440 research outputs found
Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation
Magnetic refrigeration based on the magnetocaloric effect at room temperature
is one of the most attractive alternative to the current gas
compression/expansion method routinely employed. Nevertheless, in giant
magnetocaloric materials, optimal refrigeration is restricted to the narrow
temperature window of the phase transition (Tc). In this work, we present the
possibility of varying this transition temperature into a same giant
magnetocaloric material by ion irradiation. We demonstrate that the transition
temperature of iron rhodium thin films can be tuned by the bombardment of ions
of Ne 5+ with varying fluences up to 10 14 ions cm --2 , leading to optimal
refrigeration over a large 270--380 K temperature window. The Tc modification
is found to be due to the ion-induced disorder and to the density of new
point-like defects. The variation of the phase transition temperature with the
number of incident ions opens new perspectives in the conception of devices
using giant magnetocaloric materials
New CP Violation in Neutrino Oscillations
Measurements of CP--violating observables in neutrino oscillation experiments
have been studied in the literature as a way to determine the CP--violating
phase in the mixing matrix for leptons. Here we show that such observables also
probe new neutrino interactions in the production or detection processes.
Genuine CP violation and fake CP violation due to matter effects are sensitive
to the imaginary and real parts of new couplings. The dependence of the CP
asymmetry on source--detector distance is different from the standard one and,
in particular, enhanced at short distances. We estimate that future neutrino
factories will be able to probe in this way new interactions that are up to
four orders of magnitude weaker than the weak interactions. We discuss the
possible implications for models of new physics.Comment: ReVTeX, 28 pages, 7 figues. v2: Modifications in section VIII to
reflect the fact that some of the couplings that were discussed in this
section are irrelevant to our analysis (as pointed out in hep-ph/0112329);
Added a discussion in section IX of the relevance of other future experiments
that will search for lepton flavor violatio
Confusing non-standard neutrino interactions with oscillations at a neutrino factory
Most neutrino mass theories contain non-standard interactions (NSI) of
neutrinos which can be either non-universal (NU) or flavor-changing (FC). We
study the impact of such interactions on the determination of neutrino mixing
parameters at a neutrino factory using the so-called ``golden channels''
\pnu{e}\to\pnu{\mu} for the measurement of \theta_{13}. We show that a certain
combination of FC interactions in neutrino source and earth matter can give
exactly the same signal as oscillations arising due to \theta_{13}. This
implies that information about \theta_{13} can only be obtained if bounds on
NSI are available. Taking into account the existing bounds on FC interactions,
this leads to a drastic loss in sensitivity in \theta_{13}, at least two orders
of magnitude. A near detector at a neutrino factory offers the possibility to
obtain stringent bounds on some NSI parameters. Such near site detector
constitutes an essential ingredient of a neutrino factory and a necessary step
towards the determination of \theta_{13} and subsequent study of leptonic CP
violation.Comment: 23 pages, 5 figures, improved version, accepted for publication in
Phs. Rev. D, references adde
Constraint-based, Single-point Approximate Kinetic Energy Functionals
We present a substantial extension of our constraint-based approach for
development of orbital-free (OF) kinetic-energy (KE) density functionals
intended for the calculation of quantum-mechanical forces in multi-scale
molecular dynamics simulations. Suitability for realistic system simulations
requires that the OF-KE functional yield accurate forces on the nuclei yet be
relatively simple. We therefore require that the functionals be based on DFT
constraints, local, dependent upon a small number of parameters fitted to a
training set of limited size, and applicable beyond the scope of the training
set. Our previous "modified conjoint" generalized-gradient-type functionals
were constrained to producing a positive-definite Pauli potential. Though
distinctly better than several published GGA-type functionals in that they gave
semi-quantitative agreement with Born-Oppenheimer forces from full Kohn-Sham
results, those modified conjoint functionals suffer from unphysical
singularities at the nuclei. Here we show how to remove such singularities by
introducing higher-order density derivatives. We give a simple illustration of
such a functional used for the dissociation energy as a function of bond length
for selected molecules.Comment: 16 pages, 9 figures, 2 tables, submitted to Phys. Rev.
