27,493 research outputs found
Charge asymmetry in W + jets production at the LHC
The charge asymmetry in W + jets production at the LHC can serve to calibrate
the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n
jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying
particular attention to the uncertainty in the prediction from higher-order
perturbative corrections and uncertainties in parton distribution functions. We
show that these uncertainties are generally of order a few percent, making the
experimental measurement of the charge asymmetry ratio a particularly useful
diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex
Hypersonic research engine project. Phase 2: Aerothermodynamic Integration Model (AIM) test report
The Hypersonic Research Engine-Aerothermodynamic Integration Model (HRE-AIM) was designed, fabricated, and tested in the Hypersonic Tunnel Facility. The HRE-AIM is described along with its installation in the wind tunnel facility. Test conditions to which the HRE-AIM was subjected and observations made during the tests are discussed. The overall engine performance, component interaction, and ignition limits for the design are evaluated
Signatures of orbital loop currents in the spatially resolved local density of states
Polarized neutron scattering measurements have suggested that intra-unit cell
antiferromagnetism may be associated with the pseudogap phase. Assuming that
loop current order is responsible for the observed magnetism, we calculate some
signatures of such circulating currents in the local density of states around a
single non-magnetic impurity in a coexistence phase with superconductivity. We
find a distinct C4 symmetry breaking near the disorder which is also detectable
in the resulting quasi-particle interference patterns.Comment: 5 pages, 3 figure
Plasmons on the edge of MoS2 nanostructures
Using ab initio calculations we predict the existence of one-dimensional
(1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon.
The strongest plasmon originates from a metallic edge state localized on the
sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the
dielectric function reveals that the observed deviations from the ideal 1D
plasmon behavior result from single-particle transitions between the metallic
edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S
edges of the ribbon are clearly distinguishable in calculated spatially
resolved electron energy loss spectrum owing to the different plasmonic
properties of the two edges. The edge plasmons could potentially be utilized
for tuning the photocatalytic activity of MoS2 nanoparticles
Spherical Categories
This paper is a study of monoidal categories with duals where the tensor
product need not be commutative. The motivating examples are categories of
representations of Hopf algebras and the motivating application is the
definition of 6j-symbols as used in topological field theories.
We introduce the new notion of a spherical category. In the first section we
prove a coherence theorem for a monoidal category with duals following MacLane
(1963). In the second section we give the definition of a spherical category,
and construct a natural quotient which is also spherical.
In the third section we define spherical Hopf algebras so that the category
of representations is spherical. Examples of spherical Hopf algebras are
involutory Hopf algebras and ribbon Hopf algebras. Finally we study the natural
quotient in these cases and show it is semisimple.Comment: 16 pages. Minor correction
Spatially resolved quantum plasmon modes in metallic nano-films from first principles
Electron energy loss spectroscopy (EELS) can be used to probe plasmon
excitations in nanostructured materials with atomic-scale spatial resolution.
For structures smaller than a few nanometers quantum effects are expected to be
important, limiting the validity of widely used semi-classical response models.
Here we present a method to identify and compute spatially resolved plasmon
modes from first principles based on a spectral analysis of the dynamical
dielectric function. As an example we calculate the plasmon modes of 0.5-4 nm
thick Na films and find that they can be classified as (conventional) surface
modes, sub-surface modes, and a discrete set of bulk modes resembling standing
waves across the film. We find clear effects of both quantum confinement and
non-local response. The quantum plasmon modes provide an intuitive picture of
collective excitations of confined electron systems and offer a clear
interpretation of spatially resolved EELS spectra.Comment: 7 pages, 7 figure
Driven particle in a random landscape: disorder correlator, avalanche distribution and extreme value statistics of records
We review how the renormalized force correlator Delta(u), the function
computed in the functional RG field theory, can be measured directly in
numerics and experiments on the dynamics of elastic manifolds in presence of
pinning disorder. We show how this function can be computed analytically for a
particle dragged through a 1-dimensional random-force landscape. The limit of
small velocity allows to access the critical behavior at the depinning
transition. For uncorrelated forces one finds three universality classes,
corresponding to the three extreme value statistics, Gumbel, Weibull, and
Frechet. For each class we obtain analytically the universal function Delta(u),
the corrections to the critical force, and the joint probability distribution
of avalanche sizes s and waiting times w. We find P(s)=P(w) for all three
cases. All results are checked numerically. For a Brownian force landscape,
known as the ABBM model, avalanche distributions and Delta(u) can be computed
for any velocity. For 2-dimensional disorder, we perform large-scale numerical
simulations to calculate the renormalized force correlator tensor
Delta_{ij}(u), and to extract the anisotropic scaling exponents zeta_x >
zeta_y. We also show how the Middleton theorem is violated. Our results are
relevant for the record statistics of random sequences with linear trends, as
encountered e.g. in some models of global warming. We give the joint
distribution of the time s between two successive records and their difference
in value w.Comment: 41 pages, 35 figure
Continuum Moment Equations on the Lattice
An analysis is given as to why one can not directly evaluate continuum moment
equations, i.e., equations involving powers of the position variable times
charge, current, or energy/momentum operators, on the lattice. I examine two
cases: a three point function evaluation of the nucleon magnetic moment and a
four point function (charge overlap) evaluation of the pseudoscalar charge
radius.Comment: 9 pages; 1 ps figur
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