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Register a new userElectroweak Precision Observables, New Physics and the Nature of a 126 GeV Higgs Boson
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We perform the fit of electroweak precision observables within the Standard Model with a 126 GeV Higgs boson, compare the results with the theoretical predictions and discuss the impact of recent experimental and theoretical improvements. We introduce New Physics contributions in a model-independent way and fit for the S, T and U parameters, for the $epsilon_{1,2,3,b}$ ones, for modified $Zbbar{b}$ couplings and for a modified Higgs coupling to vector bosons. We point out that composite Higgs models are very strongly constrained. Finally, we compute the bounds on dimension-six operators relevant for the electroweak fit.
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The recent discovery of a Higgs-like boson at the LHC with a mass of 126 GeV has revived the interest in supersymmetric models, which predicted a Higgs boson mass below 130 GeV long before its discovery. We compare systematically the allowed parameter space in the constrained Minimal Supersymmetric Standard Model (CMSSM) and the Next-to-Minimal Supersymmetric Model (NMSSM) by minimizing the chi^2 function with respect to all known constraints from accelerators and cosmology using GUT scale parameters. For the CMSSM the Higgs boson mass at tree level is below the Z^0 boson mass and large radiative corrections are needed to obtain a Higgs boson mass of 126 GeV, which requires stop squark masses in the multi-TeV range. In contrast, for the NMSSM light stop quarks are allowed, since in the NMSSM at tree level the Higgs boson mass can be above the Z^0 boson mass from mixing with the additional singlet Higgs boson. Predictions for the scalar boson masses are given in both models with emphasis on the unique signatures of the NMSSM, where the heaviest scalar Higgs boson decays in the two lighter scalar Higgs bosons with a significant branching ratio, in which case one should observe double Higgs boson production at the LHC. Such a signal is strongly suppressed in the CMSSM. In addition, since the LSP is higgsino-like, Higgs boson decays into LSPs can be appreciable, thus leading to invisible Higgs decays.
We present updated global fits of the Standard Model and beyond to electroweak precision data, taking into account recent progress in theoretical calculations and experimental measurements. From the fits, we derive model-independent constraints on new physics by introducing oblique and epsilon parameters, and modified $Zbbar{b}$ and $HVV$ couplings. Furthermore, we also perform fits of the scale factors of the Higgs-boson couplings to observed signal strengths of the Higgs boson.
We present results from a state-of-the-art fit of electroweak precision observables and Higgs-boson signal-strength measurements performed using 7 and 8 TeV data from the Large Hadron Collider. Based on the HEPfit package, our study updates the traditional fit of electroweak precision observables and extends it to include Higgs-boson measurements. As a result we obtain constraints on new physics corrections to both electroweak observables and Higgs-boson couplings. We present the projected accuracy of the fit taking into account the expected sensitivities at future colliders.
Indirect information about the possible scale of supersymmetry (SUSY) breaking can be obtained from the comparison of precisely measured observables (and also of exclusion limits) with accurate theory predictions incorporating SUSY loop corrections. Recent results are reviewed obtained from a combined analysis of the most sensitive electroweak precision observables (EWPO), M_W, sin^2_theta^eff, Gamma_Z, (g-2)_mu and M_h, and B-physics observables (BPO), BR(b -> s gamma), BR(B_s -> mu^+mu^-), BR(B_u -> tau u_tau) and Delta M_{B_s}. Assuming that the lightest supersymmetric particle (LSP) provides the cold dark matter density preferred by WMAP and other cosmological data, chi^2 fits are performed to the parameters of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the SUSY-breaking parameters are universal at the GUT scale, and the non-universal Higgs model (NUHM), in which this constraint is relaxed for the soft SUSY-breaking contributions to the Higgs masses. Within the CMSSM indirect bounds on the mass of the lightest CP-even Higgs boson are derived.
We examine the prospects for discovering and elucidating the weakly-coupled Higgs sector at future collider experiments. The Higgs search consists of three phases: (i) discovery of a Higgs candidate, (ii) verification of the Higgs interpretation of the signal, and (iii) 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. An improvement in precision electroweak data at future colliders can play a useful role in confirming the theoretical interpretation of the Higgs search results.
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