22,201 research outputs found
Transverse Ward-Takahashi Identity, Anomaly and Schwinger-Dyson Equation
Based on the path integral formalism, we rederive and extend the transverse
Ward-Takahashi identities (which were first derived by Yasushi Takahashi) for
the vector and the axial vector currents and simultaneously discuss the
possible anomaly for them. Subsequently, we propose a new scheme for writing
down and solving the Schwinger-Dyson equation in which the the transverse
Ward-Takahashi identity together with the usual (longitudinal) Ward-Takahashi
identity are applied to specify the fermion-boson vertex function. Especially,
in two dimensional Abelian gauge theory, we show that this scheme leads to the
exact and closed Schwinger-Dyson equation for the fermion propagator in the
chiral limit (when the bare fermion mass is zero) and that the Schwinger-Dyson
equation can be exactly solved.Comment: 22 pages, latex, no figure
KUV 01584-0939: A Helium-transferring Cataclysmic Variable with an Orbital Period of 10 Minutes
High speed photometry of KUV 01584-0939 (alias Cet3) shows that is has a
period of 620.26 s. Combined with its hydrogen-deficient spectrum, this implies
that it is an AM CVn star. The optical modulation is probably a superhump, in
which case the orbital period will be slightly shorter than what we have
observed.Comment: Published by PASP. See also the latest Early-Release Research Paper
website of the PAS
Microscopic Theory of the Single Impurity Surface Kondo Resonance
We develop a microscopic theory of the single impurity Kondo effect on a
metallic surface. We calculate the hybridization energies for the Anderson
Hamiltonian of a magnetic impurity interacting with surface and bulk states and
show that, contrary to the Kondo effect of an impurity in the bulk, the
hybridization matrix elements are strongly dependent on the momentum around the
Fermi surface. Furthermore, by calculating the tunneling conductance of a
scanning tunneling microscope (STM), we show that when the magnetic impurity is
located at a surface the Kondo effect can occur with equal strength between
bulk and surface states. We compare our results with recent experiments of Co
impurities in Cu(111) and Cu(100) surfaces and find good quantitative
agreement.Comment: New version of the original manuscript with extended discussions on
the problem of wavefunction orthogonality, the limitations of the theory,
more figures related to the STM experiments, and one correction to an earlier
result. Accepted for publication in Phys.Rev.
Detection of local-moment formation using the resonant interaction between coupled quantum wires
We study the influence of many-body interactions on the transport
characteristics of a novel device structure, consisting of a pair of quantum
wires that are coupled to each other by means of a quantum dot. Under
conditions where a local magnetic moment is formed in one of the wires, we show
that tunnel coupling to the other gives rise to an associated peak in its
density of states, which can be detected directly in a conductance measurement.
Our theory is therefore able to account for the key observations in the recent
study of T. Morimoto et al. [Appl. Phys. Lett. {\bf 82}, 3952 (2003)], and
demonstrates that coupled quantum wires may be used as a system for the
detection of local magnetic-moment formation
Interacting with digital media at home via a second screen
In recent years Interactive Television (iTV) has become a household technology on a global scale. However, iTV is still a new technology in the early stages of its evolution.
Our previous research looked at how everyday users of iTV feel about the interactive part of iTV. In a series of studies we investigated how people use iTV services; their likes, dislikes, preferences and opinions. We then developed a second screen-based prototype device in response to these findings and tested it with iTV users in their own homes. This is a work in progress paper that outlines the work carried previously in the area of controlling interactive Television via a second screen. The positive user responses led us to extend the scope of our previous research to look into other related areas such as barriers to digital interactive media and personalisation of digital interactive media at home
Prediction of the capacitance lineshape in two-channel quantum dots
We propose a set-up to realize two-channel Kondo physics using quantum dots.
We discuss how the charge fluctuations on a small dot can be accessed by using
a system of two single electron transistors arranged in parallel. We derive a
microscopic Hamiltonian description of the set-up that allows us to make
connection with the two-channel Anderson model (of extended use in the context
of heavy-Fermion systems) and in turn make detailed predictions for the
differential capacitance of the dot. We find that its lineshape, which we
determined precisely, shows a robust behavior that should be experimentally
verifiable.Comment: 4 pages, 3 figure
Electric Conductivity of the Zero-gap Semiconducting State in Alpha-(BEDT-TTF)2I3 Salt
The electric conductivity which reveals the zero gap semiconducting (ZGS)
state has been investigated as the function of temperature and life time
in order to understand the ZGS state in quarter-filled
-(BEDT-TTF)I salt with four sites in the unit cell. By treating
as a parameter and making use of the one-loop approximation, it is found
that the conductivity is proportional to and for
and independent of and for . Further the
conductivity being independent of in the ZGS state is examined in terms of
Born approximation for the impurity cattering.Comment: 5 pages, 4 figures, submitted to J. Phys. Soc. Jp
Theory of Orbital Kondo Effect with Assisted Hopping in Strongly Correlated Electron Systems: Parquet Equations, Superconductivity and Mass Enhancement
Orbital Kondo effect is treated in a model, where additional to the
conduction band there are localized orbitals close to the Fermi energy. If the
hopping between the conduction band and the localized heavy orbitals depends on
the occupation of the atomic orbitals in the conduction band then orbital Kondo
correlation occurs. The noncommutative nature of the coupling required for the
Kondo effect is formally due to the form factors associated with the assisted
hopping which in the momentum representation depends on the momenta of the
conduction electrons involved. The leading logarithmic vertex corrections are
due to the local Coulomb interaction between the electrons on the heavy orbital
and in the conduction band. The renormalized vertex functions are obtained as a
solution of a closed set of differential equations and they show power
behavior. The amplitude of large renormalization is determined by an infrared
cutoff due to finite energy and dispersion of the heavy particles. The enhanced
assisted hopping rate results in mass enhancement and attractive interaction in
the conduction band. The superconductivity transition temperature calculated is
largest for intermediate mass enhancement, . For larger mass
enhancement the small one particle weight () in the Green's function reduces
the transition temperature which may be characteristic for otherComment: 32 pages, RevTeX 3.0, figures on reques
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