300 research outputs found
Surface and Image-Potential States on the MgB_2(0001) Surfaces
We present a self-consistent pseudopotential calculation of surface and
image-potential states on for both -terminated () and
-terminated () surfaces. We find a variety of very clear surface and
subsurface states as well as resonance image-potential states n=1,2 on both
surfaces. The surface layer DOS at is increased by 55% at and by
90% at the surface compared to DOS in the corresponding bulk layers.Comment: 3 pages, 6 figure
Search for double beta decay of Zinc and Tungsten with the help of low-background ZnWO4 crystal scintillators
Double beta processes in 64-Zn, 70-Zn, 180-W, and 186-W have been searched
for with the help of large volume (0.1-0.7 kg) low background ZnWO4 crystal
scintillators at the Gran Sasso National Laboratories of the INFN. Total time
of measurements exceeds 10 thousands hours. New improved half-life limits on
double electron capture and electron capture with positron emission in 64-Zn
have been set, in particular (all the limits are at 90% C.L.): T1/2(0nu2EC)>
1.1e20 yr, T1/2(2nuECbeta+)>7.0e20 yr, and T1/2(0nuECbeta+)>4.3e20 yr. The
different modes of double beta processes in 70-Zn, 180-W, and 186-W have been
restricted at the level of 1e17-1e20 yr.Comment: 20 p., submitted to Phys. Rev.
The Majorana neutrino masses, neutrinoless double beta decay and nuclear matrix elements
The effective Majorana neutrino mass is evaluated by using the latest results
of neutrino oscillation experiments. The problems of the neutrino mass
spectrum,absolute mass scale of neutrinos and the effect of CP phases are
addressed. A connection to the next generation of the neutrinoless double beta
decay (0nbb-decay) experiments is discussed. The calculations are performed for
76Ge, 100Mo, 136Xe and 130Te by using the advantage of recently evaluated
nuclear matrix elements with significantly reduced theoretical uncertainty. An
importance of observation of the 0nbb-decay of several nuclei is stressed.Comment: 29 pages, 5 figures, EXO (10 t) experiment considere
Fermi Surfaces of Diborides: MgB2 and ZrB2
We provide a comparison of accurate full potential band calculations of the
Fermi surfaces areas and masses of MgB2 and ZrB2 with the de Haas-van Alphen
date of Yelland et al. and Tanaka et al., respectively. The discrepancies in
areas in MgB2 can be removed by a shift of sigma-bands downward with respect to
pi-bands by 0.24 eV. Comparison of effective masses lead to orbit averaged
electron-phonon coupling constants lambda(sigma)=1.3 (both orbits),
lambda(pi)=0.5. The required band shifts, which we interpret as an exchange
attraction for sigma states beyond local density band theory, reduces the
number of holes from 0.15 to 0.11 holes per cell. This makes the occurrence of
superconductivity in MgB2 a somewhat closer call than previously recognized,
and increases the likelihood that additional holes can lead to an increased Tc.Comment: 7 pages including 4 figure
Invisible Z-Boson Decays at e+e- Colliders
The measurement of the invisible Z-boson decay width at e+e- colliders can be
done "indirectly", by subtracting the Z-boson visible partial widths from the
Z-boson total width, or "directly", from the process e+e- -> \gamma \nu
\bar{\nu}. Both procedures are sensitive to different types of new physics and
provide information about the couplings of the neutrinos to the Z-boson. At
present, measurements at LEP and CHARM II are capable of constraining the
left-handed Z\nu\nu-coupling, 0.45 <~ g_L <~ 0.5, while the right-handed one is
only mildly bounded, |g_R| <= 0.2. We show that measurements at a future e+e-
linear collider at different center-of-mass energies, \sqrt{s} = MZ and
\sqrt{s}s ~ 170 GeV, would translate into a markedly more precise measurement
of the Z\nu\nu-couplings. A statistically significant deviation from Standard
Model predictions will point toward different new physics mechanisms, depending
on whether the discrepancy appears in the direct or the indirect measurement of
the invisible Z-width. We discuss some scenarios which illustrate the ability
of different invisible Z-boson decay measurements to constrain new physics
beyond the Standard Model
Bounds on the tau and muon neutrino vector and axial vector charge radius
A Majorana neutrino is characterized by just one flavor diagonal
electromagnetic form factor: the anapole moment, that in the static limit
corresponds to the axial vector charge radius . Experimental information
on this quantity is scarce, especially in the case of the tau neutrino. We
present a comprehensive analysis of the available data on the single photon
production process off Z-resonance, and we
discuss the constraints that these measurements can set on for the tau
neutrino. We also derive limits for the Dirac case, when the presence of a
vector charge radius is allowed. Finally, we comment on additional
experimental data on scattering from the NuTeV, E734, CCFR and
CHARM-II collaborations, and estimate the limits implied for and
for the muon neutrino.Comment: 20 pages, 2 eps figures. CCFR data included in the analysis.
