Light Scalars in Composite Higgs Models

Cacciapaglia, Giacomo; Ferretti, Gabriele; Flacke, Thomas; Serôdio, Hugo

doi:10.3389/fphy.2019.00022

Cited by 76 publications

(92 citation statements)

References 123 publications

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“…Three classes of cosets are commonly considered in the CHM context (see for instance Table I in Ref. [36]). They all emerge from gauge theories at the microscopic level.…”

Section: E Global Symmetries and Classification Of Mesonsmentioning

confidence: 99%

Sp(4) gauge theories on the lattice: Quenched fundamental and antisymmetric fermions

et al. 2020

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We perform lattice studies of meson mass spectra and decay constants of the Sp(4) gauge theory in the quenched approximation. We consider two species of (Dirac) fermions as matter field content, transforming in the 2-index antisymmetric and the fundamental representation of the gauge group, respectively. All matter fields are formulated as Wilson fermions. We extrapolate to the continuum and massless limits, and compare to each other the results obtained for the two species of mesons. In the case of two fundamental and three antisymmetric fermions, the long-distance dynamics is relevant for composite Higgs models. This is the first lattice study of this class of theories. The global SU (4) × SU (6) symmetry is broken to the Sp(4) × SO(6) subgroup, and the condensates align with the explicit mass terms present in the lattice formulation of the theory.The main results of our quenched calculations are that, with fermions in the 2-index antisymmetric representation of the group, the masses squared and decay constant squared of all the mesons we considered are larger than the corresponding quantities for the fundamental representation, by factors that vary between ∼ 1.2 and ∼ 2.7. We also present technical results that will be useful for future lattice investigations of dynamical simulations, of composite chimera baryons, and of the approach to large-N in the Sp(2N ) theories considered. We briefly discuss their high-temperature behaviour, where symmetry restoration and enhancement are expected. We acknowledge useful discussions withWe summarise in this Appendix our conventions in the treatment of spinors, which are useful, for example, in switching between the 2-component and the 4-component notation (see also Ref. [50]). The former is best suited to highlight the symmetries of the system, while the latter is the formalism adopted as a starting point for the lattice numerical

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“…Three classes of cosets are commonly considered in the CHM context (see for instance Table I in Ref. [36]). They all emerge from gauge theories at the microscopic level.…”

Section: E Global Symmetries and Classification Of Mesonsmentioning

confidence: 99%

Sp(4) gauge theories on the lattice: Quenched fundamental and antisymmetric fermions

et al. 2020

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“…M1, M3 SO(7) (Sp, F) (5,13), (6,12), (7,11), (8,10), (9,9), (10,8), (11,7), (12,6), (13,5) M2, M4 SO(9) (F, Sp) (5,10), (7,9), (9,8), (11,7), (13,6), (15,5) M5, M8, CVZ Sp(4) (F, A 2 ) (4,9), (6,8), (8,7), (10,6), (12,5) M6, M11 SU (4) ((F,F), A 2 ) (3,12), (4,11), (5,10), (6,9), (7,8), (8,7), (9,6), (10,5) M7, M10 SO(10) (F, (Sp,Sp)) (5,6), (9,5), (13,4), (18,…”

Section: Applications To Two-representation Composite Higgs Mod-elsmentioning

confidence: 99%

Into the conformal window: Multirepresentation gauge theories

2020

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We investigate the conformal window of four-dimensional gauge theories with fermionic matter fields in multiple representations. Of particularly relevant examples are the ultra-violet complete models with fermions in two distinct representations considered in the context of composite Higgs and top partial-compositeness. We first discuss various analytical approaches to unveil the lower edge of the conformal window and their extension to the multiple matter representations. In particular, we argue that the scheme-independent series expansion for the anomalous dimension of a fermion bilinear at an infrared fixed point, γχ χ, IR , combined with the conjectured critical condition, γχ χ, IR = 1 or equivalently γχ χ, IR (2−γχ χ, IR ) = 1, can be used to determine the boundary of conformal phase transition on fully physical grounds. In illustrative cases of SU (2) and SU (3) theories with N R Dirac fermions in various representations, we assess our results by comparing to other analytical or lattice results. *

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“…Our results clearly show that for dominant a → gg decays, which is the norm in realistic models [36], the bound on m T can be very weak: for m a 50 GeV (which is not excluded by any direct searches [38]), m T 400 GeV is still allowed while for larger m a the bound generically never passes ≈ 550 GeV. This represents a gap in the top partner coverage, which could be closed by dedicated searches tagging low-mass di-jet resonances.…”

Section: Phenomenology Of a Top Partner In Presence Of T → T A Decaysmentioning

confidence: 77%

“…The coupling to gluons allows for copious direct production of a at the LHC, and bounds from direct searches have been exhaustively studied in Refs [36,38,39]. Interestingly, there is a mass window 15 GeV m a 65 GeV where very weak constraints apply.…”

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confidence: 99%

Exotic decays of top partners: Mind the search gap

et al. 2019

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Many standard model extensions, including composite Goldstone Higgs models, predict vectorlike fermionic top-partners at the TeV scale. The intensive search programmes by ATLAS and CMS focus on decays into a 3 rd generation quark and an electroweak boson (W, Z, h). However, underlying models of partial compositeness contain additional states that give rise to exotic top partner decays. We consider a well-motivated scenario in which a charge-2/3 top-partner decays into a pseudo-scalar, T → t a, with a → gg or bb dominating below the tt threshold. We show that the constraints on the top partner mass from QCD pair production are substantially weakened, still allowing a top partner mass as light as 400 GeV.

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Light Scalars in Composite Higgs Models

Cited by 76 publications

References 123 publications

Sp(4) gauge theories on the lattice: Quenched fundamental and antisymmetric fermions

Sp(4) gauge theories on the lattice: Quenched fundamental and antisymmetric fermions

Into the conformal window: Multirepresentation gauge theories

Exotic decays of top partners: Mind the search gap

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