180 research outputs found
Higgs Sector in Extensions of the MSSM
Extensions of the Minimal Supersymmetric Standard Model (MSSM) with
additional singlet scalar fields solve the important mu-parameter fine tuning
problem of the MSSM. We compute and compare the neutral Higgs boson mass
spectra, including one-loop corrections, of the following MSSM extensions:
Next-to-Minimal Supersymmetric Standard Model (NMSSM), the nearly-Minimal
Supersymmetric Standard Model (nMSSM), and the U(1)'-extended Minimal
Supersymmetric Standard Model (UMSSM) by performing scans over model
parameters. We find that the Secluded U(1)'-extended Minimal Supersymmetric
Standard Model (sMSSM) is identical to the nMSSM if three of the additional
scalars decouple. The dominant part of the one-loop corrections are
model-independent since the singlet field does not couple to MSSM particles
other than the Higgs doublets. Thus, model-dependent parameters enter the
masses only at tree-level. We apply constraints from LEP bounds on the Standard
Model and MSSM Higgs boson masses and the MSSM chargino mass, the invisible Z
decay width, and the Z-Z' mixing angle. Some extended models permit a Higgs
boson with mass substantially below the SM LEP limit or above theoretical
limits in the MSSM. Ways to differentiate the models via masses, couplings,
decays and production of the Higgs bosons are discussed.Comment: 65 pages, 15 figures. Figure replaced and typos corrected. Version to
appear in Phys. Rev.
Higgsino Dark Matter in a SUGRA Model with Nonuniversal Gaugino Masses
We study a specific SUGRA model with nonuniversal gaugino masses as an
alternative to the minimal SUGRA model in the context of supersymmetric dark
matter. The lightest supersymmetric particle in this model comes out to be a
Higgsino dominated instead of a bino dominated lightest neutralino. The thermal
relic density of this Higgsino dark matter is somewhat lower than the
cosmologically favoured range, which means it may be only a subdominant
component of the cold dark matter. Nonetheless, it predicts favourable rates of
indirect detection, which can be seen in square-km size neutrino telescopes.Comment: Version to appear in Phys. Rev. D. A few references added in the
bibliography and a comment added in Section 2. LaTex, 16 pages, 4 figure
Higgs as a pseudo-Goldstone boson, the mu problem and gauge-mediated supersymmetry breaking
We study the interplay between the spontaneous breaking of a global symmetry
of the Higgs sector and gauge-mediated supersymmetry breaking, in the framework
of a supersymmetric model with global SU(3) symmetry. In addition to solving
the supersymmetric flavour problem and alleviating the little hierarchy
problem, this scenario automatically triggers the breaking of the global
symmetry and provides an elegant solution to the mu/Bmu problem of gauge
mediation. We study in detail the processes of global symmetry and electroweak
symmetry breaking, including the contributions of the top/stop and gauge-Higgs
sectors to the one-loop effective potential of the pseudo-Goldstone Higgs
boson. While the joint effect of supersymmetry and of the global symmetry
allows in principle the electroweak symmetry to be broken with little
fine-tuning, the simplest version of the model fails to bring the Higgs mass
above the LEP bound due to a suppressed tree-level quartic coupling. To cure
this problem, we consider the possibility of additional SU(3)-breaking
contributions to the Higgs potential, which results in a moderate fine-tuning.
The model predicts a rather low messenger scale, a small tan beta value, a
light Higgs boson with Standard Model-like properties, and heavy higgsinos.Comment: 19 pages, 6 figures. New section 3.3 on the mu/Bmu problem, more
detailed analytic computation in section 4.1, error in Fig. 5 corrected,
significant redactional changes (including abstract, introduction and
conclusion) in order to better emphasize the main results of the paper. Title
changed in journal. Final version to appear in Eur. Phys. J.
Natural Islands for a 125 GeV Higgs in the scale-invariant NMSSM
We study whether a 125 GeV standard model-like Higgs boson can be
accommodated within the scale-invariant NMSSM in a way that is natural in all
respects, i.e., not only is the stop mass and hence its loop contribution to
Higgs mass of natural size, but we do not allow significant tuning of NMSSM
parameters as well. We pursue as much as possible an analytic approach which
gives clear insights on various ways to accommodate such a Higgs mass, while
conducting complementary numerical analyses. We consider both scenarios with
singlet-like state being heavier and lighter than SM-like Higgs. With A-terms
being small, we find for the NMSSM to be perturbative up to GUT scale, it is
not possible to get 125 GeV Higgs mass, which is true even if we tune
parameters of NMSSM. If we allow some of the couplings to become
non-perturbative below the GUT scale, then the non-tuned option implies that
the singlet self-coupling, kappa, is larger than the singlet-Higgs coupling,
lambda, which itself is order 1. This leads to a Landau pole for these
couplings close to the weak scale, in particular below ~10^4 TeV. In both the
perturbative and non-perturbative NMSSM, allowing large A_lambda, A_kappa gives
"more room" to accommodate a 125 GeV Higgs, but a tuning of these A-terms may
be needed. In our analysis we also conduct a careful study of the constraints
on the parameter space from requiring global stability of the desired vacuum
fitting a 125 GeV Higgs, which is complementary to existing literature. In
particular, as the singlet-Higgs coupling lambda increases, vacuum stability
becomes more serious of an issue.Comment: 34 pages, 4 figures, references added, minor corrections to text and
figures, version to be published in JHE
Effective Two Higgs Doublets in Nonminimal Supersymmetric Models
The Higgs sectors of supersymmetric extensions of the Standard Model have two
doublets in the minimal version (MSSM), and two doublets plus a singlet in two
others: with (UMSSM) and without (NMSSM) an extra U(1)'. A very concise
comparison of these three models is possible if we assume that the singlet has
a somewhat larger breaking scale compared to the electroweak scale. In that
case, the UMSSM and the NMSSM become effectively two-Higgs-doublet models
(THDM), like the MSSM. As expected, the mass of the lightest CP-even neutral
Higgs boson has an upper bound in each case. We find that in the NMSSM, this
bound exceeds not very much that of the MSSM, unless tan(beta) is near one.
