701 research outputs found
The Oxidation State of Iron in Silicate Minerals from the Matrices of CO Carbonaceous Chondrites
No abstract available
The Oxidation State of Iron in Silicate Minerals from the Matrices of CO Carbonaceous Chondrites
No abstract available
Deviation of Atmospheric Mixing from Maximal and Structure in the Leptonic Flavor Sector
I attempt to quantify how far from maximal one should expect the atmospheric
mixing angle to be given a neutrino mass-matrix that leads, at zeroth order, to
a nu_3 mass-eigenstate that is 0% nu_e, 50% nu_mu, and 50% nu_tau. This is done
by assuming that the solar mass-squared difference is induced by an
"anarchical" first order perturbation, an approach than can naturally lead to
experimentally allowed values for all oscillation parameters. In particular,
both |cos 2theta_atm| (the measure for the deviation of atmospheric mixing from
maximal) and |U_e3| are of order sqrt(Delta m^2_sol/Delta m^2_atm) in the case
of a normal neutrino mass-hierarchy, or of order Delta m^2_sol/Delta m^2_atm in
the case of an inverted one. Hence, if any of the textures analyzed here has
anything to do with reality, next-generation neutrino experiments can see a
nonzero cos 2theta_atm in the case of a normal mass-hierarchy, while in the
case of an inverted mass-hierarchy only neutrino factories should be able to
see a deviation of sin^2 2theta_atm from 1.Comment: 12 pages, no figures, references and acknowledgments adde
A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4
We discuss a grand unified model based on SUSY SU(5) in extra dimensions and
on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing
for neutrinos with the accuracy required by the data, also leads to a natural
description of the observed pattern of quark masses and mixings.Comment: 19 page
Energy Independent Solution to the Solar Neutrino Anomaly including the SNO data
The global data on solar neutrino rates and spectrum, including the SNO
charged current rate, can be explained by LMA, LOW or the energy independent
solution -- corresponding to near-maximal mixing. All the three favour a mild
upward renormalisation of the Cl rate. A mild downward shift of the
neutrino flux is favoured by the energy independent and to a lesser extent the
LOW solution, but not by LMA. Comparison with the ratio of SK elastic and SNO
charged current scattering rates favours the LMA over the other two solutions,
but by no more than .Comment: 18 pages, latex, 3 figure
Renormalization Group Running of Lepton Mixing Parameters in See-Saw Models with Flavor Symmetry
We study the renormalization group running of the tri-bimaximal mixing
predicted by the two typical flavor models at leading order. Although the
textures of the mass matrices are completely different, the evolution of
neutrino mass and mixing parameters is found to display approximately the same
pattern. For both normal hierarchy and inverted hierarchy spectrum, the quantum
corrections to both atmospheric and reactor neutrino mixing angles are so small
that they can be neglected. The evolution of the solar mixing angle
depends on and neutrino mass spectrum, the deviation
from its tri-bimaximal value could be large. Taking into account the
renormalization group running effect, the neutrino spectrum is constrained by
experimental data on in addition to the self-consistency
conditions of the models, and the inverted hierarchy spectrum is disfavored for
large . The evolution of light-neutrino masses is approximately
described by a common scaling factor.Comment: 23 pages, 6figure
Neutrino mixing matrices with relatively large and with texture one-zero
The recent T2K, MINOS and Double Chooz oscillation data hint a relatively
large , which can be accommodated by some general modification of
the Tribimaximal/Bimaximal/Democratic mixing matrices. Using such matrices we
analyze several Majorana mass matrices with texture one-zero and show whether
they satisfy normal or inverted mass hierarchy and phenomenologically viable or
not.Comment: 16 pages, 3 figures, minor modification in the text, version to
appear in EPJ
Alteration conditions on the CM and CV parent bodies – Insights from hydrothermal experiments with the CO chondrite Kainsaz
This study simulates the hydrothermal conditions that existed on carbonaceous chondrite planetesimals in the early solar system. Our experiments are relevant to alteration conditions that existed on the CV parent body and the late stage oxidizing alteration of the CM chondrites. We conducted 11 alteration experiments using chips of the CO3 chondrite Kainsaz. Water was added to each chip and sealed in separate Teflon reaction vessels for 175 days. Samples were altered at different initial water-to-rock ratios (W/R: 0.2–0.8) and temperatures (50 °C and 150 °C). Isotopically doped 17O-rich heavy water (δ17O: +64.5‰) was used in five runs. All samples experienced pronounced alteration under a partially open system environment where gases were able to escape the reaction vessels.
