496 research outputs found
MINOS and CPT-violating neutrinos
We review the status of CPT violation in the neutrino sector. Apart from
LSND, current data favors three flavors of light stable neutrinos and
antineutrinos, with both halves of the spectrum having one smaller mass
splitting and one larger mass splitting. Oscillation data for the smaller
splitting is consistent with CPT. For the larger splitting, current data favor
an antineutrino mass-squared splitting that is an order of magnitude larger
than the corresponding neutrino splitting, with the corresponding mixing angle
less-than-maximal. This CPT-violating spectrum is driven by recent results from
MINOS, but is consistent with other experiments if we ignore LSND. We describe
an analysis technique which, together with MINOS running optimized for muon
antineutrinos, should be able to conclusively confirm the CPT-violating
spectrum proposed here, with as little as three times the current data set. If
confirmed, the CPT-violating neutrino mass-squared difference would be an order
of magnitude less than the current most-stringent upper bound on CPT violation
for quarks and charged leptons.Comment: 18 pages, title change, version to appear in Physical Review
METing SUSY on the Z peak
Recently the ATLAS experiment announced a 3 excess at the Z-peak
consisting of 29 pairs of leptons together with two or more jets, GeV and GeV, to be compared with
expected lepton pairs in the Standard Model. No excess outside the Z-peak was
observed. By trying to explain this signal with SUSY we find that only
relatively light gluinos, TeV, together with a
heavy neutralino NLSP of GeV decaying
predominantly to Z-boson plus a light gravitino, such that nearly every gluino
produces at least one Z-boson in its decay chain, could reproduce the excess.
We construct an explicit general gauge mediation model able to reproduce the
observed signal overcoming all the experimental limits. Needless to say, more
sophisticated models could also reproduce the signal, however, any model would
have to exhibit the following features, light gluinos, or heavy particles with
a strong production cross-section, producing at least one Z-boson in its decay
chain. The implications of our findings for the Run II at LHC with the scaling
on the Z peak, as well as for the direct search of gluinos and other SUSY
particles, are pointed out.Comment: 24 pages, 17 figures, simulation improved, Checkmate analysis added,
new benchmark point included. Typos corrected, conclusions unchange
Baryogenesis from a right-handed neutrino condensate
We show that the baryon asymmetry of the Universe can be generated by a
strongly coupled right handed neutrino condensate which also drives inflation.
The resulting model has only a small number of parameters, which completely
determine not only the baryon asymmetry of the Universe and the mass of the
right handed neutrino but also the inflationary phase. This feature allows us
to make predictions that will be tested by current and planned experiments. As
compared to the usual approach our dynamical framework is both economical and
predictive.Comment: 13 pages, 3 figures. Typos corrected and several points clarified.
Results unchanged. New references adde
CPT Violation Implies Violation of Lorentz Invariance
An interacting theory that violates CPT invariance necessarily violates
Lorentz invariance. On the other hand, CPT invariance is not sufficient for
out-of-cone Lorentz invariance. Theories that violate CPT by having different
particle and antiparticle masses must be nonlocal.Comment: Minor changes in the published versio
Quantum decoherence and neutrino data
In this work we perform global fits of microscopic decoherence models of
neutrinos to all available current data, including LSND and KamLAND spectral
distortion results. In previous works on related issues the models used were
supposed to explain LSND results by means of quantum gravity induced
decoherence. However those models were purely phenomenological without any
underlying microscopic basis. It is one of the main purposes of this article to
use detailed microscopic decoherence models with complete positivity, to fit
the data.The decoherence in these models has contributions not only from
stochastic quantum gravity vacua operating as a medium, but also from
conventional uncertainties in the energy of the (anti)neutrino beam. All these
contributions lead to oscillation-length independent damping factors modulating
the oscillatory terms from which one obtains an excellent fit to all available
neutrino data, including LSND and Kamland spectral distortion.Comment: 27 pages, 2 figure
Self-accelerating solutions of scalar-tensor gravity
Scalar-tensor gravity is the simplest and best understood modification of
general relativity, consisting of a real scalar field coupled directly to the
Ricci scalar curvature. Models of this type have self-accelerating solutions.
