609 research outputs found
Prospects for Detecting Supernova Neutrino Flavor Oscillations
The neutrinos from a Type II supernova provide perhaps our best opportunity
to probe cosmologically interesting muon and/or tauon neutrino masses. This is
because matter enhanced neutrino oscillations can lead to an anomalously hot
nu_e spectrum, and thus to enhanced charged current cross sections in
terrestrial detectors. Two recently proposed supernova neutrino observatories,
OMNIS and LAND, will detect neutrons spalled from target nuclei by neutral and
charged current neutrino interactions. As this signal is not flavor specific,
it is not immediately clear whether a convincing neutrino oscillation signal
can be extracted from such experiments. To address this issue we examine the
responses of a series of possible light and heavy mass targets, 9Be, 23Na,
35Cl, and 208Pb. We find that strategies for detecting oscillations which use
only neutron count rates are problematic at best, even if cross sections are
determined by ancillary experiments. Plausible uncertainties in supernova
neutrino spectra tend to obscure rate enhancements due to oscillations.
However, in the case of 208Pb, a signal emerges that is largely flavor specific
and extraordinarily sensitive to the nu_e temperature, the emission of two
neutrons. This signal and its flavor specificity are associated with the
strength and location of the first-forbidden responses for neutral and charge
current reactions, aspects of the 208Pb neutrino cross section that have not
been discussed previously. Hadronic spin transfer experiments might be helpful
in confirming some of the nuclear structure physics underlying our conclusions.Comment: 27 pages, RevTeX, 2 figure
Estimates of rates for dissociative recombination of NO + e via various mechanisms
We estimate rates for the dissociative recombination (DR) of NO +
e. Although accurate excited state potential energy curves for the excited
states of the neutral are not available, we estimate that the 1 {\Phi}
and the 1 {\Pi} states of the neutral may intersect the ground state
cation potential energy surface near its equilibrium geometry. Using fixed
nuclei scattering calculations we estimate the rate for direct DR via these
states and find it to be significant. We also perform approximate calculations
of DR triggered by the indirect mechanism, which suggest that the indirect DR
rate for NO is insignificant compared to the direct rate.Comment: Submitted to Phys Rev
Activated dynamics and effective temperature in a steady state sheared glass
We conduct nonequilibrium molecular dynamics simulations to measure the shear
stress, the average inherent structure energy, and the effective temperature
of a sheared model glass as a function of bath temperature and
shear strain rate. For above the glass transition temperature , the
rheology approaches a Newtonian limit and approaches as the
strain rate approaches zero, while for , the shear stress approaches a
yield stress and approaches a limiting value near . In the
shear-dominated regime at high , high strain rate or at low , we find
that the shear stress and the average inherent structure energy each collapse
onto a single curve as a function of . This indicates that
is controlling behavior in this regime.Comment: 4 pages, 2 figures. Revised to include additional data. Inherent
structure energy results were included, and much of the shear transformation
zone discussion was remove
Multiconfiguration Time-Dependent Hartree-Fock Treatment of Electronic and Nuclear Dynamics in Diatomic Molecules
The multiconfiguration time-dependent Hartree-Fock (MCTDHF) method is
formulated for treating the coupled electronic and nuclear dynamics of diatomic
molecules without the Born- Oppenheimer approximation. The method treats the
full dimensionality of the electronic motion, uses no model interactions, and
is in principle capable of an exact nonrelativistic description of diatomics in
electromagnetic fields. An expansion of the wave function in terms of
configurations of orbitals whose dependence on internuclear distance is only
that provided by the underlying prolate spheroidal coordinate system is
demonstrated to provide the key simplifications of the working equations that
allow their practical solution. Photoionization cross sections are also
computed from the MCTDHF wave function in calculations using short pulses.Comment: Submitted to Phys Rev
CN-Cycle Solar Neutrinos and Sun's Primordial Core Metalicity
We argue that it may be possible to exploit neutrinos from the CN cycle and
pp chain to determine the primordial solar core abundances of C and N at an
interesting level of precision. Such a measurement would allow a comparison of
the Sun's deep interior composition with it surface, testing a key assumption
of the standard solar model (SSM), a homogeneous zero-age Sun. It would also
provide a cross-check on recent photospheric abundance determinations that have
altered the once excellent agreement between the SSM and helioseismology. As
further motivation, we discuss a speculative possibility in which photospheric
abundance/helioseismology puzzle is connected with the solar-system metal
differentiation that accompanied formation of the gaseous giant planets.
The theoretical relationship between core C and N and the 13N and 15O solar
neutrino fluxes can be made more precise (and more general) by making use of
the Super-Kamiokande and SNO 8B neutrino capture rates, which calibrate the
temperature of the solar core. The primordial C and N abundances can then be
obtained from these neutrino fluxes and from a product of nuclear rates, with
little residual solar model dependence. We describe some of the recent
experimental advances that could allow this comparison to be made
(theoretically) at about the 9% level, and note that this uncertainty may be
reduced further due to ongoing work on the S-factor for 14N(p,gamma). The
envisioned measurement might be possible in deep, large-volume detectors using
organic scintillator, e.g., Borexino or SNO+Comment: 33 pages, 4 figure
Piecewise moments method: Generalized Lanczos technique for nuclear response surfaces
For some years Lanczos moments methods have been combined with large-scale shell-model calculations in evaluations of the spectral distributions of certain operators. This technique is of great value because the alternative, a state-by-state summation over final states, is generally not feasible. The most celebrated application is to the Gamow-Teller operator, which governs β decay and neutrino reactions in the allowed limit. The Lanczos procedure determines the nuclear response along a line q = 0 in the (ω,q) plane, where ω and q are the energy and three-momentum transferred to the nucleus, respectively. However, generalizing such treatments from the allowed limit to general electroweak response functions at arbitrary momentum transfers seems considerably more difficult: The response function must be determined over the entire (ω,q) plane for an operator O(q) that is not fixed, but depends explicitly on q. Such operators arise in any semileptonic process in which the momentum transfer is comparable with (or larger than) the inverse nuclear size. Here we show, for Slater determinants built on harmonic-oscillator basis functions, that the nuclear response for any multipole operator O(q) can be determined efficiently over the full response plane by a generalization of the standard Lanczos moments method. We describe the piecewise moments method and thoroughly explore its convergence properties for the test case of electromagnetic responses in a full sd-shell calculation of ^(28)Si. We discuss possible extensions to a variety of electroweak processes, including charged- and neutral-current neutrino scattering
Anapole Moment and Other Constraints on the Strangeness Conserving Hadronic Weak Interaction
Standard analyses of low-energy NN and nuclear parity-violating observables
have been based on a pi-, rho-, and omega-exchange model capable of describing
all five independent s-p partial waves. Here a parallel analysis is performed
for the one-body, exchange-current, and nuclear polarization contributions to
the anapole moments of 133Cs and 205Tl. The resulting constraints are not
consistent, though there remains some degree of uncertainty in the nuclear
structure analysis of the atomic moments.Comment: Revtex, 10 pages, 1 figur
Schiff Theorem and the Electric Dipole Moments of Hydrogen-Like Atoms
The Schiff theorem is revisited in this work and the residual - and
-odd electron--nucleus interaction, after the shielding takes effect, is
completely specified. An application is made to the electric dipole moments of
hydrogen-like atoms, whose qualitative features and systematics have important
implication for realistic paramagnetic atoms.Comment: 3 pages. Contribution to PANIC05, Particles and Nuclei International
Conference, Santa Fe, New Mexico, Oct. 24-28, 200
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