In extra dimensional models with Kaluza-Klein graviton states that are well separated in mass, such states may be observed as resonances in collider experiments. We extend previous works on such scenarios by considering the one-loop resonant production of a Z boson in association with a photon. We find the production rate to be negligible in conservative scenarios, and sufficiently small for observation to be very difficult even for reasonable luminosity in less conservative scenarios.
The asymptotic behavior of metric perturbations in Randall-Sundrum infinite brane world is carefully investigated. Perturbations generated by matter fields on the brane are shown to be regular even at the future Cauchy horizon.
The physics of the Randall-Sundrum model relevant for future linear colliders is briefly summarized. The differences between the case where Standard Model(SM) fields are on the wall and where they are in the bulk are emphasized.
The spin-2 graviton excitations in the Randall-Sundrum gravity model provides a t-channel contribution to electron Compton scattering which competes favourably with the standard QED contributions. The phenomenological implications of these contributions to the unpolarized and polarized cross-sections are evaluated.
We study the process $e^- e^- \to e^- e^-$ at a high energy $e^- e^-$ collider including the effect of graviton exchanges in the warped gravity model of Randall and Sundrum. Discovery limits for gravitons are established and the effects of polarization are discussed.
We study polarized cross-sections and forward-backward asymmetry for the process $e^+e-\to τ^+τ^-$ in the stabilized Randall-Sundrum scenario. It is shown that there is substantial deviation from the Standard Model predictions, both in terms of the actual numerical values and angular distributions.
We discuss several methods which can be used to distinguish the graviton resonances of the Randall-Sundrum model from the graviton-like resonances which may occur in other theories. The Breit-Wigner line shape of the RS graviton is found to be particularly useful. In particular we show that the "effective" graviton resonance present in the model of Dvali et al ~can be distinguished from those of the Randall-Sundrum scenario for a reasonably wide range of model parameters.
The extremely small branching ratio of $b\to ss{\bar d}$ decay in the Standard Model makes it a suitable channel to explore new-physics signals. We study this $ΔS=2$ process in Randall-Sundrum models, including the custodially protected and the bulk-Higgs Randall-Sundrum models. Exploring the experimentally favored parameter spaces of these models, it suggests a possible enhancement of the decay rate, compared to the Standard Model result, by at most two orders of magnitude.
The effective gravitational interaction below the Planck scale in the Randall-Sundrum world is shown to be the Gauss-Bonnet term. In this theory we find that there exists another static solution with a positive bulk cosmological constant. Also, there exist solutions for positive visible sector cosmological constant, which are needed for a later Friedman-Robertson-Walker universe.
The cosmology of a brane-universe embedded in a higher dimensional bulk spacetime presents some peculiarities not seen in ordinary (3+1) dimensional gravity. I summarize the current understanding, with emphasis on the suggestion by Randall and Sundrum that the bulk is 5-D anti-deSitter space, leading to a solution of the weak scale hierarchy problem.
We study the radiative lepton flavor violating l_i -> l_jγdecays in the two Higgs doublet model, respecting the Randall Sundrum scenario and estimate the contributions of the KK modes of left (right) handed charged lepton doublets (singlets) on the branching ratios. We observe that the branching ratios are sensitive to the contributions of the charged lepton KK modes.
In this talk I describe the low energy effective theory of the (supersymmetric) Randall-Sundrum scenario with arbitrary brane tensions. The distance between the branes is stabilized, at the classical level, by a potential for the radion field. In the supersymmetric case, supersymmetry can be broken by a VEV for the fifth-component of the graviphoton.
A detailed phenomenological analysis of neutral kaon mixing in "little Randall-Sundrum" models is presented. It is shown that the constraints arising from the CP-violating quantity epsilon_K can, depending on the value of the ultra-violet cutoff, be even stronger than in the original Randall-Sundrum scenario addressing the hierarchy problem up to the Planck scale. The origin of the enhancement is explained, and a bound Lambda_{UV}>several 10^3 TeV is derived, below which vast corrections to epsilon_K are generically unavoidable. Implications for non-standard Z->bb couplings are briefly discuss…
In the Randall-Sundrum model there can be a rich new phenomenology associated with Higgs-radion mixing. A photon-photon collider would provide a crucial complement to the LHC and a future ILC collider for fully determining the parameters of the model and definitively testing it.
In the Randall-Sundrum solution to the hierarchy problem, the fluctuations of the size of the extra dimension are characterized by a single scalar field, called the radion. The radion is expected to have a mass somewhat lower than the TeV scale with couplings of order 1/TeV to the trace of the energy momentum tensor. In addition, the radion can mix with the Higgs boson. Implications for phenomenology are briefly reviewed.
