384 research outputs found
Resonance production by neutrinos: I. J=3/2 Resonances
The article contains general formulas for the production of J=3/2 resonances
by neutrinos and antineutrinos. It specializes to the P_{33}(1232) resonance
whose form factors are determined by theory and experiment and then are
compared with experimental results at low and high energies. It is shown that
the minimum in the low Q^2 region is a consequence of a combined effect from
the vanishing of the vector form factors, the muon mass and Pauli blocking.
Several improvements for the future investigations are suggested.Comment: 10 pages, LaTeX, misprints corrected, 1 reference adde
Time-approximation trade-offs for inapproximable problems
In this paper we focus on problems which do not admit a constant-factor approximation in polynomial time and explore how quickly their approximability improves as the allowed running time is gradually increased from polynomial to (sub-)exponential. We tackle a number of problems: For Min Independent Dominating Set, Max Induced Path, Forest and Tree, for any r(n), a simple, known scheme gives an approximation ratio of r in time roughly rn/r. We show that, for most values of r, if this running time could be significantly improved the ETH would fail. For Max Minimal Vertex Cover we give a nontrivial √r-approximation in time 2n/r. We match this with a similarly tight result. We also give a log r-approximation for Min ATSP in time 2n/r and an r-approximation for Max Grundy Coloring in time rn/r. Furthermore, we show that Min Set Cover exhibits a curious behavior in this superpolynomial setting: for any δ > 0 it admits an mδ-approximation, where m is the number of sets, in just quasi-polynomial time. We observe that if such ratios could be achieved in polynomial time, the ETH or the Projection Games Conjecture would fail. © Édouard Bonnet, Michael Lampis and Vangelis Th. Paschos; licensed under Creative Commons License CC-BY
On the Complexity of Local Search for Weighted Standard Set Problems
In this paper, we study the complexity of computing locally optimal solutions
for weighted versions of standard set problems such as SetCover, SetPacking,
and many more. For our investigation, we use the framework of PLS, as defined
in Johnson et al., [JPY88]. We show that for most of these problems, computing
a locally optimal solution is already PLS-complete for a simple neighborhood of
size one. For the local search versions of weighted SetPacking and SetCover, we
derive tight bounds for a simple neighborhood of size two. To the best of our
knowledge, these are one of the very few PLS results about local search for
weighted standard set problems
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
Methods to Determine Neutrino Flux at Low Energies:Investigation of the Low Method
We investigate the "low-" method (developed by the CCFR/NUTEV
collaborations) to determine the neutrino flux in a wide band neutrino beam at
very low energies, a region of interest to neutrino oscillations experiments.
Events with low hadronic final state energy (of 1, 2 and 5 GeV)
were used by the MINOS collaboration to determine the neutrino flux in their
measurements of neutrino () and antineutrino (\nub_\mu) total cross
sections. The lowest energy for which the method was used in MINOS is
3.5 GeV, and the lowest \nub_\mu energy is 6 GeV. At these energies, the
cross sections are dominated by inelastic processes. We investigate the
application of the method to determine the neutrino flux for ,
\nub_\mu energies as low as 0.7 GeV where the cross sections are dominated by
quasielastic scattering and (1232) resonance production. We find that
the method can be extended to low energies by using values of 0.25
and 0.50 GeV, which is feasible in fully active neutrino detectors such as
MINERvA.Comment: 25 pages, 32 figures, to be published in European Physics Journal
Positivity constraints for lepton polarization in neutrino deep inelastic scattering
We consider the spin polarization of leptons produced in neutrino and
antineutrino nucleon deep inelastic scattering, via charged currents, and we
study the positivity constraints on the spin components in a model independent
way. These results are very important, in particular in the case of
leptons, because the polarization information is crucial in all
future neutrino oscillation experiments.Comment: 14 pages, 4 figure
On impact parameter dependence of low-x structure functions
We consider impact parameter dependence of the polarized and unpolarized
structure functions. Unitarity does not allow factorization of the structure
functions over the Bjorken x and the impact parameter b variables. On the basis
of the particular geometrical model approach we conclude that spin of
constituent quark may have a significant orbital angular momentum component
which can manifest itself through the peripherality of the spin dependent
structure functions.Comment: 5 pages, 1 figur
Mass hierarchy discrimination with atmospheric neutrinos in large volume ice/water Cherenkov detectors
Large mass ice/water Cherenkov experiments, optimized to detect low energy
(1-20 GeV) atmospheric neutrinos, have the potential to discriminate between
normal and inverted neutrino mass hierarchies. The sensitivity depends on
several model and detector parameters, such as the neutrino flux profile and
normalization, the Earth density profile, the oscillation parameter
uncertainties, and the detector effective mass and resolution. A proper
evaluation of the mass hierarchy discrimination power requires a robust
statistical approach. In this work, the Toy Monte Carlo, based on an extended
unbinned likelihood ratio test statistic, was used. The effect of each model
and detector parameter, as well as the required detector exposure, was then
studied. While uncertainties on the Earth density and atmospheric neutrino flux
profiles were found to have a minor impact on the mass hierarchy
discrimination, the flux normalization, as well as some of the oscillation
parameter (\Delta m^2_{31}, \theta_{13}, \theta_{23}, and \delta_{CP})
uncertainties and correlations resulted critical. Finally, the minimum required
detector exposure, the optimization of the low energy threshold, and the
detector resolutions were also investigated.Comment: 23 pages, 16 figure
All electromagnetic form factors
The electromagnetic form factors of spin-1/2 particles are known, but due to
historical reasons only half of them are found in many textbooks. Given the
importance of the general result, its model independence, its connection to
discrete symmetries and their violations we made an effort to derive and
present the general result based only on the knowledge of Dirac equation. We
discuss the phenomenology connected directly with the form factors, and spin
precession in external fields including time reversal violating terms. We apply
the formalism to spin-flip synchrotron radiation and suggest pedagogical
projects.Comment: Latex, 22 page
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