Randall-Sundrum Braneworld Research Articles

Electromagnetic perturbations in new brane world scenarios

In this work we consider electromagnetic dynamics in Randall-Sundrum branes. It is derived a family of four-dimensional spacetimes compatible with Randall-Sundrum brane worlds, focusing on asymptotic flat backgrounds. Maximal extensions of the solutions are constructed and their causal structures are discussed. These spacetimes include singular, non-singular and extreme black holes. Maxwell's electromagnetic field is introduced and its evolution is studied in an extensive numerical survey. Electromagnetic quasinormal mode spectra are derived and analyzed with time-dependent and high-order WKB methods. Our results indicate that the black holes in the brane are electromagnetically stable.

Quasinormal frequencies of black hole in the braneworld

We have studied scalar, electromagnetic and gravitational perturbations of the four-dimensional Reissner-Nordstr\"{o}m-like black holes with a \textit{tidal charge} in the Randall-Sundrum braneworld. The quasinormal modes of these scalar, electromagnetic, as well as axial and polar gravitational perturbations, have been studied in both normal and eikonal regimes. Calculations have shown that the black holes on the Randall-Sundrum brane are stable against scalar, electromagnetic and gravitational perturbations. Moreover, we determine the grey body factor, giving transmission and reflection of the scattered waves through the scalar, electromagnetic and gravitational effective potentials. It has been shown that the scalar perturbative fields are the most favorite to the reflected as compared to the latter. With increasing value of the tidal charge ability of the all perturbative potentials to reflect the waves decreases. Our calculations in low- and high-frequency regimes have shown that black holes on the braneworld always have a bigger absorption cross section of massless scalar waves than the Schwarzschild and standard Reissner-Nordstr\"{o}m black holes.

Kalb–Ramond fields and the CMBR

Cosmological implications on the polarization of the cosmic microwave background radiation, of a Kalb–Ramond field interacting with gauge fields and gravity as dictated by quantum consistency of heterotic string theory are surveyed. A parity violating augmentation going beyond the dictates of string theory is shown to lead to possible appearance of a B mode generated in the cosmic microwave background (CMB) in the post-last scattering epoch. This generation of the B mode of CMB appears to be dramatic when the augmentation is embedded within a Randall–Sundrum braneworld scenario of the first kind.

Does a Randall-Sundrum Brane World Effective Potential Influence Axion Walls Helping to Form a Cosmological Constant Affecting Inflation?

In 2003, Guth posed the following question in a KITP seminar in UCSB. Namely “Even if there exist 101000 vacuum states produced by String theory, does inflation produce overwhelmingly one preferred type of vacuum states over the other possible types of vacuum states”? This document tries to answer how a preferred vacuum state could be produced, and by what sort of process. We construct a di quark condensate leading to a cosmological constant in line with known physical observations. We use a phase transition bridge from a tilted washboard potential to the chaotic inflationary model pioneered by Guth which is congruent with the slow roll criteria. This permits criteria for initiation of graviton production from a domain wall formed after a transition to a chaotic inflationary potential. It also permits investigation of if or not axion wall contributions to inflation are necessary. If we reject an explicit axion mass drop off to infinitesimal values at high temperatures, we may use the Bogomolnyi inequality to rescale and reset initial conditions for the chaotic inflationary potential. Then the Randall-Sundrum brane world effective potential delineates the end of the dominant role of di quarks, and the beginning of inflation. And perhaps answers Freeman Dysons contention that Graviton production is unlikely given present astrophysical constraints upon detector systems. We end this with a description in the last appendix entry, Appendix VI, as to why, given the emphasis upon di quarks, as to the usefulness of using times before Planck time interval as to modeling our physical system and its importance as to emergent field structures used for cosmological modeling.

