148 research outputs found
Gauge-Invariant Approach to Meson Photoproduction Including the Final-State Interaction
A gauge-invariant formalism is presented for the practical treatment of
photo- and electroproduction of pseudoscalar mesons off nucleons that allows an
explicit incorporation of hadronic final-state interactions. The
semi-phenomenological approach is based on a field theory developed by one of
the authors. It generalizes an earlier approach by allowing for systematic
improvement of approximations in a controlled manner. The practical feasibility
is illustrated by applying the lowest-order result to the photoproduction of
both neutral and charged pions.Comment: Plenary talk given at the N*2005 Workshop (Oct. 2005, Tallahassee,
FL); to appear in the Proceedings (to be publ. by WorldScientific
On Infinite Quon Statistics and "Ambiguous" Statistics
We critically examine a recent suggestion that "ambiguous" statistics is
equivalent to infinite quon statistics and that it describes a dilute,
nonrelativistics ideal gas of extremal black holes. We show that these two
types of statistics are different and that the description of extremal black
holes in terms of "ambiguous" statistics cannot be applied.Comment: Latex, 9 pages, no figures, to appear in Mod.Phys.Lett.
Pairing of Parafermions of Order 2: Seniority Model
As generalizations of the fermion seniority model, four multi-mode
Hamiltonians are considered to investigate some of the consequences of the
pairing of parafermions of order two. 2-particle and 4-particle states are
explicitly constructed for H_A = - G A^+ A with A^+}= 1/2 Sum c_{m}^+ c_{-m}^+
and the distinct H_C = - G C^+ C with C^+}= 1/2 Sum c_{-m}^+ c_{m}^+, and for
the time-reversal invariant H_(-)= -G (A^+ - C^+)(A-C) and H_(+) = -G
(A^+dagger + C^+)(A+C), which has no analogue in the fermion case. The spectra
and degeneracies are compared with those of the usual fermion seniority model.Comment: 18 pages, no figures, no macro
Partition function for general multi-level systems
We describe a unified approach to calculating the partition functions of a
general multi-level system with a free Hamiltonian. Particularly, we present
new results for parastatistical systems of any order in the second quantized
approach. Anyonic- like systems are briefly discussed.Comment: Latex file, 16 page
Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling
Macroscopic resonant tunneling between the two lowest lying states of a
bistable RF-SQUID is used to characterize noise in a flux qubit. Measurements
of the incoherent decay rate as a function of flux bias revealed a Gaussian
shaped profile that is not peaked at the resonance point, but is shifted to a
bias at which the initial well is higher than the target well. The r.m.s.
amplitude of the noise, which is proportional to the decoherence rate 1/T_2^*,
was observed to be weakly dependent on temperature below 70 mK. Analysis of
these results indicates that the dominant source of low frequency (1/f) flux
noise in this device is a quantum mechanical environment in thermal
equilibrium.Comment: 4 pages 4 figure
Quantization of the Hall conductivity well beyond the adiabatic limit in pulsed magnetic fields
We measure the Hall conductivity, , on a Corbino geometry sample
of a high-mobility AlGaAs/GaAs heterostructure in a pulsed magnetic field. At a
bath temperature about 80 mK, we observe well expressed plateaux in
at integer filling factors. In the pulsed magnetic field, the
Laughlin condition of the phase coherence of the electron wave functions is
strongly violated and, hence, is not crucial for quantization.Comment: 4 pages, 4 figures, submitted to PR
Sign- and magnitude-tunable coupler for superconducting flux qubits
We experimentally confirm the functionality of a coupling element for
flux-based superconducting qubits, with a coupling strength whose sign and
magnitude can be tuned {\it in situ}. To measure the effective , the
groundstate of a coupled two-qubit system has been mapped as a function of the
local magnetic fields applied to each qubit. The state of the system is
determined by directly reading out the individual qubits while tunneling is
suppressed. These measurements demonstrate that can be tuned from
antiferromagnetic through zero to ferromagnetic.Comment: Updated text and figure
First-principle study of excitonic self-trapping in diamond
We present a first-principles study of excitonic self-trapping in diamond.
Our calculation provides evidence for self-trapping of the 1s core exciton and
gives a coherent interpretation of recent experimental X-ray absorption and
emission data. Self-trapping does not occur in the case of a single valence
exciton. We predict, however, that self-trapping should occur in the case of a
valence biexciton. This process is accompanied by a large local relaxation of
the lattice which could be observed experimentally.Comment: 12 pages, RevTex file, 3 Postscript figure
Absence of Scaling in the Integer Quantum Hall Effect
We have studied the conductivity peak in the transition region between the
two lowest integer Quantum Hall states using transmission measurements of edge
magnetoplasmons. The width of the transition region is found to increase
linearly with frequency but remains finite when extrapolated to zero frequency
and temperature. Contrary to prevalent theoretical pictures, our data does not
show the scaling characteristics of critical phenomena.These results suggest
that a different mechanism governs the transition in our experiment.Comment: Minor changes and new references include
Deformed Heisenberg algebra with reflection
A universality of deformed Heisenberg algebra involving the reflection
operator is revealed. It is shown that in addition to the well-known
infinite-dimensional representations related to parabosons, the algebra has
also finite-dimensional representations of the parafermionic nature. We
demonstrate that finite-dimensional representations are representations of
deformed parafermionic algebra with internal Z_2-grading structure. On the
other hand, any finite- or infinite-dimensional representation of the algebra
supply us with irreducible representation of osp(1|2) superalgebra. We show
that the normalized form of deformed Heisenberg algebra with reflection has the
structure of guon algebra related to the generalized statistics.Comment: 16 pages, LaTeX, to appear in Nucl. Phys.
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