51 research outputs found
Increasing the Higgs mass bound of the MSSM
In the MSSM the Higgs boson mass at tree level cannot exceed the Z boson mass. One could then ask themselves: should we throw away supersymmetry if we do not see the Higgs boson at the LHC? To answer this question it makes
sense to consider extensions of the MSSM in which the Higgs boson can be relatively heavier. We consider three possibile models from a bottom-up point of view
Supersymmetry without a light Higgs boson but with a light pseudoscalar
We consider the lambda-SUSY model, a version of the NMSSM with large lambda
H_1 H_2 S coupling, relaxing the approximation of large singlet mass and
negligible mixing of the scalar singlet with the scalar doublets. We show that
there are regions of the parameter space in which the lightest pseudoscalar can
be relatively light, with unusual consequences on the decay pattern of the
CP-even Higgs bosons and thus on the LHC phenomenology.Comment: 11 pages, 3 figures. v3: Conforms to published versio
Composite fermions in Electroweak Symmetry Breaking
If the electroweak symmetry is broken by some unspecified strong dynamics,
composite fermions may exist with definite transformation properties under
SU(2)_L x SU(2)_R/SU(2)_{L+R} and may play a role in giving masses by mixing to
all the standard quarks and leptons. Assuming this to be the case, we analyze
the role of Singlets, Doublets and Triplets in the ElectroWeak Precision Tests
and in Flavour Physics. Doublets and Triplets are generically disfavoured. In
the Singlet case, we specify the breaking patterns of the flavour group that
allow to keep the CKM picture of flavour physics and we discuss the effects of
the mixing between composite and elementary fermions. These mixings affect in
particular the rather peculiar LHC phenomenology of the composite fermions.Comment: 18 pages, 2 figures (v2: minor modifications, published version
Supersymmetry phenomenology beyond the MSSM after 5/fb of LHC data
We briefly review the status of motivated beyond-the-MSSM phenomenology in
the light of the LHC searches to date. In particular, we discuss the conceptual
consequences of the exclusion bounds, of the hint for a Higgs boson at about
125 GeV, and of interpreting the excess of direct CP violation in the charm
sector as a signal of New Physics. We try to go into the various topics in a
compact way while providing a relatively rich list of references, with
particular attention to the most recent developments.Comment: 20 pages + refs. v2: minor modifications, published versio
Reach the Bottom Line of the Sbottom Search
We propose a new search strategy for directly-produced sbottoms at the LHC
with a small mass splitting between the sbottom and its decayed stable
neutralino. Our search strategy is based on boosting sbottoms through an
energetic initial state radiation jet. In the final state, we require a large
missing transverse energy and one or two b-jets besides the initial state
radiation jet. We also define a few kinematic variables to further increase the
discovery reach. For the case that the sbottom mainly decays into the bottom
quark and the stable neutralino, we have found that even for a mass splitting
as small as 10 GeV sbottoms with masses up to around 400 GeV can be excluded at
the 95% confidence level with 20 inverse femtobarn data at the 8 TeV LHC.Comment: 16 pages, 6 figure
Beyond the Minimal Composite Higgs Model
The Higgs spectrum of the minimal composite Higgs model, based on the
SO(5)/SO(4) coset, consists of a unique Higgs doublet whose phenomenology does
not differ greatly from the Standard Model (SM). Nevertheless, extensions
beyond this minimal coset structure exhibit a richer Higgs spectrum and
therefore very different Higgs physics. We explore one of these extensions, the
SO(6)/SO(5) model, whose Higgs spectrum contains a CP-odd singlet scalar, eta,
in addition to the Higgs doublet. Due to the pseudo-Nambu-Goldstone nature of
these Higgs bosons, their physical properties can be derived from symmetry
considerations alone. We find that the mass of eta can be naturally light,
opening up the possibility that the SM Higgs decays predominantly to the
singlet, and therefore lowering the LEP bound on its mass to 86 GeV. We also
show that eta can have interesting consequences in flavour-violating processes,
as well as induce spontaneous CP-violation in the Higgs sector. The model can
also have anomalies, giving rise to interactions between the SM gauge bosons
and eta which, if measured at the LHC, would give quantitative information
about the structure of the high energy theory.Comment: 13p
Naturalness bounds in extensions of the MSSM without a light Higgs boson
Adopting a bottom-up point of view, we make a comparative study of the
simplest extensions of the MSSM with extra tree level contributions to the
lightest Higgs boson mass. We show to what extent a relatively heavy Higgs
boson, up to 200-350 GeV, can be compatible with data and naturalness. The
price to pay is that the theory undergoes some change of regime at a relatively
low scale. Bounds on these models come from electroweak precision tests and
naturalness, which often requires the scale at which the soft terms are
generated to be relatively low.Comment: 18 pages, 5 figures. v2: minor revision, added references. v3,v4:
some numerical correction
Radiation from a D-dimensional collision of shock waves: first order perturbation theory
We study the spacetime obtained by superimposing two equal Aichelburg-Sexl
shock waves in D dimensions traveling, head-on, in opposite directions.
Considering the collision in a boosted frame, one shock becomes stronger than
the other, and a perturbative framework to compute the metric in the future of
the collision is setup. The geometry is given, in first order perturbation
theory, as an integral solution, in terms of initial data on the null surface
where the strong shock has support. We then extract the radiation emitted in
the collision by using a D-dimensional generalisation of the Landau-Lifschitz
pseudo-tensor and compute the percentage of the initial centre of mass energy
epsilon emitted as gravitational waves. In D=4 we find epsilon=25.0%, in
agreement with the result of D'Eath and Payne. As D increases, this percentage
increases monotonically, reaching 40.0% in D=10. Our result is always within
the bound obtained from apparent horizons by Penrose, in D=4, yielding 29.3%,
and Eardley and Giddings, in D> 4, which also increases monotonically with
dimension, reaching 41.2% in D=10. We also present the wave forms and provide a
physical interpretation for the observed peaks, in terms of the null generators
of the shocks.Comment: 27 pages, 11 figures; v2 some corrections, including D dependent
factor in epsilon; matches version accepted in JHE
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