82 research outputs found
Global fits of the two-loop renormalized Two-Higgs-Doublet model with soft breaking
We determine the next-to-leading order renormalization group equations for
the Two-Higgs-Doublet model with a softly broken symmetry and CP
conservation in the scalar potential. We use them to identify the parameter
regions which are stable up to the Planck scale and find that in this case the
quartic couplings of the Higgs potential cannot be larger than 1 in magnitude
and that the absolute values of the S-matrix eigenvalues cannot exceed 2.5 at
the electroweak symmetry breaking scale. Interpreting the 125 GeV resonance as
the light CP-even Higgs eigenstate, we combine stability constraints,
electroweak precision and flavour observables with the latest ATLAS and CMS
data on Higgs signal strengths and heavy Higgs searches in global parameter
fits to all four types of symmetry. We quantify the maximal deviations
from the alignment limit and find that in type II and Y the mass of the heavy
CP-even (CP-odd) scalar cannot be smaller than 340 GeV (360 GeV). Also, we
pinpoint the physical parameter regions compatible with a stable scalar
potential up to the Planck scale. Motivated by the question how natural a Higgs
mass of 125 GeV can be in the context of a Two-Higgs-Doublet model, we also
address the hierarchy problem and find that the Two-Higgs-Doublet model does
not offer a perturbative solution to it beyond 5 TeV.Comment: 30 pages, 29 figures. Major update of the experimental inputs;
references adde
Current and future constraints on Higgs couplings in the nonlinear Effective Theory
We perform a Bayesian statistical analysis of the constraints on the
nonlinear Effective Theory given by the Higgs electroweak chiral Lagrangian. We
obtain bounds on the effective coefficients entering in Higgs observables at
the leading order, using all available Higgs-boson signal strengths from the
LHC runs 1 and 2. Using a prior dependence study of the solutions, we discuss
the results within the context of natural-sized Wilson coefficients. We further
study the expected sensitivities to the different Wilson coefficients at
various possible future colliders. Finally, we interpret our results in terms
of some minimal composite Higgs models.Comment: 45 pages, 9 figures, 8 tables; v2: updated references, experimental
input now includes data of Moriond 2018, extended discussion of projection to
future colliders; v3: added Appendix, matches Journal versio
Global fits in the Georgi-Machacek model
Off the beaten track of scalar singlet and doublet extensions of the Standard
Model, triplets combine an interesting LHC phenomenology with an explanation
for neutrino masses. The Georgi-Machacek model falls into this category, but it
has never been fully explored in a global fit. We use the {\texttt{HEPfit}}
package to combine recent experimental Higgs data with theoretical constraints
and obtain strong limits on the mixing angles and mass differences between the
heavy new scalars as well as their decay widths. We also find that the current
signal strength measurements allow for a Higgs to vector boson coupling with an
opposite sign to the Standard Model, but this possibility can be ruled out by
the lack of direct evidence for heavy Higgs states. For these hypothetical
particles, we identify the dominant decay channels and extract bounds on their
branching ratios from the global fit, which can be used to single out the decay
patterns relevant for the experimental searches.Comment: 23 pages, 4 figures. In v2: 30 pages, 6 figures. Updated Higgs
experimental data. Global fits updated. Major conclusions unchanged. In v3:
28 pages, 6 figures. Comments on other searches included in summary. Version
accepted for publication in PR
Constraints on coloured scalars from global fits
We consider a simple extension of the electroweak theory, incorporating one
doublet of colour-octet scalars with Yukawa couplings satisfying the
principle of minimal flavour violation. Using the HEPfit package, we perform a
global fit to the available data, including all relevant theoretical
constraints, and extract the current bounds on the model parameters. Coloured
scalars with masses below 1.05 TeV are already excluded, provided they are not
fermiophobic. The mass splittings among the different (charged and CP-even and
CP-odd neutral) scalars are restricted to be smaller than 20 GeV. Moreover, for
scalar masses smaller than 1.5 TeV, the Yukawa coupling of the coloured scalar
multiplet to the top quark cannot exceed the one of the SM Higgs doublet by
more than 80%. These conclusions are quite generic and apply in more general
frameworks (without fine tunings). The theoretical requirements of perturbative
unitarity and vacuum stability enforce relevant constraints on the quartic
scalar potential parameters that are not yet experimentally tested
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