10 research outputs found
A light neutralino in hybrid models of supersymmetry breaking
We show that in gauge mediation models where heavy messenger masses are
provided by the adjoint Higgs field of an underlying SU(5) theory, a
generalized gauge mediation spectrum arises with the characteristic feature of
having a neutralino LSP much lighter than in the standard gauge or gravity
mediation schemes. This naturally fits in a hybrid scenario where gravity
mediation, while subdominant with respect to gauge mediation, provides mu and
Bmu parameters of the appropriate size for electroweak symmetry breaking.Comment: 32 pages. v2: revised discussions of the generation of Bmu and of the
dark matter constraint; numerous small redactional changes; remarks and
references adde
Flavour violation in supersymmetric SO(10) unification with a type II seesaw mechanism
We study flavour violation in a supersymmetric SO(10) implementation of the
type II seesaw mechanism, which provides a predictive realization of triplet
leptogenesis. The experimental upper bounds on lepton flavour violating
processes have a significant impact on the leptogenesis dynamics, in particular
they exclude the strong washout regime. Requiring successful leptogenesis then
constrains the otherwise largely unknown overall size of flavour-violating
observables, thus yielding testable predictions. In particular, the branching
ratio for mu -> e gamma lies within the reach of the MEG experiment if the
superpartner spectrum is accessible at the LHC, and the supersymmetric
contribution to epsilon_K can account for a significant part of the
experimental value. We show that this scenario can be realized in a consistent
SO(10) model achieving gauge symmetry breaking and doublet-triplet splitting in
agreement with the proton decay bounds, improving on the MSSM prediction for
alpha_3(m_Z), and reproducing the measured quark and lepton masses.Comment: 40 pages, 10 figures. Accepted for publication in JHE
A Comment on Self-Tuning and Vanishing Cosmological Constant in the Brane World
In this note we elaborate on various five dimensional contributions to the
effective 4D cosmological constant in brane systems. In solutions with
vanishing 5D cosmological constant we describe a non-local mechanism of
cancellation of vacuum energy between the brane and the singularities. We
comment on a hidden fine tuning which is implied by this observation.Comment: 7 pages, Latex, final version to appear in Phys. Lett.
A light neutralino in hybrid models of supersymmetry breaking
We show that in gauge mediation models where heavy messenger masses are
provided by the adjoint Higgs field of an underlying SU(5) theory, a
generalized gauge mediation spectrum arises with the characteristic feature of
having a neutralino LSP much lighter than in the standard gauge or gravity
mediation schemes. This naturally fits in a hybrid scenario where gravity
mediation, while subdominant with respect to gauge mediation, provides mu and
Bmu parameters of the appropriate size for electroweak symmetry breaking.Comment: 32 pages. v2: revised discussions of the generation of Bmu and of the
dark matter constraint; numerous small redactional changes; remarks and
references adde
Quark flavour conserving violations of the lepton number
We study supersymmetric models of lepton and baryon number violation based on an abelian family gauge group. Due to possible lepton-Higgs mixing, the lepton violating couplings are related to the Yukawa couplings and may be generated by them even if they were absent in the original theory. Such terms may be dominant and are not given by the naive family charge counting rules. This enhancement mechanism can provide an alignment between lepton-number violating terms and Yukawa couplings: as a result they conserve quark flavour. A natural way of suppressing baryon number violation in this class of models is also proposed
A light neutralino in hybrid models of supersymmetry breaking
29 pagesWe show that in gauge mediation models where heavy messenger masses are provided by the adjoint Higgs field of an underlying SU(5) theory, a generalized gauge mediation spectrum arises with the characteristic feature of having a neutralino much lighter than in the standard gauge or gravity mediation schemes. This naturally fits in a hybrid scenario where gravity mediation, while subdominant with respect to gauge mediation, provides mu and B mu parameters in the TeV range
On messengers and metastability in gauge mediation
18 pagesOne notoriously difficult problem in perturbative gauge mediation of supersymmetry breaking via messenger fields is the generic presence of a phenomenologically unacceptable vacuum with messenger vevs, with a lower energy than the desired (MSSM) vacuum. We investigate the possibility that quantum corrections promote the latter to the ground state of the theory, and find that this is indeed feasible. For this to happen, the couplings of the messengers to the goldstino superfield must be small, and this implies an additional suppression of the MSSM soft terms with respect to the supersymmetry breaking scale. This in turns sets a lower limit on the masses of the messengers and of the supersymmetry breaking fields, which makes both sectors inaccessible at colliders. Contrary to other scenarios like direct gauge mediation, gaugino masses are unsuppressed with respect to scalar masses
Challenging the minimal supersymmetric SU(5) model
8 pages, 2 figures, plenary talk presented by B.B. at the VIIth International Conference on Interconnections between Particle Physics and Cosmology PPC13, Deadwood, South Dakota, July 8-13, 2013. To be published in the ProceedingsWe review the main constraints on the parameter space of the minimal renormalizable supersymmetric SU(5) grand unified theory. They consist of the Higgs mass, proton decay, electroweak symmetry breaking and fermion masses. Superpartner masses are constrained both from below and from above, giving hope for confirming or definitely ruling out the theory in the future. This contribution is based on Ref. [1]
A new, direct link between the baryon asymmetry and neutrino masses
We point out that, in a class of SO(10) models with matter fields in 16 and 10 representations and type II realization of the seesaw mechanism, the light neutrino masses and the CP asymmetry needed for leptogenesis are controlled by one and the same set of couplings. The generated baryon asymmetry then directly depends on the low-energy neutrino parameters, with no unknown seesaw-scale flavour parameters involved/ in particular, the necessary CP violation is provided by the CP-violating phases of the lepton mixing matrix. We compute the CP asymmetry in triplet decays for this scenario and show that it can lead to successful leptogenesis