418 research outputs found
Neutrino mixing schemes and neutrinoless double beta decay
We study the possible structure of the neutrino mass matrix taking into
consideration the solar and atmospheric neutrinos and the neutrinoless double
beta decay. We emphasize on mass matrices with vanishing elements. There are
only a very few possibilities remaining at present. We concentrate on three
generation scenarios and find that with three parameters there are few
possibilities with and without any vanishing elements. For completeness we also
present a five parameter four neutrino (with one sterile neutrino) mass matrix
which can explain all these experiments and the LSND result.Comment: 12 pages late
A Metabolic Imaging Study of Lexical and Phonological Naming Errors in Alzheimer Disease
Patients with Alzheimer disease (AD) produce a variety of errors on confrontation naming that indicate multiple loci of impairment along the naming process in this disease. We correlated brain hypometabolism, measured with 18fluoro-deoxy-glucose positron emission tomography, with semantic and formal errors, as well as nonwords deriving from phonological errors produced in a picture-naming test by 63 patients with AD. Findings suggest that neurodegeneration leads to: (1) phonemic errors, by interfering with phonological short-term memory, or with control over retrieval of phonological or prearticulatory representations, within the left supramarginal gyrus; (2) semantic errors, by disrupting general semantic or visual-semantic representations at the level of the left posterior middle and inferior occipitotemporal cortex, respectively; (3) formal errors, by damaging the lexical-phonological output interface in the left mid-anterior segment of middle and superior temporal gyri. This topography of semantic-lexical-phonological steps of naming is in substantial agreement with dual-stream neurocognitive models of word generation
Embedding Phenomenological Quark-Lepton Mass Matrices into SU(5) Gauge Models
We construct phenomenological quark-lepton mass matrices based on S
permutation symmetry in a manner fully compatible with SU(5) grand unification.
The Higgs particles we need are {\bf 5}, {\bf 45} and their conjugates. The
model gives a charge 1/3 quark vs charged lepton mass relation, and also a
good fit to mass-mixing relations for the quark sector, as well as an
attractive mixing pattern for the lepton sector, explaining a large mixing
angle between and , and either large or small
mixing angle, depending on the choice of couplings, consistent
with the currently accepted solutions to the solar neutrino problem.Comment: 12 pages, LaTex file, no figure
Large Neutrino Mixing from Renormalization Group Evolution
The renormalization group evolution equation for two neutrino mixing is known
to exhibit nontrivial fixed point structure corresponding to maximal mixing at
the weak scale. The presence of the fixed point provides a natural explanation
of the observed maximal mixing of if the and
are assumed to be quasi-degenerate at the seesaw scale without
constraining on the mixing angles at that scale. In particular, it allows them
to be similar to the quark mixings as in generic grand unified theories. We
discuss implementation of this program in the case of MSSM and find that the
predicted mixing remains stable and close to its maximal value, for all
energies below the (TeV) SUSY scale. We also discuss how a particular
realization of this idea can be tested in neutrinoless double beta decay
experiments.Comment: Latex file, 21 pages and 4 ps figures include
Nuclear matrix elements of double beta decay from beta decay
The evaluation of the nuclear matrix elements (NME) of the two-neutrino
double beta () decay and neutrinoless double beta
() decay using the proton-neutron quasiparticle random-phase
approximation (pnQRPA) is addressed. In particular, the extraction of a proper
value of the proton-neutron particle-particle interaction parameter, , of this theory is analyzed in detail. Evidence is shown, that it can be
misleading to use the experimental half-life of the decay to
extract a value for . Rather, arguments are given in favour of
using the available data on single beta decay for this purpose.Comment: 14 pages, 3 figure
Light-neutrino mass hierarchies, nuclear matrix elements, and the observability of neutrinoless double-beta decay
Results for neutrino flavor oscillations and neutrino mixing mechanisms,
obtained from the analysis of the Sudbury Neutrino Observatory (SNO), the
SuperKamiokande (SK), CHOOZ, KamLAND and WMAP data, are used to calculate the
effective neutrino mass relevant for the neutrinoless double-beta decay. The
observability of the decay of 76Ge is discussed within different light-neutrino
mass hierarchies and by presenting a systematics on the available nuclear
matrix elements.Comment: 25 pages, 1 figur
Agerelated quantitative and qualitative changes in decision making ability
Abstract. The "frontal aging hypothesis" predicts that brain senescence affects predominantly the prefrontal regions. Preliminary evidence has recently been gathered in favour of an age-related change in a typically frontal process, i.e. decision making, using the Iowa Gambling Task (IGT), but overall findings have been conflicting. Following the traditional scoring method, coupled with a qualitative analysis, in the present study we compared IGT performance of 40 young (mean age: 27.9 ± 4.7) and 40 old (mean age: 65.4 ± 8.6) healthy adults and of 18 patients affected by frontal lobe dementia of mild severity (mean age: 65.1 ± 7.4, mean MMSE score: 24.1 ± 3.9). Quantitative findings support the notion that decision making ability declines with age; moreover, it approximates the impairment observed in executive dysfunction due to neurodegeneration. Results of the qualitative analysis did not reach statistical significance for the motivational and learning decision making components considered, but approached significance for the attentional component for elderly versus young normals, suggesting a possible decrease in the ability to maintain sustained attention during complex and prolonged tasks as the putative deficit underlying impaired decision making in normal aging
Akinetic Mutism and Cognitive-Affective Syndrome Caused by Unilateral PICA Infarction
A 42-year-old man with left posterior inferior cerebellar artery (PICA) infarction presented with akinetic mutism and cognitive impairment. Initially he suffered from akinetic mutism and MRI-documented infarction in the distribution of the left PICA. Twelve days later he developed cognitive impairment. Neuropsychological tests were performed, with the results corrected for age and education being compared with published Korean norms. Impaired performances were evident on executive function testing, with difficulties in planning, abstract reasoning, set-shifting, and perseveration. Akinetic mutism and cognitive-affective syndrome may be a manifestation of unilateral PICA infarction
A neutrino mass matrix with seesaw mechanism and two-loop mass splitting
We propose a model which uses the seesaw mechanism and the lepton number
to achieve the neutrino mass spectrum and , together with a lepton mixing matrix with .
In this way, we accommodate atmospheric neutrino oscillations. A small mass
splitting is generated by breaking spontaneously and using
Babu's two-loop mechanism. This allows us to incorporate ``just so''
solar-neutrino oscillations with maximal mixing into the model. The resulting
mass matrix has three parameters only, since breaking leads
exclusively to a non-zero matrix element.Comment: 8 pages, Late
A texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande
(SK), CHOOZ and neutrinoless double beta decay , we
consider a texture of neutrino mass matrix which contains three parameters in
order to explain those neutrino experimental results. We have first fitted
parameters in a model independent way with solar and atmospheric neutrino mass
squared differences and solar neutrino mixing angle which satisfy LMA solution.
The maximal value of atmospheric neutrino mixing angle comes out naturally in
the present texture. Most interestingly, fitted parameters of the neutrino mass
matrix considered here also marginally satisfy recent limit on effective
Majorana neutrino mass obtained from neutrinoless double beta decay experiment.
We further demonstrate an explicit model which gives rise to the texture
investigated by considering an gauge group with two
extra real scalar singlets and discrete symmetry. Majorana
neutrino masses are generated through higher dimensional operators at the scale
. We have estimated the scales at which singlets get VEV's and M by
comparing with the best fitted results obtained in the present work.Comment: Journal Ref.: Phys. Rev. D66, 053004 (2002
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