Sundrum Model Research Articles

Self-interacting scalar field trapped in a Randall–Sundrum braneworld: The dynamical systems perspective

We apply the dynamical systems tools to study the linear dynamics of a self-interacting scalar field trapped on a Randall–Sundrum brane. The simplest kinds of self-interaction potentials are investigated: (a) constant potential, and (b) exponential potential. It is shown that the dynamics of the Randall–Sundrum model significantly differs from the standard four-dimensional behavior at early times: in all cases of interest the (singular) empty universe is the past attractor for every trajectory in phase space, meanwhile the kinetic energy-dominated solution is always a saddle critical point. The late-time dynamics is not affected by the brane effects.

Smoothing out negative tension brane

We propose an extension of the five-dimensional gravitational action with an external source in order to allow arbitrary smoothing of the negative tension brane in the Randall–Sundrum model. This extended action can be derived from a model with an auxiliary four form field coupled to the gravity. We point out a further generalization of our model in relation to tachyon condensation. A possible mechanism for radion stabilization in our model is also discussed.

Minimal flavor violation in the lepton sector of the Randall–Sundrum model

We propose a realization of Minimal Flavor Violation in the lepton sector of the Randall–Sundrum model. With the MFV assumption, the only source of flavor violation are the 5D Yukawa couplings, and the usual two independent sources of flavor violation are related. In the limit of massless neutrinos, the bulk mass matrices and 5D Yukawa matrices are simultaneously diagonalized, and hence the absence of FCNCs. In the case of massive neutrinos, the contributions to FCNCs in the charged lepton sector are highly suppressed, due to the smallness of neutrino masses. In addition, the MFV assumption also allows suppressing one-loop charged current contributions to flavor changing processes by reducing the size of the Yukawa couplings, which is not possible in the generic anarchical case. We found that the first KK mass scale as low as ∼3 TeV can be allowed. In both cases, we present a set of numerical results that give rise to realistic lepton masses and mixing angles. Mild hierarchy in the 5D Yukawa matrix of O(25) in our numerical example is required to be consistent with two large and one small mixing angles. This tuning could be improved by having a more thorough search of the parameter space.

Dielectron and diphoton channels in 2HDM

It was observed recently that [L. Randall, Mark B. Wise, arXiv: 0807.1746 [hep-ph]], any particle in the Standard Model cannot decay to e + e − and γγ final states with comparably measurable branching ratios. This is also true for most extensions of the Standard Model, with the Randall–Sundrum model as an outstanding exception. In this Letter, we show that two-Higgs-Doublet-Models (2HDM) yield another possible exception if certain parameters are properly chosen. In addition, we have checked that this model survives the tests of low energy processes, including the anomalous magnetic moment and electric dipole moment of leptons, lepton-flavor-violating decays μ − → e − γ and e − e + e − .

Cosmological Kaluza–Klein branes in black brane spacetimes

We discuss the cosmological evolution of a brane in the D(>6)-dimensional black brane spacetime in the context of the Kaluza–Klein (KK) braneworld scheme, i.e., to consider KK compactification on the brane. The bulk spacetime is composed of two copies of a patch of D-dimensional black three-brane solution. The near-horizon geometry is given by AdS5×S(D−5) while in the asymptotic infinity the spacetime approaches D-dimensional Minkowski. We consider the brane motion from the near-horizon region toward the spatial infinity, which induces cosmology on the brane. As is expected, in the early times, namely when the brane is located in the near-horizon region, the effective cosmology on the brane coincides with that in the second Randall–Sundrum (RS II) model. Then, the brane cosmology starts to deviate from the RS type one since the dynamics of KK compactified dimensions becomes significant. We find that the brane Universe cannot reach the asymptotic infinity, irrespectively of the components of matter on the brane.

A six-dimensional (Z2)3 symmetric model with warped physical space

The Randall–Sundrum model is studied in six dimension with AdS4 or dS4 metric in the physical four-dimensional space. Two solutions are found, one with induced five-dimensional gravity terms added to the induced cosmological constant terms. We study the graviton modes in both solutions by transforming the mass eigenvalue equation to a Schrodinger equation with a volcano potential. The spectrum of gravitational excitations depends on the input parameters of the theory, the six-dimensional and the effective four-dimensional cosmological constants. The model gives a physically acceptable spectrum if the four-dimensional cosmological constant is sufficiently small.

