684 research outputs found
Charged lepton contributions to the solar neutrino mixing and theta_13
A charged lepton contribution to the solar neutrino mixing induces a
contribution to theta_13, barring cancellations/correlations, which is
independent of the model building options in the neutrino sector. We illustrate
two robust arguments for that contribution to be within the expected
sensitivity of high intensity neutrino beam experiments. We find that the case
in which the neutrino sector gives rise to a maximal solar angle (the natural
situation if the hierarchy is inverse) leads to a theta_13 close to or
exceeding the experimental bound depending on the precise values of theta_12,
theta_23, an unknown phase and possible additional contributions. We finally
discuss the possibility that the solar angle originates predominantly in the
charged lepton sector. We find that the construction of a model of this sort is
more complicated. We comment on a recent example of natural model of this type.Comment: 10 pages, 1 figur
Bi-Maximal Neutrino Mixing in the MSSM with a Single Right-Handed Neutrino
We discuss neutrino masses in the framework of a minimal extension of the
minimal supersymmetric standard model (MSSM) consisting of an additional single
right-handed neutrino superfield with a heavy Majorana mass , which
induces a single light see-saw mass leaving two neutrinos massless
at tree-level. This trivial extension to the MSSM may account for the
atomospheric neutrino data via oscillations by
assuming a near maximal mixing angle and taking . In order to account for
the solar neutrino data we appeal to one-loop radiative corrections involving
internal loops of SUSY particles, which we show can naturally generate an
additional light neutrino mass again with near
maximal mixing angle . The resulting scheme corresponds
to so-called ``bi-maximal'' neutrino mixing involving ``just-so'' solar
oscillations.Comment: 18 pages, Latex. References to bi-maximal mixing fixe
Low Scale Technicolour at LEP
We discuss the phenomenology of an technicolour model with a low
technicolour confinement scale . Such a low
technicolour scale may give rise to the first hints of technicolour being seen
at LEPI and spectacular technicolour signals at LEPII.Comment: 12 pages+1 figure (available by post), Latex, SHEP92/93-2
Quark and Lepton Mass Patterns and the Absolute Neutrino Mass Scale
We investigate what could be learned about the absolute scale of neutrino
masses from comparisons among the patterns within quark and lepton mass
hierarchies. First, we observe that the existing information on neutrino masses
fits quite well to the unexplained, but apparently present regularities in the
quark and charged lepton sectors. Second, we discuss several possible mass
patterns, pointing out that this quite generally leads towards hierarchical
neutrino mass patterns especially disfavoring the vacuum solution.Comment: final version to be published in PRD, 5 pages, 2 figures, RevTe
Fine-Tuning Constraints on Supergravity Models
We discuss fine-tuning constraints on supergravity models. The tightest
constraints come from the experimental mass limits on two key particles: the
lightest CP even Higgs boson and the gluino. We also include the lightest
chargino which is relevant when universal gaugino masses are assumed. For each
of these particles we show how fine-tuning increases with the experimental mass
limit, for four types of supergravity model: minimal supergravity, no-scale
supergravity (relaxing the universal gaugino mass assumption), D-brane models
and anomaly mediated supersymmetry breaking models. Among these models, the
D-brane model is less fine tuned.The experimental propects for an early
discovery of Higgs and supersymmetry at LEP and the Tevatron are discussed in
this framework.Comment: 17 pages, Latex, including 5 eps figure
Anomalous 4-Jet Events at LEP: a Signal of Low Scale Technicolour?
We suggest that the anomalous 4-jet events recently reported by ALEPH may be
the first indication of low scale technicolour. According to our interpretation
about half of the events are due to resonantly enhanced pair production of
charged technipions, of mass around 55 GeV, each decaying into a pair of jets,
the other half being due to standard processes. The resonant enhancement is due
to a nearby technirho resonance in the mass range 150-200 GeV, leading to
hugely enhanced signals at the forthcoming LEP run at GeV since
the CM energy would be closer to the peak of the resonance.Comment: 11 pages, latex, no figure
Supersymmetric Hybrid Inflation with Non-Minimal KĂ€hler potential
Minimal supersymmetric hybrid inflation based on a minimal Kahler potential predicts a spectral index n_s\gsim 0.98. On the other hand, WMAP three year data prefers a central value n_s \approx 0.95. We propose a class of supersymmetric hybrid inflation models based on the same minimal superpotential but with a non-minimal Kahler potential. Including radiative corrections using the one-loop effective potential, we show that the prediction for the spectral index is sensitive to the small non-minimal corrections, and can lead to a significantly red-tilted spectrum, in agreement with WMAP.Minimal supersymmetric hybrid inflation based on a minimal Kahler potential predicts a spectral index n_s\gsim 0.98. On the other hand, WMAP three year data prefers a central value n_s \approx 0.95. We propose a class of supersymmetric hybrid inflation models based on the same minimal superpotential but with a non-minimal Kahler potential. Including radiative corrections using the one-loop effective potential, we show that the prediction for the spectral index is sensitive to the small non-minimal corrections, and can lead to a significantly red-tilted spectrum, in agreement with WMAP.Minimal supersymmetric hybrid inflation based on a minimal KĂ€hler potential predicts a spectral index nsâł0.98 . On the other hand, WMAP three year data prefers a central value nsâ0.95 . We propose a class of supersymmetric hybrid inflation models based on the same minimal superpotential but with a non-minimal KĂ€hler potential. Including radiative corrections using the one-loop effective potential, we show that the prediction for the spectral index is sensitive to the small non-minimal corrections, and can lead to a significantly red-tilted spectrum, in agreement with WMAP
Flavour Democracy in Strong Unification
We show that the fermion mass spectrum may naturally be understood in terms
of flavour democratic fixed points in supersymmetric theories which have a
large domain of attraction in the presence of "strong unification". Our
approach provides an alternative to the approximate Yukawa texture zeroes of
the Froggatt-Nielsen mechanism. We discuss a particular model based on a broken
gauged family symmetry which illustrates our approach.Comment: 21 Pages plain latex; includes 5 eps figure
Dilaton Stabilisation in -term Inflation
Dilaton stabilisation is usually considered to pose a serious obstacle to
successful -term inflation in superstring theories. We argue that the
physics of gaugino condensation is likely to be modified during the
inflationary phase in such a way as to enhance the gaugino condensation scale.
This enables dilaton stabilisation during inflation with the -term still
dominating the vacuum energy at the stable minimum.Comment: 13 pages, Latex, 1 figur
Neutrino Masses in SUSY Models
In this talk we assume the conventional see-saw mechanism, and contruct a
hierarchical pattern of three active neutrinos with bi-maximal mixing. In order
to enforce the hierarchy we use the single right handed neutrino dominance
mechanism which is a very nice way to ensure a neutrino mass hierarchy in the
presence of large mixing angles. We show how this mechanism can be organised in
the framework of a U(1) family symmetry, then discuss a realistic
string-inspired model which includes such a symmetry.Comment: Invited Talk at EuroConference on Frontiers in Particle Astrophysics
and Cosmology, San Feliu de Guixols, Spain, 30 September - 5 October 2000. 15
pages, Late
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