Stabilizing electroweak vacuum in a vectorlike fermion model

Xiao, Ming-Lei; Yu, Jiang-Hao

doi:10.1103/physrevd.90.014007

Cited by 50 publications

(49 citation statements)

References 72 publications

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“…Recently, a number of studies have looked at models where additional scalars and vector-like quarks are introduced [39][40][41][42][43][44][45][46][47]. Within the context of a vector-like SU(2) W singlet fermion, these studies have focused either on renormalizable interactions between the new scalar sector and the new fermion sector [45,46], or focused on renormalizable interactions induced through mixing that arises in the scalar sector and its effects on the SM Yukawa interactions [40,41,47].…”

Section: Real Scalar Triplet With a Vector-like Electroweak Singlet Qmentioning

confidence: 99%

Vector-like quarks with a scalar triplet

2015

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We study a minimal extension to the Standard Model with an additional real scalar triplet, $\Sigma$, and a single vector-like quark, $T$. This class of models appear naturally in extensions of the Littlest Higgs model that incorporate dark matter without the need of $T$-parity. We assume the limit that the triplet does not develop a vacuum expectation value and that all dimension five operators coupling the triplet to Standard Model fields and the vector-like quarks are characterized by the scale $\Lambda$ at which we expect new physics to arise. We introduce new non-renormalizable interactions between the new scalar sector and fermion sector that allow mixing between the Standard Model third generation up-type quark and the vector-like quark in a way that leads to the cancellation of the leading quadratic divergences to the one-loop corrections from the top quark to the mass of the Higgs boson. Within this framework, new decay modes of the vector-like quark to the real scalar triplet and SM particles arise and bring forth an opportunity to probe this model with existing and future LHC data. We contrast constraints from direct colliders searches with low energy precision measurements and find that heavy vector-like top quarks with a mass as low as $650$ GeV are consistent with current experimental constraints in models where new physics arises at scales below $2$ TeV

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Section: Real Scalar Triplet With a Vector-like Electroweak Singlet Qmentioning

confidence: 99%

Vector-like quarks with a scalar triplet

2015

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“…For simplicity, we consider the Yukawa matrix y X = y X 1 N X ×N X . In the MS scheme the one-loop β-functions of the gauge couplings 8 are given by (see also [90,91])…”

Section: Theoretical Setup: One-loop Beta Functions and Matchingmentioning

confidence: 99%

A new scalar resonance at 750 GeV: towards a proof of concept in favor of strongly interacting theories

Son

Urbano

2016

J. High Energ. Phys.

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We interpret the recently observed excess in the diphoton invariant mass as a new spin-0 resonant particle. On theoretical grounds, an interesting question is whether this new scalar resonance belongs to a strongly coupled sector or a well-defined weakly coupled theory. A possible UV-completion that has been widely considered in literature is based on the existence of new vector-like fermions whose loop contributions -Yukawa-coupled to the new resonance -explain the observed signal rate. The large total width preliminarily suggested by data seems to favor a large Yukawa coupling, at the border of a healthy perturbative definition. This potential problem can be fixed by introducing multiple vectorlike fermions or large electric charges, bringing back the theory to a weakly coupled regime. However, this solution risks to be only a low-energy mirage: large multiplicity or electric charge can dangerously reintroduce the strong regime by modifying the renormalization group running of the dimensionless couplings. This issue is also tightly related to the (in)stability of the scalar potential. First, we study -in the theoretical setup described above -the parametric behavior of the diphoton signal rate, total width, and one-loop β functions. Then, we numerically solve the renormalization group equations, taking into account the observed diphoton signal rate and total width, to investigate the fate of the weakly coupled theory. We find that -with the only exception of few fine-tuned directions -weakly coupled interpretations of the excess are brought back to a strongly coupled regime if the running is taken into account.

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“…New quarks can have right and left handed couplings to the W boson and are color triplets [6]. VLQs appear in several extensions of the SM, such as extra dimensions [7], supersymmetry [8], composite Higgs [9,10] and little Higgs [11] models, in which they cancel top-quark loop contributions to the Higgs mass [12]. Depending on the model, VLQs can be realized in different multiplets, such as in singlets, doublets and triplets [13].…”

Section: Introductionmentioning

confidence: 99%

Search for the production of single vector-like and excited quarks in the Wt final state in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

Aad¹,

Abbott²,

Abdallah³

et al. 2016

J. High Energ. Phys.

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A search for vector-like quarks and excited quarks in events containing a top quark and a W boson in the final state is reported here. The search is based on 20.3 fb −1 of proton-proton collision data taken at the LHC at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector. Events with one or two leptons, and one, two or three jets are selected with the additional requirement that at least one jet contains a b-quark. Single-lepton events are also required to contain at least one large-radius jet from the hadronic decay of a high-p T W boson or a top quark. No significant excess over the expected background is observed and upper limits on the cross-section times branching ratio for different vector-like quark and excited-quark model masses are derived. For the excited-quark production and decay to W t with unit couplings, quarks with masses below 1500 GeV are excluded and coupling-dependent limits are set. Only final states in which the B or b * decay into Wt are considered. The corresponding leading-order (LO) Feynman diagrams for these processes are shown in figure 1. Keywords: Exotics, Hadron-Hadron scatteringFigure 1. Leading-order Feynman diagrams for the production and decay of (a) a single B together with a light quark and (b) a single b * . The cross-section for singlet B production is proportional to the square of the bZB coupling strength λ. The production via Higgs-boson exchange is also possible, although the Z-induced process is dominant. The B can decay into Zb, Hb and Wt with the branching ratios given by the VLQ couplings 1 for singlet B. The light quark in the final state gives rise to a forward jet. The cross-section for singlet B production with subsequent decay to Wt has been calculated in the TS-10 model [10,14], a four-dimensional version of a model with composite fermions in a 10 representation of SO(5). The cross-section is given in table 1 for two values of the coupling parameter λ, for which the 2 × 2 mass mixing matrix of the b-quark and the B has been diagonalised. The largest value of λ for which the B decay width is still smaller than the experimental mass resolution is λ = 3. A top-quark mass of 172.5 GeV is assumed throughout.In addition to the Zb, Hb and Wt couplings, the b * also has a chromomagnetic coupling f g to a gluon and a b-quark [15][16][17], making it both a vector-like quark and an excited quark [18]. Complete models of VLQs usually contain other particles and interactions which result in an effective chromomagnetic coupling. Examples of such models are 1 At high singlet B masses they are roughly 1:1:2 [6].-2 -JHEP02(2016)110 technicolour [19, 20], topcolour [21, 22], extra dimension models [23, 24] or models with a heavy partner of the gluon [25], which gives rise to the effective gb coupling. The strength of the coupling is assumed to be f g = 1 in this paper unless otherwise indicated. The b * in the VLQ case has f L = f R = 1, but it is also allowed to have purely left-handed (f L = 1, f R = 0) or purely right-handed (f L = 0, f R = 1) coup...

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Stabilizing electroweak vacuum in a vectorlike fermion model

Cited by 50 publications

References 72 publications

Vector-like quarks with a scalar triplet

Vector-like quarks with a scalar triplet

A new scalar resonance at 750 GeV: towards a proof of concept in favor of strongly interacting theories

Search for the production of single vector-like and excited quarks in the Wt final state in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

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