Electroweak precision tests for triplet scalars

Abstract

Electroweak precision observables are fundamentally important for testing the standard model (SM) or its extensions. The influences to observables from new physics within the electroweak sector can be expressed in terms of oblique parameters S, T, U. The recently reported W mass excess anomaly by CDF modifies these parameters in a significant way. By performing the global fit with the CDF new W mass measurement data, we obtain S = 0.03 ± 0.03, T = 0.06 ± 0.02 and U = 0.16 ± 0.03 (or S = 0.14 ± 0.03, T = 0.24 ± 0.02 with U = 0) which is significantly away from zero as SM would predict. The CDF excess strongly indicates the need of new physics beyond SM. We carry out a global fit to study the influence of two different cases of simple extensions by a hyper-charge Y = 1 triplet scalar ∆ (corresponding to the type-II seesaw model) and a Y = 0 real triplet scalar Σ on electroweak precision tests to determine parameter space in these models to solve the W mass anomaly and discuss the implications. We find that these triplets can affect the oblique parameters significantly at the tree and loop levels. For Y = 1 case, there are seven new scalars in the model. The tree and scalar loop effects on oblique parameters can be expressed in terms of three parameters, the neutral CP-even mass mH , potential parameter λ4 and triplet vev v∆. Our global fit obtains mH = 296.02 ± 10.18 GeV, λ4 = 2.58 ± 0.09 and v∆ = 4.82 ± 0.34 GeV. These parameter correspondingly results in mass difference ∆m 2 = (197.49 ± 3.45GeV) 2 . Using these fit values, we further obtain m H ++ = 98.09 ± 20.02GeV, which satisfies the current LHC constraints. We also further adopt the phenomenological analysis, such as vacuum stability and perturbative unitarity, Higgs data and triple Higgs self-coupling. Furthermore, we find that the future lepton colliders can feasibly search for doubly charged H ++ via pair production H ++ H −− and decay channel to four W final states. For Y = 0 case, there are four new scalars in the model. The tree and new scalar effects on the oblique parameters can be parameterized by the singly charged mass m H + , the mass difference ∆m = m H + − m H 0 and triplet vev vΣ. Our global fit obtains m H + = 77.16 ± 17.12 GeV, ∆m = −14.27 ± 4.22 GeV and vΣ = 3.20 ± 0.30 GeV. However, these strongly violate the perturbative unitarity of the potential parameter b4, which can only be satisfied within 3σ errors.

Top-quark FCNC decays, LFVs, lepton $g-2$, and $W$ mass anomaly with inert charged Higgses

“…Moreover, the new observation has a 7σ deviation from the SM prediction m W = 80.361 GeV [74]. If the W -mass anomaly is confirmed by the measurements at the LHC with more cumulative data, it would be a solid piece of evidence that exhibits the effects of new physics [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92].…”

Custodial symmetry violation in scalar extensions of the standard model*

“…We note that Ref. [94] studied the compatibility of the spectrum preferred by the CDF II W mass with other EWPOs and Higgs precision data in an inert complex triplet extension (with hypercharge ) of the SM, and Ref. [95] studied both complex and real triplet extensions by directly performing a global fit to EWPOs with CDF II via Bayesian analysis.…”

Low-mass doubly-charged Higgs bosons at LHC

“…Lately, Refs. [76][77][78][79] have demonstrated that the recently reported measurement of the W -bosoon mass by the CDF experiment [80] which substantially differs from the global EW fit [81] can be explained within the type-II see-saw model predicting such low-mass H ±± and slightly heavier singly-charged and neutral scalars. Therefore, it is paramount to look for such H ±± at the LHC.…”