29,145 research outputs found
Exact Event Rates of Lepton Flavor Violating Processes in Supersymmetric SU(5) Model
Event rates of various lepton flavor violating processes in the minimal
supersymmetric SU(5) model are calculated, using exact formulas which include
Yukawa vertices of lepton-slepton-Higgsino. We find subtlety in evaluating
event rates due to partial cancellation between diagrams. This cancellation
typically reduces the event rates significantly, and the size of the reduction
strongly depends on superparticle mass spectrum.Comment: 11pages, 8 figures. Fig.5 where the mu-e conversion rates in nuclei
was shown was incorrect due to an error in our numerical computation.It is
replaced in this corrected version. All conclusions remain unchange
Hydrogen dissociation on the Mg(0001) surface from quantum Monte Carlo calculations
We have used diffusion Monte Carlo (DMC) simulations to calculate the energy
barrier for H dissociation on the Mg(0001) surface. The calculations employ
pseudopotentials and systematically improvable B-spline basis sets to expand
the single particle orbitals used to construct the trial wavefunctions.
Extensive tests on system size, time step, and other sources of errors,
performed on periodically repeated systems of up to 550 atoms, show that all
these errors together can be reduced to eV. The DMC dissociation
barrier is calculated to be eV, and is compared to those
obtained with density functional theory using various exchange-correlation
functionals, with values ranging between 0.44 and 1.07 eV.Comment: 6 pages, 4 figures, to appear in Physical Review
New Universality of Lyapunov Spectra in Hamiltonian Systems
A new universality of Lyapunov spectra {\lambda_i} is shown for Hamiltonian
systems. The universality appears in middle energy regime and is different from
another universality which can be reproduced by random matrices in the
following two points. One is that the new universality appears in a limited
range of large i/N rather than the whole range, where N is degrees of freedom.
The other is Lyapunov spectra do not behave linearly while random matrices give
linear behavior even on 3D lattice. Quadratic terms with smaller nonlinear
terms of potential functions play an intrinsic role in the new universality.Comment: 19 pages, 16 Encapsulated Postscript figures, LaTeX (100 kb
Scaling property and peculiar velocity of global monopoles
We investigate the scaling property of global monopoles in the expanding
universe. By directly solving the equations of motion for scalar fields, we
follow the time development of the number density of global monopoles in the
radiation dominated (RD) universe and the matter dominated (MD) universe. It is
confirmed that the global monopole network relaxes into the scaling regime and
the number per hubble volume is a constant irrespective of the cosmic time. The
number density of global monopoles is given by during the RD era and during the MD era. We also examine the peculiar velocity of global
monopoles. For this purpose, we establish a method to measure the peculiar
velocity by use of only the local quantities of the scalar fields. It is found
that during the RD era and during
the MD era. By use of it, a more accurate analytic estimate for the number
density of global monopoles is obtained.Comment: 17 pages, 8 figures, to appear in Phys. Rev.
Hierarchical Mass Structure of Fermions in Warped Extra Dimension
The warped bulk standard model has been studied in the Randall-Sundrum
background on interval with the bulk gauge symmetry
. With the assumption of no
large cancellation between the fermion flavor mixing matrices, we present a
simple analytic method to determine the bulk masses of standard model fermions
in the almost universal bulk Yukawa coupling model. We also predict
element of MNS matrix to be near the experimental upper bound when the neutrino
masses are of Dirac type.Comment: 16 page
Multiple buoyancy driven flows in a vertical cylinder heated from below
The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height to radius of the cylinder) between 0.5 and 2.25. Extensive calculations of the neutral stability curve for the static solution and of the nonlinear motions along the bifurcating flow families show a continuous evolution of the primary cellular motion from a single toroidal cell to two and three cells nested radially in the cylinder, instead of the sharp transitions found for a cylinder with shear-free sidewalls. The smooth transitions in flow structure with Rayleigh number and lambda are explained by nonlinear connectivity between the first two bifurcating flow families formed either by a secondary bifurcation point for Lambda or = Lambda * approximately 0.80 or by a limit point for Lambda Lambda *. The transition between these two modes may be described by the theory of multiple limit point bifurcation
Stability criteria of the Vlasov equation and quasi-stationary states of the HMF model
We perform a detailed study of the relaxation towards equilibrium in the
Hamiltonian Mean-Field (HMF) model, a prototype for long-range interactions in
-particle dynamics. In particular, we point out the role played by the
infinity of stationary states of the associated Vlasov dynamics. In this
context, we derive a new general criterion for the stability of any spatially
homogeneous distribution, and compare its analytical predictions with numerical
simulations of the Hamiltonian, finite , dynamics. We then propose and
verify numerically a scenario for the relaxation process, relying on the Vlasov
equation. When starting from a non stationary or a Vlasov unstable stationary
initial state, the system shows initially a rapid convergence towards a stable
stationary state of the Vlasov equation via non stationary states: we
characterize numerically this dynamical instability in the finite system by
introducing appropriate indicators. This first step of the evolution towards
Boltzmann-Gibbs equilibrium is followed by a slow quasi-stationary process,
that proceeds through different stable stationary states of the Vlasov
equation. If the finite system is initialized in a Vlasov stable homogenous
state, it remains trapped in a quasi-stationary state for times that increase
with the nontrivial power law . Single particle momentum distributions
in such a quasi-stationary regime do not have power-law tails, and hence cannot
be fitted by the -exponential distributions derived from Tsallis statistics.Comment: To appear in Physica
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