105 research outputs found
Simulating spin-3/2 particles at colliders
Support for interactions of spin-3/2 particles is implemented in the
FeynRules and ALOHA packages and tested with the MadGraph 5 and CalcHEP event
generators in the context of three phenomenological applications. In the first,
we implement a spin-3/2 Majorana gravitino field, as in local supersymmetric
models, and study gravitino and gluino pair-production. In the second, a
spin-3/2 Dirac top-quark excitation, inspired from compositness models, is
implemented. We then investigate both top-quark excitation and top-quark
pair-production. In the third, a general effective operator for a spin-3/2
Dirac quark excitation is implemented, followed by a calculation of the angular
distribution of the s-channel production mechanism.Comment: 20 pages, 7 figure
Higgs Decays in the Low Scale Type I See-Saw Model
The couplings of the low scale type I see-saw model are severely constrained
by the requirement of reproducing the correct neutrino mass and mixing
parameters, by the non-observation of lepton number and charged lepton flavour
violating processes and by electroweak precision data. We show that all these
constraints still allow for the possibility of an exotic Higgs decay channel
into a light neutrino and a heavy neutrino with a sizable branching ratio. We
also estimate the prospects to observe this decay at the LHC and discuss its
complementarity to the indirect probes of the low scale type I see-saw model
from experiments searching for the decay.Comment: 15 pages, 8 figures; references added and results unchanged; matched
with the published version on PL
Sterile neutrino portal to Dark Matter I: the U(1) BâL case
In this paper we explore the possibility that the sterile neutrino and Dark Matter sectors in the Universe have a common origin. We study the consequences of this assumption in the simple case of coupling the dark sector to the Standard Model via a global U(1)BâL, broken down spontaneously by a dark scalar. This dark scalar provides masses to the dark fermions and communicates with the Higgs via a Higgs portal coupling. We find an interesting interplay between Dark Matter annihilation to dark scalars â the CP-even that mixes with the Higgs and the CP-odd which becomes a Goldstone boson, the Majoron â and heavy neutrinos, as well as collider probes via the coupling to the Higgs. Moreover, Dark Matter annihilation into sterile neutrinos and its subsequent decay to gauge bosons and quarks, charged leptons or neutrinos lead to indirect detection signatures which are close to current bounds on the gamma ray flux from the galactic center and dwarf galaxies
Muon conversion to electron in nuclei in type-I seesaw models
We compute the muon to electron conversion in the type-I seesaw model, as a
function of the right-handed neutrino mixings and masses. The results are
compared with previous computations in the literature. We determine the
definite predictions resulting for the ratios between the muon to electron
conversion rate for a given nucleus and the rate of two other processes which
also involve a mu-e flavour transition: mu -> e gamma and mu -> eee. For a
quasi-degenerate mass spectrum of right-handed neutrino masses -which is the
most natural scenario leading to observable rates- those ratios depend only on
the seesaw mass scale, offering a quite interesting testing ground. In the case
of sterile neutrinos heavier than the electroweak scale, these ratios vanish
typically for a mass scale of order a few TeV. Furthermore, the analysis
performed here is also valid down to very light masses. It turns out that
planned mu -> e conversion experiments would be sensitive to masses as low as 2
MeV. Taking into account other experimental constraints, we show that future mu
-> e conversion experiments will be fully relevant to detect or constrain
sterile neutrino scenarios in the 2 GeV-1000 TeV mass range.Comment: 32 pages 14 figures, references added and some minor precisions;
results unchange
The inert Zee model
ABSTRACT: We study a realization of the topology of the Zee model for the generation of neutrino masses at one-loop with a minimal set of vector-like fermions. After imposing an exact Z2 symmetry to avoid tree-level Higgs-mediated avor changing neutral currents, one dark matter candidate is obtained from the subjacent inert doublet model, but with the presence of new co-annihilating particles. We show that the model is consistent with the constraints coming from lepton avor violation processes, oblique parameters, dark matter and neutrino oscillation data
Gravity-mediated (or composite) Dark Matter confronts astrophysical data
We consider the astrophysical bounds on a new form of dark matter, the so called Gravity-mediated Dark Matter. In this scenario, dark matter communicates with us through a mediator sector composed of gravitational resonances, namely a new scalar (radion) and a massive spin-two resonance (massive graviton). We consider specific models motivated by natural electroweak symmetry breaking or weak-scale dark matter in the context of models in warped extra-dimensions and their composite duals. The main Dark Matter annihilation mechanism is due to the interactions of KK gravitons to gauge bosons that propagate in bulk. We impose the bounds on monochromatic or continuum photons from Fermi-LAT and HESS. We also explore scenarios in which the Fermi gamma-ray line could be a manifestation of Gravity-mediated Dark Matter
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