Localization and quasilocalization of a spin-1/2fermion field on a two-field thick braneworld

Localization of a spin-$1/2$ fermion on the braneworld is an important and interesting problem. It is well known that a five-dimensional free massless fermion $\Psi$ minimally coupled to gravity cannot be localized on the Randall-Sundrum braneworld. In order to trap such a fermion, the coupling between the fermion and bulk scalar fields should be introduced. In this paper, localization and quasilocalization of a bulk fermion on the thick braneworld generated by two scalar fields (a kink scalar $\phi$ and a dilaton scalar $\pi$) are investigated. Two types of couplings between the fermion and two scalars are considered. One coupling is the usual Yukawa coupling $-\eta\bar{\Psi}\phi\Psi$ between the fermion and kink scalar, another one is $\lambda\bar{\Psi}\Gamma^{M}\partial_{M}\pi\gamma^{5}\Psi$ between the fermion and dilaton scalar. The left-chiral fermion zero mode can be localized on the brane, and both the left- and right-chiral fermion massive Kaluza-Klein modes may be localized or quasilocalized. Hence the four-dimensional massless left-chiral fermion and massive Dirac fermions, whose lifetime is infinite or finite, can be obtained on the brane.

Complete cosmic scenario in the Randall-Sundrum braneworld from the dynamical systems perspective

The paper deals with dynamical system analysis of a coupled scalar field in the Randall-Sundrum(RS)2 brane world. The late time attractor describes the final state of the cosmic evolution. In RS2 based phantom model there is no late-time attractor and consequently there is uncertainty in cosmic evolution. In this paper, we have shown that it is possible to get late-time attractor when gravity is coupled to scalar field. Finally, in order to predict the final evolution of the universe, we have also studied classical stability of the model. It is found that there are late time attractors which are both locally as well as classically stable and so our model can realise the late time cosmic acceleration.

First law and a variational principle for static asymptotically Randall-Sundrum black holes

We give a new, intrinsic, mass definition for spacetimes asymptotic to the Randall-Sundrum braneworld models, RS1 and RS2. For this mass, we prove a first law for static black holes, including variations of the bulk cosmological constant, brane tensions, and RS1 interbrane distance. Our first law defines a thermodynamic volume and a gravitational tension that are braneworld analogs of the corresponding quantities in asymptotically AdS black hole spacetimes and asymptotically flat compactifications, respectively. We also prove the following related variational principle for asymptotically RS black holes: instantaneously static initial data that extremizes the mass yields a static black hole, for variations at fixed apparent horizon area, AdS curvature length, cosmological constant, brane tensions, and RS brane warp factors. This variational principle is valid with either two branes (RS1) or one brane (RS2), and is applicable to variational trial solutions.

Dark matter relic density in Gauss-Bonnet braneworld cosmology

The relic density of symmetric and asymmetric dark matter in a Gauss-Bonnet (GB) modified Randall-Sundrum (RS) type II braneworld cosmology is investigated. The existing study of symmetric dark matter in a GB braneworld (Okada and Okada, 2009) found that the expansion rate was reduced compared to that in standard General Relativity (GR), thereby delaying particle freeze-out and resulting in relic abundances which are suppressed by up to \U0001d4aa(10−2). This is in direct contrast to the behaviour observed in RS braneworlds where the expansion rate is enhanced and the final relic abundance boosted. However, this finding that relic abundances are suppressed in a GB braneworld is based upon a highly contrived situation in which the GB era evolves directly into a standard GR era, rather than passing through a RS era as is the general situation. This collapse of the RS era requires equating the mass scale mα of the GB modification and the mass scale mσ of the brane tension. However, if the GB contribution is to be considered as the lowest order correction from string theory to the RS action, we would expect mα > mσ. We investigate the effect upon the relic abundance of choosing more realistic values for the ratio ℛm ≡ mα/mσ and find that the relic abundance can be either enhanced or suppressed by more than two orders of magnitude. However, suppression only occurs for a small range of parameter choices and, overwhelmingly, the predominant situation is that of enhancement as we recover the usual Randall-Sundrum type behaviour in the limit ℛm ≫ 1. We use the latest observational bound ΩDMh2 = 0.1187 ± 0.0017 to constrain the various model parameters and briefly discuss the implications for direct/indirect dark matter detection experiments as well as dark matter particle models.

