14,357 research outputs found
Which long-baseline neutrino experiments are preferable?
We discuss the physics of superbeam upgrades, where we focus on T2KK, a NuMI
beam line based experiment NOvA*, and a wide band beam (WBB) experiment
independent of the NuMI beam line. For T2KK, we find that the Japan-Korea
baseline helps resolve parameter degeneracies, but the improvement due to
correlated systematics between the two detectors (using identical detectors) is
only moderate. For an upgrade of NOvA with a liquid argon detector, we
demonstrate that the Ash River site is preferred compared to alternatives, such
as at the second oscillation maximum, and is the optimal site within the U.S.
For a WBB experiment, we find that high proton energies and long decay tunnels
are preferable. We compare water Cherenkov and liquid argon technologies, and
find the break-even point in detector cost at about 4:1. In order to compare
the physics potential of the different experimental configurations, we use the
concept of exposure to normalize the performance. We find that experiments with
WBBs are the best experimental concept. NOvA* could be competitive with
sufficient luminosity. If > 0.01, a WBB experiment can
perform better than a neutrino factory.Comment: 31 pages, 13 figures, 5 tables. Version to appear in PR
A Census Of Highly Symmetric Combinatorial Designs
As a consequence of the classification of the finite simple groups, it has
been possible in recent years to characterize Steiner t-designs, that is
t-(v,k,1) designs, mainly for t = 2, admitting groups of automorphisms with
sufficiently strong symmetry properties. However, despite the finite simple
group classification, for Steiner t-designs with t > 2 most of these
characterizations have remained longstanding challenging problems. Especially,
the determination of all flag-transitive Steiner t-designs with 2 < t < 7 is of
particular interest and has been open for about 40 years (cf. [11, p. 147] and
[12, p. 273], but presumably dating back to 1965). The present paper continues
the author's work [20, 21, 22] of classifying all flag-transitive Steiner
3-designs and 4-designs. We give a complete classification of all
flag-transitive Steiner 5-designs and prove furthermore that there are no
non-trivial flag-transitive Steiner 6-designs. Both results rely on the
classification of the finite 3-homogeneous permutation groups. Moreover, we
survey some of the most general results on highly symmetric Steiner t-designs.Comment: 26 pages; to appear in: "Journal of Algebraic Combinatorics
Topologically non-trivial quantum layers
Given a complete non-compact surface embedded in R^3, we consider the
Dirichlet Laplacian in a layer of constant width about the surface. Using an
intrinsic approach to the layer geometry, we generalise the spectral results of
an original paper by Duclos et al. to the situation when the surface does not
possess poles. This enables us to consider topologically more complicated
layers and state new spectral results. In particular, we are interested in
layers built over surfaces with handles or several cylindrically symmetric
ends. We also discuss more general regions obtained by compact deformations of
certain layers.Comment: 15 pages, 6 figure
First-principles investigation of Ag-Cu alloy surfaces in an oxidizing environment
In this paper we investigate by means of first-principles density functional
theory calculations the (111) surface of the Ag-Cu alloy under varying
conditions of pressure of the surrounding oxygen atmosphere and temperature.
This alloy has been recently proposed as a catalyst with improved selectivity
for ethylene epoxidation with respect to pure silver, the catalyst commonly
used in industrial applications. Here we show that the presence of oxygen leads
to copper segregation to the surface. Considering the surface free energy as a
function of the surface composition, we construct the convex hull to
investigate the stability of various surface structures. By including the
dependence of the free surface energy on the oxygen chemical potential, we are
able compute the phase diagram of the alloy as a function of temperature,
pressure and surface composition. We find that, at temperature and pressure
typically used in ethylene epoxidation, a number of structures can be present
on the surface of the alloy, including clean Ag(111), thin layers of copper
oxide and thick oxide-like structures. These results are consistent with, and
help explain, recent experimental results.Comment: 10 pages, 6 figure
Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data
The MOST (Microvariability & Oscillations of STars) satellite obtains
ultraprecise photometry from space with high sampling rates and duty cycles.
Astronomical photometry or imaging missions in low Earth orbits, like MOST, are
especially sensitive to scattered light from Earthshine, and all these missions
have a common need to extract target information from voluminous data cubes.
They consist of upwards of hundreds of thousands of two-dimensional CCD frames
(or sub-rasters) containing from hundreds to millions of pixels each, where the
target information, superposed on background and instrumental effects, is
contained only in a subset of pixels (Fabry Images, defocussed images,
mini-spectra). We describe a novel reduction technique for such data cubes:
resolving linear correlations of target and background pixel intensities. This
stepwise multiple linear regression removes only those target variations which
are also detected in the background. The advantage of regression analysis
versus background subtraction is the appropriate scaling, taking into account
that the amount of contamination may differ from pixel to pixel. The
multivariate solution for all pairs of target/background pixels is minimally
invasive of the raw photometry while being very effective in reducing
contamination due to, e.g., stray light. The technique is tested and
demonstrated with both simulated oscillation signals and real MOST photometry.Comment: 16 pages, 23 figure
Precision on leptonic mixing parameters at future neutrino oscillation experiments
We perform a comparison of the different future neutrino oscillation
experiments based on the achievable precision in the determination of the
fundamental parameters theta_{13} and the CP phase, delta, assuming that
theta_{13} is in the range indicated by the recent Daya Bay measurement. We
study the non-trivial dependence of the error on delta on its true value. When
matter effects are small, the largest error is found at the points where CP
violation is maximal, and the smallest at the CP conserving points. The
situation is different when matter effects are sizable. As a result of this
effect, the comparison of the physics reach of different experiments on the
basis of the CP discovery potential, as usually done, can be misleading. We
have compared various proposed super-beam, beta-beam and neutrino factory
setups on the basis of the relative precision of theta_{13} and the error on
delta. Neutrino factories, both high-energy or low-energy, outperform
alternative beam technologies. An ultimate precision on theta_{13} below 3% and
an error on delta of < 7^{\circ} at 1 sigma (1 d.o.f.) can be obtained at a
neutrino factory.Comment: Minor changes, matches version accepted in JHEP. 30 pages, 9 figure
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