We implement Dirac neutrinos in the minimal custodial Randall-Sundrum setting via the Krauss-Wilczek mechanism. We demonstrate by giving explicit lepton mass matrices that with neutrinos in the normal hierarchy, lepton mass and mixing patterns can be naturally reproduced at the scale set by the constraints from electroweak precision measurements, and at the same time without violating bounds set by lepton flavour violations. Our scenario generically predicts a nonzero neutrino mixing angle $θ_{13}$, as well as the existence of sub-TeV right-handed Kaluza-Klein neutrinos, which partner the right-handed Standard Model charged leptons. These relatively light KK neutrinos may be searched for at the LHC.
Dirac neutrinos arising from gauged discrete symmetry à la Krauss-Wilczek are implemented in the minimal custodial Randall-Sundrum model. In the case of a normal hierarchy, all lepton masses and mixing pattern can be naturally reproduced at the TeV scale set by the electroweak constraints, while simultanously satisfy bounds from lepton flavour violation. A nonzero neutrino mixing angle, $θ_{13}$, is generic in the scenario, as well as the existence of sub-TeV right-handed Kaluza-Klein neutrinos, which may be searched for at the LHC.
We present a warped extra dimension model with the custodial symmetry $SU(2)_L\times SU(2)_R\times U(1)_X\times P_{LR}$ based on the flavor symmetry $S_4\times Z_2\times Z'_2$, and the neutrinos are taken to be Dirac particles. At leading order, the democratic lepton mixing is derived exactly, and the high dimensional operators introduce corrections of order $λ_c$ to all the three lepton mixing angles such that agreement with the experimental data can be achieved. The neutrino mass spectrum is predicted to be of the inverted hierarchy and the second octant of $θ_{23}$ is preferred. We suggest …
The seesaw mechanism provides a simple explanation for the lightness of the known neutrinos. Under the standard assumption of a weak scale Dirac mass and a heavy sterile Majorana scale the neutrino mass is naturally suppressed below the weak scale. However, Nature may employ Dirac and Majorana scales that are much less than typically assumed, possibly even far below the weak scale. In this case the seesaw mechanism alone would not completely explain the lightness of the neutrinos. In this work we consider a warped framework that realizes this possibility by combining naturally suppressed Dirac…
We show how leptogenesis can occur at the TeV scale with neutrinos that possess almost purely Dirac masses and negligible Majorana mass contributions as a consequence of the small wavefunction overlap in a warped fifth dimension. Lepton number violation at the Planck scale is introduced via a Majorana mass term on the Planck brane. Such a Majorana mass operator leads to the small mass splitting of otherwise degenerate Kaluza-Klein excited states on the TeV brane. This tiny mass splitting can compensate for the small Yukawa couplings to give a CP asymmetry large enough to produce the sufficient…
Interaction of bulk gravitons to Standard Model particles is examined in the scenario of warped extra dimension. It is found that the length of the extra dimension is of physical importance as it determines the decay widths of graviton Kaluza-Klein modes. We show that cosmology as well as collider signals of the Kaluza-Klein modes are very different for different choices of the length of the fifth dimension.
We explore the possibility to discriminate between certain strongly-coupled technicolor (TC) models and warped extra-dimensional models where the Standard Model fields are propagating in the extra dimension. We consider a generic QCD-like TC model with running coupling as well as two TC models with walking dynamics. We argue that due to the different production mechanisms for the lowest-lying composite tensor state in these TC theories compared to the first Kaluza-Klein graviton mode of warped extra-dimensional case, it is possible to distinguish between these models based on the angular analy…
We consider a five dimensional model with warped geometry where the standard model fermions and gauge bosons correspond to bulk fields. Fermion masses and CKM mixings can be explained in a geometrical picture, without hierarchical Yukawa couplings. We discuss various flavor violating processes induced by (excited) gauge boson exchange and non-renormalizable operators. Some of them, such as muon-electron conversion, are in the reach of next generation experiments.
A classically scale-invariant scalar singlet can be a MeV-scale dark matter, with a feeble Higgs portal coupling at $\mathcal{O}(10^{-10})$. Besides, an $\mathcal{O}(0.1)$ self-interaction coupling could further serve to alleviate the small-scale problems in the Universe. We show that, such a dark matter candidate can naturally arise in the warped extra dimension, with the huge span of parameter space predicted well within $\mathcal{O}(1)$ fundamental parameters.
