1,480 research outputs found
Isotopic tiling theory for hyperbolic surfaces
In this paper, we develop the mathematical tools needed to explore isotopy
classes of tilings on hyperbolic surfaces of finite genus, possibly
nonorientable, with boundary, and punctured. More specifically, we generalize
results on Delaney-Dress combinatorial tiling theory using an extension of
mapping class groups to orbifolds, in turn using this to study tilings of
covering spaces of orbifolds. Moreover, we study finite subgroups of these
mapping class groups. Our results can be used to extend the Delaney-Dress
combinatorial encoding of a tiling to yield a finite symbol encoding the
complexity of an isotopy class of tilings. The results of this paper provide
the basis for a complete and unambiguous enumeration of isotopically distinct
tilings of hyperbolic surfaces
Estimates of weak and electromagnetic nuclear decay signatures for neutrino reactions in Super-Kamiokande
We estimate possible delayed β decay signatures of the neutrino induced reactions on 16O in a two-step model: the primary neutrino (ν,l) process, where l is the lepton in the final state, is described within the random phase approximation, while the subsequent decay of the excited nuclear state in the final channel is treated within the statistical model. We calculate partial reaction cross sections leading to β unstable nuclei. We consider neutrino energies up to 500 MeV, relevant for atmospheric neutrino detection in Super-Kamiokande, and supernova neutrino spectra
Weak reactions on 12C within the Continuum Random Phase Approximation with partial occupancies
We extend our previous studies of the neutrino-induced reactions on 12C and
muon capture to include partial occupation of nuclear subshells in the
framework of the continuum random phase approximation. We find, in contrast to
the work by Auerbach et al., that a partial occupation of the p1/2 subshell
reduces the inclusive cross sections only slightly. The extended model
describes the muon capture rate and the 12C(nu_e,e-)12N cross section very
well. The recently updated flux and the improved model bring the calculated
12C(nu_mu,mu^-)12N cross section (~ 17.5 10^{-40} cm^2) and the data (12.4 +/-
0.3(stat.) +/- 1.8(syst.) 10^{-40} cm^2) closer together, but does not remove
the discrepancy fully.Comment: 12 pages, 2 figure
The role of -induced reactions on lead and iron in neutrino detectors
We have calculated cross sections and branching ratios for neutrino induced
reactions on ^{208}Pb and ^{56}Fe for various supernova and
accelerator-relevant neutrino spectra. This was motivated by the facts that
lead and iron will be used on one hand as target materials in future neutrino
detectors, on the other hand have been and are still used as shielding
materials in accelerator-based experiments. In particular we study the
inclusive ^{56}^{56}Co and ^{208}^{208}Bi cross
sections and calculate the neutron energy spectra following the decay of the
daughter nuclei. These reactions give a potential background signal in the
KARMEN and LSND experiment and are discussed as a detection scheme for
supernova neutrinos in the proposed OMNIS and LAND detectors. We also study the
neutron-emission following the neutrino-induced neutral-current excitation of
^{56}Fe and ^{208}Pb.Comment: 23 pages (including 7 figures
Quasielastic neutrino scattering from oxygen and the atmospheric neutrino problem
We examine several phenomena beyond the scope of Fermi-gas models that affect
the quasielastic scattering (from oxygen) of neutrinos in the 0.1 -- 3.0 GeV
range. These include Coulomb interactions of outgoing protons and leptons, a
realistic finite-volume mean field, and the residual nucleon-nucleon
interaction. None of these effects are accurately represented in the Monte
Carlo simulations used to predict event rates due to and neutrinos
from cosmic-ray collisions in the atmosphere. We nevertheless conclude that the
neglected physics cannot account for the anomalous to ratio observed
at Kamiokande and IMB, and is unlikely to change absolute event rates by more
than 10--15\%. We briefly mention other phenomena, still to be investigated in
detail, that may produce larger changes.Comment: In Revtex version 2. 14 pages, 3 figures (available on request from
J. Engel, tel. 302-831-4354, [email protected]
Neutrino–nucleus reactions and nuclear structure
The methods used in the evaluation of the neutrino–nucleus cross section are reviewed. Results are shown for a variety of targets of practical importance. Many of the described reactions are accessible in future experiments with neutrino sources from the pion and muon decays at rest, which might be available at the neutron spallation facilities. Detailed comparison between the experimental and theoretical results would establish benchmarks needed for verification and/or parameter adjustment of the nuclear models. Having a reliable tool for such calculation is of great importance in a variety of applications, e.g. the neutrino oscillation studies, detection of supernova neutrinos, description of the neutrino transport in supernovae and description of the r-process nucleosynthesis
Muon capture on nuclei with N > Z, random phase approximation, and in-medium renormalization of the axial-vector coupling constant
We use the random phase approximation to describe the muon capture rate on
Ca,Ca, Fe, Zr, and Pb. With
Ca as a test case, we show that the Continuum Random Phase
Approximation (CRPA) and the standard RPA give essentially equivalent
descriptions of the muon capture process. Using the standard RPA with the free
nucleon weak form factors we reproduce the experimental total capture rates on
these nuclei quite well. Confirming our previous CRPA result for the
nuclei, we find that the calculated rates would be significantly lower than the
data if the in-medium quenching of the axial-vector coupling constant were
employed.Comment: submitted to Phys. Rev.
Neutrino induced transitions between the ground states of the A=12 triad
Neutrino induced reactions on C, an ingredient of liquid
scintillators, have been studied in several experiments. We show that for
currently available neutrino energies, 300 MeV, calculated
exclusive cross sections CN for both muon
and electron neutrinos are essentially model independent, provided the
calculations simultaneously describe the rates of several other reactions
involving the same states or their isobar analogs. The calculations agree well
with the measured cross sections, which can be therefore used to check the
normalization of the incident neutrino spectrum and the efficiency of the
detector.Comment: 9 pages REVTEX, 2 postscript figures, text and figures available at
http://www.krl.caltech.edu/preprints/MAP.htm
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