Search for RS gravitons via [formula omitted] decays

The original Randall–Sundrum (RS) model with a warped extra dimension along with extensions provides the possibility for a simultaneous solution to Planck-weak hierarchy problem as well as the flavor puzzle in the Standard Model (SM). The most distinctive feature of this scenario is the existence of Kaluza–Klein (KK) gravitons whose masses and couplings to the SM fields are set by the TeV scale. In some realistic versions of this framework, the largest coupling of the gravitons to the observed particles is to the top quark and unphysical Higgses (WL± and ZL) with the KK graviton (G) masses predicted to be ≳4 TeV. We extend earlier works on the KK graviton decays to the tt¯ final state and to the “gold-plated”ZLZL modes (with each Z decaying to e+e− or to μ+μ−) by studying the resonant production of the gravitons and their subsequent decay to WLWL pair. We find that with 300 fb−1 integrated luminosity of data the semileptonic G→W(→lνl)W(→2jets) mode offers a good opportunity to search for the RS KK graviton mode with mass lighter than ∼3–3.5 TeV at the CERN LHC. Efficient WW mass reconstruction in the semileptonic mode combined with an analysis of dilepton mass distribution in the purely leptonic channel, pp→W(→lνl)W(→l′νl′) may help to observe KK Z′ and KK graviton separately. Suitably defined average energy of the charged lepton in the semileptonic mode may be used to distinguish decays from longitudinal versus transverse W-bosons.

The little Randall–Sundrum model at the large hadron collider

We present a predictive warped model of flavor that is cut off at an ultraviolet scale O(103) TeV. This “Little Randall–Sundrum (LRS)” model is a volume-truncation, by a factor y≈6, of the RS scenario and is holographically dual to dynamics with number of colors larger by y. The LRS couplings between Kaluza–Klein states and the Standard Model fields, including the proton constituents, are explicitly calculable without ad hoc assumptions. Assuming separate gauge and flavor dynamics, a number of unwanted contributions to precision electroweak, Zbb¯ and flavor observables are suppressed in the LRS framework, compared with the corresponding RS case. An important consequence of the LRS truncation, independent of precise details, is a significant enhancement of the clean (golden) di-lepton LHC signals, by O(y3), due to a larger “ρ-photon” mixing and a smaller inter-composite coupling.

ENERGY–MOMENTUM FOR RANDALL–SUNDRUM MODELS

We investigate the conservation law of energy–momentum for Randall–Sundrum models by the general displacement transform. The energy–momentum current has a superpotential and are therefore identically conserved. It is shown that for Randall–Sundrum solution, the momentum vanishes and most of the bulk energy is localized near the Planck brane. The energy density is ε = ε0e-3k|y|.

Randall–Sundrum model with [formula omitted] and bulk brane viscosity

We study the effect of the inclusion of bulk brane viscosity on brane world (BW) cosmology in the framework of the Eckart's theory, we focus in the Randall–Sundrum model with negative tension on the brane.

GHOSTS AND TACHYONS IN THE FIFTH DIMENSION

We present several solutions for the five-dimensional gravity models in the presence of bulk ghosts and tachyons to argue that these "troublesome" fields can be a useful model-building tool. The ghost-like signature of the kinetic term for a bulk scalar creates a minimum in the scale factor, removing the necessity for a negative tension brane in models with the compactified fifth dimension. It is shown that the model with the positive tension branes and a ghost field in the bulk leads to the radion stabilization. The bulk scalar with the variable sign kinetic term can be used to model both positive and negative tension branes of a finite width in the compact dimension. Finally, we present several ghost and tachyon field configurations in the bulk that lead to the localization of gravity in four dimensions, including one solution with the Gaussian profile for the metric, gμν(y) = ημν exp {-αy2}, which leads to a stronger localization of gravity than the Randall–Sundrum model.

The effects of lepton KK modes on the electric dipole moments of the leptons in the Randall–Sundrum scenario

We study the charged lepton electric dipole moments in the Randall–Sundrum model where the leptons and the gauge fields are accessible to the extra dimension. We observe that the electric dipole moment of the electron (muon; tau) reaches a value of the order of 10-26 e cm (10-20 e cm; 10-20 e cm) with the inclusion of the lepton KK modes.

Chern–Simons [formula omitted] supergravity in a Randall–Sundrum background

Chern–Simons AdS supergravity theories are gauge theories for the super-AdS group. These theories possess a fermionic symmetry which differs from standard supersymmetry. In this paper, we study five-dimensional Chern–Simons AdS supergravity in a Randall–Sundrum scenario with two Minkowski 3-branes. After making modifications to the D = 5 Chern–Simons AdS supergravity action and fermionic symmetry transformations, we obtain a Z 2 -invariant total action S = S ˜ bulk + S brane and fermionic transformations δ ˜ ϵ . While δ ˜ ϵ S ˜ bulk = 0 , the fermionic symmetry is broken by S brane . Our total action reduces to the original Randall–Sundrum model when S ˜ bulk is restricted to its gravitational sector. We solve the Killing spinor equations for a bosonic configuration with vanishing su ( N ) and u ( 1 ) gauge fields.

