14 research outputs found
Dirac Gauginos in Low Scale Supersymmetry Breaking
It has been claimed that Dirac gaugino masses are necessary for realistic
models of low-scale supersymmetry breaking, and yet very little attention has
been paid to the phenomenology of a light gravitino when gauginos have Dirac
masses. We begin to address this deficit by investigating the couplings and
phenomenology of the gravitino in the effective Lagrangian approach. We pay
particular attention to the phenomenology of the scalar octets, where new decay
channels open up. This leads us to propose a new simplified effective scenario
including only light gluinos, sgluons and gravitinos, allowing the squarks to
be heavy -- with the possible exception of the third generation. Finally, we
comment on the application of our results to Fake Split Supersymmetry.Comment: 40 pages, 3 figures. Minor typos fixed; matches version in Nuclear
Physics
Aspects of Effective Supersymmetric Theories
This work consists of two parts. In the first part we construct the complete
extension of the Minimal Supersymmetric Standard Model by higher dimensional
effective operators and study its phenomenology. These operators encapsulate
the effects on LHC physics of possible new degrees of freedom at the multiTeV
scale. The effective analysis includes the case where the multiTeV physics is
the supersymmetry breaking sector itself. Beyond the new effective couplings,
the analysis suggests an interpretation of the 'little hierarchy problem' as an
indication of new physics at multiTeV scale. In the second part we explore the
power of constrained superfields in extended supersymmetry. It is known that in
N = 2 supersymmetry the gauge kinetic function cannot depend on hypermultiplet
scalars. However, it is also known that the low energy effective action of a
D-brane in an N = 2 supersymmetric bulk includes the DBI action, where the
gauge kinetic function does depend on the dilaton. We show how the
nonlinearization of the second SUSY (imposed by the presence of the D-brane)
opens this possibility, by constructing the global N = 1 linear + 1 nonlinear
invariant coupling of a hypermultiplet with a gauge multiplet. The constructed
theory enjoys interesting features, including a novel super-Higgs mechanism
without gravity.Comment: Ph.D. thesis. Advisor: Prof. Ignatios Antoniadis. 236 pages, 9
figure
Low Scale Supersymmetry Breaking and its LHC Signatures
We study the most general extension of the MSSM Lagrangian that includes
scenarios in which supersymmetry is spontaneously broken at a low scale f. The
spurion that parametrizes supersymmetry breaking in the MSSM is promoted to a
dynamical superfield involving the goldstino, with (and without) its scalar
superpartner, the sgoldstino. The low energy effective Lagrangian is written as
an expansion in terms of m_{SUSY}/sqrt{f}, where m_{SUSY} is the induced
supersymmetry breaking scale, and contains, in addition to the usual MSSM
Lagrangian with the soft terms, couplings involving the component fields of the
goldstino superfield and the MSSM fields. This Lagrangian can provide
significant corrections to the usual couplings in the Standard Model and the
MSSM. We study how these new corrections affect the Higgs couplings to gauge
bosons and fermions, and how LHC bounds can be used in order to constrain f. We
also discuss that, from the effective field theory point of view, the couplings
of the goldstino interactions are not determined by any symmetry, and their
usual simple relation to the soft terms is corrected by higher-dimensional
operators.Comment: 46 pages, 3 figure
Flavour models with Dirac and fake gluinos
International audienceIn the context of supersymmetric models where the gauginos may have both Majorana and Dirac masses we investigate the general constraints from flavour-changing processes on the scalar mass matrices. One finds that the chirality-flip suppression of flavour-changing effects usually invoked in the pure Dirac case holds in the mass insertion approximation but not in the general case, and fails in particular for inverted hierarchy models. We quantify the constraints in several flavour models which correlate fermion and scalar superpartner masses. We also discuss the limit of very large Majorana gaugino masses compared to the chiral adjoint and Dirac masses, where the remaining light eigenstate is the " fake " gaugino, including the consequences of suppressed couplings to quarks beyond flavour constraints
Signatures of top flavour-changing dark matter
We develop the phenomenology of scenarios in which a dark matter candidate
interacts with a top quark through flavour-changing couplings, employing a
simplified dark matter model with an s-channel vector-like mediator. We study
in detail the top-charm flavour-changing interaction, by investigating the
single top plus large missing energy signature at the LHC as well as
constraints from the relic density and direct and indirect dark matter
detection experiments. We present strategies to distinguish between the
top-charm and top-up flavour-changing models by taking advantage of the lepton
charge asymmetry as well as by using charm-tagging techniques on an extra jet.
We also show the complementarity between the LHC and canonical dark matter
experiments in exploring the viable parameter space of the models.Comment: 40 pages, 9 figures, 6 table
Two-Dimensional Euler Equations in a Time Dependent Domain
We provide a unified presentation of extensions of the Minimal Dark Matter framework in which new fermionic electroweak multiplets are coupled to each other via the Standard Model Higgs doublet. We study systematically the generic features of all the possibilities, starting with a singlet and two doublets (akin to Bino-Higgsino dark matter) up to a Majorana quintuplet coupled to two Weyl quadruplets. We pay special attention to this last case, since it has not yet been discussed in the literature. We estimate the parameter space for viable dark matter candidates. This includes an estimate for the mass of a quasi-pure quadruplet dark matter candidate taking into account the Sommerfeld effect. We also argue how the coupling to the Higgs can bring the Minimal Dark Matter scenario within the reach of present and future direct detection experiments.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
The Hypermultiplet with Heisenberg Isometry in N=2 Global and Local Supersymmetry
The string coupling of N=2 supersymmetric compactifications of type II string
theory on a Calabi-Yau manifold belongs to the so-called universal dilaton
hypermultiplet, that has four real scalars living on a quaternion-Kaehler
manifold. Requiring Heisenberg symmetry, which is a maximal subgroup of
perturbative isometries, reduces the possible manifolds to a one-parameter
family that describes the tree-level effective action deformed by the only
possible perturbative correction arising at one-loop level. A similar argument
can be made at the level of global supersymmetry where the scalar manifold is
hyper-Kaehler. In this work, the connection between global and local
supersymmetry is explicitly constructed, providing a non-trivial gravity
decoupled limit of type II strings already in perturbation theory.Comment: 24 page
Singlet-Doublet model: dark matter searches and LHC constraints
Abstract: The Singlet-Doublet model of dark matter is a minimal extension of the Standard Model with dark matter that is a mixture of a singlet and a non-chiral pair of electroweak doublet fermions. The stability of dark matter is ensured by the typical parity symmetry, and, similar to a âBino-Higgsinoâ system, the extra matter content improves gauge coupling unification. We revisit the experimental constraints on the Singlet-Doublet dark matter model, combining the most relevant bounds from direct (spin independent and spin dependent) and indirect searches. We show that such comprehensive analysis sets strong constraints on a large part of the 4-dimensional parameter space, closing the notorious âblind-spotsâ of spin independent direct searches. Our results emphasise the complementarity of direct and indirect searches in probing dark matter models in diverse mass scale regimes. We also discuss the LHC bounds on such scenario, which play a relevant role in the low mass region of the dark matter candidate.SCOPUS: ar.jinfo:eu-repo/semantics/publishe