4,175 research outputs found
Radiative Neutrino Mass in Type III Seesaw Model
The simplest type III seesaw model as originally proposed introduces one
lepton triplet. It thus contains four active neutrinos, two massive and two
massless at tree level. We determine the radiative masses that the latter
receive first at two loops. The masses are generally so tiny that they are
definitely excluded by the oscillation data, if the heavy leptons are not very
heavy, say, within the reach of LHC. To accommodate the data on masses, the
seesaw scale must be as large as the scale of grand unification. This indicates
that the most economical type III model would entail no new physics at low
energies beyond the tiny neutrino masses.Comment: 21 pages, 1 figure; v2: added 3 sentences in sec 4 for
clarifications, version published on 7 Apr 2009 in PR D79, 073003 (2009
Radiative and flavor-violating transitions of leptons from interactions with color-octet particles
It has been recently proposed that neutrino mass could originate from Yukawa
interactions of leptons with new colored particles. This raises the interesting
possibility of testing mass generation through copious production of those
particles at hadron colliders. A realistic assessment of it however should take
into account how large those interactions could be from available precision
results. In this work we make a systematic analysis to the flavor structure in
Yukawa couplings, provide a convenient parametrization to it, and investigate
the rare radiative and pure leptonic decays of the muon and tau leptons. For
general values of parameters the muon decays set stringent constraints on the
couplings, and all rare tau decays are far below the current experimental
sensitivity. However, there is room in parameter space in which the muon decays
could be significantly suppressed by destructive interference between colored
particles without generically reducing the couplings themselves. This is also
the region of parameters that is relevant to collider physics. We show that for
this part of parameter space some tau decays can reach or are close to the
current level of precision.Comment: 20 pages, 7 figure
Dietary Patterns in Urbanised Blacks: A study in Guguletu, Cape Town, 1971
A survey of dietary patterns was made in Guguletu, an urban Black township near Cape Town. The subjects comprised Black children and adults eating adult-type food. They were divided into 5 groups-3 groups of families according to income (well-to-do, medium and poor), one group of bachelors and one group recently removed from the coastal district of Simonstown. Dietary patterns were studied quantitatively and qualitatively. A computerised food table was compiled for obtaining data on the intake of 28 nutrients by families and individuals, per week and per day. Qualitative data were provided by respondents interviewed in their homes and bachelor quarters. Interviews included questions on taboos, cooking methods and meal patterns, as well as daily food intake and weekly purchasing. Transition from rural to urban living brings about a taste for sophisticated 'town foods' but the basic anthropological predilection for c'arbohydrate remains unchanged, and meat was found to be the most valued food. Fat consumption increases in an urban community. Total food consumption was inversely related to family size, the highest calorie intake being noted among the bachelors. Riboflavin intake fell short of the National Research Council's recommended daily allowances as did niacin, tryptophan and calcium. The dietary pattern developing in an urban Black township clearly needs modification to ensure adequate nutrient intake and to prevent destruction of nutrients by faulty cooking methods.S. Afr. Med. J., 48, 485 (1974
Line tension and structure of smectic liquid crystal multilayers at the air-water interface
At the air/water interface, 4,-8-alkyl[1,1,-biphenyl]-4-carbonitrile (8CB)
domains with different thicknesses coexist in the same Langmuir film, as
multiple bilayers on a monolayer. The edge dislocation at the domain boundary
leads to line tension, which determines the domain shape and dynamics. By
observing the domain relaxation process starting from small distortions, we
find that the line tension is linearly dependent on the thickness difference
between the coexisting phases in the film. Comparisons with theoretical
treatments in the literature suggest that the edge dislocation at the boundary
locates near the center of the film, which means that the 8CB multilayers are
almost symmetric with respect to the air/water interface.Comment: 21 pages, 6 figure
Drell-Hearn-Gerasimov Sum-Rule for the Deuteron in Nuclear Effective Field Theory
The Drell-Hearn-Gerasimov sum rule for the deuteron is studied in nuclear
effective field theory. The low-energy theorem for the spin-dependent Compton
amplitude is derived to the next-to-leading order in low-energy
expansion. The spin-dependent photodisintegration cross section
is calculated to the same order, and its contribution to
the dispersive integral is evaluated.Comment: 8 pages, 2 figure
Methanol immersion reduces spherical aberration of water dipping lenses at long wavelengths used in multi-photon laser scanning microscopy
Dipping objectives were tested for multi-photon laser scanning microscopy, since their large working distances are advantageous for thick specimens and the absence of a coverslip facilitates examination of living material. Images of fluorescent bead specimens, particularly at wavelengths greater than 850 nm showed defects consistent with spherical aberration. Substituting methanol for water as the immersion medium surrounding the beads corrected these defects and produced an increase in fluorescence signal intensity. The same immersion method was applied to two representative biological samples of fixed tissue: mouse brain labeled with FITC for tubulin and mouse gut in which the Peyer’s patches were labeled with Texas Red bilosomes. Tissue morphology was well preserved by methanol immersion of both tissues; the two-photon-excited fluorescence signal was six times higher than in water and the depth of penetration of useful imaging was doubled. No modification of the microscope was needed except the provision of a ring to retain a sufficient depth of methanol for imaging
Neutrino mixing contribution to the cosmological constant
We show that the non-perturbative vacuum structure associated with neutrino
mixing leads to a non-zero contribution to the value of the cosmological
constant. Such a contribution comes from the specific nature of the mixing
phenomenon. Its origin is completely different from the one of the ordinary
contribution of a massive spinor field. We estimate this neutrino mixing
contribution by using the natural cut--off appearing in the quantum field
theory formalism for neutrino mixing and oscillation.Comment: 7 page
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
We study spin-dependent sum rules for forward virtual Compton
scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at
order . We show how these sum rules can be evaluated from low energy
expansions (in the virtual photon energy) of the forward VVCS amplitudes. We
study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher
terms in the low energy expansion, which can be related to the generalized
forward spin polarizabilities of the nucleon. The dependence of these
observables on the photon virtuality can be accessed, at small and
intermediate values, from existing and forthcoming data at Jefferson Lab.Comment: 16 pages,4 fig
Sum Rules and Spin-Dependent Polarizabilities of the Deuteron in Effective Field Theory
We construct sum rules for the forward vector and tensor polarizabilities for
any spin- target and apply them to the spin-1 deuteron. We calculate these
polarizabilities of the deuteron to the next-to-leading order in the pionless
effective field theory.Comment: 10 pages, figures include
Exploring the timelike region for the elastic form factor in the light-front quantization
Even though the Drell-Yan-West formulation is the most rigorous and
well-established framework to compute the exclusive processes, its utility has
been limited only to the spacelike region because of the intrinsic kinematic
constraint . We present an explicit example demonstrating how one may
obtain the necessary information (i.e. nonvalence or so called Z-graph
contribution) in the timelike region of exclusive process without encountering
a formidable task of direct calculation that has hindered so far the progress
in this area. In the analysis of bound state form factors using an
exactly solvable model of dimensional scalar field theory interacting
with gauge fields, the results analytically continued from the spacelike region
coincide exactly with the direct results in the timelike region. This example
verifies that the method of analytic continuation is capable of yielding the
effect of complicate nonvalence contributions. The meson peaks analogous to the
vector meson dominance(VMD) phenomena are also generated at the usual VMD
positions.Comment: 21 pages, 8 figures, we changed the title, added some references and
included some paragraphs in the introduction and conclusions; version to
appear in Nucl. Phys.
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