Radion cosmology and stabilization

We solve the Einstein's equation in five-dimensional spacetime for Randall Sundrum Brane world model with time dependent radion field to study variation of brane scale factor with time. We have shown that as radion field decreases with time compactifying the extra dimension, the scale factor increases exponentially with time leading to inflationary scenario. We have also proposed a time dependent generalization of Goldberger-Wise moduli stabilization mechanism to explain the time evolution of the radion field to reach a stable value after which the scale factor on the brane exits from inflationary expansion.

DGP braneworld with a bubble of nothing

We construct exact solutions with the bubble of nothing in the Dvali-Gabadadze-Porrati braneworld model. The configuration with a single brane can be constructed, unlike in the Randall-Sundrum braneworld model. The geometry on the single brane looks like the Einstein-Rosen bridge. We also discuss the junction of multibranes. Surprisingly, even without any artificial matter fields on the branes such as three-dimensional tension of the codimension-two objects, two branes can be connected in certain configurations. We investigate solutions of multibranes too. The presence of solutions may indicate the semiclassical instability of the models.

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.

New localization mechanism of fermions on braneworlds

It is known that by introducing the Yukawa coupling between the fermion and the background scalar field, a bulk spin-half fermion can be localized on general Randall-Sundrum braneworlds generated by a kinklike background scalar. However, this localization mechanism does not work anymore for Randall-Sundrum braneworlds generated by a scalar whose configuration is an even function of the extra dimension. In this paper, we present a new localization mechanism for spin-half fermions for such a class of braneworld models, in which extra dimension has the topology $S^1/Z_2$. By two examples, it is shown that the new localization mechanism produces interesting results. In the first model with the brane generated by two scalars, the zero mode of the left-handed fermion is localized on the brane and there is a mass gap between the fermion zero mode and excited KK modes. In the second model with the brane generated by a dilaton scalar, the zero mode of the left- or right-chiral fermion can be localized on the brane and there is no mass gap.

Strong Planck constraints on braneworld and non-commutative inflation

We place observational likelihood constraints on braneworld and non-commutative inflation for a number of inflaton potentials, using Planck, WMAP polarization and BAO data. Both braneworld and non-commutative scenarios of the kind considered here are limited by the most recent data even more severely than standard general-relativity models. At more than 95 % confidence level, the monomial potential V(ϕ)∝ϕp is ruled out for p ⩾ 2 in the Randall-Sundrum (RS) braneworld cosmology and, for p > 0, also in the high-curvature limit of the Gauss-Bonnet (GB) braneworld and in the infrared limit of non-commutative inflation, due to a large scalar spectral index. Some parameter values for natural inflation, small-varying inflaton models and Starobinsky inflation are allowed in all scenarios, although some tuning is required for natural inflation in a non-commutative spacetime.

Tolman IV solution in the Randall-Sundrum braneworld

In the context of the Randall-Sundrum braneworld, the minimal geometric deformation approach is used to generate an analytic interior solution to four-dimensional effective Einstein field equations for a spherically symmetric compact distribution. This solution represents the braneworld version of the well-known Tolman IV solution in general relativity. By using this analytic solution, an exhaustive analysis of the braneworld effects on realistic stellar interiors is developed, finding strong evidence in favor of the hypothesis that compactness is reduced due to bulk effects on stellar configurations.

Asymptotic behavior of a scalar field with an arbitrary potential trapped on a Randall-Sundrum’s braneworld: the effect of a negative dark radiation term on a Bianchi I brane

