18,679 research outputs found
Strongly interacting neutrinos as the highest energy cosmic rays
We show that all features of the ultrahigh energy cosmic ray spectrum from
10^{17} eV to 10^{21} eV can be described with a simple power-like injection
spectrum of protons under the assumption that the neutrino-nucleon
cross-section is significantly enhanced at center of mass energies above
\approx 100 TeV. In our scenario, the cosmogenic neutrinos produced during the
propagation of protons through the cosmic microwave background initiate air
showers in the atmosphere, just as the protons. The total air shower spectrum
induced by protons and neutrinos shows excellent agreement with the
observations. A particular possibility for a large neutrino-nucleon
cross-section exists within the Standard Model through electroweak
instanton-induced processes.Comment: 8 pages, 4 figures, talk given at Beyond the Desert '03, Castle
Ringberg, 9-14 June, 200
Maximized string order parameters in the valence bond solid states of quantum integer spin chains
We propose a set of maximized string order parameters to describe the hidden
topological order in the valence bond solid states of quantum integer spin-S
chains. These optimized string order parameters involve spin-twist angles
corresponding to rotations around or -axes, suggesting a
hidden symmetry. Our results also suggest that a local
triplet excitation in the valence bond solid states carries a
topological charge measured by these maximized string order parameters.Comment: 5 pages, 1 figur
Identification of the dominant diffusing species in silicide formation
Implanted noble gas atoms of Xe have been used as diffusion markers in the growth study of three silicides: Ni2Si, VSi2, and TiSi2. Backscattering of MeV He has been used to determine the displacement of the markers. We found that while Si atoms predominate the diffusion in VSi2 and TiSi2, Ni atoms are the faster moving species in Ni2Si
String order and hidden topological symmetry in the SO(2n+1) symmetric matrix product states
We have introduced a class of exactly soluble Hamiltonian with either
SO(2n+1) or SU(2) symmetry, whose ground states are the SO(2n+1) symmetric
matrix product states. The hidden topological order in these states can be
fully identified and characterized by a set of nonlocal string order
parameters. The Hamiltonian possesses a hidden
topological symmetry. The breaking of this hidden symmetry leads to
degenerate ground states with disentangled edge states in an open chain system.
Such matrix product states can be regarded as cluster states, applicable to
measurement-based quantum computation.Comment: 5 pages, 1 figur
Phonon anomaly in BaFe2As2
The detailed optical properties of BaFe2As2 have been determined over a wide
frequency range above and below the structural and magnetic transition at T_N =
138 K. A prominent in-plane infrared-active mode is observed at 253 cm^{-1}
(31.4 meV) at 295 K. The frequency of this vibration shifts discontinuously at
T_N; for T < T_N the frequency of this mode displays almost no temperature
dependence, yet it nearly doubles in intensity. This anomalous behavior appears
to be a consequence of orbital ordering in the Fe-As layers.Comment: 4 pages, 3 figures and one table (minor revisions
Dispersive Coupling Between the Superconducting Transmission Line Resonator and the Double Quantum Dots
Realization of controllable interaction between distant qubits is one of the
major problems in scalable solid state quantum computing. We study a
superconducting transmission line resonator (TLR) as a tunable dispersive
coupler for the double-dot molecules. A general interaction Hamiltonian of
two-electron spin-based qubits and the TLR is presented, where the double-dot
qubits are biased at the large detuning region and the TLR is always empty and
virtually excited. Our analysis o the main decoherence sources indicates that
various major quantum operations can be reliably implemented with current
technology.Comment: 10 pages, 5 figure
Synthesis of Spatially and Intrinsically Constrained Curves Using Simulated Annealing
A general technique is presented for automatic generation of B-spline curves in a spatially constrained environment, subject to specified intrinsic shape properties. Spatial constraints are characterized by a distance metric relating points on the curve to polyhedral models of obstacles which the curve should avoid. The shape of the curve is governed by constraints based on intrinsic curve properties such as parametric variation and curvature. To simultaneously address the independent goals of global obstacle avoidance and local control of intrinsic shape properties, curve synthesis is formulated as a combinatorial optimization problem and solved via simulated annealing. Several example applications are presented which demonstrate the robustness of the technique. The synthesis of both uniform and nonuniform B-spline curves is also demonstrated. An extension of the technique to general sculptured surface model synthesis is briefly described, and a preliminary example of simple surface synthesis presented
Conformal Covariantization of Moyal-Lax Operators
A covariant approach to the conformal property associated with Moyal-Lax
operators is given. By identifying the conformal covariance with the second
Gelfand-Dickey flow, we covariantize Moyal-Lax operators to construct the
primary fields of one-parameter deformation of classical -algebras.Comment: 13 pages, Revtex, no figures, v.2: typos corrected, references added
and conclusion modifie
Transient quantum transport in double-dot Aharonov-Bohm interferometers
Real-time nonequilibrium quantum dynamics of electrons in double-dot
Aharonov-Bohm (AB) interferometers is studied using an exact solution of the
master equation. The building of the coherence between the two electronic paths
shows up via the time-dependent amplitude of the AB oscillations in the
transient transport current, and can be enhanced by varying the applied bias on
the leads, the on-site energy difference between the dots and the asymmetry of
the coupling of the dots to the leads. The transient oscillations of the
transport current do not obey phase rigidity. The circulating current has an
anti-symmetric AB oscillation in the flux. The non-degeneracy of the on-site
energies and the finite bias cause the occupation in each dot to have an
arbitrary flux dependence as the coupling asymmetry is varied.Comment: 11 pages, 5 figure
Entangling two superconducting LC coherent modes via a superconducting flux qubit
Based on a pure solid-state device consisting of two superconducting LC
circuits coupled to a superconducting flux qubit, we propose in this paper that
the maximally entangled coherent states of the two LC modes can be generated
for arbitrary coherent states through flux qubit controls.Comment: 5 pages, 2 figure
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