38 research outputs found
Top-Quark Phenomenology in Models with Bilinearly and Spontaneously Broken R-parity
We study unconventional decays of the top-quark in the framework of SUSY
models with spontaneously broken R-parity. In particular we discuss an
effective theory which consists of the MSSM plus bilinearly broken R-parity. We
demonstrate that the decay modes t -> stau + b and t -> tau + sbottom can have
large branching ratios even in scenarios where the tau-neutrino mass is very
small. We show that existing Tevatron data already probe the theoretical
parameters, with promising prospects for further improvement at the Run 2 of
the Tevatron.Comment: 12 pages, 6 eps-figure
Tau Lepton Mixing with Charginos and its Effects on Chargino Searches at e+e- Colliders
In bilinear R-Parity violating models where a term \epsilon_3L_3H_2 is
introduced in the superpotential, the tau lepton can mix with charginos. We
show that this mixing is fully compatible with LEP1 precision measurements of
the Z\tau\tau and W\tau\nu_\tau couplings even for large values of \epsilon_3
and of the induced vacuum expectation value v_3 of the tau-sneutrino. The
single production of charginos at e+e- colliders is possible in this case and
we present numerical values of the cross-section at LEP1, LEP2 and an NLC. We
find maximum values of 10 pb at LEP1 and 1 fb at NLC, while the corresponding
values at LEP2 are too small to observe.Comment: 16 pages (including 7 figures), LaTex, uses axodraw.sty (included
Minimalistic Neutrino Mass Model
We consider the simplest model which solves the solar and atmospheric
neutrino puzzles, in the sense that it contains the smallest amount of beyond
the Standard Model ingredients. The solar neutrino data is accounted for by
Planck-mass effects while the atmospheric neutrino anomaly is due to the
existence of a single right-handed neutrino at an intermediate mass scale
between 10^9 GeV and 10^14 GeV. Even though the neutrino mixing angles are not
exactly predicted, they can be naturally large, which agrees well with the
current experimental situation. Furthermore, the amount of lepton asymmetry
produced in the early universe by the decay of the right-handed neutrino is
very predictive and may be enough to explain the current baryon-to-photon ratio
if the right-handed neutrinos are produced out of thermal equilibrium. One
definitive test for the model is the search for anomalous seasonal effects at
Borexino.Comment: 19 pages, 3 figures, references added, results unchange
Geotomography with solar and supernova neutrinos
We show how by studying the Earth matter effect on oscillations of solar and
supernova neutrinos inside the Earth one can in principle reconstruct the
electron number density profile of the Earth. A direct inversion of the
oscillation problem is possible due to the existence of a very simple analytic
formula for the Earth matter effect on oscillations of solar and supernova
neutrinos. From the point of view of the Earth tomography, these oscillations
have a number of advantages over the oscillations of the accelerator or
atmospheric neutrinos, which stem from the fact that solar and supernova
neutrinos are coming to the Earth as mass eigenstates rather than flavour
eigenstates. In particular, this allows reconstruction of density profiles even
over relatively short neutrino path lengths in the Earth, and also of
asymmetric profiles. We study the requirements that future experiments must
meet to achieve a given accuracy of the tomography of the Earth.Comment: 35 pages, 7 figures; minor textual changes in section
CP Violation and Neutrino Oscillations
We review the basic mechanisms of neutrino mass generation and the
corresponding structure of the lepton mixing matrix. We summarize the status of
three-neutrino oscillation parameters as determined from current observations,
using state-of-the-art solar and atmospheric neutrino fluxes, as well as latest
experimental data as of September 2007. We also comment on recent attempts to
account for these results and to understand flavour from first principles. We
discuss extensively the prospects for probing the strength of CP violation in
two near term accelerator neutrino oscillation experiments, T2K and NOvA, as
well as possible extensions such as T2KK and a second large off-axis detector
near the NOvA detector. We also briefly discuss the possibility of probing the
effect of Majorana phases in future neutrinoless double beta decay searches and
discuss other implications of leptonic CP violation such as leptogenesis.
Finally we comment on the issue of robustness of the current oscillation
interpretation and possible ways of probing for non-standard neutrino
interactions in precision oscillation studies.Comment: 78 pages, 46 figures, minor misprint corrections, a few new
references and an acknowledgement to a funding agency. Review to be published
in Prog. Part. Nucl. Phy
Testing a lepton quarticity flavor theory of neutrino oscillations with the DUNE experiment
Oscillation studies play a central role in elucidating at least some aspects of the flavor problem. Here we examine the status of the predictions of a lepton quarticity flavor theory of neutrino oscillations against the existing global sample of oscillation data. By performing quantitative simulations we also determine the potential of the upcoming DUNE experiment in narrowing down the currently ill-measured oscillation parameters θ23 and δCP. We present the expected improved sensitivity on these parameters for different assumptions
Are the B decay anomalies related to neutrino oscillations?
Neutrino oscillations are solidly established, with a hint of CP violation just emerging. Similarly, there are hints of lepton universality violation in b→sb→s transitions at the level of 2.6σ. By assuming that the unitary transformation between weak and mass charged leptons equals the leptonic mixing matrix measured in neutrino oscillation experiments, we predict several lepton flavor violating (LFV) B meson decays. We are led to the tantalizing possibility that some LFV branching ratios for B decays correlate with the leptonic CP phase δ characterizing neutrino oscillations. Moreover, we also consider implications for ℓi→ℓjℓkℓkℓi→ℓjℓkℓk decays
Scotogenic dark matter and Dirac neutrinos from unbroken gauged symmetry
We propose a simple extension of the standard model where neutrinos get
naturally small "scotogenic" Dirac masses from an unbroken gauged
symmetry, ensuring dark matter stability. The associated gauge boson gets mass
through the Stueckelberg mechanism. Two scenarios are identified, and the
resulting phenomenology briefly sketched.Comment: 9 pages, 3 tables, 1 figur
Two-Body Decays of the Lightest Stop in Supergravity with and without R-Parity
We study the decays of the lightest top squark in supergravity models with
and without R-parity. Using the simplest model with an effective explicit
bilinear breaking of R-parity and radiative electroweak symmetry breaking we
show that, below the threshold for decays into charginos , the lightest stop decays mainly into third generation fermions,
instead of the R-parity conserving mode , even for tiny tau--neutrino mass values. Moreover we show that,
even above the threshold for decays into charginos, the decay may be dominant. We study the role played by the universality of the
boundary conditions on the soft supersymmetry breaking terms. This new decay
mode as well as the cascades originated by the
conventional decay followed by the R-parity violating
neutralino decays can provide new signatures for stop production at LEP and the
Tevatron.Comment: Latex, 27 pages, including 11 figures. Version to be published in
Nucl. Phys.