2,104 research outputs found
Variations on Supersymmetry Breaking and Neutrino Spectra
The problem of generating light neutrinos within supersymmetric models is
discussed. It is shown that the hierarchy of scales induced by supersymmetry
breaking can give rise to suppression factors of the correct order of magnitude
to produce experimentally allowed neutrino spectra.Comment: 18 pages, LaTeX, Contribution to "Neutrino Workshop", Fuji-Yoshida,
Japan, August 200
Theory of Interaction of Memory Patterns in Layered Associative Networks
A synfire chain is a network that can generate repeated spike patterns with
millisecond precision. Although synfire chains with only one activity
propagation mode have been intensively analyzed with several neuron models,
those with several stable propagation modes have not been thoroughly
investigated. By using the leaky integrate-and-fire neuron model, we
constructed a layered associative network embedded with memory patterns. We
analyzed the network dynamics with the Fokker-Planck equation. First, we
addressed the stability of one memory pattern as a propagating spike volley. We
showed that memory patterns propagate as pulse packets. Second, we investigated
the activity when we activated two different memory patterns. Simultaneous
activation of two memory patterns with the same strength led the propagating
pattern to a mixed state. In contrast, when the activations had different
strengths, the pulse packet converged to a two-peak state. Finally, we studied
the effect of the preceding pulse packet on the following pulse packet. The
following pulse packet was modified from its original activated memory pattern,
and it converged to a two-peak state, mixed state or non-spike state depending
on the time interval
Stau-catalyzed Li Production in Big-Bang Nucleosynthesis
If the gravitino mass is in the region from a few GeV to a few 10's GeV, the
scalar lepton X such as stau is most likely the next lightest supersymmetry
particle. The negatively charged and long-lived X^- may form a Coulomb bound
state (A X) with a nucleus A and may affect the big-bang nucleosynthesis
through catalyzed fusion process. We calculate a production cross section of
Li6 from the catalyzed fusion (He4 X^-) + d \to Li6 + X^- by solving the
Schr\"{o}dinger equation exactly for three-body system of He4, d, and X. We
utilize the state-of-the-art coupled-channel method, which is known to be very
accurate to describe other three-body systems in nuclear and atomic reactions.
The importance of the use of appropriate nuclear potential and the exact
treatment of the quantum tunneling in the fusion process are emphasized. We
find that the astrophysical S-factor at the Gamow peak corresponding to T=10
keV is 0.038 MeV barn. This leads to the Li6 abundance from the catalyzed
process as Li6|_{CBBN}\simeq 4.3\times 10^{-11} (D/2.8\times 10^{-5})
([n_{X^-}/s]/10^{-16}) in the limit of long lifetime of X. Particle physics
implication of this result is also discussed.Comment: 16 pages, 7 figure
Transport Coefficients of the Yukawa One Component Plasma
We present equilibrium molecular-dynamics computations of the thermal
conductivity and the two viscosities of the Yukawa one-component plasma. The
simulations were performed within periodic boundary conditions and Ewald sums
were implemented for the potentials, the forces, and for all the currents which
enter the Kubo formulas. For large values of the screening parameter, our
estimates of the shear viscosity and the thermal conductivity are in good
agreement with the predictions of the Chapman-Enskog theory.Comment: 11 pages, 2 figure
Monte Carlo simulations of the screening potential of the Yukawa one-component plasma
A Monte Carlo scheme to sample the screening potential H(r) of Yukawa plasmas
notably at short distances is presented. This scheme is based on an importance
sampling technique. Comparisons with former results for the Coulombic
one-component plasma are given. Our Monte Carlo simulations yield an accurate
estimate of H(r) as well for short range and long range interparticle
distances.Comment: to be published in Journal of Physics A: Mathematical and Genera
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