Moduli stabilization in 5D gauged supergravity with universal hypermultiplet and boundary superpotentials

We study a four-dimensional effective theory of the five-dimensional (5D) gauged supergravity with a universal hypermultiplet and perturbative superpotential terms at the orbifold fixed points. Among eight independent isometries of the scalar manifold, we focus on three directions for gauging by the graviphoton. The class of models we consider includes the 5D heterotic M-theory and the supersymmetric Randall–Sundrum model as special limits of the gauging parameters. We analyze the vacuum structure of such models, especially the nature of moduli stabilization, from the viewpoint of the effective theory. We also discuss the uplifting of supersymmetric anti-de Sitter vacua.

Hybrid compactifications and brane gravity in six dimensions

We consider a six-dimensional axisymmetric Einstein–Maxwell model of warped braneworlds. The bulk is bounded by two branes, one of which is a conical 3-brane and the other is a 4-brane wrapped around the axis of symmetry. The latter brane is assumed to be our universe. If the tension of the 3-brane is fine-tuned, it folds the internal two-dimensional space in a narrow cone, making sufficiently small the Kaluza–Klein circle of the 4-brane. An arbitrary energy–momentum tensor can be accommodated on this ring-like 4-brane. We study linear perturbations sourced by matter on the brane, and show that weak gravity is apparently described by a four-dimensional scalar–tensor theory. The extra scalar degree of freedom can be interpreted as the fluctuation of the internal space volume (or that of the circumference of the ring), the effect of which turns out to be suppressed at long distances. Consequently, four-dimensional Einstein gravity is reproduced on the brane. We point out that as in the Randall–Sundrum model, the brane bending mode is crucial for recovering the four-dimensional tensor structure in this setup.

ANGULAR MOMENTUM CONSERVATION LAW FOR RANDALL–SUNDRUM MODELS

In Randall–Sundrum models, by the use of general Noether theorem, the covariant angular momentum conservation law is obtained with respect to the local Lorentz transformations. The angular momentum current also has superpotential and is therefore identically conserved. The space-like components Jijof the angular momentum for Randall–Sundrum models are zero. But the component J04is infinite.

Simulation of beyond standard model physics in Herwig++

We present a new approach for the simulation of beyond standard model (BSM) physics within the Herwig++ event generator. Our approach is more generic than previous methods with the aim of minimising the effort of implementing further new physics models. Spin correlations, which are important for BSM models due to new heavy fermions and bosons, are discussed and their effects demonstrated for the minimal supersymmetric standard model (MSSM) and Randall–Sundrum model using our new framework.

KK gravitons and unitarity violation in the Randall–Sundrum model

We show that perturbative unitarity for W L + W L − → W L + W L − scattering places significant constraints on the Randall–Sundrum theory with two 3-branes, with matter confined to the TeV brane. The exchange of massive 4D Kaluza–Klein gravitons leads to amplitudes growing linearly with the CM energy squared. Summing over KK gravitons up to a scale Λ ¯ and testing unitarity at s = Λ ¯ , one finds that unitarity is violated for Λ ¯ below the ‘naive dimensional analysis’ scale, Λ NDA . We evaluate Λ ¯ as a function of the curvature ratio m 0 / m Pl for the pure gravity theory. We then demonstrate that unitarity need not be violated at Λ ¯ in the presence of a heavy Higgs boson. In fact, much larger Higgs masses are consistent with unitarity than if no KK gravitons are present. Observation of the mass and width (or cross section) of one or more KK gravitons at the LHC will directly determine m 0 / m Pl and the scale Λ ˆ W specifying the couplings of matter to the KK gravitons. With this information in hand and a measurement of the Higgs boson mass, one can determine the precise scale Λ ¯ below which unitarity will remain valid.

CP VIOLATION FROM A HIGHER DIMENSIONAL MODEL

It is shown that Randall–Sundrum model has the EDM term which violates the CP-symmetry. The comparison with the case of Kaluza–Klein theory is done. The chiral property, localization, anomaly phenomena are examined. We evaluate the bulk quantum effect using the method of the induced effective action. This is a new origin of the CP-violation.

Solutions to large B and L breaking in the Randall–Sundrum model

Abstract The stability of proton and neutrino masses are discussed in the Randall–Sundrum model. We show that relevant operators should be suppressed, if the hierarchical Yukawa matrices are explained only by configurations of wavefunctions for fermions and the Higgs field along the extra dimension. We assume a Z N discrete gauge symmetry to suppress those operators. In the Dirac neutrino case, there is an infinite number of symmetries which may forbid the dangerous operators. In the Majorana neutrino case, the discrete gauge symmetries should originate from U ( 1 ) X gauge symmetries which are broken on the Planck brane. We also comment on the n − n ¯ oscillation as a phenomenon which can distinguish those discrete gauge symmetries.