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تسجيل مستخدم جديدPrecision Measurements of Higgs Couplings: Implications for New Physics Scales
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The measured properties of the recently discovered Higgs boson are in good agreement with predictions from the Standard Model. However, small deviations in the Higgs couplings may manifest themselves once the currently large uncertainties will be improved as part of the LHC program and at a future Higgs factory. We review typical new physics scenarios that lead to observable modifications of the Higgs interactions. They can be divided into two broad categories: mixing effects as in portal models or extended Higgs sectors, and vertex loop effects from new matter or gauge fields. In each model we relate coupling deviations to their effective new physics scale. It turns out that with percent level precision the Higgs couplings will be sensitive to the multi-TeV regime.
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Giacomo Cacciapaglia
, Aldo Deandrea
, Guillaume Drieu La Rochelle andn Jean-Baptiste Flament
2014
After the discovery of a scalar resonance, resembling the Higgs boson, its couplings have been extensively studied via the measurement of various production and decay channels on the invariant mass peak. Recently, it has been suggested the possibilit
y to use off-shell measurements: in particular, CMS has published results based on the high- invariant mass cross section of the process $gg to ZZ$, which contains the contribution of the Higgs. While this measurement has been interpreted as a constraint on the Higgs width after very specific assumptions are taken on the Higgs couplings, in this letter we show that a much more model-independent interpretation is possible.
We consider the Higgs boson decay processes and its production and provide a parameterisation tailored for testing models of new physics. The choice of a particular parameterisation depends on a non-obvious balance of quantity and quality of the avai
lable experimental data, envisaged purpose for the parameterisation and degree of model independence. At present only simple parameterisations with a limited number of fit parameters can be performed, but this situation will improve with the forthcoming experimental LHC data. It is therefore important that different approaches are considered and that the most detailed information is made available to allow testing the different aspects of the Higgs boson physics and the possible hints beyond the Standard Model.
If one removes any emph{ad hoc} symmetry assumptions, the general two Higgs doublet model should have additional Yukawa interactions independent from fermion mass generation, in general involving flavor changing neutral Higgs couplings. These extra c
ouplings can affect the discovered Higgs boson $h$ through fermion loop contributions. We calculate the renormalized $hZZ$ coupling at one-loop level %by on-shell and minimal subtraction scheme, and evaluate the dependence on heavy Higgs boson mass and extra Yukawa coupling $rho_{tt}$. Precision measurements at future colliders can explore the parameter space, and can give stronger bound on $rho_{tt}$ than the current bound from flavor experiments. As a side result, we find that if $rho_{tt}cosgamma < 0$, where $cosgamma$ is the exotic Higgs component of $h$, the $rho_{tt}$-induced top loop contribution cancels against bosonic loop contributions, and one may have alignment without decoupling, namely $sin(-gamma) simeq 1$, but exotic scalar bosons could have masses at several hundred GeV.
We study the off-shell production of the Higgs boson at the LHC to probe Higgs physics at higher energy scales utilizing the process $g g rightarrow h^{*} rightarrow ZZ$. We focus on the energy scale dependence of the off-shell Higgs propagation, and
of the top quark Yukawa coupling, $y_t (Q^2)$. Extending our recent study in arXiv:1710.02149, we first discuss threshold effects in the Higgs propagator due to the existence of new states, such as a gauge singlet scalar portal, and a possible continuum of states in a conformal limit, both of which would be difficult to discover in other traditional searches. We then examine the modification of $y_t (Q^2)$ from its Standard Model (SM) prediction in terms of the renormalization group running of the top Yukawa, which could be significant in the presence of large flat extra-dimensions. Finally, we explore possible strongly coupled new physics in the top-Higgs sector that can lead to the appearance of a non-local $Q^2$-dependent form factor in the effective top-Higgs vertex. We find that considerable deviations compared to the SM prediction in the invariant mass distribution of the $Z$-boson pair can be conceivable, and may be probed at a $2sigma$-level at the high-luminosity 14 TeV HL-LHC for a new physics scale up to $mathcal{O}(1 {~rm TeV})$, and at the upgraded 27 TeV HE-LHC for a scale up to $mathcal{O}(3 {~rm TeV})$. For a few favorable scenarios, $5sigma$-level observation may be possible at the HE-LHC for a scale of about $mathcal{O}(1 {~rm TeV})$.
The program HiggsSignals confronts the predictions of models with arbitrary Higgs sectors with the available Higgs signal rate and mass measurements, resulting in a likelihood estimate. A new version of the program, HiggsSignals-2, is presented that
contains various improvements in its functionality and applicability. In particular, the new features comprise improvements in the theoretical input framework and the handling of possible complexities of beyond-the-SM Higgs sectors, as well as the incorporation of experimental results in the form of Simplified Template Cross Section (STXS) measurements. The new functionalities are explained, and a thorough discussion of the possible statistical interpretations of the HiggsSignals results is provided. The performance of HiggsSignals is illustrated for some example analyses. In this context the importance of public information on certain experimental details like efficiencies and uncertainty correlations is pointed out. HiggsSignals is continuously updated to the latest experimental results and can be obtained at https://www.gitlab.com/higgsbounds/higgssignals .
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