Little Higgs Model Limits from LHC - Input for Snowmass 2013

Abstract

The status of several prominent model implementations of the Little Higgs paradigm, the Littlest Higgs with and without discrete T-parity as well as the Simplest Little Higgs are reviewed. For this, we are taking into account a fit of 21 electroweak precision observables from LEP, SLC, Tevatron together with the full 25 fb −1 of Higgs data reported by ATLAS and CMS. For the Littlest Higgs with T-parity an outlook on corresponding direct searches at the 8 TeV LHC is included. We compare their competitiveness with the EW and Higgs data in terms of their exclusion potential. This contribution to the Snowmass procedure contains preliminary results of [1] and serves as a guideline for which regions in parameter space of Little Higgs models are still compatible for the upcoming LHC runs and future experiments at the energy frontier. For this purpose we propose two different benchmark scenarios for the Littlest Higgs with T-parity, one with heavy mirror quarks, one with light ones.

Lepton flavor violation in hadronic decays of the tau lepton in the simplest little Higgs model

“…We could fix the scale of compositeness in the SLH model as that f ∼ 1 TeV. However analyses of the model from Higgs data and Electroweak Precision Observables [48,49] seem to indicate that, at 95 % C.L., values of f < ∼ 3.5 TeV should be excluded for our model. That, of course, also delays the appearance of a strongly coupled region.…”

“…For the inclusion of the quark sector we use the anomaly-free embedding that does not need the role of an ultraviolet completion in order to cancel a gauge anomaly in the extended sector. The model has already been confronted with LHC data [48,49] and keeps its strength waiting for more precise determinations.…”

Top Partner Discovery in the T → tZ channel at the LHC

“…Recent studies including constraints from EWPT, Higgs observables and results from direct searches for new particles, have set a lower bound on the scale f to be [51,56,57] (f LHT, A ) EWPT+Higgs 694 GeV (2.9)…”

Precise predictions for $A_H q_-$ associated production in the littlest Higgs model with $T$ parity at the LHC

“…In the LH, a set of new heavy gauge bosons (A H , Z H , W ± H ) and a vectorlike quark (T ) are introduced to cancel the quadratic divergence of the Higgs boson mass contributed by the SM gauge boson loops and the top quark loop, respectively. However, the present precision electroweak constraints [11,12,13] require the LH to be characterized by a large value of the global symmetry-breaking scale f , so the fine tuning between the cutoff scale and the electroweak scale is again needed. Fortunately, this problem can be solved by introducing a discrete symmetry, the T parity, to the LH [14,15].…”

“…Recently, from the analyses of Higgs data from the ATLAS and CMS Collaborations combined with other experimental results, we get the constraint on the scale f in the LHT as f > 694 GeV given in Ref. [12] and f > 665 GeV provided in Ref. [13].…”