While the warped extra-dimensional models provide an attractive solution to both the gauge and the flavor hierarchy problems, the mass scale of new particles predicted by the minimal models would be beyond the reach of the LHC. Models of extended warped extra dimensions have been proposed to evade these issues and their collider implications have been investigated for the last decade. This white paper summarizes the recent developments in the context of collider phenomenology. The strategies and lessons are broad, and provide a template to extend the experimental program, to cover a wider clas…
We review Electroweak breaking in warped Extra Dimensions and show how it is constrained by Electroweak precision tests. We then proceed to describe a model which is based on a bulk Higgs field and a metric that is deformed from the usual five dimensional Anti de Sitter space near the Infrared (IR) boundary. It allows to softly decouple the Higgs field from the Kaluza Klein excitations near the IR and thus reduces their contribution to the precision observables.
We propose an interpretation of the diboson excess recently observed by the ATLAS and CMS collaborations in terms of Kaluza-Klein excitations of electroweak gauge bosons stemming from a realization of a warped extra-dimensional model that is protected by a custodial symmetry. Besides accounting for the LHC diboson data, this scenario also leads to an explanation of the anomalies that have been observed in the measurements of the forward-backward asymmetries for bottom quarks at LEP and top quarks at the Tevatron.
The neutrino pulse from SN1987A provides one of the most rigourous constraints on models of extra dimensions. Previously, calculations have been done to bound the size of these extra dimensions in the case when the metric was factorizable. Here we consider the case of 2 `weakly warped' extra dimensions. We find that even though weak warping seems only to affect the zero mode this can have a measurable effect on the supernovae bounds. In any braneworld model such warping is necessarily present and as such should be taken into account in supernovae bounds and in searches for corrections to Newto…
Warped Extra Dimension scenarios are a rich playground for phenomenology of heavy resonances at LHC. The Radion and the KK-graviton are inevitable signatures of this class of models. On face of the latest LHC experimental results on the direct searches for Beyond Standard Model physics we update the phenomenological predictions for production and decay of such resonances in its main production modes. We also highlight the phenomenology results relevant to collider searches in individual channels, and provide tools for interpretation of current and future experimental analyses using two specifi…
The warped bulk standard model has been studied in the Randall-Sundrum background on $S^1/\Z\times\Z'$ interval with the bulk gauge symmetry $SU(3)\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}$. With the assumption of no large cancellation between the fermion flavor mixing matrices, we present a simple analytic method to determine the bulk masses of standard model fermions in the almost universal bulk Yukawa coupling model. We also predict $U_{e3}$ element of MNS matrix to be near the experimental upper bound when the neutrino masses are of Dirac type.
In this work, we calculate the top quark rare decays t-cgamma and t-cg in the framework where the standard model is embedded in a warped extra dimension with the custodial symmetry SU(3)c*SU(2)L*SU(2)R*U(1)x*PLR. Adopting reasonable assumptions on the parameter space,we numerically find the branching ratios of t-cgamma exceeding 10^-6 and that of t-cg exceeding 10^-5 respectively, which can be detected in near future.
We show how the seesaw mechanism for neutrino masses can be realized within a five dimensional (5D) warped geometry framework. Intermediate scale standard model (SM) singlet neutrino masses, needed to explain the atmospheric and solar neutrino oscillations, are shown to be proportional to M_Pl\exp((2c-1)πkR), where c denotes the coefficient of the 5D Dirac mass term for the singlet neutrino which also has a Planck scale Majorana mass localized on the Planck-brane, and kR~11 in order to resolve the gauge hierarchy problem. The case with a bulk 5D Majorana mass term for the singlet neutrino is b…
Extra dimension is one of the most attractive candidates beyond the Standard Model. In warped extra dimensional space-time, not only gauge hierarchy problem but also quark-lepton mass hierarchy can be naturally explained. In this setup, a sizable parity violation through Kaluza-Klein gluon exchange appears in QCD process such as helicity dependent top pair production. We investigate this QCD parity violating process by use of $SO(5) \times U(1)$ gauge-Higgs unification model. We evaluate LHC observable quantities, i.e., a charge asymmetry and a forward-backward asymmetry of the top pair produc…
We present an analysis of the loop-induced couplings of the Higgs boson to the massless gauge fields (gluons and photons) in the warped extra dimension models where all Standard Model fields propagate in the bulk. We show that in such models corrections to the hgg and $hγγ$ couplings are potentially very large. These corrections can lead to generically sizable deviations in the production and decay rates of the Higgs boson, even when the new physics states lie beyond the direct reach of the LHC.
