8,554 research outputs found
Pauli-Potential and Green Function Monte-Carlo Method for Many-Fermion Systems
The time evolution of a many-fermion system can be described by a Green's
function corresponding to an effective potential, which takes
anti-symmetrization of the wave function into account, called the
Pauli-potential. We show that this idea can be combined with the Green's
Function Monte Carlo method to accurately simulate a system of many
non-relativistic fermions. The method is illustrated by the example of systems
of several (2-9) fermions in a square well.Comment: 12 pages, LaTeX, 4 figure
Upper bound on the cutoff in lattice Electroweak theory
We investigate numerically lattice Weinberg - Salam model without fermions
for realistic values of the fine structure constant and the Weinberg angle. We
also analyze the data of the previous numerical investigations of lattice
Electroweak theory. We have found that moving along the line of constant
physics when the lattice spacing is decreased, one should leave the
physical Higgs phase of the theory at a certain value of . Our estimate of
the minimal value of the lattice spacing is .Comment: Latex, 21 pages, 3 figures, to appear in JHE
The heavy-quark pole masses in the Hamiltonian approach
From the fact that the nonperturbative self-energy contribution
to the heavy meson mass is small: ; MeV \cite{ref.01}, strong restrictions on the pole
masses and are obtained. The analysis of the and the
spectra with the use of relativistic (string) Hamiltonian gives
(2-loop) GeV and (2-loop) GeV which
correspond to the running mass GeV and GeV. The masses
and , which define the heavy quarkonia spin structure, are shown to
be by MeV larger than the pole ones.Comment: 18 pages, no figures, 8 table
The Hyperfine Splittings in Bottomonium and the Mesons
A universal description of the hyperfine splittings (HFS) in bottomonium and
the mesons is obtained with a universal strong coupling
constant in a spin-spin potential. Other
characteristics are calculated within the Field Correlator Method, taking the
freezing value of the strong coupling independent of . The HFS MeV, MeV are obtained in full
agreement with experiment both for and . In bottomonium,
MeV for agrees with the BaBar
data, while a smaller HFS, equal to 64(1) MeV, is obtained for . We
predict HFS MeV, MeV, and MeV, which gives
MeV, MeV, and MeV.Comment: 5 pages revtex
Effect of disorder on the conductance of a Cu atomic point contact
We present a systematic study of the effect of the disorder in copper point
contacts. We show that peaks in the conductance histogram of copper point
contacts shift upon addition of nickel impurities. The shift increases
initially linerarly with the nickel concentration, thus confirming that it is
due to disorder in the nanowire, in accordance with predictions. In general,
this shift is modelled as a resistance R_s which is placed in series with the
contact resistance R_c. However, we obtain different R_s values for the two
peaks in the histogram, R_s being larger for the peak at higher conductance.Comment: 6 pages, 4 figure
Nambu monopoles in lattice Electroweak theory
We considered the lattice electroweak theory at realistic values of
and and for large values of the Higgs mass. We investigated
numerically the properties of topological objects that are identified with
quantum Nambu monopoles. We have found that the action density near the Nambu
monopole worldlines exceeds the density averaged over the lattice in the
physical region of the phase diagram. Moreover, their percolation probability
is found to be an order parameter for the transition between the symmetric and
the broken phases. Therefore, these monopoles indeed appear as real physical
objects. However, we have found that their density on the lattice increases
with increasing ultraviolet cutoff. Thus we conclude, that the conventional
lattice electroweak theory is not able to predict the density of Nambu
monopoles. This means that the description of Nambu monopole physics based on
the lattice Weinberg - Salam model with finite ultraviolet cutoff is
incomplete. We expect that the correct description may be obtained only within
the lattice theory that involves the description of TeV - scale physics.Comment: LATE
Magnetic properties of Co doped Nb clusters
From magnetic deflection experiments on isolated Co doped Nb clusters we made
the interesting observation of some clusters being magnetic, while others
appear to be non-magnetic. There are in principle two explanations for this
behavior. Either the local moment at the Co site is completely quenched or it
is screened by the delocalized electrons of the cluster, i.e. the Kondo effect.
In order to reveal the physical origin, we conducted a combined theoretical and
experimental investigation. First, we established the ground state geometry of
the clusters by comparing the experimental vibrational spectra with those
obtained from a density functional theory study. Then, we performed an analyses
based on the Anderson impurity model. It appears that the non-magnetic clusters
are due to a complete quenching of the local Co moment and not due to the Kondo
effect. In addition, the magnetic behavior of the clusters can be understood
from an inspection of their electronic structure. Here magnetism is favored
when the effective hybridization around the chemical potential is small, while
the absence of magnetism is signalled by a large effective hybridization around
the chemical potential.Comment: 14 pages, 8 figure
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