2,490 research outputs found
Scanning tunneling microscopy and spectroscopy of sodium-chloride overlayers on the stepped Cu(311) surface: Experimental and theoretical study
The physical properties of ultrathin NaCl overlayers on the stepped Cu(311)
surface have been characterized using scanning tunneling microscopy (STM) and
spectroscopy, and density functional calculations. Simulations of STM images
and differential conductance spectrum were based on the Tersoff-Hamann
approximation for tunneling with corrections for the modified tunneling barrier
at larger voltages and calculated Kohn-Sham states. Characteristic features
observed in the STM images can be directly related to calculated electronic and
geometric properties of the overlayers. The measured apparent barrier heights
for the mono-, bi-, and trilayers of NaCl and the corresponding
adsorption-induced changes in the work function, as obtained from the distance
dependence of the tunneling current, are well reproduced by and understood from
the calculated results. The measurements revealed a large reduction of the
tunneling conductance in a wide voltage region, resembling a band gap. However,
the simulated spectrum showed that only the onset at positive sample voltages
may be viewed as a valence band edge, whereas the onset at negative voltages is
caused by the drastic effect of the electric field from the tip on the
tunneling barrier
Lower and upper bounds on the fidelity susceptibility
We derive upper and lower bounds on the fidelity susceptibility in terms of
macroscopic thermodynamical quantities, like susceptibilities and thermal
average values. The quality of the bounds is checked by the exact expressions
for a single spin in an external magnetic field. Their usefulness is
illustrated by two examples of many-particle models which are exactly solved in
the thermodynamic limit: the Dicke superradiance model and the single impurity
Kondo model. It is shown that as far as divergent behavior is considered, the
fidelity susceptibility and the thermodynamic susceptibility are equivalent for
a large class of models exhibiting critical behavior.Comment: 19 page
Spin three gauge theory revisited
We study the problem of consistent interactions for spin-3 gauge fields in
flat spacetime of arbitrary dimension n>3. Under the sole assumptions of
Poincar\'e and parity invariance, local and perturbative deformation of the
free theory, we determine all nontrivial consistent deformations of the abelian
gauge algebra and classify the corresponding deformations of the quadratic
action, at first order in the deformation parameter. We prove that all such
vertices are cubic, contain a total of either three or five derivatives and are
uniquely characterized by a rank-three constant tensor (an internal algebra
structure constant). The covariant cubic vertex containing three derivatives is
the vertex discovered by Berends, Burgers and van Dam, which however leads to
inconsistencies at second order in the deformation parameter. In dimensions n>4
and for a completely antisymmetric structure constant tensor, another covariant
cubic vertex exists, which contains five derivatives and passes the consistency
test where the previous vertex failed.Comment: LaTeX, 37 pages. References and comments added. Published versio
Cohomological BRST aspects of the massless tensor field with the mixed symmetry (k,k)
The main BRST cohomological properties of a free, massless tensor field that
transforms in an irreducible representation of GL(D,R), corresponding to a
rectangular, two-column Young diagram with k>2 rows are studied in detail. In
particular, it is shown that any non-trivial co-cycle from the local BRST
cohomology group H(s|d) can be taken to stop either at antighost number (k+1)
or k, its last component belonging to the cohomology of the exterior
longitudinal derivative H(gamma) and containing non-trivial elements from the
(invariant) characteristic cohomology H^{inv}(delta|d).Comment: Latex, 50 pages, uses amssym
Partial separability revisited: Necessary and sufficient criteria
We extend the classification of mixed states of quantum systems composed of
arbitrary number of subsystems of arbitrary dimensions. This extended
classification is complete in the sense of partial separability and gives
1+18+1 partial separability classes in the tripartite case contrary to a former
1+8+1. Then we give necessary and sufficient criteria for these classes, which
make it possible to determine to which class a mixed state belongs. These
criteria are given by convex roof extensions of functions defined on pure
states. In the special case of three-qubit systems, we define a different set
of such functions with the help of the Freudenthal triple system approach of
three-qubit entanglement.Comment: v3: 22 pages, 5 tables, 1 figure, minor corrections (typos),
clarification in the Introduction. Accepted in Phys. Rev. A. Comments are
welcom
Pentagrams and paradoxes
Klyachko and coworkers consider an orthogonality graph in the form of a
pentagram, and in this way derive a Kochen-Specker inequality for spin 1
systems. In some low-dimensional situations Hilbert spaces are naturally
organised, by a magical choice of basis, into SO(N) orbits. Combining these
ideas some very elegant results emerge. We give a careful discussion of the
pentagram operator, and then show how the pentagram underlies a number of other
quantum "paradoxes", such as that of Hardy.Comment: 14 pages, 4 figure
Deep-Inelastic Final States in a Space-Time Description of Shower Development and Hadronization
We extend a quantum kinetic approach to the description of hadronic showers
in space, time and momentum space to deep-inelastic collisions, with
particular reference to experiments at HERA. We follow the history of hard
scattering events back to the initial hadronic state and forward to the
formation of colour-singlet pre-hadronic clusters and their decays into
hadrons. The time evolution of the space-like initial-state shower and the
time-like secondary partons are treated similarly, and cluster formation is
treated using a spatial criterion motivated by confinement and a
non-perturbative model for hadronization. We calculate the time evolution of
particle distributions in rapidity, transverse and longitudinal space. We also
compare the transverse hadronic energy flow and the distribution of observed
hadronic masses with experimental data from HERA, and find encouraging results.
The techniques developed in this paper may be applied in the future to more
complicated processes such as eA, pp, pA and AA collisions.Comment: 44 pages plus 14 postscript figure
BRST cohomological results on the massless tensor field with the mixed symmetry of the Riemann tensor
The basic BRST cohomological properties of a free, massless tensor field with
the mixed symmetry of the Riemann tensor are studied in detail. It is shown
that any non-trivial co-cycle from the local BRST cohomology group can be taken
to stop at antighost number three, its last component belonging to the
cohomology of the exterior longitudinal derivative and containing non-trivial
elements from the (invariant) characteristic cohomology.Comment: 39 page
Higher-Spin Gauge Fields Interacting with Scalars: The Lagrangian Cubic Vertex
We apply a recently presented BRST procedure to construct the Largangian
cubic vertex of higher-spin gauge field triplets interacting with massive free
scalars. In flat space, the spin-s triplet propagates the series of irreducible
spin-s, s-2,..,0/1 modes which couple independently to corresponding conserved
currents constructed from the scalars. The simple covariantization of the flat
space result is not enough in AdS, as new interaction vertices appear. We
present in detail the cases of spin-2 and spin-3 triplets coupled to scalars.
Restricting to a single irreducible spin-s mode we uncover previously obtained
results. We also present an alternative derivation of the lower spin results
based on the idea that higher-spin gauge fields arise from the gauging of
higher derivative symmetries of free matter Lagrangians. Our results can be
readily applied to holographic studies of higher-spin gauge theories.Comment: 26 pages, v2: references adde
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