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 electron (muon; tau) electric dipole moment reaches to the 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.
Recently proposed stabilization mechanism of the Randall-Sundrum metric gives rise to a scalar radion, which couples universally to matter with a weak interaction ($\simeq 1$ TeV) scale. Demanding that gauge boson scattering as described by the effective low enerrgy theory be unitary upto a given scale leads to significant constraints on the mass of such a radion.
We extend the Randall-Sundrum(RS) model by adding a fundamental scalar field in the bulk, then study the multi-field assisted inflationary solution on brane. We will show that this model satisfies not only the observation, but also provides a solution to hierarchy problem. Furthermore in comparison with the chaotic inflation model with a single field in four space-time dimension, the parameters in our model required for a successful inflation are natural.
We study 5D gauge symmetries in the Randall-Sundrum geometry that are hidden from the standard model through either small 5D gauge coupling, or through vanishing quantum numbers for the standard model fields. Geometric warping of 5D gravity creates a TeV scale bridge from the standard model to the hidden sector gauge fields. We apply these concepts to a revival of the electroweak axion model, in which the dynamics of Peccei-Quinn symmetry breaking occur at the TeV scale.
In the framework of Randall-Sundrum model, we discuss the evolution of microscopic black holes created by cosmic particles hitting a neutron or a strange star. We set up the general equations of evolution for the black hole mass and momentum in a dense medium, and discuss the possibility of collapse due to the black hole's growth inside the star.
I present phenomenological implications of the Randall-Sundrum model for indirect searches, specifically a selection of flavor observables and Higgs-related collider searches. I review the interplay of constraints from CP violation in flavor physics, possible effects in rare decays, and model-specific protection mechanisms. Deviations in the Higgs couplings to fermions and, at one-loop, to gluons are unexpectedly strong and lead to strong modifications in Higgs searches.
The Randall-Sundrum model with gauge fields and fermions in the bulk has several attractive features including the gauge coupling unification, a candidate for the dark matter, and an explanation for the hierarchical Yukawa couplings. In this paper, we point out that the 1st Kaluza-Klein modes of right-handed neutrinos may be produced at colliders, for both Dirac and Majorana neutrino cases. Furthermore, we can see whether the neutrino masses are Dirac type or Majorana type from the mass spectrum of KK particles.
We study the effects of localization of the U(1)_Y gauge boson around the visible brane and the contributions of the KK modes of Z bosons on the BR of the LFV τ-> μ\bar{ν_i} ν_i decay. We observe that the BR is sensitive to the amount of localization of Z boson in the bulk of the Randall Sundrum background.
The dynamical fermion mass generation on the D3-brane in the Randall-Sundrum space-time is discussed in a model with bulk fermions in interaction with fermions on the branes. It is found that the dynamical fermion masses are generated at the natural (R.-S.) radius of the compactified extra space and may be made small compared with masses of the Kaluza-Klein modes which is of order of TeV.
We calculate the $B\Bbar$ mixing in the Randall-Sundrum bulk model. In this model, all the Standard Model fields except the Higgs can reside in the bulk. Two suggestive models of "mixed" and "relaxed" scenarios are considered. We find that the enhancement of the loop function is 0.51% for the "relaxed" and 1.07% for the "mixed" scenario when the first 4th KK modes are included, for a bulk fermion mass parameter $ν=-0.3$.
We consider Higgs pair production at the Large Hadron Collider (LHC) in a Randall-Sundrum scenario containing a radion field. It is shown that the enhanced effective coupling of the radion to gluons, together with contributions from a low-lying radion pole, can provide larger event rates compared to most new physics possibilities considered so far. We present the results for both an intermediate mass Higgs and a heavy Higgs, with a detailed discussion of the background elimination procedure.
Quantum interference of helicity amplitudes provides a powerful tool for measuring the spins of new particles. By looking at the azimuthal angular dependence of the differential cross-section in the production followed by decay of a new particle species one can determine its spin by looking at the various cosine modes. The heavy spin-2 Kaluza-Klein (KK) graviton provides a unique signature with a $\cos{(4 ϕ)}$ mode. We study the feasibility of this approach to measuring the spin of the KK graviton in the Randall-Sundrum Model at the LHC.
Characteristic features of dynamical symmetry breaking are investigated in Randall-Sundrum (RS) background. To study the influence of bulk fermion or bulk gauge field I consider a five-dimensional four-fermion interaction model and a non-Abelian gauge field theory as simple models where the chiral symmetry is broken down dynamically. Using a four-dimensional Lagrangian induced from the five-dimensional theory, I calculate the dynamically generated fermion mass and show how the extra dimension affects the chiral phase transition in the RS background.
