Quantum gauge models without (classical) Higgs mechanism (original) (raw)
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Higgs couplings and precision electroweak data
Journal of High Energy Physics, 2013
In light of the discovery of a Higgs-like particle at the LHC, we revisit the status of the precision electroweak data, focusing on two discrepant observables: 1) the long-standing 2.4σ deviation in the forward-backward asymmetry of the bottom quark A b F B , and 2) the 2.3σ deviation in R b , the ratio of the Z → bb partial width to the inclusive hadronic width, which is now in tension after a recent calculation including new two-loop electroweak corrections. We consider possible resolutions of these discrepancies. Taking the data at face value, the most compelling scenario is that new physics directly affects A b F B and R b , bringing the prediction into accord with the measured values. We propose a modified 'Beautiful Mirrors' scenario which contains new vector-like quarks that mix with the b quark, modifying the Zbb vertex and thus correcting A b F B and R b . We show that this scenario can lead to modifications to the production rates of the Higgs boson in certain channels, and in particular a sizable enhancement in the diphoton channel. We also describe additional collider tests of this scenario.
2002
We discuss the experimental and theoretical uncertainties on precision electroweak observables and their relationship to the indirect constraints on the Higgs boson mass, M H , in the Standard Model (SM). The critical experimental measurements (M W , sin 2 θ eff , m t , ...) are evaluated in terms of their present uncertainties and their prospects for improved precision at future colliders, and their contribution to the constraints on M H . In addition, the current uncertainties of the theoretical predictions for M W and sin 2 θ eff due to missing higher order corrections are estimated and expectations and necessary theoretical improvements for future colliders are explored. The constraints from rare B decays are also discussed. Analysis of the present experimental and theoretical precisions yield a current upper bound on M H of ∼ 200 GeV. Including anticipated improvements corresponding to the prospective situation at future colliders (Tevatron Run II, LHC, LC/GigaZ), we find a relative precision of about 25% to 8% (or better) is achievable in the indirect determination of M H .
Consequences of Recent Electroweak Data and W-mass for the Top Quark and Higgs Masses
We critically reexamine the precision tests of the standard model by coupling the current world average value of M W with the recent LEP electroweak data with the aid of a modified ZFITTER program to include the dominant two-loop and QCD-EW mixed terms. The results show a clear evidence of nonvanishing electroweak radiative corrections. The recent CDF m t is a solution of the minimal χ 2-fits to the recent LEP data set and M W = 80.23(18) GeV but with a heavy Higgs scalar, i.e., m t = 179 GeV and m H = 300 GeV. We discuss how sensitive m t and m H are depending on the exact value of M W even within the present uncertainty, as well as on α s and α(M Z). We show how the future improvements on M W can discriminate different values of m t and m H from the electroweak data and provide a crucial and decisive test for the standard model.
Test of the Littlest Higgs model through the correlation among W boson, top quark and Higgs masses
2008
Motivated by the recent precision measurements of the W boson mass and top quark mass, we test the Littlest Higgs model by confronting the prediction of M_W with the current and prospective measurements of M_W and M_t as well as through the correlation among M_W, M_t and Higgs mass. We argue that the current values and accuracy of M_W and M_t measurements tend to favor the Littlest Higgs model over the standard model, although the most recent electroweak data may appear to be consistent with the standard model prediction. In this analysis, the upper bound on the global SU(5) symmetry breaking scale turned out to be 26.3 TeV. We also discuss how the masses of the heavy gauge boson M_B in the Littlest Higgs model can be predicted from the constraints on the model parameters.
Future Directions in Higgs Phenomenology
The search for the weakly-coupled Higgs sector at future colliders consists of three phases: discovery of a Higgs candidate, verification of the Higgs interpretation of the signal, and precision measurements of Higgs sector properties. The discovery of one Higgs boson with Standard Model properties is not sufficient to expose the underlying structure of the electroweak symmetry breaking dynamics. It is critical to search for evidence for a non-minimal Higgs sector and/or new physics associated with electroweak symmetry breaking dynamics.
Mass of the Higgs boson in the standard electroweak model
Physical Review D, 2010
An updated global analysis within the Standard Model (SM) of all relevant electroweak precision and Higgs boson search data is presented with special emphasis on the implications for the Higgs boson mass, MH . Included are, in particular, the most recent results on the top quark and W boson masses, updated and significantly shifted constraints on the strong coupling constant, αs, from τ decays and other low energy measurements such as from atomic parity violation and neutrino deep inelastic scattering. The latest results from searches for Higgs production and decay at the Tevatron are incorporated together with the older constraints from LEP 2. I find a trimodal probability distribution for MH with a fairly narrow preferred 90% CL window, 115 GeV ≤ MH ≤ 148 GeV.
Indirect determination of the Higgs mass through electroweak radiative corrections
Electroweak precision observables allow stringent tests of the Standard Model at the quantum level and imply interesting bounds on the mass of the Higgs boson through higher-order loop effects. Very significant constraints come especially from the determination of the mass of the W boson and from the effective leptonic weak mixing angle. After shortly reviewing the status of theoretical computations of the W mass, the new calculation of two-loop corrections with closed fermion loops to the effective leptonic weak mixing angle is discussed in detail. The phenomenological implications of the new result are analyzed including an estimate of remaining uncertainties.
Electroweak and supersymmetry breaking from the Higgs boson discovery
Physical Review D, 2014
We will explore the consequences on the electroweak breaking condition, the mass of supersymmetric partners and the scale at which supersymmetry breaking is transmitted, for arbitrary values of the supersymmetric parameters tan β and the stop mixing X t , which follow from the Higgs discovery with a mass m H ≃ 126 GeV at the LHC. Within the present uncertainty on the top quark mass we deduce that radiative breaking requires tan β ≳ 8 for maximal mixing X t ≃ ffiffi ffi 6 p , and tan β ≳ 20 for small mixing X t ≲ 1.8. The scale at which supersymmetry breaking is transmitted M can be of order the unification or Planck scale only for large values of tan β and negligible mixing X t ≃ 0. On the other hand for maximal mixing and large values of tan β supersymmetry should break at scales as low as M ≃ 10 5 GeV. The uncertainty in those predictions stemming from the uncertainty in the top quark mass, i.e. the top Yukawa coupling, is small (large) for large (small) values of tan β. In fact for tan β ¼ 1 the uncertainty on the value of M is several orders of magnitude.
Constraints placed on the Higgs sector from precision electroweak measurements
In this lecture, I would like to investigate what precision electroweak measurements have to tell us about the Higgs sector. I will show that the radiative corrections to electroweak interaction observables coming from the Higgs sector can be summarized into three parameters S, T, and U. The precision measurements of the observables will constrain S and T. By comparing these constraints with the theoretically predicted values of S and T, we will be able to tell which Higgs sector theories are more viable than others.