A custodial symmetry for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mi>Z</mml:mi><mml:mi>b</mml:mi><mml:mover accent="true"><mml:mi>b</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math>

Agashe, Kaustubh; Contino, Roberto; Rold, Leandro Da; Pomarol, Alex

doi:10.1016/j.physletb.2006.08.005

Cited by 501 publications

(320 citation statements)

References 18 publications

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“…We plot in Fig. 2 the lower bounds obtained on the mass m KK of the first KK-mode for the electroweak gauge bosons W, Z and γ from the 95% CL bounds 5 This apparent fine tuning is an artifact of the first order formulation and has no observable physical consequences for a > 2. Indeed for a > 2 the parameter M 0 has no physical impact neither on the background nor in the spectrum.…”

Section: In the Left [Right] Panel We Plot The Ratio T /T Rs [S/s Rmentioning

confidence: 99%

“…In this case one has to worry only for large contributions to the S parameter, which yield bounds on KK masses of O(3) TeV. Moreover, the presence of extra matter, in particular the SU(2) R -symmetric partner of the RH top quark, generate large anomalous (volume enhanced) contributions to the Zbb vertex which should be controled by introducing a discrete left-right symmetry [5].…”

Section: Introductionmentioning

confidence: 99%

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Warped electroweak breaking without custodial symmetry

2011

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We propose an alternative to the introduction of an extra gauge (custodial) symmetry to suppress the contribution of KK modes to the T parameter in warped theories of electroweak breaking. The mechanism is based on a general class of warped 5D metrics and a Higgs propagating in the bulk. The metrics are nearly AdS in the UV region but depart from AdS in the IR region, towards where KK fluctuations are mainly localized, and have a singularity outside the slice between the UV and IR branes. This gravitational background is generated by a bulk stabilizing scalar field which triggers a natural solution to the hierarchy problem. Depending on the model parameters, gauge-boson KK modes can be consistent with present bounds on EWPT for m KK 1 TeV at 95% CL. The model contains a light Higgs mode which unitarizes the four-dimensional theory. The reduction in the precision observables can be traced back to a large wave function renormalization for this mode.

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Section: In the Left [Right] Panel We Plot The Ratio T /T Rs [S/s Rmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Warped electroweak breaking without custodial symmetry

2011

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“…The q 1L and q 2L multiplets mix together on the Planckbrane resulting in the SM doublet Q L mainly composed here by the q 2L component [16]; the universal mixing angle between the doublets is taken at sin 2 θ 12 2/3.…”

Section: The Theoretical Modelmentioning

confidence: 99%

Forward–backward asymmetries of the bottom and top quarks in warped extra-dimensional models: LHC predictions from the LEP and Tevatron anomalies

Djouadi¹,

Moreau²,

Richard³

2011

Physics Letters B

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Abstract: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 b FB ) and top (A t FB ) quarks can thus be seen as early signatures of warped extradimensional scenarios. We propose a realization of such a scenario, with a gauge custodial symmetry in the bulk, which allows to address simultaneously the A b FB anomaly and the discrepancies observed recently on A t FB at high top quark rapidities and tt invariant masses. We then show that the various phenomenological constraints arising from LEP, Tevatron and LHC can be satisfied within the considered model. The model predicts new features, induced by a Kaluza-Klein excitation of the gluon at a mass ∼ 1.5-2 TeV, in top quark pair production at the √ s = 7 TeV LHC.

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“…Any model of new physics which attempts to solve the hierarchy problem, or that aims at modifying the properties of the Higgs boson, will likely predict the presence of heavy partners of the top. Among these new states, vector-like quarks occupy a special place for their role in model building, as they are often predicted by models based on new symmetries: in extra dimensional models, for example, they appear as Kaluza-Klein recurrences of the standard model quarks; in little Higgs type models they ensure the cancellation of the top Yukawa divergent loop [1]; in models where a new strongly-coupled sector is responsible for the breaking of the electroweak (EW) symmetry they emerge as part of the composite sector [2] or are predicted when a custodial symmetry is introduced to protect the coupling Zbb from large deviations [3]. The presence of TeV scale vectorlike quarks is also an interesting possibility for their effect on the Higgs properties: for instance, supersymmetric models with vector-like quarks can ease the MSSM tension in the Higgs mass whose value is lifted from the tree level prediction m H ∼ m Z via loop contributions [4][5][6]; they have also been proposed as a solution [7][8][9] for the apparent excess in the H → γγ rate observed by both CMS and ATLAS (for a general discussion of the effect of new particles to the H → γγ decay mode see [10,11]).…”

Section: Introductionmentioning

confidence: 99%

“…Several decay modes of the t ′ and b ′ have been considered both by experimental searches and phenomenological studies, and a dedicated search for the exotic one X 5/3 is available from CMS [17]. In this paper we will focus in detail on the production and decays of such a state with electric charge 5/3, which is motivated, for example, by a custodial symmetry in models of composite Higgs [3]. It can only interact with SM up-type quarks through charged currents, while decays to a t ′ are only allowed for large mass splitting.…”

Section: Introductionmentioning

confidence: 99%

Heavy vector-like quark with charge 5/3 at the LHC

Cacciapaglia

Deandrea

Panizzi

et al. 2013

J. High Energ. Phys.

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We study the phenomenology at the Large Hadron Collider of an exotic vectorlike quark with charge +5/3. We relax the assumption of a 100% branching into W t and allow for an arbitrary rate into W plus light quarks, thus covering all possible scenarios. Sizeable decays into light quarks can be achieved, for instance, in a model where the X 5/3 quark is embedded in a doublet with hypercharge 7/6, which also contains a t ′ quark. We study the bounds on the parameter space of this model, and perform a detailed simulation of the X 5/3 pair production and decays. We show that the final state with W tW q, where q = u or c, contributes to the same sign dilepton searches, and that the reach can be improved with alternative cuts optimised on such final state.

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A custodial symmetry for Zbb¯

Cited by 501 publications

References 18 publications

Warped electroweak breaking without custodial symmetry

Warped electroweak breaking without custodial symmetry

Forward–backward asymmetries of the bottom and top quarks in warped extra-dimensional models: LHC predictions from the LEP and Tevatron anomalies

Heavy vector-like quark with charge 5/3 at the LHC

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