We point out that the discovery of a light Higgs boson in the γγ, ZZ and WW decay channels at the LHC, with cross sections not far from the predictions of the Standard Model, would have important implications for the parameters of warped extra-dimension models. Due to loop effects of Kaluza-Klein particles, these models predict a significant reduction of the Higgs production cross section via gluon-gluon fusion, combined with an enhancement of the ratio Br(h->γγ)/Br(h->ZZ). LHC measurements of these decays will probe Kaluza-Klein masses up to the 10 TeV range, exceeding by far the reach for di…
We construct models with a Kaluza-Klein (KK) parity in a five- dimensional warped geometry, in an attempt to address the little hierarchy problem present in setups with bulk Standard Model fields. The lightest KK particle (LKP) is stable and can play the role of dark matter. We consider the possibilities of gluing two identical slices of 5D AdS in either the UV (IR-UV-IR model) or the IR region (UV-IR-UV model) and discuss the model-building issues as well as phenomenological properties in both cases. In particular, we find that the UV-IR-UV model is not gravitationally stable and that additio…
We analyze the flavor violation in warped extra dimension due to radion mediation. We show that ΔS=2 and ΔB=2 flavor violating processes impose stringent constraints on radion mass, m_ϕand the scale Λ_ϕ. In particular, for Λ_ϕ~ O(1) TeV, B_d^0-\bar{B}^0_d implies that m_ϕ~ 65 GeV. We also study radion contributions to lepton flavor violating processes: τ-> (e,μ) ϕ, τ-> eμ^+μ^- and B -> l_i l_j. We show that BR(B_s -> μ^+ μ^-) can be of order 10^{-8}, which is reachable at the LHCb. The radion search at LHC, through the flavor violation decays into τμor top-charm quarks, is also considered.
Models with warped extra dimensions, and their strongly coupled duals, offer a nice solution to the hierarchy problem and a very appealing realisation of flavour. Compatibility with the very stringent electroweak and flavour tests have made a generic picture emerge, with a composite Higgs, partial compositeness and custodial symmetry as the main ingredients. We review the main features of this picture and discuss how -and when- models with warped extra dimensions could be discovered at the Large Hadron Collider.
We investigate and compare additional CP-even, CP-odd and charged scalar states appearing in two popular Beyond the Standard Model scenarios. We focus on the simplest possible Higgs sector within warped extra-dimensions and supersymmetry, with the aim to differentiate between them. In each case, we analyze the couplings of the new Higgs states, looking for distinguishing signatures. We show that the couplings of the Standard Model gauge bosons to the first Kaluza-Klein Higgs states of the extra-dimensional setup (CP-even, CP-odd and charged) are very similar to those of the heavy Higgs states …
The minimal renormalizable supersymmetric SO(10) model, an SO(10) framework with only one 10 and one 126 Higgs multiplets in the Yukawa sector, is attractive because of its high predictive power for the neutrino oscillation data. However, this model suffers from problems related to running of gauge couplings. The gauge coupling unification may be spoiled due to the presence of Higgs multiplets much lighter than the grand unification (GUT) scale. In addition, the gauge couplings blow up around the GUT scale because of the presence of Higgs multiplets of large representations. We consider the mi…
The recent B-meson anomalies are coherently explained at the TeV scale by 4321 gauge models with hierarchical couplings reminiscent of the Standard Model Yukawas. We show that such models arise as the low-energy limit of a complete theory of flavor, based on a warped fifth dimension where each Standard Model family is quasi-localized in a different brane. The Higgs is identified as a pseudo-Nambu-Goldstone boson emerging from the same dynamics responsible for 4321 symmetry breaking. This novel construction unifies quarks and leptons in a flavor non-universal manner, provides a natural descript…
Generic extensions of the Standard Model that respect baryon and lepton numbers have accidentally stable particles. Typical examples are the lightest exotic neutral fermion, or "neutralino", and fields with non-trivial lepton and baryon charges. In this paper we show that an accidentally stable neutralino is a natural dark matter candidate in models with warped extra dimensions. We find that annihilation into other Kaluza-Klein resonances is often allowed and very efficient. The observed dark matter abundance may then be obtained with couplings of order unity and a compactification scale above…
