6,029 research outputs found
Matter Enhanced Neutrino Oscillations with a Realistic Earth Density Profile
We have investigated matter enhanced neutrino oscillations with a
mantle-core-mantle step function and a realistic Earth matter density profile
in both a two and a three neutrino scenario. We found that the realistic Earth
matter density profile can be well approximated with the mantle-core-mantle
step function and that there could be an influence on the oscillation channel
due to resonant enhancement of one of the mixing angles.Comment: 8 pages, 5 figures (PostScript), MPLA LaTe
Matter profile effect in neutrino factory
We point out that the matter profile effect --- the effect of matter density
fluctuation on the baseline --- is very important to estimate the parameters in
a neutrino factory with a very long baseline. To make it clear, we propose the
method of the Fourier series expansion of the matter profile. By using this
method, we can take account of both the matter profile effect and its
ambiguity. For very long baseline experiment, such as L=7332km, in the analysis
of the oscillation phenomena we need to introduce a new parameter ---
the Fourier coefficient of the matter profile --- as a theoretical parameter to
deal with the matter profile effects.Comment: 21 pages, 15 figure
Nambu-Goldstone Modes in Gravitational Theories with Spontaneous Lorentz Breaking
Spontaneous breaking of Lorentz symmetry has been suggested as a possible
mechanism that might occur in the context of a fundamental Planck-scale theory,
such as string theory or a quantum theory of gravity. However, if Lorentz
symmetry is spontaneously broken, two sets of questions immediately arise: what
is the fate of the Nambu-Goldstone modes, and can a Higgs mechanism occur? A
brief summary of some recent work looking at these questions is presented here.Comment: 6 pages. Presented at the meeting "From Quantum to Cosmos,"
Washington, D.C., May 2006; published in Int. J. Mod. Phys. D16:2357-2363,
200
Breaking Eight-fold Degeneracies in Neutrino CP Violation, Mixing, and Mass Hierarchy
We identify three independent two-fold parameter degeneracies (\delta,
\theta_{13}), sgn(\delta m^2_{31}) and (\theta_{23}, \pi/2-\theta_{23})
inherent in the usual three-neutrino analysis of long-baseline neutrino
experiments, which can lead to as much as an eight-fold degeneracy in the
determination of the oscillation parameters. We discuss the implications these
degeneracies have for detecting CP violation and present criteria for breaking
them. A superbeam facility with a baseline at least as long as the distance
between Fermilab and Homestake (1290 km) and a narrow band beam with energy
tuned so that the measurements are performed at the first oscillation peak can
resolve all the ambiguities other than the (\theta_{23}, \pi/2-\theta_{23})
ambiguity (which can be resolved at a neutrino factory) and a residual (\delta,
\pi-\delta) ambiguity. However, whether or not CP violation occurs in the
neutrino sector can be ascertained independently of the latter two ambiguities.
The (\delta,\pi-\delta) ambiguity can be eliminated by performing a second
measurement to which only the \cos\delta terms contribute. The hierarchy of
mass eigenstates can be determined at other oscillation peaks only in the most
optimistic conditions, making it necessary to use the first oscillation
maximum. We show that the degeneracies may severely compromise the ability of
the proposed SuperJHF-HyperKamiokande experiment to establish CP violation. In
our calculations we use approximate analytic expressions for oscillation
probabilitites that agree with numerical solutions with a realistic Earth
density profile.Comment: Revtex (singlespaced), 35 pages, 15 postscript figures, uses
psfig.st
Heavy quarks in deeply virtual Compton scattering
A detailed study of the heavy quark h=c,b,... contributions to deeply virtual
Compton scattering is performed at both the amplitude and the cross section
level, and their phenomenological relevance is discussed. For this purpose I
calculate the lowest order off-forward photon-gluon scattering amplitude with a
massive quark loop and the corresponding hard scattering coefficients. In a
first numerical analysis these fixed order perturbation theory results are
compared with the conventional intrinsic "massless" parton approach considering
generalized parton distributions for the heavy quarks. The differences between
these two prescriptions can be quite significant, especially at small
skewedness where the massless approach largely overestimates the deeply virtual
Compton scattering cross section.Comment: 15 pages, 12 eps-figures, LaTeX2e; (V2) include correct figure 3b,
remove 'bottom' from figure caption
Signed zeros of Gaussian vector fields-density, correlation functions and curvature
We calculate correlation functions of the (signed) density of zeros of
Gaussian distributed vector fields. We are able to express correlation
functions of arbitrary order through the curvature tensor of a certain abstract
Riemann-Cartan or Riemannian manifold. As an application, we discuss one- and
two-point functions. The zeros of a two-dimensional Gaussian vector field model
the distribution of topological defects in the high-temperature phase of
two-dimensional systems with orientational degrees of freedom, such as
superfluid films, thin superconductors and liquid crystals.Comment: 14 pages, 1 figure, uses iopart.cls, improved presentation, to appear
in J. Phys.
