13,192 research outputs found
The Zeta Function Method and the Harmonic Oscillator Propagator
We show how the pre-exponential factor of the Feynman propagator for the
harmonic oscillator can be computed by the generalized -function method.
Besides, we establish a direct equivalence between this method and Schwinger's
propertime method.Comment: 12 latex pages, no figure
Charged currents, color dipoles and xF_3 at small x
We develop the light-cone color dipole description of highly asymmetric
diffractive interactions of left-handed and right-handed electroweak bosons. We
identify the origin and estimate the strength of the left-right asymmetry
effect in terms of the light-cone wave functions. We report an evaluation of
the small-x neutrino-nucleon DIS structure functions xF_3 and 2xF_1 and present
comparison with experimental data.Comment: 11 pages, 3 figures, misprints correcte
Designing arrays of Josephson junctions for specific static responses
We consider the inverse problem of designing an array of superconducting
Josephson junctions that has a given maximum static current pattern as function
of the applied magnetic field. Such devices are used for magnetometry and as
Terahertz oscillators. The model is a 2D semilinear elliptic operator with
Neuman boundary conditions so the direct problem is difficult to solve because
of the multiplicity of solutions. For an array of small junctions in a passive
region, the model can be reduced to a 1D linear partial differential equation
with Dirac distribution sine nonlinearities. For small junctions and a
symmetric device, the maximum current is the absolute value of a cosine Fourier
series whose coefficients (resp. frequencies) are proportional to the areas
(resp. the positions) of the junctions. The inverse problem is solved by
inverse cosine Fourier transform after choosing the area of the central
junction. We show several examples using combinations of simple three junction
circuits. These new devices could then be tailored to meet specific
applications.Comment: The article was submitted to Inverse Problem
Localization of Gauge Fields and Monopole Tunnelling
We study the dynamical localization of a massless gauge field on a
lower-dimensional surface (2-brane). In flat space, the necessary and
sufficient condition for this phenomenon is the existence of confinement in the
bulk. The resulting configuration is equivalent to a dual Josephson junction.
This duality leads to an interesting puzzle, as it implies that a localized
massless theory, even in the Abelian case, must become confining at
exponentially large distances. Through the use of topological arguments we
clarify the physics behind this large-distance confinement and identify the
instantons of the brane world-volume theory that are responsible for its
appearance. We show that they correspond to the (condensed) bulk magnetic
charges (monopoles), that occasionally tunnel through the brane and induce weak
confinement of the brane theory. We consider the possible generalization of
this effect to higher dimensions and discuss phenomenological bounds on the
confinement of electric charges at exponentially large distances within our
Universe.Comment: 11 pages, 3 figures, improvements in the presentation, version to
appear in Physical Review
Quantum Noise Measurement of a Carbon Nanotube Quantum Dot in the Kondo Regime
The current emission noise of a carbon nanotube quantum dot in the Kondo
regime is measured at frequencies of the order or higher than the
frequency associated with the Kondo effect , with the Kondo
temperature. The carbon nanotube is coupled via an on-chip resonant circuit to
a quantum noise detector, a superconductor-insulator-superconductor junction.
We find for a Kondo effect related singularity at a
voltage bias , and a strong reduction of this singularity
for , in good agreement with theory. Our experiment
constitutes a new original tool for the investigation of the non-equilibrium
dynamics of many-body phenomena in nanoscale devices.Comment: 6 pages, 4 figure
High Frequency Quantum Admittance and Noise Measurement with an On-chip Resonant Circuit
By coupling a quantum detector, a superconductor-insulator-superconductor
junction, to a Josephson junction \textit{via} a resonant circuit we probe the
high frequency properties, namely the ac complex admittance and the current
fluctuations of the Josephson junction at the resonant frequencies. The
admittance components show frequency dependent singularities related to the
superconducting density of state while the noise exhibits a strong frequency
dependence, consistent with theoretical predictions. The circuit also allows to
probe separately the emission and absorption noise in the quantum regime of the
superconducting resonant circuit at equilibrium. At low temperature the
resonant circuit exhibits only absorption noise related to zero point
fluctuations, whereas at higher temperature emission noise is also present.Comment: 15 pages, 15 figure
Phase diffusion and charging effects in Josephson junctions
The supercurrent of a Josephson junction is reduced by phase diffusion. For
ultrasmall capacitance junctions the current may be further decreased by
Coulomb blockade effects. We calculate the Cooper pair current by means of
time-dependent perturbation theory to all orders in the Josephson coupling
energy and obtain the current-voltage characteristic in closed form in a range
of parameters of experimental interest. The results comprehend phase diffusion
of the coherent Josephson current in the classical regime as well as the
supercurrent peak due to incoherent Cooper pair tunneling in the strong Coulomb
blockade regime.Comment: 4 pages, 3 figures, RevTe
QCD Corrections to Dilepton Production near Partonic Threshold in proton-antiproton Scattering
We present a recent study of the QCD corrections to dilepton production near
partonic threshold in transversely polarized \bar{p}p scattering. We analyze
the role of the higher-order perturbative QCD corrections in terms of the
available fixed-order contributions as well as of all-order soft-gluon
resummations for the kinematical regime of proposed experiments at GSI-FAIR. We
find that perturbative corrections are large for both unpolarized and polarized
cross sections, but that the spin asymmetries are stable. The role of the far
infrared region of the momentum integral in the resummed exponent and the
effect of the NNLL resummation are briefly discussed.Comment: 6 pages, 8 figures, to appear in the proceedings of the "7th
International Symposium on Radiative Corrections (RADCOR05)", Shonan Village,
Japan, 200
Josephson Vortex Bloch Oscillations: Single Pair Tunneling Effect
We consider the Josephson vortex motion in a long one--dimensional Josephson
junction in a thin film. We show that this Josephson vortex is similar to a
mesoscopic capacitor. We demonstrate that a single Cooper pair tunneling
results in nonlinear Bloch--type oscillations of a Josephson vortex in a
current-biased Josephson junction. We find the frequency and the amplitude of
this motion.Comment: 7 pages, 2 figures included as postscript files, LaTe
Shapiro steps in Josephson junctions with alternating critical current density
We treat theoretically Shapiro steps in tunnel Josephson junctions with
spatially alternating critical current density. Explicit analytical formulas
for the width of the first integer (normal) and half-integer (anomalous)
Shapiro steps are derived for short junctions. We develop coarse-graining
approach, which describes Shapiro steps in the voltage-current curves of the
asymmetric grain boundaries in YBCO thin films and different
superconductor-ferromagnet-superconductor Josephson-type heterostructures.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.
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