Light sterile neutrinos are a popular extension of the Standard Model and are being discussed as a possible explanation for various neutrino oscillation anomalies, including the LSND, MiniBooNE, Reactor and Gallium anomalies. In order to avoid inconsistencies with constraints derived from disappearance experiments and cosmology, altered dispersion relations - which may originate from extra dimensions - have been proposed as a possible solution, dubbed as "neutrino shortcuts in the extra dimension". In this paper we develop a neutrino mass model with an asymmetrically warped extra dimension and…
We study the effect of the infrared (IR) geometry on the phenomenology of warped extra dimensions with gauge and fermion fields in the bulk. We focus in particular on a "mass gap" metric which is AdS in the ultraviolet, but asymptotes to flat space in the IR, breaking conformal symmetry. These metrics can be dialed to approximate well the geometries arising in certain classes of warped string compactifications. We find, similar to our earlier results on the Kaluza-Klein (KK) graviton, that these metrics give rise to phenomenologically significant shifts in the separation of KK gauge modes in t…
Within the paradigm of warped extra dimensions, third generation quarks are expected to be the most sensitive to effects beyond the Standard Model. The anomalies observed at the LEP and Tevatron colliders in the forward-backward asymmetries of the bottom (A_FB^b) and top (A_FB^t) quarks can thus be seen as early signatures of warped extra-dimensional scenarios. We propose a realization of such a scenario, with a gauge custodial symmetry in the bulk, which allows to address simultaneously the A_FB^b anomaly and the discrepancies observed recently on A_FB^t at high top quark rapidities and ttbar…
In this talk, I present results for the most important Higgs-boson production cross sections at the LHC and the Tevatron as well as the branching fractions of the relevant decay channels in the custodial Randall-Sundrum model. The results are based on a complete one-loop calculation, taking into account all possible Kaluza-Klein particles in the loop. Due to the strong infrared localization of the top quark and the Kaluza-Klein excitations, the SM predictions receive sizable corrections in the model at hand. This could effect Higgs searches significantly.
The theoretical tools required to construct models in warped extra dimensions are presented. This includes how to localise zero modes in the warped bulk and how to obtain the holographic interpretation using the AdS/CFT correspondence. Several models formulated in warped space are then discussed including nonsupersymmetric and supersymmetric theories as well as their dual interpretation. Finally it is shown how grand unification occurs in warped models.
We study dark matter interacting via a massive spin-2 mediator. To have a consistent effective theory for the spin-2 particle, we work in a warped extra-dimensional model such that the mediator(s) are the Kaluza-Klein (KK) modes of the 5D graviton. We pay close attention to dark matter annihilations into KK-gravitons. Due to the high energy behavior of longitudinal modes of spin-2 fields, these channels exhibit a tremendous growth at large center of mass energies $\sqrt{s}$ if only one spin-2 mediator is considered. For the first time, we include the full KK-tower in this dark matter productio…
We analyze fermion masses and mixing in a general warped extra dimensional model, where all the Standard Model (SM) fields, including the Higgs, are allowed to propagate in the bulk. In this context, a slightly broken flavor symmetry imposed universally on all fermion fields, without distinction, can generate the full flavor structure of the SM, including quarks, charged leptons and neutrinos. For quarks and charged leptons, the exponential sensitivity of their wave-functions to small flavor breaking effects yield naturally hierarchical masses and mixing as it is usual in warped models with fe…
We discuss the signatures of the spin-2 graviton excitations predicted by the Randall-Sundrum model with one warped extra dimension, in dilepton and diphoton production at LHC. By using a specific angular analysis, we assess the ranges in mass and coupling constant where such gravitons can be discriminated against competitor spin-1 and spin-0 objects, that potentially could manifest themselves in these processes with the same mass and rate of events. Depending on the value of the coupling constant to quarks and leptons, the numerical results indicate graviton identification mass ranges up to 1…
