Heavy vector-like top partners at the LHC and flavour constraints

Self Cite

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.

Section: Mixing Parameters In the Non-sm Doublet Modelmentioning

confidence: 99%

Section: Mixing Parameters In the Non-sm Doublet Modelmentioning

confidence: 99%

Section: Mixing Parameters In the Non-sm Doublet Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Cacciapaglia

Deandrea

Panizzi

et al. 2013

Self Cite

Non-minimal Universal Extra Dimensions with Brane Local Terms: the top quark sector

Datta

Nishiwaki

Niyogi

2014

Abstract:We study the physics of Kaluza-Klein (KK) top quarks in the framework of a non-minimal Universal Extra Dimension (nmUED) with an orbifolded (S 1 /Z 2 ) flat extra spatial dimension in the presence of brane-localized terms (BLTs). In general, BLTs affect the masses and the couplings of the KK excitations in a non-trivial way including those for the KK top quarks. On top of that, BLTs also influence the mixing of the top quark chiral states at each KK level and trigger mixings among excitations from different levels with identical KK parity (even or odd). The latter phenomenon of mixing of KK levels is not present in the popular UED scenario known as the minimal UED (mUED) at the tree level. Of particular interest are the mixings among the KK top quarks from level '0' and level '2' (driven by the mass of the Standard Model (SM) top quark). These open up new production modes in the form of single production of a KK top quark and the possibility of its direct decays to SM particles leading to rather characteristic signals at the colliders. Experimental constraints and the restrictions they impose on the nmUED parameter space are discussed. The scenario is implemented in MadGraph 5 by including the quark, lepton, the gauge-boson and the Higgs sectors up to the second KK level. A few benchmark scenarios are chosen for preliminary studies of the decay patterns of the KK top quarks and their production rates at the LHC in various different modes. Recast of existing experimental analyzes in scenarios having similar states is found to be not so straightforward for the KK top quarks of the nmUED scenario under consideration.

Fermionic extensions of the Standard Model in light of the Higgs couplings

Bizot

Frigerio

2016

As the Higgs boson properties settle, the constraints on the Standard Model extensions tighten. We consider all possible new fermions that can couple to the Higgs, inspecting sets of up to four chiral multiplets. We confront them with direct collider searches, electroweak precision tests, and current knowledge of the Higgs couplings. The focus is on scenarios that may depart from the decoupling limit of very large masses and vanishing mixing, as they offer the best prospects for detection. We identify exotic chiral families that may receive a mass from the Higgs only, still in agreement with the hγγ signal strength. A mixing θ between the Standard Model and non-chiral fermions induces order θ 2 deviations in the Higgs couplings. The mixing can be as large as θ ∼ 0.5 in case of custodial protection of the Z couplings or accidental cancellation in the oblique parameters. We also notice some intriguing effects for much smaller values of θ, especially in the lepton sector. Our survey includes a number of unconventional pairs of vector-like and Majorana fermions coupled through the Higgs, that may induce order one corrections to the Higgs radiative couplings. We single out the regions of parameters where hγγ and hgg are unaffected, while the hγZ signal strength is significantly modified, turning a few times larger than in the Standard Model in two cases. The second run of the LHC will effectively test most of these scenarios.