Randall-Sundrum Brane World Scenario Research Articles

Scalar absorption cross section of rotating black holes with tidal charge

The absorption cross section of rotating black holes in the Randall-Sundrum brane-world scenario for massless scalar waves is obtained via the partial-wave method. A variety of incidence directions with respect to the black hole rotation axis is considered. Special attention is given to near-extreme black holes, in which cases the absorption cross section increases as the tidal charge becomes more negative. It is shown that black holes with different configurations can present capture cross sections/shadows of same size. However, in such cases, the absorption spectra are different mainly for small frequencies. Numeric results are compared with the capture cross sections in the high-frequency limit, and with the black hole area in the low-frequency limit showing good agreement.

Electromagnetic absorption, emission and scattering spectra of black holes with tidal charge

The effects of the tidal charge of black holes predicted in the Randall-Sundrum brane-world scenario on the electromagnetic cross sections and emission rate is studied. Although quantitatively different, the cross sections and emission rates of such black holes are similar to the ones of Schwarzschild black holes. The increase of the tidal-charge intensity makes the absorption cross sections increase and the interference-fringe widths of the differential scattering cross sections narrow. The electromagnetic emission rate increases initially with the increase of the tidal-charge intensity, but reaches a maximum. This results from the combination of opposite behaviors of the absorption cross section and the black hole temperature, as this last decreases with the increase of the tidal-charge intensity. It is shown that the cross sections obtained via the partial-wave method agree well with the high-frequency approximations, and can also been simulated by their scalar analogues in certain limits.

Fine tuning problem of the cosmological constant in a generalized Randall-Sundrum model * *Supported by State Key Program of National Natural Science Foundation of China (11535005), the National Natural Science Foundation of China (11647087), the Natural Science Foundation of Yangzhou Polytechnic Institute (201917) and the Natural Science Foundation of Changzhou Institute of Technology (YN1509)

To solve the cosmological constant fine tuning problem, we investigate an (n+1)-dimensional generalized Randall-Sundrum brane world scenario with two -branes instead of two 3-branes. Adopting an anisotropic metric ansatz, we obtain the positive effective cosmological constant of order and only require a solution . Meanwhile, both the visible and hidden branes are stable because their tensions are positive. Therefore, the fine tuning problem can be solved quite well. Furthermore, the Hubble parameter as a function of redshift is in good agreement with the cosmic chronometers dataset. The evolution of the universe naturally shifts from deceleration to acceleration. This suggests that the evolution of the universe is intrinsically an extra-dimensional phenomenon. It can be regarded as a dynamic model of dark energy that is driven by the evolution of the extra dimensions on the brane.

Warm brane inflation with an exponential potential: A consistent realization away from the swampland

It has very recently been realized that coupling branes to higher dimensional quantum gravity theories and considering the consistency of what lives on the branes, one is able to understand whether such theories can belong either to the swampland or to the landscape. In this regard, in the present work, we study a warm inflation model embedded in the Randall-Sundrum braneworld scenario. It is explicitly shown that this model belongs to the landscape by supporting a strong dissipative regime with an inflaton steep exponential potential. The presence of extra dimension effects from the braneworld allow achieving this strong dissipative regime, which is shown to be both theoretically and observationally consistent. In fact, such strong dissipation effects, which decrease towards the end of inflation, together with the extra dimension effect, allow the present realization to simultaneously satisfy all previous restrictions imposed on such a model and to evade the recently proposed swampland conjectures. The present implementation of this model, in terms of an exponential potential for the scalar field, makes it also a possible candidate for describing the late-time Universe in the context of a dissipative quintessential inflation model and we discuss this possibility in the Conclusions.

Anisotropic evolution of 4-brane in a 6D generalized Randall-Sundrum model * * Supported by the Key Program of National Natural Science Foundation of China (11535005), the National Natural Science Foundation of China (11647087 and 11805097), the Natural Science Foundation of Yangzhou Polytechnic Institute (201917), and the Natural Science Foundation of Changzhou Institute of Technology (YN1509)

We investigate a 6D generalized Randall-Sundrum brane world scenario with a bulk cosmological constant. Each stress-energy tensor on the brane is shown to be similar to a constant vacuum energy. This is consistent with the Randall-Sundrum model, in which each 3-brane Lagrangian yielded a constant vacuum energy. By adopting an anisotropic metric ansatz, we obtain the 5D Friedmann-Robertson-Walker field equations. In a slightly later period, the expansion of the universe is proportional to the square root of time, , which is similar to the period of the radiation-dominated regime. Moreover, we investigate the case with two and two . In a large range of , we obtain the 3D effective cosmological constant , which is independent of the integral constant. Here, the scale factor is an exponential expansion, which is consistent with our present observation of the universe. Our results demonstrate that it is possible to construct a model that solves the dark energy problem, while guaranteeing a positive brane tension.