We propose the inverse seesaw mechanism as a way to understand small Majorana masses for neutrinos in warped extra dimension models with seesaw scale in the TeV range. The ultra-small lepton number violation needed in implementing inverse seesaw mechanism in 4D models is explained in this model as a consequence of lepton number breaking occurring on the Planck brane. We construct realistic models based on this idea that fit observed neutrino oscillation data for both normal and inverted mass patterns. We compute the corrections to light neutrino masses from the Kaluza-Klein modes and show that…
We investigate a natural realization of a light Abelian hidden sector in an extended Randall-Sundrum (RS) model. In addition to the usual RS bulk we consider a second warped space containing a bulk U(1)_x gauge theory with a characteristic IR scale of order a GeV. This Abelian hidden sector can couple to the standard model via gauge kinetic mixing on a common UV brane. We show that if such a coupling induces significant mixing between the lightest U(1)_x gauge mode and the standard model photon and Z, it can also induce significant mixing with the heavier U(1)_x Kaluza-Klein (KK) modes. As a r…
We propose a realistic theory of fermion masses and mixings using a five-dimensional warped scenario where all fermions propagate in the bulk and the Higgs field is localized on the IR brane. The assumed $T'$ flavor symmetry is broken on the branes by flavon fields, providing a consistent scenario where fermion mass hierarchies arise from adequate choices of the bulk mass parameters, while quark and lepton mixing angles are restricted by the family symmetry. Neutrino mass splittings, mixing parameters and the Dirac CP phase all arise from the type-I seesaw mechanism and are tightly correlated,…
In this thesis, we have studied the possibility to identify one of the right-handed neutrinos entering the type-I seesaw mechanism as a Dark Matter (DM) candidate, within the warped extra-dimensions paradigm. As a first step, we have reviewed the existing literature on the Randall-Sundrum scenarios and the Goldberger-Wise stabilization mechanism. We have discussed a feasible realization of the type-I seesaw mechanism, implemented by warped compactification of an extra dimension. Taking advantage of recent studies, we have explored how the thermal DM can be included in the warped scenario. We h…
Extra dimensions have interesting consequences for flavor physics. We consider a setup where the standard model fermions and gauge fields reside in the bulk of a warped extra dimension. Fermion masses and mixings are explained by flavor dependent fermion locations, without relying on hierarchical Yukawa couplings. We discuss various flavor violating processes induced by (Kaluza-Klein) gauge boson exchange and non-renormalizable operators. Experimental constraints are satisfied with a Kaluza-Klein scale of about 10 TeV. Some processes, such as muon-electron conversion, are within reach of next …
Randall-Sundrum models based on SU(2)_L * SU(2)_R with custodial symmetry are compelling frameworks for building alternative models of electroweak symmetry breaking. A particular feature of these models is the likely presence of light Kaluza-Klein fermions related to the right-handed top quark. These can be as light as a few hundred GeV and still compatible with EW precision constraints. In this article, we study the detectability of four-W final states at the LHC, which arise from the pair-production and tW decay of light Kaluza-Klein bottom quarks as well as light Kaluza-Klein quarks carryin…
A minimal solution to the flavor problem of warped extra-dimension models, i.e. the excessive mixed-chirality contribution to CP violation in K-Kbar mixing arising from Kaluza-Klein (KK) gluon exchange, is proposed. Extending the strong-interaction gauge group in the bulk by an additional SU(3), and breaking this symmetry to QCD via boundary conditions, the constraints arising from the epsilon_K parameter are significantly relaxed. As a result, KK scales M_KK ~ 2 TeV are consistent with all flavor observables without significant fine-tuning. The model predicts the existence of an extended Higg…
The aim of these proceedings is to present the main predictions of the Randall-Sundrum model with custodial protection for particle-antiparticle mixing and rare decays of K and B_(s,d) mesons, putting particular attention on the testability of the resulting NP effects at future experiments. Before giving numerical results, we discuss theoretical expectations, residing in the flavor structure of the model. The high energy scale M_KK is chosen in such a way that direct searches of new particles at the LHC are possible, still being consistent with electroweak precision observables.
