31,116 research outputs found
Some Issues in a Gauge Model of Unparticles
We address in a recent gauge model of unparticles the issues that are
important for consistency of a gauge theory, i.e., unitarity and Ward identity
of physical amplitudes. We find that non-integrable singularities arise in
physical quantities like cross section and decay rate from gauge interactions
of unparticles. We also show that Ward identity is violated due to the lack of
a dispersion relation for charged unparticles although the Ward-Takahashi
identity for general Green functions is incorporated in the model. A previous
observation that the unparticle's (with scaling dimension d) contribution to
the gauge boson self-energy is a factor (2-d) of the particle's has been
extended to the Green function of triple gauge bosons. This (2-d) rule may be
generally true for any point Green functions of gauge bosons. This implies that
the model would be trivial even as one that mimics certain dynamical effects on
gauge bosons in which unparticles serve as an interpolating field.Comment: v1:16 pages, 3 figures. v2: some clarifications made and presentation
improved, calculation and conclusion not modified; refs added and updated.
Version to appear in EPJ
WZW action in odd dimensional gauge theories
It is shown that Wess-Zumino-Witten (WZW) type actions can be constructed in
odd dimensional space-times using Wilson line or Wilson loop. WZW action
constructed using Wilson line gives anomalous gauge variations and the WZW
action constructed using Wilson loop gives anomalous chiral transformation. We
show that pure gauge theory including Yang-Mills action, Chern-Simons action
and the WZW action can be defined in odd dimensional space-times with even
dimensional boundaries. Examples in 3D and 5D are given. We emphasize that this
offers a way to generalize gauge theory in odd dimensions. The WZW action
constructed using Wilson line can not be considered as action localized on
boundary space-times since it can give anomalous gauge transformations on
separated boundaries. We try to show that such WZW action can be obtained in
the effective theory when making localized chiral fermions decouple.Comment: 19 pages, text shortened, reference added. Version to appear in PR
Interfacial chemical oxidative synthesis of multifunctional polyfluoranthene.
A novel polyfluoranthene (PFA) exhibiting strong visual fluorescence emission, a highly amplified quenching effect, and widely controllable electrical conductivity is synthesized by the direct cationic oxidative polymerization of fluoranthene in a dynamic interface between n-hexane and nitromethane containing fluoranthene and FeCl3, respectively. A full characterization of the molecular structure signifies that the PFAs have a degree of polymerization from 22-50 depending on the polymerization conditions. A polymerization mechanism at the interface of the hexane/nitromethane biphasic system is proposed. The conductivity of the PFA is tunable from 6.4 × 10-6 to 0.074 S cm-1 by doping with HCl or iodine. The conductivity can be significantly enhanced to 150 S cm-1 by heat treatment at 1100 °C in argon. A PFA-based chemosensor shows a highly selective sensitivity for Fe3+ detection which is unaffected by other common metal ions. The detection of Fe3+ likely involves the synergistic effect of well-distributed π-conjugated electrons throughout the PFA helical chains that function as both the fluorophore and the receptor units
Beyond the single-atom response in absorption lineshapes: Probing a dense, laser-dressed helium gas with attosecond pulse trains
We investigate the absorption line shapes of laser-dressed atoms beyond the
single-atom response, by using extreme ultraviolet (XUV) attosecond pulse
trains to probe an optically thick helium target under the influence of a
strong infrared (IR) field. We study the interplay between the IR-induced phase
shift of the microscopic time-dependent dipole moment and the
resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our
experimental and theoretical results show that as the optical depth increases,
this interplay leads initially to a broadening of the IR-modified line shape,
and subsequently to the appearance of new, narrow features in the absorption
line.Comment: 5 pages, 5 figure
On the Connection Between Momentum Cutoff and Operator Cutoff Regularizations
Operator cutoff regularization based on the original Schwinger's proper-time
formalism is examined. By constructing a regulating smearing function for the
proper-time integration, we show how this regularization scheme simulates the
usual momentum cutoff prescription yet preserves gauge symmetry even in the
presence of the cutoff scales. Similarity between the operator cutoff
regularization and the method of higher (covariant) derivatives is also
observed. The invariant nature of the operator cutoff regularization makes it a
promising tool for exploring the renormalization group flow of gauge theories
in the spirit of Wilson-Kadanoff blocking transformation.Comment: 28 pages in plain TeX, no figures. revised and expande
Response to Comment on "Pairing and Phase Separation in a Polarized Fermi Gas"
Zwierlein and Ketterle rely on subjective arguments and fail to recognize
important differences in physical parameters between our experiment and theirs.
We stand by the conclusions of our original report
Direction finding with partly calibrated uniform linear arrays
A new method for direction finding with partly calibrated uniform linear arrays (ULAs) is presented. It is based on the conventional estimation of signal parameters via rotational invariance techniques (ESPRIT) by modeling the imperfections of the ULAs as gain and phase uncertainties. For a fully calibrated array, it reduces to the conventional ESPRIT algorithm. Moreover, the direction-of-arrivals (DOAs), unknown gains, and phases of the uncalibrated sensors can be estimated in closed form without performing a spectral search. Hence, it is computationally very attractive. The Cramér-Rao bounds (CRBs) of the partly calibrated ULAs are also given. Simulation results show that the root mean squared error (RMSE) performance of the proposed algorithm is better than the conventional methods when the number of uncalibrated sensors is large. It also achieves satisfactory performance even at low signal-to-noise ratios (SNRs). © 2011 IEEE.published_or_final_versio
Adaptive beamforming for uniform linear arrays with unknown mutual coupling
This letter proposes a new adaptive beamforming algorithm for uniform linear arrays (ULAs) with unknown mutual coupling. It is based on the fact that the mutual coupling matrix (MCM) of a ULA can be approximated as a banded symmetric Toeplitz matrix as the mutual coupling between two sensor elements is inversely related to their separation, and hence it is negligible when they are separated by a few wavelengths. Taking advantage of this specific structure of the MCM, a new approach to calibrate the signal steering vector is proposed. By incorporating this improved steering vector estimate with a diagonally loaded robust beamformer, a new adaptive beamformer for ULA with unknown mutual coupling is obtained. Simulation results show that the proposed steering vector estimate considerably improves the robustness of the beamformer in the presence of unknown mutual coupling. Moreover, with appropriate diagonal loading, it is found that the proposed beamformer can achieve nearly optimal performance at all signal-to-noise ratio (SNR) levels. © 2002-2011 IEEE.published_or_final_versio
An improved eigendecomposition-based algorithm for frequencies estimation of two sinusoids
published_or_final_versio
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