714 research outputs found
Neutrino masses from higher than d=5 effective operators
We discuss the generation of small neutrino masses from effective operators
higher than dimension five, which open new possibilities for low scale see-saw
mechanisms. In order to forbid the radiative generation of neutrino mass by
lower dimensional operators, extra fields are required, which are charged under
a new symmetry. We discuss this mechanism in the framework of a two Higgs
doublet model. We demonstrate that the tree level generation of neutrino mass
from higher dimensional operators often leads to inverse see-saw scenarios in
which small lepton number violating terms are naturally suppressed by the new
physics scale. Furthermore, we systematically discuss tree level
generalizations of the standard see-saw scenarios from higher dimensional
operators. Finally, we point out that higher dimensional operators can also be
generated at the loop level. In this case, we obtain the TeV scale as new
physics scale even with order one couplings.Comment: 22 pages, 3 figures, 2 tables. Some references adde
Neutrino masses in R-parity violating supersymmetric models
We study neutrino masses and mixing in R-parity violating supersymmetric
models with generic soft supersymmetry breaking terms. Neutrinos acquire masses
from various sources: Tree level neutrino--neutralino mixing and loop effects
proportional to bilinear and/or trilinear R-parity violating parameters. Each
of these contributions is controlled by different parameters and have different
suppression or enhancement factors which we identified. Within an Abelian
horizontal symmetry framework these factors are related and specific
predictions can be made. We found that the main contributions to the neutrino
masses are from the tree level and the bilinear loops and that the observed
neutrino data can be accommodated once mild fine-tuning is allowed.Comment: 18 pages; minor typos corrected. To be published in Physical Review
Symmetry of the Atomic Electron Density in Hartree, Hartree-Fock, and Density Functional Theory
The density of an atom in a state of well-defined angular momentum has a
specific finite spherical harmonic content, without and with interactions.
Approximate single-particle schemes, such as the Hartree, Hartree-Fock, and
Local Density Approximations, generally violate this feature. We analyze, by
means of perturbation theory, the degree of this violation and show that it is
small. The correct symmetry of the density can be assured by a
constrained-search formulation without significantly altering the calculated
energies. We compare our procedure to the (different) common practice of
spherically averaging the self-consistent potential. Kohn-Sham density
functional theory with the exact exchange-correlation potential has the correct
finite spherical harmonic content in its density; but the corresponding exact
single particle potential and wavefunctions contain an infinite number of
spherical harmonics.Comment: 11 pages, 6 figures. Expanded discussion of spherical harmonic
expansion of Hartree density. Some typos corrected, references adde
The combustion of waste, industrial glycerol in a fluidised bed
Large quantities of glycerol are produced as a somewhat useless, industrial by-product, when producing biodiesel. Thus, the combustion of this waste (containing glycerol, less volatile, non-glyceride oils, ash and water) in a fluidised bed has been investigated. The fuel entered the bottom of the bed (on its axis) as bubbles of vapour, which rose up the bed, surrounded by bubbles of fluidising air. While more difficult to burn than medicinal glycerol, continuous burning of the waste was sustained for a total of ∼ 4 h in a bed of silica sand (500 – 710 μm) at 750°C, fluidised by air. However, after ∼ 4 h, fluidisation ceased, because the silica sand agglomerated into globules a few mm wide, probably cemented by a eutectic of K2SO4 and KOH; this industrial glycerol did originally contain potassium and sulphate ions, from its manufacture. Under similar conditions, when burning the waste in a bed of fluidised alumina (Al2O3) particles (355 – 425 μm), the bed de-fluidised after almost ½ h, and then sintered into a cake, again possibly cemented by the potassium salts K2SO4 and KOH. As for combustion, there was evidence that waste glycerol can be burned in a fluidised bed of SiO2 particles autonomously, without supplying heat. In such a fluidised bed, it appeared that glycerol vapour, inside a bubble, first decomposes thermally, yielding CO and H2. The less volatile oils were slower to evaporate and decompose. Combustion of the waste fuel with air occurred in a bed of SiO2 particles only to a limited extent in rising bubbles, depending on the bed’s depth. Otherwise, burning occurred above the fluidised particles, just as a mixture of methane or propane in air burns, when fluidising a hot bed of silica particles. The role of the particles is to inhibit combustion by scavenging radicals
TeV-scale seesaw from a multi-Higgs model
We suggest new simple model of generating tiny neutrino masses through a
TeV-scale seesaw mechanism without requiring tiny Yukawa couplings. This model
is a simple extension of the standard model by introducing extra one Higgs
singlet, and one Higgs doublet with a tiny vacuum expectation value.