The style of alteration (Fe-alkali metasomatism) is similar in all cases. The principal alteration minerals formed are Fe-oxyhydroxides (goethite) and Fe-oxides (magnetite), with smaller quantities of Fe-sulphides. Minor phases formed include fayalite, sulphates (gypsum and Fe-sulphate) and calcite. Nanophase, poorly crystalline phyllosilicates formed in the high-temperature samples but are absent from the low-temperature experiments. In all instances, Mg-rich chondrule silicates remained chemically unaltered although some grains suffered hydrothermal fracture. Chondrule mesostases remained largely unaffected. By contrast, kamacite readily dissolved, acting as a source of Fe and Ni for the fluid phase. A new generation of nanophase Fe-sulphides formed within the matrix, while pre-existing pyrrhotite group sulphides experienced Ni enrichment ( 10 at%) were formed in the 150 °C samples, most likely by sulphidation of taenite.
Matrix alteration cemented grains together, reducing porosity. The fine-grained matrix shows highly variable degrees of alteration, with minimally altered matrix in direct contact with regions of heavily altered matrix. Chondrule fine-grained rims (FGRs) were preferentially altered. These textures imply that the unaltered matrix readily reacted with the fluid phase, resulting in an efficient depletion of dissolved ions (Fe2+ and S2-), limiting reactivity until further primary phases were dissolved. At larger length-scales the distribution of heavily altered matrix reveals the presence of large ∼100 µm wide channels that meander through the specimens. Their textures resemble features seen in some CM chondrites and the ungrouped CO-like chondrite MIL 07687. We suggest that alteration fronts developed by sustained rapid reaction of matrix with dissolved cations in solution. Our observations provide a mechanism for the establishment and maintenance of geochemical microenvironments on chondritic asteroids. The effects of open system loss notwithstanding, our experiments demonstrate that more advanced alteration is correlated with higher initial W/R ratios.
The use of 17O-rich doped water allowed the isotopic effects of aqueous alteration to be observed. Bulk rock compositions evolved towards the initial water composition, reflecting the incorporation of heavy O into hydrated minerals. Additionally, altered samples shifted in δ18O space, reflecting the competing effects of water–mineral fractionation and mass fractionation due to the preferential escape of isotopically light water
High-spatial resolution functional chemistry of nitrogen compounds in the observed UK meteorite fall Winchcombe
Organic matter in extraterrestrial samples is a complex material that might have played an important role in the delivery of prebiotic molecules to the early Earth. We report here on the identification of nitrogen-containing compounds such as amino acids and N-heterocycles within the recent observed meteorite fall Winchcombe by high-spatial resolution spectroscopy techniques. Although nitrogen contents of Winchcombe organic matter are low (N/C ~ 1–3%), we were able to detect the presence of these compounds using a low-noise direct electron detector. These biologically relevant molecules have therefore been tentatively found within a fresh, minimally processed meteorite sample by high spatial resolution techniques conserving the overall petrographic context. Carbon functional chemistry investigations show that sizes of aromatic domains are small and that abundances of carboxylic functional groups are low. Our observations demonstrate that Winchcombe represents an important addition to the collection of carbonaceous chondrites and still preserves pristine extraterrestrial organic matter
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