The Randall Sundrum (RS) models receive significant constraints from the neutral Kaon system. The CP violating observable $ε_K$, in Randall Sundrum scenario, requires the lightest KK gluon to be heavier than $\sim$ 24 TeV. The constraint is even stronger in the Little Randall Sundrum models (LRS), $\gtrsim$ 32 TeV. The LRS models are motivated for their possible visibility at the Large Hardon Collider (LHC). We show that the stringent constraints from K-physics can be relaxed in the LRS models, in the presence of the Brane Localised Kinetic Terms (BLKT). In particular, for a range of values, a…
We study the radiative lepton flavor violating l_1->l_2γdecays in the two Higgs doublet model with localized new Higgs doublet in the Randall Sundrum background. We estimate the contributions of the KK modes of new Higgs bosons and left (right) handed charged lepton doublets (singlets) on the branching ratios of the decays considered. We observe that there is an enhancement in the branching ratios with the addition of new Higgs boson and lepton KK modes.
There are many interesting issues in the brane world with a large/warped extra dimension. We focus on the cosmological aspects. We review the cosmological solutions of the brane world and how the conventional four-dimensional cosmology is recovered by including the effect of stabilization. Its implications on the mass hierarchy and the cosmological constant are discussed.
We present next-to-leading order QCD corrections to production of two $W$ bosons at the LHC in the Randall-Sundrum model. Various kinematical distributions are obtained to order $α_s$ in QCD by taking into account all the parton level subprocesses. We estimate the impact of the QCD corrections on various observables and find that they are significant. We also show the reduction in factorization scale uncertainty when ${\cal O}(α_s)$ effects are included.
We investigate inflation with a class of concave inflaton potentials of the form $\sim ϕ^n$ $(0<n<1)$ in the Randall-Sundrum model with an infinite extra spatial dimension. We show that this class of models is much more in good agreement with observations compared to the standard inflation. We also find the range of the five-dimensional Planck scale ($M_5$) and show that large tensor-to-scalar ratios do not eliminate small-field inflation in braneworld cosmology.
We compute the pair production cross section of two Kaluza Klein modes in the Randall-Sundrum model at $e^+e^-$ and hadron hadron colliders. These processes are interesting because they get dominant contribution from the graviton interaction at next to leading order. Hence they provide a nontrivial test of the low scale gravity models. All the Feynman rules at next to leading order are also presented. These rules may be useful for many phenomenological applications including the computation of higher order loop corrections.
We predict the branching ratios of the lepton flavor violating radion decays r -> e^{\pm} μ^{\pm}, r -> e^{\pm} τ^{\pm} and r ->μ^{\pm} τ^{\pm} in the framework of the Randall-Sundrum scenario that the lepton flavor violation is carried by the scalar unparticle mediation. We observe that their BRs are strongly sensitive to the unparticle scaling dimension and, for its small values, the branching ratios can reach to the values of the order of 10^{-8}, for the heavy lepton flavor case.
We investigate a dynamical mechanism to generate fermion mass in the Randall-Sundrum background. We consider four-fermion interaction models where the fermion field propagates in an extra-dimension, i.e. the bulk four-fermion interaction model. It is assumed that two types of fermions with opposite parity exist in the bulk. We show that electroweak-scale mass is dynamically generated for a specific fermion anti-fermion condensation, even if all the scale parameters in the Lagrangian are set to the Planck scale.
The radion may be the lightest new state present in the Randall-Sundrum(RS) model. We examine the couplings of the radion to the Standard Model(SM) fields in the scenario where they propagate in the bulk and expand into Kaluza-Klein towers. These couplings are then contrasted with those of the more familiar case where the SM fields are confined to the TeV brane. We find that the couplings of the radion to both $gg$ and $γγ$ can be significantly different in these two cases. Implications for radion collider phenomenology are discussed.
We study the top pair production cross section at the LHC in the context of Randall-Sundrum model including the Kaluza-Klein (KK) excited gravitons. It is shown that the recent measurement of the cross section of this process at the LHC restricts the parameter space in Randall-Sundrum (RS) model considerably. We show that the coupling parameter ($\frac{k}{\bar{M}_{pl}}$) is excluded by this measurement from 0.03 to 0.22 depending on the mass of first KK excited graviton ($m_1$). We also study the effect of KK excitations on the spin correlation of the top pairs. It is shown that the spin asymm…
We study production and decay of a radion predicted in the Randall-Sundrum model at the LHC. The radion is a scalar particle and its production and decay channels are quite similar to those of the Higgs boson. We find constraints on the model parameter space taking account of the results of the Higgs boson search at the LHC. We also study a possibility discriminating the radion from the scalar particles in the other model such as the supersymmetric standard model at the LHC experiments.
