100 research outputs found
Bounding wide composite vector resonances at the LHC
In composite Higgs models (CHMs), electroweak precision data generically push
colourless composite vector resonances to a regime where they dominantly decay
into pairs of light top partners. This greatly attenuates their traces in
canonical collider searches, tailored for narrow resonances promptly decaying
into Standard Model final states. By reinterpreting the CMS same-sign dilepton
(SS2) analysis at the Large Hadron Collider (LHC), originally designed to
search for top partners with electric charge , we demonstrate its
significant coverage over this kinematical regime. We also show the reach of
the 13 TeV run of the LHC, with various integrated luminosity options, for a
possible upgrade of the SS2 search. The top sector of CHMs is found to be
more fine-tuned in the presence of colourless composite resonances in the few
TeV range.Comment: 9 pages, 5 figures. Minor corrections for publication in JHE
Top Partner Discovery in the channel at the LHC
In this paper we study the discovery potential of the LHC run II for heavy
vector-like top quarks in the decay channel to a top and a boson. Despite
the usually smaller branching ratio compared to charged-current decays, this
channel is rather clean and allows for a complete mass reconstruction of the
heavy top. The latter is achieved in the leptonic decay channel of the
boson and in the fully hadronic top channel using boosted jet and jet
substructure techniques. To be as model-independent as possible, a simplified
model approach with only two free parameters has been applied. The results are
presented in terms of parameter space regions for evidence or
discovery for such new states in that channel.Comment: 24 pages, 8 figures, version 2 updated to JHEP 01 (2015) 08
Novel signatures for vector-like quarks
We consider supersymmetric extensions of the standard model with a vector-like doublet (T B) of quarks with charge 2/3 and â1/3, respectively. Compared to non-supersymmetric models, there is a variety of new decay modes for the vector-like quarks, involving the extra scalars present in supersymmetry. The importance of these new modes, yielding multi-top, multi-bottom and also multi-Higgs signals, is highlighted by the analysis of several benchmark scenarios. We show how the triangles commonly used to represent the branching ratios of the âstandardâ decay modes of the vector-like quarks involving W, Z or Higgs bosons can be generalised to include additional channels. We give an example by recasting the limits of a recent heavy quark search for this more general case.The work of J.A. Aguilar-Saavedra has been supported by MINECO Projects FPA 2016-
78220-C3-1-P and FPA 2013-47836-C3-2-P (including ERDF), and by Junta de Andaluc a
Project FQM-101. The work of D.E. L opez-Fogliani has been supported by the Argentinian
CONICET. The work of C. Mu~noz has been supported in part by the Programme SEV-
2012-0249 `Centro de Excelencia Severo Ochoa'. D.E. L opez-Fogliani and C. Mu~noz also
acknowledge the support of the Spanish grant FPA2015-65929-P (MINECO/FEDER, UE),
and MINECO's Consolider-Ingenio 2010 Programme under grant MultiDark CSD2009-
00064
Exploring holographic Composite Higgs models
Simple Composite Higgs models predict new vector-like fermions not too far from the electroweak scale, yet LHC limits are now sensitive to the TeV scale. Motivated by this tension, we explore the holographic dual of the minimal model, MCHM5, to try and alleviate this tension without increasing the fine-tuning in the Higgs potential. Interestingly, we find that lowering the UV cutoff in the 5D picture allows for heavier top partners and less fine-tuning. In the 4D dual this corresponds to increasing the number of âcoloursâ N , thus increasing the decay constant of the Goldstone Higgs. This is essentially a âLittle Randall-Sundrum Modelâ, which are known to reduce some flavour and electroweak constraints. Furthermore, in anticipation of the ongoing efforts at the LHC to put bounds on the top Yukawa, we demonstrate that deviations from the SM can be suppressed or enhanced with respect to what is expected from mere symmetry arguments in 4D. We conclude that the 5D holographic realisation of the MCHM5 with a small UV cutoff is not in tension with the current experimental data
A First Top Partner Hunter's Guide
We provide a systematic effective lagrangian description of the phenomenology of the lightest top-partners in composite Higgs models. Our construction is based on symmetry, on selection rules and on plausible dynamical assumptions. The structure of the resulting simplified models depends on the quantum numbers of the lightest top partner and of the operators involved in the generation of the top Yukawa. In all cases the phenomenology is conveniently described by a small number of parameters, and the results of experimental searches are readily interpreted as a test of naturalness. We recast presently available experimental bounds on heavy fermions into bounds on top partners: LHC has already stepped well inside the natural region of parameter space
On the Flavor Structure of Natural Composite Higgs Models & Top Flavor Violation
Abstract: We explore the up flavor structure of composite pseudo Nambu-Goldstone-boson Higgs models, where we focus on the flavor anarchic minimal SO(5) case. We identify the different sources of flavor violation in this framework and emphasise the differences from the anarchic Randall-Sundrum scenario. In particular, the fact that the flavor symmetry does not commute with the symmetries that stabilize the Higgs potential may constrain the flavor structure of the theory. In addition, we consider the interplay between the fine tuning of the model and flavor violation. We find that generically the tuning of this class of models is worsen in the anarchic case due to the contributions from the additional fermion resonances. We show that, even in the presence of custodial symmetry, large top flavor violating rate are naturally expected. In particular, t \u2192 cZ branching ratio of order of 10 125 is generic for this class of models. Thus, this framework can be tested in the next run of the LHC as well as in other future colliders. We also find that the top flavor violation is weakly correlated with the increase amount of fine tuning. Finally, other related flavor violation effects, such as t \u2192 ch and in the D system, are found to be too small to be observed by the current and near future colliders. \ua9 2014, The Author(s)
Supersymmetry with a pNGB Higgs and partial compositeness
We study the consequences of combining SUSY with a pseudo Nambu-Goldstone boson Higgs coming from an SO(5)/SO(4) coset and "partial compositeness". In particular, we focus on how electroweak symmetry breaking and the Higgs mass are reproduced in models where the symmetry SO(5) is linearly realized. The global symmetry forbids tree-level contributions to the Higgs potential coming from D-terms, differently from what happens in most of the SUSY little-Higgs constructions. While the stops are generally heavy, light fermion top partners below 1TeV are predicted. In contrast to what happens in non-SUSY composite Higgs models, they are necessary to reproduce the correct top, rather than Higgs, mass. En passant, we point out that, independently of SUSY, models where tR is fully composite and embedded in the 5 of SO(5) generally predict a too light Higgs. Open Access, \ua9 2014 The Authors
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