Experimental constraints, electroweak precision data and no large flavor
changing neutral currents, are satisfied since the extra doublet only has a
Yukawa interaction with lepton doublets and right-handed neutrinos, and their
masses are heavy of order a TeV-scale. Since active light neutrinos are
Majorana particles, this model predicts a neutrinoless double beta decay.Comment: 21 pages, 8 figure
Stability of the Scalar Potential and Symmetry Breaking in the Economical 3-3-1 Model
A detailed study of the criteria for stability of the scalar potential and
the proper electroweak symmetry breaking pattern in the economical 3-3-1 model,
is presented. For the analysis we use, and improve, a method previously
developed to study the scalar potential in the two-Higgs-doublet extension of
the standard model. A new theorem related to the stability of the potential is
stated. As a consequence of this study, the consistency of the economical 3-3-1
model emerges.Comment: to be published in EPJ C, 13 page
New Leptoquark Mechanism of Neutrinoless Double Beta Decay
A new mechanism for neutrinoless double beta (\znbb) decay based on
leptoquark exchange is discussed. Due to the specific helicity structure of the
effective four-fermion interaction this contribution is strongly enhanced
compared to the well-known mass mechanism of \znbb decay. As a result the
corresponding leptoquark parameters are severely constrained from
non-observation of \znbb-decay. These constraints are more stringent than
those derived from other experiments.Comment: LaTeX, 6 pages, 1 figur
NN,N\Delta Couplings and the Quark Model
We examine mass-corrected SU(6) symmetry predictions in the quark model
relating vector, axial-vector and strong NN and N\Delta couplings, and
demonstrate that the experimental N\Delta value is significantly higher than
predicted in each case. Nevertheless the Goldberger-Treiman relation is
satisfied in both sectors. Possible origins of the discrepancy of the quark
model predictions with experiment are discussed.Comment: 22 pg. Latex file, figures available by reques
Reopening the window on charged dark matter
We reexamine the limits on charged dark matter particles. We show that if
their mass and charge fall in the range 100(q_X/e)^2< m_X < 10^8(q_X/e) TeV,
then magnetic fields prevent particles in the halo from entering the galactic
disk, while those initially trapped inside are accelerated through the Fermi
mechanism and ejected within about 0.1-1 Gyrs. Consequently, previous
constraints on charged dark matter based on terrestrial non-observation are
invalid within that range. Further, we find that charged massive particles may
simultaneously solve several long-standing astrophysical problems, including
the underabundance of dwarf galaxies, the shallow density profiles in the cores
of the LSB galaxies, the absence of cooling flows in the cores of galaxy
clusters, and several others.Comment: 9 pages, 1 figure, accepted for publication in JCA
Low Energy Chiral Lagrangian in Curved Space-Time from the Spectral Quark Model
We analyze the recently proposed Spectral Quark Model in the light of Chiral
Perturbation Theory in curved space-time. In particular, we calculate the
chiral coefficients , as well as the coefficients ,
, and , appearing when the model is coupled to gravity. The
analysis is carried for the SU(3) case. We analyze the pattern of chiral
symmetry breaking as well as elaborate on the fulfillment of anomalies.
Matching the model results to resonance meson exchange yields the relation
between the masses of the scalar, tensor and vector mesons,
. Finally, the
large- limit suggests the dual relations in the vector and scalar
channels, and .Comment: 18 pages, no figure
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