Effective Mass of Radion via GW Mechanism with a Non-Minimally Coupled Bulk Scalar Field

In the Randall-Sundrum braneworld scenario via the Goldberger-Wise mechanism, the effective mass of 4D radion, where the bulk scalar field is coupled to 5D gravity, has been investigated in two different case of the self-coupling constants, infinite and finite cases. It is shown that in the finite case, the modulus parameter should be greater than the finite coupling constants.

Spinors fields in co-dimension one braneworlds

In this work we analyze the zero mode localization and resonances of 1/2−spin fermions in co-dimension one Randall-Sundrum braneworld scenarios. We consider delta-like, domain walls and deformed domain walls membranes. Beyond the influence of the spacetime dimension D we also consider three types of couplings: (i) the standard Yukawa coupling with the scalar field and parameter η1, (ii) a Yukawa-dilaton coupling with two parameters η2 and λ and (iii) a dilaton derivative coupling with parameter h. Together with the deformation parameter s, we end up with five free parameter to be considered. For the zero mode we find that the localization is dependent of D, because the spinorial representation changes when the bulk dimensionality is odd or even and must be treated separately. For case (i) we find that in odd dimensions only one chirality can be localized and for even dimension a massless Dirac spinor is trapped over the brane. In the cases (ii) and (iii) we find that for some values of the parameters, both chiralities can be localized in odd dimensions and for even dimensions we obtain that the massless Dirac spinor is trapped over the brane. We also calculated numerically resonances for cases (ii) and (iii) by using the transfer matrix method. We find that, for deformed defects, the increasing of D induces a shift in the peaks of resonances. For a given λ with domain walls, we find that the resonances can show up by changing the spacetime dimensionality. For example, the same case in D = 5 do not induces resonances but when we consider D = 10 one peak of resonance is found. Therefore the introduction of more dimensions, diversely from the bosonic case, can change drastically the zero mode and resonances in fermion fields.

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.

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.

Bulk antisymmetric tensor fields coupled to a dilaton in a Randall-Sundrum model

A string-inspired 3-form-dilaton-gravity model is studied in a Randall-Sundrum brane world scenario. As expected, the rank-3 antisymmetric field is exponentially suppressed. For each mass level, the mass spectrum is bigger than the one for the Kalb-Ramond field. The coupling between the dilaton and the massless Kaluza-Klein mode of the 3-form is calculated and the coupling constant of the cubic interactions obtained numerically. This coupling are of the order of Tev$^{-1}$, therefore there exist a possibility to find some signal of it at Tev scale.

Gravitational effects of rotating braneworld black holes

We study the light deflection effect and the relativistic periastron and frame-dragging precessions for a rotating black hole localized on the brane in the Randall-Sundrum braneworld scenario. Focusing on a light ray, which passes through the field of the black hole in its equatorial plane, we first calculate the deflection angle in the weak field limit. We obtain an analytical formula, involving the related perturbative parameters of the field up to the second order. We then proceed with the numerical calculation of the deflection angle in the strong field limit when the light ray passes at the closest distance of approach to the limiting photon orbit. We show that the deflection angles for the light ray, winding maximally rotating Kerr and braneworld black holes in the same direction as their rotation, become essentially indistinguishable from each other for a specific value of the negative tidal charge. The same feature occurs in the relativistic precession frequencies at characteristic radii, for which the radial epicyclic frequency of the test particle motion attains its highest value. These results show that to distinguish between these two types of black holes one also needs to know the precise value of the angular momentum from independent observations, which for a maximally rotating braneworld black hole must exceed the Kerr bound in general relativity.

Randall-Sundrum scenario with bulk dilaton and torsion

We consider a string-inspired torsion-dilaton-gravity action in a Randall-Sundrum braneworld scenario and show that, in an effective four-dimensional theory on the visible brane, the rank-2 antisymmetric Kalb-Ramond field (source of torsion) is exponentially suppressed. The result is similar to our earlier result in [B. Mukhopadhyaya, S. Sen, and S. SenGupta, Phys. Rev. Lett. 89, 121101 (2002); Phys. Rev. Lett. 89, 259902(E) (2002)], where no dilaton was present in the bulk. This offers an explanation of the apparent invisibility of torsion in our space-time. However, in this case the trilinear couplings {approx}TeV{sup -1} between the dilaton and torsion may lead to new signals in TeV-scale experiments, bearing the stamp of extra warped dimensions.

