3,446 research outputs found
Landau-Ginzburg orbifolds with discrete torsion
We complete the classification of (2,2) vacua that can be constructed from
Landau--Ginzburg models by abelian twists with arbitrary discrete torsions.
Compared to the case without torsion the number of new spectra is surprisingly
small. In contrast to a popular expectation mirror symmetry does not seem to be
related to discrete torsion (at least not in the present compactification
framework): The Berglund-H"ubsch construction naturally extends to orbifolds
with torsion; for more general potentials, on the other hand, the new spectra
neither have nor provide mirror partners in our class of models.Comment: 12 pages, LaTe
The triton in a finite volume
Understanding the volume dependence of the triton binding energy is an
important step towards lattice simulations of light nuclei. We calculate the
triton binding energy in a finite cubic box with periodic boundary conditions
to leading order in the pionless effective field theory. Higher order
corrections are estimated and the proper renormalization of our results is
verified explicitly. We present results for the physical triton as well as for
the pion-mass dependence of the triton spectrum near the ``critical'' pion
mass, Mpi_c ~ 197 MeV, where chiral effective field theory suggests that the
nucleon-nucleon scattering lengths in the singlet- and triplet-channels diverge
simultaneously. An extension of the Luescher formula to the three-body system
is implicit in our results.Comment: 11 pages, 4 figure
Coherent field emission image of graphene predicted with a microscopic theory
Electrons in the mono-layer atomic sheet of graphene have a long coherence
length of the order of micrometers. We will show that this coherence is
transmitted into the vacuum via electric field assisted electron emission from
the graphene edge. The emission current density is given analytically. The
parity of the carbon pi-electrons leads to an image whose center is dark as a
result of interference. A dragonfly pattern with a dark body perpendicular to
the edge is predicted for the armchair edge whose emission current density is
vanishing with the mixing angle of the pseudo-spin. The interference pattern
may be observed up to temperatures of thousand Kelvin as evidence of coherent
field emission. Moreover, this phenomenon leads to a novel coherent electron
line source that can produce interference patterns of extended objects with
linear sizes comparable to the length of the graphene edge.Comment: 6 pages, 3 figure
Searching for K3 Fibrations
We present two methods for studying fibrations of Calabi-Yau manifolds
embedded in toric varieties described by single weight systems. We analyse
184,026 such spaces and identify among them 124,701 which are K3 fibrations. As
some of the weights give rise to two or three distinct types of fibrations, the
total number we find is 167,406. With our methods one can also study elliptic
fibrations of 3-folds and K3 surfaces. We also calculate the Hodge numbers of
the 3-folds obtaining more than three times as many as were previously known.Comment: 21 pages, LaTeX2e, 4 eps figures, uses packages
amssymb,latexsym,cite,epi
Physisorption of an electron in deep surface potentials off a dielectric surface
We study phonon-mediated adsorption and desorption of an electron at
dielectric surfaces with deep polarization-induced surface potentials where
multi-phonon transitions are responsible for electron energy relaxation.
Focusing on multi-phonon processes due to the nonlinearity of the coupling
between the external electron and the acoustic bulk phonon triggering the
transitions between surface states, we calculate electron desorption times for
graphite, MgO, CaO, (\text{Al}_2\text{O}_3), and (\text{SiO}_2) and electron
sticking coefficients for (\text{Al}_2\text{O}_3), CaO, and (\text{SiO}_2). To
reveal the kinetic stages of electron physisorption, we moreover study the time
evolution of the image state occupancy and the energy-resolved desorption flux.
Depending on the potential depth and the surface temperature we identify two
generic scenarios: (i)adsorption via trapping in shallow image states followed
by relaxation to the lowest image state and desorption from that state via a
cascade through the second strongly bound image state in not too deep
potentials and (ii)adsorption via trapping in shallow image states but followed
by a relaxation bottleneck retarding the transition to the lowest image state
and desorption from that state via a one step process to the continuum in deep
potentials.Comment: 12 pages, 7 figure
An Abundance of K3 Fibrations from Polyhedra with Interchangeable Parts
Even a cursory inspection of the Hodge plot associated with Calabi-Yau
threefolds that are hypersurfaces in toric varieties reveals striking
structures. These patterns correspond to webs of elliptic-K3 fibrations whose
mirror images are also elliptic-K3 fibrations. Such manifolds arise from
reflexive polytopes that can be cut into two parts along slices corresponding
to the K3 fibers. Any two half-polytopes over a given slice can be combined
into a reflexive polytope. This fact, together with a remarkable relation on
the additivity of Hodge numbers, explains much of the structure of the observed
patterns.Comment: 30 pages, 15 colour figure
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