762 research outputs found
A Neutrino Mass Matrix Model with many Quantum charges and No SUSY
We present a model based on our favourite gauge group which we call Anti-GUT
and which in its extended form to be applied for neutrinos in the see-saw
picture consists in that we have for each family separately a set of gauge
fields as in the Standard Model plus a gauged (B-L)-charge. It may function as
a concrete model manifestation of the type of model suggested by some general
statistical considerations as to what a mass matrix model is to be to match
naturally the rough features of the spectrum and the baryon asymmetry so nicely
obtained in see-saw models along the Fukugita-Yanagida scheme.Comment: 20 pages, Latex2e; Contribution to The Scandinavian Neutrino
Workshop, Uppsala, Sweden, 8-10 February 200
Naturalness of Neutralino Dark Matter
We investigate the level of fine-tuning of neutralino Dark Matter below 200
GeV in the low-energy phenomenological minimal supersymmetric Standard Model
taking into account the newest results from XENON100 and the Large Hadron
Collider as well as all other experimental bounds from collider physics and the
cosmological abundance. We find that current and future direct Dark Matter
searches significantly rule out a large area of the untuned parameter space,
but solutions survive which do not increase the level of fine-tuning. As
expected, the level of tuning tends to increase for lower cross-sections, but
regions of resonant neutralino annihilation still allow for a band at light
masses, where the fine-tuning stays small even below the current experimental
limits for direct detection cross-sections. For positive values of the
supersymmetric Higgs mass parameter \mu large portions of the allowed parameter
space are excluded, but there still exist untuned solutions at higher
neutralino masses which will essentially be ruled out if XENON1t does not
observe a signal.For negative \mu untuned solutions are not much constrained by
current limits of direct searches and, if the neutralino mass was found outside
the resonance regions, a negative \mu-term would be favored from a fine-tuning
perspective. Light stau annihilation plays an important role to fulfill the
relic density condition in certain neutralino mass regions. Finally we discuss,
in addition to the amount of tuning for certain regions in the neutralino
mass-direct detection cross-section plane, the parameter mapping distribution
if the allowed model parameter space is chosen to be scanned homogeneously
(randomized).Comment: v2: 29 pages, 16 figures. Published versio
Neutrino Oscillations in Extended Anti-GUT Model
What we call the Anti-GUT model is extended a bit to include also
right-handed neutrinos and thus make use of the see-saw mechanism for neutrino
masses. This model consists in assigning gauge quantum numbers to the known
Weyl fermions and the three see-saw right-handed neutrinos. Each family
(generation) is given its own Standard Model gauge fields and a gauge field
coupled to the quantum number for that family alone. Further we assign a
rather limited number of Higgs fields, so as to break these gauge groups down
to the Standard Model gauge group and to fit, w.r.t. order of magnitude, the
spectra and mixing angles of the quarks and leptons. We find a rather good fit,
which for neutrino oscillations favours the small mixing angle MSW solution,
although the mixing angle predicted is closest to the upper side of the
uncertainty range for the measured solar neutrino mixing angle. An idea for
making a ``finetuning''-principle to ``explain'' the large ratios found
empirically in physics, and answer such questions as ``why is the weak scale
low compared to the Planck scale?'', is proposed. A further very speculative
extension is supposed to ``explain'' why we have three families.Comment: 40 page LaTeX file; talk given at the Second Tropical Workshop on
Particle Physics and Cosmology, San Juan, Puerto Rico, May 200
LHC Tests of Light Neutralino Dark Matter without Light Sfermions
We address the question how light the lightest MSSM neutralino can be as dark
matter candidate in a scenario where all supersymmetric scalar particles are
heavy. The hypothesis that the neutralino accounts for the observed dark matter
density sets strong requirements on the supersymmetric spectrum, thus providing
an handle for collider tests. In particular for a lightest neutralino below 100
GeV the relic density constraint translates into an upper bound on the Higgsino
mass parameter in case all supersymmetric scalar particles are heavy. One
can define a simplified model that highlights only the necessary features of
the spectrum and their observable consequences at the LHC. Reinterpreting
recent searches at the LHC we derive limits on the mass of the lightest
neutralino that, in many cases, prove to be more constraining than dark matter
experiments themselves.Comment: 22 pages, 8 figure
Boundary-Induced Phase Transitions in Equilibrium and Non-Equilibrium Systems
Boundary conditions may change the phase diagram of non-equilibrium
statistical systems like the one-dimensional asymmetric simple exclusion
process with and without particle number conservation. Using the quantum
Hamiltonian approach, the model is mapped onto an XXZ quantum chain and solved
using the Bethe ansatz. This system is related to a two-dimensional vertex
model in thermal equilibrium. The phase transition caused by a point-like
boundary defect in the dynamics of the one-dimensional exclusion model is in
the same universality class as a continous (bulk) phase transition of the
two-dimensional vertex model caused by a line defect at its boundary.
(hep-th/yymmnnn)Comment: Latex 10pp, Geneva preprint UGVA-DPT 1993/07-82
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