However, the upper bound in the UMSSM may be substantially enhanced.Comment: 8 pages, 1 table, 3 figure
Dijet signals of the Little Higgs model with T-parity
The Littest Higgs model with T-parity (LHT), apart from offering a viable
solution to the naturalness problem of the Standard Model, also predicts a set
of new fermions as well as a candidate for dark matter. We explore the
possibility of discovering the heavy T-odd quark Q_H at the LHC in a final
state comprising two hard jets with a large missing transverse momentum. Also
discussed is the role of heavy flavor tagging.Comment: Changes in text. Some references adde
Requirements on collider data to match the precision of WMAP on supersymmetric dark matter
If future colliders discover supersymmetric particles and probe their
properties, one could predict the dark matter density of the Universe and would
constrain cosmology with the help of precision data provided by WMAP and
PLANCK.
We investigate how well the relic density can be predicted in minimal
supergravity (mSUGRA), with and without the assumption of mSUGRA when analysing
data. We determine the parameters to which the relic density is most sensitive,
and quantify the collider accuracy needed. Theoretical errors in the prediction
are investigated in some detail.Comment: 42 pages, 16 figures. v2 incorporates referee's comments: minor
corrections/clarifications with additional figures to show regions of m12-m0
plane considere
Solving the mu problem with a heavy Higgs boson
We discuss the generation of the mu-term in a class of supersymmetric models
characterized by a low energy effective superpotential containing a term lambda
S H_1 H_2 with a large coupling lambda~2. These models generically predict a
lightest Higgs boson well above the LEP limit of 114 GeV and have been shown to
be compatible with the unification of gauge couplings. Here we discuss a
specific example where the superpotential has no dimensionful parameters and we
point out the relation between the generated mu-term and the mass of the
lightest Higgs boson. We discuss the fine-tuning of the model and we find that
the generation of a phenomenologically viable mu-term fits very well with a
heavy lightest Higgs boson and a low degree of fine-tuning. We discuss
experimental constraints from collider direct searches, precision data, thermal
relic dark matter abundance, and WIMP searches finding that the most natural
region of the parameter space is still allowed by current experiments. We
analyse bounds on the masses of the superpartners coming from Naturalness
arguments and discuss the main signatures of the model for the LHC and future
WIMP searches.Comment: Extended discussion of the LHC phenomenology, as published on JHEP
plus an addendum on the existence of further extremal points of the
potential. 47 pages, 16 figure
Charged Higgs bosons in the Next-to MSSM (NMSSM)
The charged Higgs boson decays and
are studied in the framework of the next-to Minimal Supersymmetric Standard
Model (NMSSM). It is found that the decay rate for can
exceed the rates for the and channels both below and above
the top-bottom threshold. The dominance of is most readily
achieved when has a large doublet component and small mass. We also study
the production process at the LHC followed by the decay
which leads to the signature . We suggest
that is a promising discovery channel for a light charged
Higgs boson in the NMSSM with small or moderate and dominant decay
mode . This signature can also arise from
the Higgsstrahlung process followed by the decay . It is shown that there exist regions of parameter space where these
processes can have comparable cross sections and we suggest that their
respective signals can be distinguished at the LHC by using appropriate
reconstruction methods.Comment: 20 pages, 22 eps figures, more reference adde
Higgs and non-universal gaugino masses: no SUSY signal expected yet?
So far, no supersymmetric particles have been detected at the Large Hadron
Collider (LHC). However, the recent Higgs results have interesting implications
for the SUSY parameter space. In this paper, we study the consequences of an
LHC Higgs signal for a model with non-universal gaugino masses in the context
of SU(5) unification. The gaugino mass ratios associated with the higher
representations produce viable spectra that are largely inaccessible to the
current LHC and direct dark matter detection experiments. Thus, in light of the
Higgs results, the non-observation of SUSY is no surprise.Comment: supplementary file containing plots with log priors in ancillary
files. v2: added some comments on more general settings and references,
accepted for publication in JHE
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