Model building within the Randall-Sundrum (RS) framework generally involves placing the Standard Model fields in the bulk. Such fields may possess non-zero values for their associated brane-localized kinetic terms (BLKTs) in addition to possible bulk mass parameters. In this paper we clearly identify the regions of the RS model parameter space where the presence of bulk mass terms and BLKTs yield a setup which is free from both ghost and tachyon instabilities. Such physically acceptable parameter space regions can then be used to construct realistic and phenomenologically viable RS models.
Virtual effects of gravitons in the production of diphotons at the upgraded Tevatron and at the LHC are analysed with the idea of probing the parameter space of the Randall-Sundrum (RS) model. It is shown that this process yields stringent constraints on the parameter space of the RS model. We show that data on diphoton production from Tevatron Run II will be sensitive to a masses of the first graviton resonance in the range of 700-1150 GeV, while at LHC the mass range probed will be in the region of 3.5 -- 5.5 TeV.
The first results on next-to-leading order QCD corrections to production of two $Z$ bosons in hadronic collisions in the extra dimension model of Randall and Sundrum are presented. Various kinematical distributions are obtained to order $α_s$ in QCD by taking into account all the parton level subprocesses. We estimate the impact of the QCD corrections on various observables and find that they are significant. We also show the reduction in factorization scale uncertainty when ${\cal O}(α_s)$ effects are included.
Braneworld modifications to the Friedmann expansion law can have an important effect on the cosmological evolution of the early universe. In particular, the primordial particle abundances crucially depend on the rate at which the universe expanded at early times. In this article, we study the production of stable and unstable gravitinos, both from thermal creation and from the decay of a heavy scalar, in the Randall-Sundrum II braneworld context. We conclude that, depending on the value of the 5D fundamental Planck mass, some of the usual standard cosmology constraints on the reheating tempera…
In the Randall-Sundrum model, we study top-antitop pair production and top spin correlations at the Large Hadron Collider. In addition to the Standard Model processes, there is a new contribution to the top-antitop pair production process mediated by graviton Kaluza-Klein modes in the s-channel. We calculate the density matrix for the top-antitop pair production including the new contribution. With a reasonable parameter choice in the Randall-Sundrum model, we find a sizable deviation of the top-antitop pair production cross section and the top spin correlations from those in the Standard Mode…
We study the Randall-Sundrum model with a small 4D effective cosmological constant on the brane, and drive a corrected radion potential following the Goldberger-Wise mechanism. We then discuss the effect of the 4D effective cosmological constant on the stability of the brane-system, and find that to quintessence determined by updated observation, the proper distance between the two branes required to solve the hierarchy problem can exist. However, during inflation, whether we can get an reasonable hierarchy scale is still uncertain.
Lepton flavor violation in the Randall-Sundrum model with bulk neutrinos is considered. Grossman and Neubert recently proposed that the existence of tiny neutrino masses and large mixing could be explained by the presence of the bulk neutrinos in the Randall-Sundrum background. Since the zero mode wave functions of the bulk neutrinos are localized on Planck brane, the Dirac Yukawa couplings on our brane are exponentially suppressed enough to generate tiny neutrino masses. However, the existence of Kaluza-Klein modes of these bulk neutrinos enhance lepton flavor violating processes such as $μ\t…
We examine the effects of boundary kinetic terms in the Randall-Sundrum model with gauge fields in the bulk. We derive the resulting gauge Kaluza-Klein (KK) state wavefunctions and their corresponding masses, as well as the KK gauge field couplings to boundary fermions, and find that they are modified in the presence of the boundary terms. In particular, for natural choices of the parameters, these fermionic couplings can be substantially suppressed compared to those in the conventional Randall-Sundrum scenario. This results in a significant relaxation of the bound on the lightest gauge KK mas…
If the lowest lying Kaluza-Klein states in Randall-Sundrum (RS1) models have masses in the 10-100 TeV range, direct production of these states at the LHC or ILC is impossible, and electroweak precision measurements may not be sufficiently sensitive. We address the possibility that high-precision measurements of top pair production at the ILC may provide the first evidence of these states. We consider RS1 models with fermions on and off the brane, with bulk left and right handed mass terms, discuss brane kinetic terms and calculate corrections to top pair production in these models.
