7,939 research outputs found
A note on BRST quantization of SU(2) Yang-Mills mechanics
The quantization of SU(2) Yang-Mills theory reduced to 0+1 space-time
dimensions is performed in the BRST framework. We show that in the unitary
gauge the BRST procedure has difficulties which can be solved by
introduction of additional singlet ghost variables. In the Lorenz gauge
one has additional unphysical degrees of freedom, but the BRST
quantization is free of the problems in the unitary gauge.Comment: 17 page
Electronic structure of few-electron concentric double quantum rings
The ground state structure of few-electron concentric double quantum rings is
investigated within the local spin density approximation. Signatures of
inter-ring coupling in the addition energy spectrum are identified and
discussed. We show that the electronic configurations in these structures can
be greatly modulated by the inter-ring distance: At short and long distances
the low-lying electron states localize in the inner and outer rings,
respectively, and the energy structure is essentially that of an isolated
single quantum ring. However, at intermediate distances the electron states
localized in the inner and the outer ring become quasi-degenerate and a rather
entangled, strongly-correlated system is formed.Comment: 16 pages (preprint format), 6 figure
Extracting the top-quark running mass using +1-jet events produced at the Large Hadron Collider
We present the calculation of the next-to-leading order QCD corrections for
top-quark pair production in association with an additional jet at hadron
colliders, using the modified minimal subtraction scheme to renormalize the
top-quark mass. The results are compared to measurements at the Large Hadron
Collider run I. In particular, we determine the top-quark running mass from a
fit of the theoretical results presented here to the LHC data
InAs/InP single quantum wire formation and emission at 1.5 microns
Isolated InAs/InP self-assembled quantum wires have been grown using in situ
accumulated stress measurements to adjust the optimal InAs thickness. Atomic
force microscopy imaging shows highly asymmetric nanostructures with average
length exceeding more than ten times their width. High resolution optical
investigation of as-grown samples reveals strong photoluminescence from
individual quantum wires at 1.5 microns. Additional sharp features are related
to monolayer fluctuations of the two dimensional InAs layer present during the
early stages of the quantum wire self-assembling process.Comment: 4 pages and 3 figures submitted to Applied Physics Letter
Higher dimensional VSI spacetimes
We present the explicit metric forms for higher dimensional vanishing scalar
invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes
belong to the higher dimensional Kundt class. We determine all of the VSI
spacetimes which admit a covariantly constant null vector, and we note that in
general in higher dimensions these spacetimes are of Ricci type III and Weyl
type III. The Ricci type N subclass is related to the chiral null models and
includes the relativistic gyratons and the higher dimensional pp-wave
spacetimes. The spacetimes under investigation are of particular interest since
they are solutions of supergravity or superstring theory.Comment: 14 pages, changes in second paragraph of the discussio
Type III Einstein-Yang-Mills solutions
We construct two distinct classes of exact type III solutions of the D=4
Einstein-Yang-Mills system. The solutions are embeddings of the non-abelian
plane waves in spacetimes in Kundt's class. Reduction of the solutions to type
N leads to generalized and Kundt waves. The geodesic equations are briefly
discussed.Comment: revtex, 4 pages, minor changes, some factors and references
corrected, footnote adde
Effect of direct bubble-bubble interactions on linear-wave propagation in bubbly liquids
We study the influence of bubble-bubble interactions on the propagation of linear acoustic waves in bubbly liquids. Using the full model proposed by Fuster and Colonius J. Fluid Mech. 688, 253 ( 2011)], numerical simulations reveal that direct bubble-bubble interactions have an appreciable effect for frequencies above the natural resonance frequency of the average size bubble. Based on the new results, a modification of the classical wave propagation theory is proposed. The results obtained are in good agreement with previously reported experimental data where the classical linear theory systematically overpredicts the effective attenuation and phase velocity
New modelling technique for aperiodic-sampling linear systems
A general input-output modelling technique for aperiodic-sampling linear
systems has been developed. The procedure describes the dynamics of the system
and includes the sequence of sampling periods among the variables to be
handled. Some restrictive conditions on the sampling sequence are imposed in
order to guarantee the validity of the model. The particularization to the
periodic case represents an alternative to the classic methods of
discretization of continuous systems without using the Z-transform. This kind
of representation can be used largely for identification and control purposes.Comment: 19 pages, 0 figure
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
We study the metal-insulator transition in individual self-assembled quantum
wires and report optical evidences of metallic liquid condensation at low
temperatures. Firstly, we observe that the temperature and power dependence of
the single nanowire photoluminescence follow the evolution expected for an
electron-hole liquid in one dimension. Secondly, we find novel spectral
features that suggest that in this situation the expanding liquid condensate
compresses the exciton gas in real space. Finally, we estimate the critical
density and critical temperature of the phase transition diagram at
cm and K, respectively.Comment: 4 pages, 5 figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
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