The need for new search strategies for fourth generation quarks at the LHC

Geller, Michael; Bar‐Shalom, Shaouly; Eilam, G.

doi:10.1016/j.physletb.2012.06.075

Cited by 12 publications

(27 citation statements)

References 92 publications

(107 reference statements)

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“…This minimal framework has, however, several drawbacks [16] and, more importantly, it fails to account for the existence of the recently discovered 125 GeV Higgs-like particle [17]. On the other hand, a fourth-generation framework with two (or more) Higgs doublets, such as the h4G2HDM discussed here, where the new heavy quarks have masses of Oð500 GeVÞ, is not only consistent with the current Higgs data 3 , but it can also have specific flavor structures, which may give rise to new signatures of fourth-generation quarks at the LHC [16,18], and substantially relax the current bounds on their masses [19]. Moreover, the lightest Higgs state in these class of models may be a good candidate for the recently discovered 125 GeV Higgs-like particle [20].…”

Section: Introductionsupporting

confidence: 62%

“…In particular, in [12] the condensates which drive DEWSB are formed by exchanges of the fundamental Higgs, while in [14] a hybrid setup similar to ours was constructed in the top-condensation scenario. 3 For discussions on the phenomenology of multi-Higgs fourthgeneration models, see e.g., [13,16,[18][19][20][21]. couplings are sub-critical and, therefore, do not play any role in DEWSB (see also discussion below).…”

Section: Dynamical Ew Symmetry Breaking With Heavy Fermions: a Hymentioning

confidence: 99%

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Hybrid dynamical electroweak symmetry breaking with heavy quarks and the 125 GeV Higgs boson

2014

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Existing models of dynamical electroweak symmetry breaking (EWSB) find it very difficult to get a Higgs of mass lighter than m t . Consequently, in light of the LHC discovery of the ∼125 GeV Higgs, such models face a significant obstacle. Moreover, with three generations those models have a superheavy cutoff around 10 17 GeV, requiring a significant fine-tuning. To overcome these twin difficulties, we propose a hybrid framework for EWSB, in which the Higgs mechanism is combined with a Nambu-Jona-Lasinio mechanism. The model introduces a strongly coupled doublet of heavy quarks with a mass around 500 GeV, which forms a condensate at a compositeness scale Λ about a few TeV, and an additional unconstrained scalar doublet which behaves as a "fundamental" doublet at Λ. This "fundamental"-like doublet has a vanishing quartic term at Λ and is, therefore, not the SM doublet, but should rather be viewed as a pseudo-Goldstone boson of the underlying strong dynamics. This setup is matched at the compositeness scale Λ to a tightly constrained hybrid two Higgs doublet model, where both the composite and unconstrained scalars participate in EWSB. This allows us to get a good candidate for the recently observed 125 GeV scalar which has properties very similar to the Standard Model Higgs. The heavier (mostly composite) CP-even scalar has a mass around 500 GeV, while the pseudoscalar and the charged Higgs particles have masses in the range 200-300 GeV. 1 One possible way out, which we will not consider here, is that the lightest scalar state is the pseudoscalar associated with DEWSB (see e.g., [5]), since its mass does not receive large corrections from loops of the heavy fermions and thus can, in principle, be held small without fine-tuning. PHYSICAL REVIEW D 89, 035012 (2014) 1550-7998=2014=89(3)=035012 (8) 035012-1

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Section: Introductionsupporting

confidence: 62%

Section: Dynamical Ew Symmetry Breaking With Heavy Fermions: a Hymentioning

confidence: 99%

Hybrid dynamical electroweak symmetry breaking with heavy quarks and the 125 GeV Higgs boson

2014

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“…For example, if b ′ → tH − dominates the b ′ decays, then gg → b ′b′ will lead to, e.g., a ttH − H + → 4t + 2b signature as opposed to the "standard" 2t + 2W one when the b ′ decays via b ′ → tW [93]. Clearly, these new 4th generation quark signatures deserve a detailed investigation which is beyond the scope of this paper and will be considered elsewhere [94].…”

Section: Phenomenology Of the Yukawa Sector In The 4g2hdm-imentioning

confidence: 97%

Two Higgs doublets with fourth-generation fermions: Models for TeV-scale compositeness

2011

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We construct a class of two Higgs doublets models with a 4th sequential generation of fermions that may effectively accommodate the low energy characteristics and phenomenology of a dynamical electroweak symmetry breaking scenario which is triggered by the condensates of the 4th family fermions. In particular, we single out the heavy quarks by coupling the "heavier" Higgs doublet (Φ h ) which possesses a much larger VEV only to them while the "lighter" doublet (Φ ℓ ) couples only to the light fermions. We study the constraints on these models from precision electroweak data as well as from flavor data. We also discuss some distinct new features that have direct consequences on the production and decays of the 4th family quarks and leptons in high energy colliders; in particular the conventional search strategies for t ′ and b ′ may need to be significantly revised.

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“…For the 4th generation fermion masses involved in the loops of the decays h → V V (i.e., in the 1-loop NLO corrections for the cases h → ZZ * , W W * ), we have used the approximation of a degenerate 4th generation fermion sector, where we have tested below two representative cases: on Γ(h → V V ) is negligible). It is important to note that, while the first case (M 4G = 400 GeV) is excluded for the SM4 [20], it is not necessarily excluded for the 4G2HDM, since in this model the decay patterns of t ′ and b ′ can have a completely different topology, e.g., having BR (t ′ → th) ∼ 1, for which the current limits (which are based on the "standard" SM4 decays t ′ → bW and b ′ → tW ) do not apply, see [52].…”

Section: Model XXmentioning

confidence: 99%

125 GeV Higgs state in the context of four generations with two Higgs doublets

et al. 2012

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We interpret the recent discovery of a 125 GeV Higgs-like state in the context of a two Higgs doublets model with a heavy 4th sequential generation of fermions, in which one Higgs doublet couples only to the 4th generation fermions, while the second doublet couples to the lighter fermions of the 1st-3rd families. This model is designed to accommodate the apparent heaviness of the 4th generation fermions and to effectively address the low-energy phenomenology of a dynamical electroweak symmetry breaking scenario. The physical Higgs states of the model are, therefore, viewed as composites primarily of the 4th generation fermions. We find that the lightest Higgs, h, is a good candidate for the recently discovered 125 GeV spin-zero particle, when tan β ∼ O(1), for typical 4th generation fermion masses of M4G = 400 − 600 GeV, and with a large t − t ′ mixing in the right-handed quarks sector. This, in turn, leads to BR(t ′ → th) ∼ O(1), which drastically changes the t ′ decay pattern. We also find that, based on the current Higgs data, this two Higgs doublet model generically predicts an enhanced production rate (compared to the SM) in the pp → h → τ τ channel and a reduced V V → h → γγ and pp/pp → V → hV → V bb ones. Finally, the heavier CP-even Higgs is excluded by the current data up to mH ∼ 500 GeV, while the pseudoscalar state, A, can be as light as 130 GeV. These heavier Higgs states and the expected deviations from the SM in some of the Higgs production channels can be further excluded or discovered with more data.

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The need for new search strategies for fourth generation quarks at the LHC

Cited by 12 publications

References 92 publications

Hybrid dynamical electroweak symmetry breaking with heavy quarks and the 125 GeV Higgs boson

Hybrid dynamical electroweak symmetry breaking with heavy quarks and the 125 GeV Higgs boson

Two Higgs doublets with fourth-generation fermions: Models for TeV-scale compositeness

125 GeV Higgs state in the context of four generations with two Higgs doublets

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