1,211 research outputs found
G-Fano threefolds, I
We classify Fano threefolds with only terminal singularities whose canonical
class is Cartier and divisible by 2, and satisfying an additional assumption
that the -invariant part of the Weil divisor class group is of rank 1 with
respect to an action of some group . In particular, we find a lot of
examples of Fano 3-folds with "many" symmetries.Comment: 36 pages, LaTeX2
Toric -Fano Threefolds
We classify toric Fano threefolds having at worst terminal singularities such
that a rank of a -invariant part of a class group equals one, where is a
group acting on the variety by automorphisms
The Hubbard model on a complete graph: Exact Analytical results
We derive the analytical expression of the ground state of the Hubbard model
with unconstrained hopping at half filling and for arbitrary lattice sites.Comment: Email:[email protected]
Unscreened Coulomb repulsion in the one dimensional electron gas
A tight binding model of electrons interacting via bare Coulomb repulsion is
numerically investigated by use of the Density Matrix Renormalization Group
method which we prove applicable also to very long range potentials. From the
analysis of the elementary excitations, of the spin and charge correlation
functions and of the momentum distribution, a picture consistent with the
formation of a one dimensional "Wigner crystal" emerges, in quantitative
agreement with a previous bosonization study. At finite doping, Umklapp
scattering is shown to be ineffective in the presence of long range forces.Comment: RevTex, 5 pages with 8 eps figures. To be published on Phys. Rev.
Theory of the Half-Polarized Quantum Hall States
We report a theoretical analysis of the half-polarized quantum Hall states
observed in a recent experiment. Our numerical results indicate that the ground
state energy of the quantum Hall and states versus spin
polarization has a downward cusp at half the maximal spin polarization. We map
the two-component fermion system onto a system of excitons and describe the
ground state as a liquid state of excitons with non-zero values of exciton
angular momentum.Comment: 4 pages (RevTeX), 3 figures (PostScript), added reference
An exchange-correlation energy for a two-dimensional electron gas in a magnetic field
We present the results of a variational Monte Carlo calculation of the
exchange-correlation energy for a spin-polarized two-dimensional electron gas
in a perpendicular magnetic field. These energies are a necessary input to the
recently developed current-density functional theory. Landau-level mixing is
included in a variational manner, which gives the energy at finite density at
finite field, in contrast to previous approaches. Results are presented for the
exchange-correlation energy and excited-state gap at 1/7, 1/5, 1/3, 1,
and 2. We parameterize the results as a function of and in a form
convenient for current-density functional calculations.Comment: 36 pages, including 6 postscript figure
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