In this work we present a phase space analysis of a quintessence field and a perfect fluid trapped in a Randall-Sundrum's Braneworld of type 2. We consider a homogeneous but anisotropic Bianchi I brane geometry. Moreover, we consider the effect of the projection of the five dimensional Weyl tensor onto the three-brane in the form of a negative Dark Radiation term. For the treatment of the potential we use the "Method of $f$-devisers" that allows investigating arbitrary potentials in a phase space. We present general conditions on the potential in order to obtain the stability of standard 4D and non-standard 5D de Sitter solutions, and we provide the stability conditions for both scalar field-matter scaling solutions, scalar field-dark radiation solutions and scalar field-dominated solutions. We find that the shear-dominated solutions are unstable (particularly, contracting shear-dominated solutions are of saddle type). As a main difference with our previous work, the traditionally ever-expanding models could potentially re-collapse due to the negativity of the dark radiation. Additionally, our system admits a large class of static solutions that are of saddle type. These kinds of solutions are important at intermediate stages in the evolution of the universe, since they allow the transition from contracting to expanding models and viceversa. New features of our scenario are the existence of a bounce and a turnaround, which lead to cyclic behavior, that are not allowed in Bianchi I branes with positive dark radiation term. Finally, as specific examples we consider the potentials $V\propto\sinh^{-\alpha}(\beta\phi)$ and $V\propto\left[\cosh\left(\xi\phi \right)-1\right]$ which have simple $f$-devisers.

On the many-field [formula omitted] brane

We consider the Randall–Sundrum braneworld theory with a single extra dimension of infinite extent to investigate generalized f(R) braneworld models in the presence of several real scalar fields. In particular, we solve the modified Einstein equations for the case of flat brane, with zero cosmological constant, and for the case of bent brane, with a nonvanishing cosmological constant. In both cases we found explicit solutions for the scalar fields with analytical expressions for the respective warp factors.

The role of exterior Weyl fluids on compact stellar structures in Randall–Sundrum gravity

In the context of the Randall–Sundrum braneworld, the minimal geometric deformation approach is used to generate a new physically acceptable interior solution to Einstein’s field equations for a spherically symmetric compact distribution. This new solution is used to elucidate the role of exterior Weyl stresses from bulk gravitons on compact stellar distributions. We found strong evidences showing that the exterior dark radiation always increases both the pressure and the compactness of stellar structures, and that the exterior ‘dark pressure’ always reduces them.

Phase space analysis of quintessence fields trapped in a Randall–Sundrum braneworld: anisotropic Bianchi I brane with a positive dark radiation term

In this paper we investigate, from the dynamical systems perspective, the evolution of a scalar field with an arbitrary potential trapped in a Randall–Sundrum's braneworld of type 2. We consider a homogeneous but anisotropic Bianchi I (BI) brane filled with a perfect fluid. We also consider the effect of the projection of the five-dimensional (5D) Weyl tensor onto the three-brane in the form of a positive dark radiation term. Using the center manifold theory, we obtain sufficient conditions for the asymptotic stability of the de Sitter solution with standard 4D behavior. We also prove that there are no late-time de Sitter attractors with 5D modifications since they are always saddle-like. This fact correlates with a transient primordial inflation. We present here sufficient conditions on the potential for the stability of the scalar field–matter scaling solution, the scalar-field-dominated solution and the scalar field–dark radiation scaling solution. We illustrate our analytical findings using a simple f-deviser as a toy model. All these results are generalizations of our previous results obtained for FRW branes.

Phase space analysis of quintessence fields trapped in a Randall–Sundrum braneworld: a refined study

In this paper, we investigate, from the perspective of dynamical systems, the evolution of a scalar field with an arbitrary potential trapped in a Randall–Sundrum's braneworld of type II. We consider an homogeneous and isotropic Friedmann–Robertson–Walker brane filled also with a perfect fluid. Center manifold theory is employed to obtain sufficient conditions for the asymptotic stability of the de Sitter solution. We obtain conditions on the potential for the stability of scaling solutions as well for the stability of the scalar-field-dominated solution. We prove the fact that there are not late-time attractors with 5D-modifications (they are saddle like). This fact correlates with a transient primordial inflation. In the particular case of a scalar field with the potential V = V0e−χϕ + Λ, we prove that for χ < 0 the de Sitter solution is asymptotically stable. However, for χ > 0, the de Sitter solution is unstable (of saddle type).

GRAVITATIONAL WAVES IN BRANEWORLD SCENARIOS WITH AdS BACKGROUND

In this paper, we investigate gravitational waves as metric perturbations around a general warped five-dimensional background. We find an analytical solution in Randall–Sundrum braneworld model and analyze the implications of braneworld models in the gravitational waves propagation.