Thermodynamics of anomaly-driven cosmology

The Friedmann equations of general relativity can be derived from the first law of thermodynamics when the entropy of the apparent horizon of a spatially isotropic universe is given by the Bekenstein–Hawking entropy. We point out that if the entropy of the apparent horizon receives a logarithmic correction, the first law of thermodynamics leads to a modified Friedmann equation which corresponds precisely to the time–time component of the semi-classical Einstein field equations sourced by the trace anomaly of the super-Yang–Mills theory. This correspondence allows for a thermodynamic description of the dynamics of the Randall–Sundrum braneworld scenario.

Cosmological bounce from a deformed Heisenberg algebra

The implications of a deformed Heisenberg algebra on the Friedmann-Robertson-Walker cosmological models are investigated. We consider the Snyder noncommutative space in which the translation group is undeformed and the rotational invariance preserved. When this framework is implemented to one-dimensional systems (which is this case) the modifications are uniquely fixed up to a sign. A cosmological quantum bounce a la loop quantum cosmology is then obtained. We also get the Randall-Sundrum braneworld scenario, and this way a Snyder-deformed quantum cosmology can be considered as a common phenomenological description for both theories.

Cosmological constant, brane tension and large hierarchy in a generalized Randall-Sundrum braneworld scenario

Sherpa Romeo green journal. Open access article. Creative Commons Attribution License (CC BY 4.0) applies.

Second Randall-Sundrum brane world scenario with a nonminimally coupled bulk scalar field

In our previous work of [K. Farakos and P. Pasipoularides, Phys. Lett. B 621, 224 (2005).] we studied the stability of the RS2 model with a nonminimally coupled bulk scalar field $\ensuremath{\phi}$, and we found that in appropriate regions of $\ensuremath{\xi}$ the standard RS2 vacuum becomes unstable. The question that arises is whether there exists other new static stable solutions where the system can relax. In this work, by solving numerically the Einstein equations with the appropriate boundary conditions on the brane, we find that depending on the value of the nonminimal coupling $\ensuremath{\xi}$, this model possesses three classes of new static solutions with different characteristics. We also examine what happens when the fine-tuning of the RS2 model is violated, and we obtain that these three classes of solutions are preserved in appropriate regions of the parameter space of the problem. The stability properties and possible physical implications of these new solutions are discussed in the main part of this paper. Especially in the case where $\ensuremath{\xi}={\ensuremath{\xi}}_{c}$ (${\ensuremath{\xi}}_{c}$ is the five-dimensional conformal coupling) and the fine-tuning is violated, we obtain a physically interesting static stable solution.

Loop cosmological dynamics and dualities with Randall-Sundrum braneworlds

The discrete quantum geometric effects play an important role in dynamical evolution in the loop quantum cosmology. These effects which are significant at the high energies lead to the quadratic energy density modifications to the Friedmann equation, as in the Randall-Sundrum braneworld scenarios but with a negative sign. We investigate the scalar field dynamics in this scenario and show the existence of a phase of super-inflation independent of the inverse scale factor modifications as found earlier. In this regime the scalar field mimics the dynamics of a phantom field and vice versa. We also find various symmetries between the expanding phase, the contracting phase and the phantom phase in the loop quantum cosmology. We then construct the scaling solutions in the loop quantum cosmology and show their dual relationship with those of the Randall-Sundrum cosmology.

LINEARIZED GRAVITY AS A GAUGE THEORY

We discuss linearized gravity from the point of view of a gauge theory. In (3+1) dimensions our analysis allows to consider linearized gravity in the context of the MacDowell–Mansouri formalism. Our observations may be of particular interest in the strong–weak coupling duality for linearized gravity, in Randall–Sundrum brane world scenario and in Ashtekar formalism.

Cosmological perturbations during radion stabilization

We consider the evolution of cosmological perturbations during radion stabilization, which we assume to happen after a period of inflation in the early universe. Concentrating on the Randall-Sundrum brane world scenario, we find that, if matter is present both on the positive and negative tension branes, the coupling of the radion to matter fields could have significant impact on the evolution of the curvature perturbation and on the production of entropy perturbations. We investigate both the case of a long-lived and a short-lived radion and outline similarities and differences to the curvaton scenario.

Gauge hierarchy from a topological viewpoint?

In this Letter we explore an alternative to the central point of the Randall–Sundrum brane world scenario, namely, the particular non-factorizable metric, in order to solve the hierarchy problem. From a topological viewpoint, we show that the exponential factor, crucial in the Randall–Sundrum model, appears in our approach, only due to the brane existence instead of a special metric background. Our results are based in a topological gravity theory via a non-standard interaction between scalar and non-Abelian degrees of freedom and in calculations about localized modes of matter fields on the brane. We point out that we obtain the same results of the Randall–Sundrum model using only one 3-brane, since a specific choice of a background metric is no longer required.