From the warped extra-dimensional model interpretation of the two forward-backward asymmetries observed on heavy quarks at LEP1, AFBb, and at Tevatron, AFBt, one predicts that LHC could observe, with the luminosity collected in 2011-2012, significant excesses in the diboson production for large invariant masses of the Z+W system, mZW, and, the W+W system, mWW.
We consider supersymmetric theories with a warped extra dimension where supersymmetry is broken by boundary conditions that preserve an R-symmetry. It is shown that this supersymmetry breaking mechanism naturally invokes the Stuckelberg formalism for the gravitino in order to give a four-dimensional theory with a smooth massless limit.
Recent CDF measurement of the Bs-Bs oscillation frequency, at the Tevatron imposes significant constraint on various models for new physics. A warped extra-dimension model with custodial isospin symmetry accommodates the Bd-Bd mixing at tree level mainly through the Kaluza-Klein gluons. This is due to the misalignment between the bulk gauge eigenstates and the localized Yukawa eigenstates of the bulk fermions. We adopt the universal 5D Yukawa coupling model where all Yukawa couplings are of order one. The SM fermion mass spectra and mixings are controlled by the bulk Dirac mass parameters. Wit…
We consider six dimensional brane world models with a compact and a warped extra dimension with five dimensional branes. We find that such scenarios have many interesting features arising from both ADD and Randall-Sundrum -models. In particular we study a class of models with a single 5D brane and a finite warped extra dimension, where one of the brane dimensions is compact. In these models the hierarchy problem can be solved on a single positive tension brane.
Field theory in the presence of extra dimensions has offered interesting solutions to the gauge hierarchy problem, and inspired many attempts to understand the fermion mass generation mechanism. We study the behaviour of a bulk fermion field subject to non-standard boundary conditions under Z2 symmetry in a slice of (5D) AdS. These pseudo-Majorana boundary conditions relate the 5d spinor fields to their 5d charge conjugate and generate Majorana spinors in four-dimensions. There is a zero mode localized on the visible brane and the masses of Kaluza-Klein excitations are naturally of order the w…
In order to explain the non-hierarchical neutrino mixing angles and the absence of lepton flavor violating processes in the context of warped extra dimensions one needs to introduce bulk flavor symmetries. We present a simple model of lepton masses and mixings in RS models based on the A4 non-abelian discrete symmetry. The virtues of this choice are: (i) the natural appearance of the tri-bimaximal mixing pattern; (ii) the complete absence of tree-level flavor violations in the neutral sector; (iii) the absence of flavor gauge bosons; (iv) the hierarchies in the charged lepton masses are explai…
We present the electroweak and flavour structure of a model with a warped extra dimension and the bulk gauge group SU(3) x SU(2)_L x SU(2)_R x P_LR x U(1)_X. The presence of SU(2)_R implies an unbroken custodial symmetry in the Higgs system allowing to eliminate large contributions to the T parameter, whereas the P_LR symmetry and the enlarged fermion representations provide a custodial symmetry for flavour diagonal and flavour changing couplings of the SM Z boson to left-handed down-type quarks. We diagonalise analytically the mass matrices of charged and neutral gauge bosons including the fi…
Higher dimensional theories which address some of the problematic issues of the Standard Model(SM) naturally involve some form of $D=4+n$-dimensional Lorentz invariance violation (LIV). In such models the fundamental physics which leads to, e.g., field localization, orbifolding, the existence of brane terms and the compactification process all can introduce LIV in the higher dimensional theory while still preserving 4-d Lorentz invariance. In this paper, attempting to capture some of this physics, we extend our previous analysis of LIV in 5-d UED-type models to those with 5-d warped extra dime…
The processes gg -> h and h -> gamma gamma are of paramount importance in the context of Higgs search at the LHC. These processes are loop driven and hence could be sensitive to the presence of any new colored fermion states having a large coupling with the Higgs. Such a scenario arises in a warped extra dimensional theory, where the Higgs is confined to the TeV brane and the hierarchy of fermion masses is addressed by localizing them at different positions in the bulk. We show that the Yukawa coupling of the Higgs with the fermion Kaluza-Klein (KK) states can be order one irrespective of thei…