It is investigated that a dynamical mechanism to generate a low mass fermion in Randall-Sundrum (RS) background. We consider a five-dimensional four- fermion interaction model with two kinds of bulk fermion fields and take all the mass scale in the five-dimensional spacetime at the Planck scale. Evaluating the effective potential of the induced four-dimensional model, I calculate the dynamically generated fermion mass. It is shown that dynamical symmetry breaking takes place and one of the fermion mass is generated at the electroweak scale in four dimensions.
In recent Letter by Cheung et al.[PRL {\bf 108},141602(2012)], one very interesting suggestion for the excess around 125 GeV seen at the LHC is a RS radion with $Λ_ϕ=680$GeV. In this note, we show that taking constraints on the RS graviton into account, it is unlikely to have a 125 GeV RS radion with $Λ_ϕ=680$GeV and accommodate with both experimental and theoretically constraints.
We study the dijet production in Randall-Sundrum model at the LHC with QCD next-to-leading(NLO) order accuracy. Our results show that the QCD NLO corrections can increase the total cross sections by more than $80\%$ and reduce the scale dependence. We also explore in detail several important kinematic distributions at the NLO level. Moreover, we discuss the upper limits of the KK graviton excluded mass range and the allowed parameter space for the coupling constant and KK graviton mass, using the experiment data.
In Randall-Sundrum models, one typically expects the radion to be the lightest new "gravity" state, as it is dual to a composite pseudo-Goldstone boson associated with conformal symmetry breaking in the IR. Here, we investigate the effects of localized brane curvature on the properties of the radion in Goldberger-Wise stabilized Randall-Sundrum models. We point out that both the radion mass and coupling to brane matter are sensitive to the brane curvature. Radion/Higgs kinetic mixing, via an IR-localized non-minimal coupling to the Higgs, is also investigated, in relation to the ghost-like rad…
This Master's thesis will introduce the Randall-Sundrum RSI model and overview its general features and basic phenomenology, with the goal of understanding its 5-dimensional geometric structure in terms of its 4-dimensional AdS/CFT dual theory. We discuss mode expansions, boundary terms, field content, and supersymmetry, leading up to a discussion of the AdS/CFT correspondence in RSI models. Low-energy 4d Yukawa hierarchies and gauge couplings are understood in terms of the bulk 5d theory. A few simple Standard Model and MSSM-like constructions are considered, and their 4d dual theories are di…
In the stabilised Randall-Sundrum brane world scenario, the radion can have phenomenologically testable effects, which can be measured against precisely measured electroweak physics data. We investigate the effect of two loop radion corrections to $K_L$ - $K_S$ mass difference to set a bound on the radion mass and vacuum expectation value. It is found that the leading two loop corrections are of the order $[Log(\frac{Λ^2}{m_ϕ^2}) ]^2$ where $Λ$ is the cut-off scale ${\cal O}(\sim$TeV) and $m_ϕ$ is the radion mass.
Randall and Sundrum have proposed that we live on a brane embedded in 5-dimensional anti-deSitter space, as a solution to the hierarchy problem. We examine the possibility of using a scalar field in the 5-D bulk as the inflaton, and show that it gives results which are indistinguishable from an inflaton which is restricted to our brane. This makes it difficult to get large enough density perturbations in simple one-field inflationary models, since mass scales on our brane are supposed to be limited by a cutoff of order 1 TeV.
Scenarios based on the existence of large or warped (Randall-Sundrum model) extra dimensions have been proposed for addressing the long standing puzzle of gauge hierarchy problem. Within the contexts of both those scenarios, a novel and original type of mechanism generating small (Dirac) neutrino masses, which relies on the presence of additional right-handed neutrinos that propagate in the bulk, has arisen. The main objective of the present study is to determine whether this geometrical mechanism can produce reasonable neutrino masses also in the interesting multi-brane extensions of the Rand…
We study the effects of extra dimension on the muon anomalous magnetic moment in the stabilized Randall-Sundrum scenario. The effects of the Kaluza-Klein states heavier than the cut-off scale expected to be of order $Λ_π$ are neglected. Contribution from the spin-2 Kaluza-Klein states dominates over that from the spin-0 radion. The recent BNL E821 results impose a strict constraint on the parameter space of the model: $Λ_π\approx 0.4 - 2.1$ TeV with $k/ M_{\rm Pl} =0.01 - 0.1$. Small $k/M_{\rm Pl}$ is preferred if $Λ_π$ is TeV scale.
Considering the Randall-Sundrum background, we calculate the total cross-section for $ϕϕ^\star \to G γ$ in the framework of the scalar electrodynamics.
