9,959 research outputs found
"Just So" Neutrino Oscillations Are Back
Recent evidence for oscillations of atmospheric neutrinos at Super-Kamiokande
suggest, in the simplest see-saw interpretation, neutrino masses such that
`just so' vacuum oscillations can explain the solar neutrino deficit. Super-K
solar neutrino data provide preliminary support for this interpretation. We
describe how the just-so signal---an energy dependent seasonal variation of the
event rate, might be detected within the coming years and provide general
arguments constraining the sign of the variation. The expected variation at
radiochemical detectors may be below present sensitivity, but a significant
modulation in the Be signal could shed light on the physics of the solar
core---including a direct measure of the solar core temperature.Comment: 4 pages, revtex, 4 ps figs: new refs added, and Super-K energy
resolution function incorporate
Next--to--Leading Order QCD corrections for the --mixing with an extended Higgs sector
We present a calculation of the B0-B0--mixing including Next--to--Leading
Order (NLO) QCD corrections within the Two Higgs Doublet Model (2HDM). The QCD
corrections at NLO are contained in the factor denoted by eta_2 which modifies
the result obtained at the lowest order of perturbation theory. In the Standard
Model case, we confirm the results for eta_2 obtained by Buras, Jamin and
Weisz. The factor eta_2 is gauge and renormalization prescription invariant and
it does not depend on the infrared behaviour of the theory, which constitutes
an important test of the calculations. The NLO--calculations within the 2HDM
enhance the LO--result up to 18%, which affects the correlation between M_H and
V_{td}.Comment: 22 pages (LaTeX), 22 Postscript figures, version to appear in Nucl.
Phys. B, corrected some typos and a sign in the program, which results in
changes in Eqs. (71), (74) and (75). Due to these changes Eqs. (23) and (34)
may be written in a more compact wa
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Boron carboxylate catalysis of homoallylboration.
Boron tris(trifluoroacetate) is identified as the first effective catalyst for the homoallyl- and homocrotylboration of aldehydes by cyclopropylcarbinylboronates. NMR spectroscopic studies and theoretical calculations of key intermediates and transition states both suggest that a ligand-exchange mechanism, akin to our previously reported PhBCl2-promoted homoallylations, is operative. Our experimental and theoretical results also suggest that the catalytic activity of boron tris(trifluoroacetate) might originate from more facile catalytic turnover of the trifluoroacetate ligands (in agreement with DFT calculations) or from a lower propensity for formation of off-pathway reservoir intermediates (as observed by (1)H NMR). This work shows that carboxylates are viable catalytic ligands for homoallyl- and homocrotylations of carbonyl compounds and opens the door to the development of catalytic asymmetric versions of this transformation
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