We study top quark flavor violation in the framework of a warped extra dimension with the Standard Model (SM) fields propagating in the bulk. Such a scenario provides solutions to both the Planck-weak hierarchy problem and the flavor puzzle of the SM without inducing a flavor problem. We find that, generically, tcZ couplings receive a huge enhancement, in particular the right handed ones can be O(1%). This results in BR(t -> c Z) at or above the sensitivity of the Large Hadron Collider (LHC). At the International Linear Collider (ILC), single top production, via e^+ e^- -> t \bar c, can be a s…
The CDF and D0 experiments have reported on the measurement of the forward-backward asymmetry of top quark pair production at the Tevatron and the result is that it is more than 2 standard deviations above the predicted value in the Standard Model. This has to be added to the longstanding anomaly in the forward-backward asymmetry for bottom quark production at LEP which is 3 standard deviations different from the Standard Model value. The discrepancy in the bottom asymmetry can be accounted for by the contributions of Kaluza-Klein excitations of electroweak gauge bosons at LEP in warped extra …
We study the effect of bulk fermions on electroweak precision observables in a recently proposed model with warped extra dimensions and no custodial symmetry. We find that the top-quark mass, together with the corrections to the Zbb vertex and the one-loop contribution to the T parameter, which is finite, impose important constraints that single out a well defined region of parameter space. New massive vector bosons can be as light as 1.5 TeV and have large couplings to the t_R quark, and suppressed couplings to the t_L, b_L and lighter quarks. We discuss the implications for searches of model…
Warped extra dimensions allow a novel way of solving the hierarchy problem, with all fundamental mass parameters of the theory naturally of the order of the Planck scale. The observable value of the Higgs vacuum expectation value is red-shifted, due to the localization of the Higgs field in the extra dimension. It has been recently observed that, when the gauge fields propagate in the bulk, unification of the gauge couplings may be achieved. Moreover, the propagation of fermions in the bulk allows for a simple solution to potentially dangerous proton decay problems. However, bulk gauge fields …
We propose a new flavor paradigm for models with warped extra dimensions. The idea is to impose the minimal amount of flavor protection to make warped models compatible with all current flavor and electroweak precision constraints. We discuss a particular realization of this minimal flavor protection in the quark sector, by means of a flavor symmetry acting on the right handed down sector. Hierarchical quark masses and mixing angles are naturally reproduced through wave function localization, and flavor violating processes are predicted, in the absence of large brane kinetic terms for the righ…
Gauge Higgs Unification in Warped Extra Dimensions provides an attractive solution to the hierarchy problem. The extension of the Standard Model gauge symmetry to $SO(5)xU(1)_X$ allows the incorporation of the custodial symmetry $SU(2)_R$ plus a Higgs boson doublet with the right quantum numbers under the gauge group. In the minimal model, the Higgs mass is in the range 110-150 GeV, while a light Kaluza Klein (KK) excitation of the top quark appears in the spectrum, providing agreement with precision electroweak measurements and a possible test of the model at a high luminosity LHC. The extens…
Warped extra dimensions can address both the Planck-weak and flavor hierarchies of the Standard Model (SM). In this paper we discuss the SM neutrino mass generation in a scenario in which a SM singlet bulk fermion - coupled to the Higgs and the lepton doublet near the IR brane - is given a Majorana mass of order the Planck scale on the UV brane. Despite the resemblance to a type I seesaw mechanism, a careful investigation based on the mass basis for the singlet 4D modes reveals a very different picture. Namely, the SM neutrino masses are generated dominantly by the exchange of the TeV-scale ma…
We study constraints on the radion mass and couplings in the Randall-Sundrum model from the recent LHC data on the Standard Model (SM) Higgs boson searches. When the radion is heavy enough so that it can decay into a pair of on-shell Z-bosons, we find that the ZZ channel gives a stringent constraint. For example, if the radion mass m_ϕis 200 GeV, the scale Λ_ϕwhich characterizes the interactions of the radion with the SM fields must be larger than 5 TeV. Even for m_ϕ=1 TeV, we find that the lower bound on Λ_ϕis 2 TeV.
