane cosmology. We focus on two special cases: a generalized Randall–Sundrum model without any Gauss–Bonnet terms, and a stringy model, without any bare cosmological constants, and positive Gauss–Bonnet coupling. Even though we assume there is no vacuum energy on the brane, we find late time de Sitter cosmologies can occur. Remarkably, in certain parameter regions, this acceleration is preceded by a period of matter/radiation domination, with H2 ∝ ρ, all the way back to nucleosynthesis.

BRANE-PRODUCTION AND THE NEUTRINO–NUCLEON CROSS SECTION AT ULTRAHIGH ENERGIES IN LOW SCALE GRAVITY MODELS

The observed ultrahigh energy cosmic rays (UHECR) might require a modification of the basic laws of physics. In low scale gravity models, where the neutrino–nucleon cross section rises to typical hadronic values at energies above 1020 eV, the neutrino becomes a candidate for the primary that initiates these showers. We calculate the neutrino–nucleon cross section at ultrahigh energies by assuming that it is dominated by the production of p-branes. We show, using a generalized Randall–Sundrum model, that the neutrino–nucleon cross-section at neutrino energies of 1020 eV is of the order of 100 mb, which is required for explaining the UHECR events. Similar results also follow in other models such as the Lykken–Randall model.

Fifth Force from Fifth Dimension: A Comparison Between Two Different Approaches

We investigate the dynamics of particles moving in a spacetime augmented by one extra dimension in the context of the induced matter theory of gravity. We examine the appearance of a fifth force as an effect caused by the extra dimension and discuss two different approaches to the fifth force formalism. We then give two simple examples of application of both approaches by considering the case of a Ricci-flat warped-product manifold and a generalized Randall–Sundrum space.

Viscous Bianchi type I universes in brane cosmology

We consider the dynamics of a viscous cosmological fluid in the generalized Randall–Sundrum model for an anisotropic, Bianchi type I brane. To describe the dissipative effects we use the Israel–Hiscock–Stewart full causal thermodynamic theory. By assuming that the matter on the brane obeys a barotropic linear equation of state, and that the bulk viscous pressure has a power-law dependence on the energy density, the general solution of the field equations can be obtained in an exact parametric form. The solutions obtained describe generally a non-inflationary braneworld. In the large time limit the brane universe isotropizes, ending in an isotropic and homogeneous state. The evolution of the temperature and the comoving entropy of the universe is also considered, and it is shown that due to viscous dissipative processes a large amount of entropy is created in the early stages of evolution of the braneworld.