On the Optimum Long Baseline for the Next Generation Neutrino Oscillation Experiments
For high energy long baseline neutrino oscillation experiments, we propose a
Figure of Merit criterion to compare the statistical quality of experiments at
various oscillation distances under the condition of identical detectors and a
given neutrino beam. We take into account all possible experimental errors
under general consideration. In this way the Figure of Merit is closely related
to the usual statistical criterion of number of sigmas. We use a realistic
neutrino beam for an entry level neutrino factory and a possible superbeam from
a meson source and a 100 kt detector for the calculation. We considered in
detail four oscillation distances, 300 km, 700 km, 2100 km and 3000 km, in the
neutrino energy range of 0.5-20 GeV for a 20 GeV entry level neutrino factory
and a 50 GeV superbeam. We found that the very long baselines of 2100 km and
3000 km are preferred for the neutrino factory according to the figure of merit
criterion. Our results also show that, for a neutrino factory, lower primary
muon energies such as 20 GeV are preferred rather than higher ones such as 30
or 50 GeV. For the superbeam, the combination of a long baseline such as 300 km
and a very long baseline like 2100 km will form a complete measurement of the
oscillation parameters besides the CP phase. To measure the CP phase in a
superbeam, a larger detector (a factor 3 beyond what is considered in this
article) and/or a higher intensity beam will be needed to put some significant
constraints on the size of the CP angle.Comment: 21 LaTeX pages, 13 PS figures, typos corrected, references adde
Analysis and optimization of a free-electron laser with an irregular waveguide
Using a time-dependent approach the analysis and optimization of a planar
FEL-amplifier with an axial magnetic field and an irregular waveguide is
performed. By applying methods of nonlinear dynamics three-dimensional
equations of motion and the excitation equation are partly integrated in an
analytical way. As a result, a self-consistent reduced model of the FEL is
built in special phase space. The reduced model is the generalization of the
Colson-Bonifacio model and takes into account the intricate dynamics of
electrons in the pump magnetic field and the intramode scattering in the
irregular waveguide. The reduced model and concepts of evolutionary computation
are used to find optimal waveguide profiles. The numerical simulation of the
original non-simplified model is performed to check the effectiveness of found
optimal profiles. The FEL parameters are chosen to be close to the parameters
of the experiment (S. Cheng et al. IEEE Trans. Plasma Sci. 1996, vol. 24, p.
750), in which a sheet electron beam with the moderate thickness interacts with
the TE01 mode of a rectangular waveguide. The results strongly indicate that
one can improve the efficiency by a factor of five or six if the FEL operates
in the magnetoresonance regime and if the irregular waveguide with the
optimized profile is used
Three-Dimensional Ab Initio Quantum Dynamics of the Photodesorption of CO from Cr<sub>2</sub>O<sub>3</sub>(0001): Stereodynamic Effects
Having performed the first three-dimensional ab initio quantum dynamical study of photodesorption from solid surfaces, we gained mechanistic understanding of the rotational alignment observed in the CO/Cr2O3(0001) system. Our study is based on potential energy surfaces obtained by embedded cluster calculations for both the electronic ground and excited state of the adsorbate substrate complex. Stochastic wave packet calculations demonstrate the importance of the angular degrees of freedom for the microscopic picture of the desorption process in addition to the desorption coordinate
Learning from Minimum Entropy Queries in a Large Committee Machine
In supervised learning, the redundancy contained in random examples can be
avoided by learning from queries. Using statistical mechanics, we study
learning from minimum entropy queries in a large tree-committee machine. The
generalization error decreases exponentially with the number of training
examples, providing a significant improvement over the algebraic decay for
random examples. The connection between entropy and generalization error in
multi-layer networks is discussed, and a computationally cheap algorithm for
constructing queries is suggested and analysed.Comment: 4 pages, REVTeX, multicol, epsf, two postscript figures. To appear in
Physical Review E (Rapid Communications
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