37 research outputs found
(SUSY) Higgs Search at the LHC
The discovery of the Standard Model (SM) or supersymmetric (SUSY) Higgs
bosons belongs to the main endeavors of the Large Hadron Collider (LHC). In
this article the status of the signal and background calculations for Higgs
boson production at the LHC is reviewed.Comment: 6 pages, 4 figures, plenary talk given at SUSY08, Seoul, Kore
Vector-like Bottom Quarks in Composite Higgs Models
Like many other models, Composite Higgs Models feature the existence of heavy
vector-like quarks. Mixing effects between the Standard Model fields and the
heavy states, which can be quite large in case of the top quark, imply
deviations from the SM. In this work we investigate the possibility of heavy
bottom partners. We show that they can have a significant impact on electroweak
precision observables and the current Higgs results if there is a sizeable
mixing with the bottom quark. We explicitly check that the constraints from the
measurement of the CKM matrix element are fulfilled, and we test the
compatibility with the electroweak precision observables. In particular we
evaluate the constraint from the coupling to left-handed bottom quarks.
General formulae have been derived which include the effects of new bottom
partners in the loop corrections to this coupling and which can be applied to
other models with similar particle content. Furthermore, the constraints from
direct searches for heavy states at the LHC and from the Higgs search results
have been included in our analysis. The best agreement with all the considered
constraints is achieved for medium to large compositeness of the left-handed
top and bottom quarks.Comment: additional figures, extended discussion of numerical result
NLO QCD Corrections to Higgs Pair Production including Dimension-6 Operators
New Physics that becomes relevant at some high scale beyond the
experimental reach, can be described in the effective theory approach by adding
higher-dimensional operators to the Standard Model (SM) Lagrangian. In Higgs
pair production through gluon fusion, which gives access to the trilinear Higgs
self-coupling, this leads not only to modifications of the SM couplings but
also induces novel couplings not present in the SM. For a proper prediction of
the cross section, higher order QCD corrections that are important for this
process, have to be taken into account. The various higher-dimensional
contributions are affected differently by the QCD corrections. In this paper,
we provide the next-to-leading order (NLO) QCD corrections to Higgs pair
production including dimension-6 operators in the limit of large top quark
masses. Depending on the dimension-6 coefficients entering the Lagrangian, the
new operators affect the relative NLO QCD corrections by several per cent,
while modifying the cross section by up to an order of magnitude.Comment: 14 pages, 6 figure
Natural NMSSM Higgs Bosons
We study the phenomenology of Higgs bosons close to 126 GeV within the scale
invariant unconstrained next-to-minimal supersymmetric Standard Model (NMSSM),
focusing on the regions of parameter space favoured by low fine-tuning
considerations, namely stop masses of order 400 GeV to 1 TeV and an effective
parameter between 100-200 GeV, with large (but perturbative)
and low 2-4. We perform scans over the above parameter space,
focusing on the observable Higgs cross sections into , ,
, , final states, and study the correlations between these
observables. We show that the signal strength may be enhanced
up to a factor of about two not only due to the effect of singlet-doublet
mixing, which occurs more often when the 126 GeV Higgs boson is the
next-to-lightest CP-even one, but also due to light stops (and to a lesser
extent light chargino and charged Higgs loops). There may be also smaller
enhancements in the Higgs decay channels into , , correlated with the
enhancement. However there is no such correlation observed
involving the Higgs decay channels into , . The requirement of
having perturbative couplings up to the GUT scale favours the interpretation of
the 126 GeV Higgs boson as being the second lightest NMSSM CP-even state, which
can decay into pairs of lighter neutralinos, CP-even or CP-odd Higgs bosons,
leading to characteristic signatures of the NMSSM. In a non-negligible part of
the parameter range the increase in the rate is due to the
superposition of rates from nearly degenerate Higgs bosons. Resolving these
Higgs bosons would rule out the Standard Model, and provide evidence for the
NMSSM
Gauge-independent Renormalization of the N2HDM
The Next-to-Minimal 2-Higgs-Doublet Model (N2HDM) is an interesting benchmark
model for a Higgs sector consisting of two complex doublet and one real singlet
fields. Like the Next-to-Minimal Supersymmetric extension (NMSSM) it features
light Higgs bosons that could have escaped discovery due to their singlet
admixture. Thereby, the model allows for various different Higgs-to-Higgs decay
modes. Contrary to the NMSSM, however, the model is not subject to
supersymmetric relations restraining its allowed parameter space and its
phenomenology. For the correct determination of the allowed parameter space,
the correct interpretation of the LHC Higgs data and the possible distinction
of beyond-the-Standard Model Higgs sectors higher order corrections to the
Higgs boson observables are crucial. This requires not only their computation
but also the development of a suitable renormalization scheme. In this paper we
have worked out the renormalization of the complete N2HDM and provide a scheme
for the gauge-independent renormalization of the mixing angles. We discuss the
renormalization of the soft breaking parameter and
the singlet vacuum expectation value . Both enter the Higgs self-couplings
relevant for Higgs-to-Higgs decays. We apply our renormalization scheme to
different sample processes such as Higgs decays into bosons and decays into
a lighter Higgs pair. Our results show that the corrections may be sizeable and
have to be taken into account for reliable predictions