In Quest of Neutrino Masses at (eV) Scale
Neutrino oscillation and tritium beta decay experiments taken simultaneously
into account are able to access the so far imperceptible absolute neutrino
masses at the electronvolt level. The neutrino mass spectrum derived in this
way is independent of the nature of neutrinos (Dirac or Majorana). Furthermore,
the lack of neutrinoless double beta decay gives additional constraints on the
Majorana neutrino mass spectrum. A case of three neutrinos is examined.
Influence of different solutions to the solar neutrino deficit problem on the
results is discussed. Apart from the present situation, four qualitatively
distinct experimental situations which are possible in the future are
investigated: when the two decay experiments give only upper bounds on
effective neutrino masses, when either one of them gives a positive result, and
when both give positive results. The discussion is carried out by taking into
account the present experimental errors of relevant neutrino parameters as well
as their much more precise expected estimations (e.g. by factories). It
is shown in which cases the upgraded decay experiments simultaneously with
neutrino oscillation data may be able to fix the absolute scale of the neutrino
mass spectrum, answer the question of the neutrino nature and put some light on
CP phases in the lepton sector.Comment: 30 pages, 6 figs, to appear in PR
Phenomenology of Maximal and Near-Maximal Lepton Mixing
We study the phenomenological consequences of maximal and near-maximal mixing
of the electron neutrino with other (=tau and/or muon) neutrinos. We
describe the deviations from maximal mixing in terms of a parameter
and quantify the present experimental
status for . We find that the global analysis of solar neutrino
data allows maximal mixing with confidence level better than 99% for
eV^2\lsim\Delta m^2\lsim2\times10^{-7} eV. In the mass ranges \Delta
m^2\gsim 1.5\times10^{-5} eV and eV^2\lsim\Delta
m^2\lsim2\times10^{-7} eV the full interval is allowed
within 4(99.995 % CL). We suggest ways to measure in future
experiments. The observable that is most sensitive to is the rate
[NC]/[CC] in combination with the Day-Night asymmetry in the SNO detector. With
theoretical and statistical uncertainties, the expected accuracy after 5 years
is . We also discuss the effects of maximal and
near-maximal -mixing in atmospheric neutrinos, supernova neutrinos, and
neutrinoless double beta decay.Comment: 49 pages Latex file using RevTeX. 16 postscript figures included. (
Fig.2 and Fig.4 bitmapped for compression,better resolution at
http://ific.uv.es/~pppac/). Improved presentation: some statements included
and labels added in figures. Some misprint corrected. Final version to appear
in Phys. Rev D. Report no: IFIC/00-40, IASSNS-HEP-00-5
Neutrino hierarchy from CP-blind observables with high density magnetized detectors
High density magnetized detectors are well suited to exploit the outstanding
purity and intensities of novel neutrino sources like Neutrino Factories and
Beta Beams. They can also provide independent measurements of leptonic mixing
parameters through the observation of atmospheric muon-neutrinos. In this
paper, we discuss the combination of these observables from a multi-kton iron
detector and a high energy Beta Beam; in particular, we demonstrate that even
with moderate detector granularities the neutrino mass hierarchy can be
determined for values greater than 4.Comment: 16 pages, 7 figures. Added a new section discussing systematic errors
(sec 5.2); sec.5.1 and 4 have been extended. Version to appear in EPJ
Theoretical and experimental evidence of level repulsion states and evanescent modes in sonic crystal stubbed waveguides
The complex band structures calculated using the Extended Plane Wave
Expansion (EPWE) reveal the presence of evanescent modes in periodic systems,
never predicted by the classical \omega(\vec{k}) methods, providing novel
interpretations of several phenomena as well as a complete picture of the
system. In this work we theoretically and experimentally observe that in the
ranges of frequencies where a deaf band is traditionally predicted, an
evanescent mode with the excitable symmetry appears changing drastically the
interpretation of the transmission properties. On the other hand, the
simplicity of the sonic crystals in which only the longitudinal polarization
can be excited, is used to interpret, without loss of generality, the level
repulsion between symmetric and antisymmetric bands in sonic crystals as the
presence of an evanescent mode connecting both repelled bands. These evanescent
modes, obtained using EPWE, explain both the attenuation produced in this range
of frequencies and the transfer of symmetry from one band to the other in good
agreement with both experimental results and multiple scattering predictions.
Thus, the evanescent properties of the periodic system have been revealed
necessary for the design of new acoustic and electromagnetic applications based
on periodicity
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