651 research outputs found
Radiocarbon and blue optically stimulated luminescence chronologies of the Oitavos consolidated dune (Western Portugal)
The dune of Oitavos, the underlying paleosol, and Helix sp. gastropod shells found within the paleosol were dated using a combination of radiocarbon and blue optically stimulated luminescence (OSL). The organic component of the paleosol produced a significantly older age (~20,000 cal BP) than the OSL age measurement (~15,000 yr), while 14C age measurements on the inorganic component and the gastropods produced ages of ~35,000 yr and ~34,000 yr, respectively. Rare-earth
element analyses provide evidence that the gastropods incorporate geological carbonate, making them an unreliable indicator of the age of the paleosol. We propose that the 14C age of the small organic component of the paleosol is also likely to be unreliable due to incorporation of residual material. The OSL age measurement of the upper paleosol (~15,000 yr) is consistent with the age for the base of the dune (~14,500 yr). The younger OSL age for the top of the dune (~12,000 yr) suggests that it was built up by at least 2 sand pulses or that there was a remobilization of material at the top during its evolution, prior to consolidation
Resonant leptogenesis and tribimaximal leptonic mixing with A4 symmetry
We investigate the viability of thermal leptogenesis in type-I seesaw models
with leptonic flavour symmetries that lead to tribimaximal neutrino mixing. We
consider an effective theory with an A4 x Z3 x Z4 symmetry, which is
spontaneously broken at a scale much higher than the electroweak scale. At the
high scale, leptonic Yukawa interactions lead to exact tribimaximal mixing and
the heavy Majorana neutrino mass spectrum is exactly degenerate. In this
framework, leptogenesis becomes viable once this degeneracy is lifted either by
renormalization group effects or by a soft breaking of the A4 symmetry. The
implications for low-energy neutrino physics are discussed.Comment: 14 pages, 15 figures; final version to appear in Phys. Rev.
Leptogenesis
I present the theoretical basis for Leptogenesis and its implications for the
structure of the universe. It is suggested that density fluctuations grow
during the transition period and remnants of this effect should be sought in
the universe. The relation between theories with Majorana neutrinos and low
energy phenomena, including oscillations, advanced considerably during the past
two years with a consistent picture developed in several models.Comment: 9 pages, 3 figures.To appear in the proceedings of The IXth
International Symposium on Particles, Strings and Cosmology at the Tata
Institute of Fundamental Research, Mumbai (Bombay), India, during 3-8 January
200
A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing
We present a see-saw model for Tri-Bimaximal mixing which is based on a
very economical flavour symmetry and field content and still possesses all the
good features of models. In particular the charged lepton mass
hierarchies are determined by the flavour symmetry itself
without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is
exact in leading order while all the mixing angles receive corrections of the
same order in next-to-the-leading approximation. As a consequence the predicted
value of is within the sensitivity of the experiments which will
take data in the near future. The light neutrino spectrum, typical of
see-saw models, with its phenomenological implications, also including
leptoproduction, is studied in detail.Comment: 20 pages, 2 figure
Leptonic CP Violation and Neutrino Mass Models
We discuss leptonic mixing and CP violation at low and high energies,
emphasizing possible connections between leptogenesis and CP violation at low
energies, in the context of lepton flavour models. Furthermore we analyse weak
basis invariants relevant for leptogenesis and for CP violation at low
energies. These invariants have the advantage of providing a simple test of the
CP properties of any lepton flavour model.Comment: 26 pages, no figures, submitted to the Focus Issue on `Neutrino
Physics` edited by F. Halzen, M. Lindner and A. Suzuki, to be published in
New Journal of Physic
Large Neutrino Mixing with Universal Strength of Yukawa Couplings
We analyse, within the framework of universal strength for Yukawa couplings
(USY), various structures for the Dirac and Majorana neutrino mass matrices
giving rise, through the see-saw mechanism, to a degenerate mass spectrum. A
specific USY ansatz is presented for the charged lepton and neutrino effective
mass matrix, leading to quasi-degenerate neutrinos and a leptonic mixing matrix
which provides a large angle solution for both the atmospheric and solar
neutrino problems.Comment: 7 pages, ReVTeX, small comments adde
Radiation from a D-dimensional collision of shock waves: first order perturbation theory
We study the spacetime obtained by superimposing two equal Aichelburg-Sexl
shock waves in D dimensions traveling, head-on, in opposite directions.