In an example inspired by string dilaton couplings, scalar-tensor gravity
coupled to ordinary matter exhibits a de Sitter type expansion, even in the
presence of a {\it negative} cosmological constant whose magnitude exceeds that
of the matter density. This unusual behavior does not require phantoms, ghosts
or other exotic sources. More generally, we show that any expansion history can
be interpreted as arising partly or entirely from scalar-tensor gravity. To
distinguish any quintessence or inflation model from its scalar-tensor
variants, we use the fact that scalar-tensor models imply deviations of the
post-Newtonian parameters of general relativity, and time variation of the
Newton's gravitational coupling . We emphasize that next-generation probes
of modified GR and the time variation of are an essential complement to
dark energy probes based on luminosity-distance measurements.Comment: 14 pages, 3 figure
Constraining Models of New Physics in Light of Recent Experimental Results on
We study extensions of the Standard Model where the charged current weak
interactions are governed by the CKM matrix and where all tree-level decays are
dominated by their Standard Model contribution. We constrain both analytically
and numerically the ratio and the phase difference between the New Physics and
the Standard Model contributions to the mixing amplitude of the neutral
system using the experimental results on , ,
and . We present new results concerning models with minimal
flavor violation and update the relevant parameter space. We also study the
left-right symmetric model with spontaneously broken CP, probing the viability
of this model in view of the recent results for and other
observables.Comment: 32 pages, including 9 figures, typos and error in fig. 1 corrected,
minor modificiation in the text, conclusions unchanged, to appear in PR
Gravity triggered neutrino condensates
In this work we use the Schwinger-Dyson equations to study the possibility
that an enhanced gravitational attraction triggers the formation of a right
handed neutrino condensate, inducing dynamical symmetry breaking and generating
a Majorana mass for the right handed neutrino at a scale appropriate for the
see-saw mechanism. The composite field formed by the condensate phase could
drive an early epoch of inflation. We find that to the lowest order, the theory
does not allow dynamical symmetry breaking. Nevertheless, thanks to the large
number of matter fields in the model, the suppression by additional powers in G
of higher order terms can be compensated, boosting them up to their lowest
order counterparts. This way chiral symmetry can be broken dynamically and the
infrared mass generated turns out to be in the expected range for a successful
see-saw scenario.Comment: 16 pages, 10 figure
Are the New Physics Contributions from the Left-Right Symmetric Model Important for the Indirect CP Violation in the Neutral B Mesons?
Several works analyzing the new physics contributions from the Left-Right
Symmetric Model to the CP violation phenomena in the neutral B mesons can be
found in the literature. These works exhibit interesting and experimentally
sensible deviations from the Standard Model predictions but at the expense of
considering a low right scale \upsilon_R around 1 TeV. However, when we stick
to the more conservative estimates for \upsilon_R which say that it must be at
least 10^7 GeV, no experimentally sensible deviations from the Standard Model
appear for indirect CP violation. This estimate for \upsilon_R arises when the
generation of neutrino masses is considered. In spite of the fact that this
scenario is much less interesting and says nothing new about both the CP
violation phenomenon and the structure of the Left-Right Symmetric Model, this
possibility must be taken into account for the sake of completeness and when
considering the see-saw mechanism that provides masses to the neutrino sector.Comment: LaTex file. 19 pages, 4 figures. Change in the way the paper address
the problem. As a result, change in title, abstract, and some sections.
Conclusions unchanged. Version to appear in Foundations of Physics Letter
On Neutrino Masses and a Low Breaking Scale of Left-Right Symmetry
In left-right symmetric models (LRSM) the light neutrino masses arise from
two sources: the seesaw mechanism and a VEV of an SU(2) triplet. If the
left-right symmetry breaking, , is low, v_R\lsim15\TeV, the
contributions to the light neutrino masses from both the seesaw mechanism and
the triplet Yukawa couplings are expected to be well above the experimental
bounds. We present a minimal LRSM with an additional U(1) symmetry in which the
masses induced by the two sources are below the eV scale and the two-fold
problem is solved. We further show that, if the U(1) symmetry is also
responsible for the lepton flavor structure, the model yields a small mixing
angle within the first two lepton generations.Comment: 18 pages references added published versio
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