Conclusion unchange
What can we learn from neutrinoless double beta decay experiments?
We assess how well next generation neutrinoless double beta decay and normal
neutrino beta decay experiments can answer four fundamental questions. 1) If
neutrinoless double beta decay searches do not detect a signal, and if the
spectrum is known to be inverted hierarchy, can we conclude that neutrinos are
Dirac particles? 2) If neutrinoless double beta decay searches are negative and
a next generation ordinary beta decay experiment detects the neutrino mass
scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless
double beta decay is observed with a large neutrino mass element, what is the
total mass in neutrinos? 4) If neutrinoless double beta decay is observed but
next generation beta decay searches for a neutrino mass only set a mass upper
limit, can we establish whether the mass hierarchy is normal or inverted? We
base our answers on the expected performance of next generation neutrinoless
double beta decay experiments and on simulations of the accuracy of
calculations of nuclear matrix elements.Comment: Added reference
Neutrino masses from beta decays after KamLAND and WMAP (Updated including the NC enhanced SNO data)
The first data released by the KamLAND collaboration have confirmed the
strong evidence in favour of the LMA solution of the solar neutrino problem.
Taking into account the ranges for the oscillation parameters allowed by the
global analysis of the solar, CHOOZ and KamLAND data, we update the limits on
the neutrinoless double beta decay effective neutrino mass parameter and
analyze the impact of all the available data from neutrinoless double beta
decay experiments on the neutrino mass bounds, in view of the latest WMAP
results. For the normal neutrino mass spectrum the range (0.05-0.23) eV is
obtained for the lightest neutrino mass if one takes into account the
Heidelberg-Moscow evidence for neutrinoless double beta decay and the
cosmological bound. It is also shown that under the same conditions the mass of
the lightest neutrino may not be bounded from below if the spectrum is of the
inverted type. Finnaly, we discuss how future experiments can improve the
present bounds on the lightest neutrino mass set by the Troitsk, Mainz and WMAP
results. In the addendum we update the allowed ranges for the effective
Majorana neutrino mass parameter in view of the latest NC enhanced SNO data.Comment: Updated including the recent NC enhanced SNO data. Refferences added
and typos correcte
Probing New Physics Models of Neutrinoless Double Beta Decay with SuperNEMO
The possibility to probe new physics scenarios of light Majorana neutrino
exchange and right-handed currents at the planned next generation neutrinoless
double beta decay experiment SuperNEMO is discussed. Its ability to study
different isotopes and track the outgoing electrons provides the means to
discriminate different underlying mechanisms for the neutrinoless double beta
decay by measuring the decay half-life and the electron angular and energy
distributions.Comment: 17 pages, 14 figures, to be published in E.P.J.
CABARET in the ocean gyres
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 30 (2009): 155-168, doi:10.1016/j.ocemod.2009.06.009.A new high-resolution Eulerian numerical method is proposed for modelling quasigeostrophic ocean
dynamics in eddying regimes. The method is based on a novel, second-order non-dissipative and lowdispersive
conservative advection scheme called CABARET. The properties of the new method are
compared with those of several high-resolution Eulerian methods for linear advection and gas
dynamics. Then, the CABARET method is applied to the classical model of the double-gyre ocean
circulation and its performance is contrasted against that of the common vorticity-preserving Arakawa
method. In turbulent regimes, the new method permits credible numerical simulations on much coarser
computational grids.Supports from the Royal Society of London and from the Mary Sears Visitor Grant are
acknowledged by SK with gratitude. The work of VG was supported by the Russian Foundation for
Basic Research (RFBR), grant 06-01-00819a. Funding for PB was provided by the NSF grant 0725796
- …