Considering the collision in a boosted frame, one shock becomes stronger than
the other, and a perturbative framework to compute the metric in the future of
the collision is setup. The geometry is given, in first order perturbation
theory, as an integral solution, in terms of initial data on the null surface
where the strong shock has support. We then extract the radiation emitted in
the collision by using a D-dimensional generalisation of the Landau-Lifschitz
pseudo-tensor and compute the percentage of the initial centre of mass energy
epsilon emitted as gravitational waves. In D=4 we find epsilon=25.0%, in
agreement with the result of D'Eath and Payne. As D increases, this percentage
increases monotonically, reaching 40.0% in D=10. Our result is always within
the bound obtained from apparent horizons by Penrose, in D=4, yielding 29.3%,
and Eardley and Giddings, in D> 4, which also increases monotonically with
dimension, reaching 41.2% in D=10. We also present the wave forms and provide a
physical interpretation for the observed peaks, in terms of the null generators
of the shocks.Comment: 27 pages, 11 figures; v2 some corrections, including D dependent
factor in epsilon; matches version accepted in JHE
Degenerate and Quasi Degenerate Majorana Neutrinos
We study mixing and CP violation of three left-handed Majorana neutrinos in
the limit of exactly degenerate masses, identify the weak-basis invariant
relevant for CP violation and show that the leptonic mixing matrix is
parametrized only by two angles and one phase. After the lifting of the
degeneracy, this parametrization accommodates the present data on atmospheric
and solar neutrinos, as well as double beta decay. Some of the leptonic mixing
ansatze suggested in the literature correspond to special cases of this
parametrization.Comment: 9 page
Autosomal dominant optic atrophy and cataract “plus” phenotype including axonal neuropathy
Objective To characterize the phenotype in individuals with OPA3-related autosomal dominant optic atrophy and cataract (ADOAC) and peripheral neuropathy (PN).
Methods Two probands with multiple affected relatives and one sporadic case were referred for evaluation of a PN. Their phenotype was determined by clinical ± neurophysiological assessment. Neuropathologic examination of sural nerve and skeletal muscle, and ultrastructural analysis of mitochondria in fibroblasts were performed in one case. Exome sequencing was performed in the probands.
Results The main clinical features in one family (n = 7 affected individuals) and one sporadic case were early-onset cataracts (n = 7), symptoms of gastrointestinal dysmotility (n = 8), and possible/confirmed PN (n = 7). Impaired vision was an early-onset feature in another family (n = 4 affected individuals), in which 3 members had symptoms of gastrointestinal dysmotility and 2 developed PN and cataracts. The less common features among all individuals included symptoms/signs of autonomic dysfunction (n = 3), hearing loss (n = 3), and recurrent pancreatitis (n = 1). In 5 individuals, the neuropathy was axonal and clinically asymptomatic (n = 1), sensory-predominant (n = 2), or motor and sensory (n = 2). In one patient, nerve biopsy revealed a loss of large and small myelinated fibers. In fibroblasts, mitochondria were frequently enlarged with slightly fragmented cristae. The exome sequencing identified OPA3 variants in all probands: a novel variant (c.23T>C) and the known mutation (c.313C>G) in OPA3.
Conclusions A syndromic form of ADOAC (ADOAC+), in which axonal neuropathy may be a major feature, is described. OPA3 mutations should be included in the differential diagnosis of complex inherited PN, even in the absence of clinically apparent optic atrophy
Minimal Scenarios for Leptogenesis and CP Violation
The relation between leptogenesis and CP violation at low energies is
analyzed in detail in the framework of the minimal seesaw mechanism. Working,
without loss of generality, in a weak basis where both the charged lepton and
the right-handed Majorana mass matrices are diagonal and real, we consider a
convenient generic parametrization of the Dirac neutrino Yukawa coupling matrix
and identify the necessary condition which has to be satisfied in order to
establish a direct link between leptogenesis and CP violation at low energies.
In the context of the LMA solution of the solar neutrino problem, we present
minimal scenarios which allow for the full determination of the cosmological
baryon asymmetry and the strength of CP violation in neutrino oscillations.
Some specific realizations of these minimal scenarios are considered. The
question of the relative sign between the baryon asymmetry and CP violation at
low energies is also discussed.Comment: 36 pages, 5 figures; minor corrections and references updated. Final
version to appear in Phys. Rev.
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