The Minimal Moose for a Little Higgs

163

226

We derive constraints on the sign of couplings in an effective Higgs Lagrangian using prime principles such as the naturalness principle, global symmetries, and unitarity. Specifically, we study four dimension-six operators, O H , O y , O g , and O γ , which contribute to the production and decay of the Higgs boson at the Large Hadron Collider (LHC), among other things. Assuming the Higgs is a fundamental scalar, we find: 1) the coefficient of O H is positive except when there are triplet scalars, resulting in a reduction in the Higgs on-shell coupling from their standard model (SM) expectations if no other operators contribute, 2) the linear combination of O H and O y controlling the overall Higgs coupling to fermion is always reduced, 3) the sign of O g induced by a new colored fermion is such that it interferes destructively with the SM top contribution in the gluon fusion production of the Higgs, if the new fermion cancels the top quadratic divergence in the Higgs mass, and 4) the correlation between naturalness and the sign of O γ is similar to that of O g , when there is a new set of heavy electroweak gauge bosons. Next considering a composite scalar for the Higgs, we find the reduction in the on-shell Higgs couplings persists. If further assuming a collective breaking mechanism as in little Higgs theories, the coefficient of O H remains positive even in the presence of triplet scalars. In the end, we conclude that the gluon fusion production of the Higgs boson is reduced from the SM rate in all composite Higgs models. Our study suggests a wealth of information could be revealed by precise measurements of the Higgs couplings, providing strong motivations for both improving on measurements at the LHC and building a precision machine such as the linear collider.

Section: B the General Fermion Mass Matrixmentioning

confidence: 87%

“…Notice that, by SU(2) L invariance, the total contribution of the heavy multiplets should start at O(v 2 ), corresponding to the O g operator. 6 The exact one-loop computation parametrized by the function I g (m 2 h /m 2 t ) reduces to the first term inside bracket in the m h /m t → ∞ limit.…”

Section: A Higgs Low-energy Theoremsmentioning

confidence: 99%

Theoretical constraints on the Higgs effective couplings

Low

Rattazzi

Vichi

2010

163

226

“…It also features a very strong potential for the discovery or exclusion of new physics/particles, thus opening the possibility of investigating both strongly and weakly coupled extensions of the Standard Model. New vector-like (VL) fermions are often present in many of the extensions of the SM, especially in relation with the top sector (top partners, as for example in composite Higgs models [1][2][3][4], extradimensional models [5][6][7][8][9][10][11], little Higgs models [12][13][14], gauge-Higgs models [15,16], gauge coupling unification [17,18] and models with an extended custodial symmetry [19,20]). Both CMS [21] and ATLAS [22] have recently devoted a considerable effort in the analyses apt to setting bounds on this type of new particles.…”

Section: Introductionmentioning

confidence: 99%

Interplay of vector-like top partner multiplets in a realistic mixing set-up

Cacciapaglia

Deandrea

Gaur

et al. 2015

The ATLAS and CMS collaborations at the LHC have performed analyses on the existing data sets, studying the case of one vector-like fermion or multiplet coupling to the standard model Yukawa sector. In the near future, with more data available, these experimental collaborations will start to investigate more realistic cases. The presence of more than one extra vector-like multiplet is indeed a common situation in many extensions of the standard model. The interplay of these vector-like multiplet between precision electroweak bounds, flavour and collider phenomenology is a important question in view of establishing bounds or for the discovery of physics beyond the standard model. In this work we study the phenomenological consequences of the presence of two vector-like multiplets. We analyse the constraints on such scenarios from tree-level data and oblique corrections for the case of mixing to each of the SM generations. In the present work, we limit to scenarios with two top-like partners and no mixing in the down-sector.

“…The most popular models use the simplest symmetry: a new parity (Z 2 ) symmetry. R parity in supersymmetry [13], KK parity in Universal Extra Dimensions [14][15][16] and warped extra dimension [20,21], and T parity in little Higgs models [22][23][24][25][26] all fall into this simple category. Nevertheless, larger symmetry groups such as the Z 3 group have also been employed [27].…”

Section: Jhep03(2016)098mentioning

confidence: 99%

Same-sign dilepton excesses and vector-like quarks

Chen

Cheng

Low

2016

Multiple analyses from ATLAS and CMS collaborations, including searches for ttH production, supersymmetric particles and vector-like quarks, observed excesses in the same-sign dilepton channel containing b-jets and missing transverse energy in the LHC Run 1 data. In the context of little Higgs theories with T parity, we explain these excesses using vector-like T-odd quarks decaying into a top quark, a W boson and the lightest T-odd particle (LTP). For heavy vector-like quarks, decay topologies containing the LTP have not been searched for at the LHC. The bounds on the masses of the T-odd quarks can be estimated in a simplified model approach by adapting the search limits for top/bottom squarks in supersymmetry. Assuming a realistic decay branching fraction, a benchmark with a 750 GeV T-odd b quark is proposed. We also comment on the possibility to fit excesses in different analyses in a common framework.