15,393 research outputs found
Instanton Effects in Three-Dimensional Supersymmetric Gauge Theories with Matter
Using standard field theory techniques we compute perturbative and instanton
contributions to the Coulomb branch of three-dimensional supersymmetric QCD
with N=2 and N=4 supersymmetry and gauge group SU(2). For the N=4 theory with
one massless flavor, we confirm the proposal of Seiberg and Witten that the
Coulomb branch is the double-cover of the centered moduli space of two BPS
monopoles constructed by Atiyah and Hitchin. Introducing a hypermultiplet mass
term, we show that the asymptotic metric on the Coulomb branch coincides with
the metric on Dancer's deformation of the monopole moduli space. For the N=2
theory with flavors, we compute the one-loop corrections to the metric
and complex structure on the Coulomb branch. We then determine the
superpotential including one-loop effects around the instanton background.
These calculations provide an explicit check of several results previously
obtained by symmetry and holomorphy arguments.Comment: 24 pages, Late
The Quantum Dynamics of Heterotic Vortex Strings
We study the quantum dynamics of vortex strings in N=1 SQCD with U(N_c) gauge
group and N_f=N_c quarks. The classical worldsheet of the string has N=(0,2)
supersymmetry, but this is broken by quantum effects. We show how the pattern
of supersymmetry breaking and restoration on the worldsheet captures the
quantum dynamics of the underlying 4d theory. We also find qualitative matching
of the meson spectrum in 4d and the spectrum on the worldsheet.Comment: 13 page
Electron spectra close to a metal-to-insulator transition
A high-resolution investigation of the electron spectra close to the
metal-to-insulator transition in dynamic mean-field theory is presented. An
all-numerical, consistent confirmation of a smooth transition at zero
temperature is provided. In particular, the separation of energy scales is
verified. Unexpectedly, sharp peaks at the inner Hubbard band edges occur in
the metallic regime. They are signatures of the important interaction between
single-particle excitations and collective modes.Comment: RevTeX 4, 4 pages, 4 eps figures; published versio
Heterotic Vortex Strings
We determine the low-energy N=(0,2) worldsheet dynamics of vortex strings in
a large class of non-Abelian N=1 supersymmetric gauge theories.Comment: 44 pages, 3 figures. v2: typos corrected, reference adde
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Unraveling the Cationic and Anionic Redox Reactions in a Conventional Layered Oxide Cathode
Increasing interest in high-energy lithium-ion batteries has triggered the demand to clarify the reaction mechanism in battery cathodes during high-potential operation. However, the reaction mechanism often involves both transition-metal and oxygen activities that remain elusive. Here we report a comprehensive study of both cationic and anionic redox mechanisms of LiNiO2 nearly full delithiation. Selection of pure LiNiO2 removes the complication of multiple transition metals. Using combined X-ray absorption spectroscopy, resonant inelastic X-ray scattering, and operando differential electrochemical mass spectrometry, we are able to clarify the redox reactions of transition metals in the bulk and at the surface, reversible lattice oxygen redox, and irreversible oxygen release associated with surface reactions. Many findings presented here bring attention to different types of oxygen activities and metal-oxygen interactions in layered oxides, which are of crucial importance to the advancement of a Ni-rich layered oxide cathode for high capacity and long cycling performance
Electron Transfer in Donor-Acceptor Systems: Many-Particle Effects and Influence of Electronic Correlations
We investigate electron transfer processes in donor-acceptor systems with a
coupling of the electronic degrees of freedom to a common bosonic bath. The
model allows to study many-particle effects and the influence of the local
Coulomb interaction U between electrons on donor and acceptor sites. Using the
non-perturbative numerical renormalization group approach we find distinct
differences between the electron transfer characteristics in the single- and
two-particle subspaces. We calculate the critical electron-boson coupling
alpha_c as a function of and show results for density-density correlation
functions in the whole parameter space. The possibility of many-particle
(bipolaronic) and Coulomb-assisted transfer is discussed.Comment: 4 pages, 4 figure
Kinematic approach to off-diagonal geometric phases of nondegenerate and degenerate mixed states
Off-diagonal geometric phases have been developed in order to provide
information of the geometry of paths that connect noninterfering quantal
states. We propose a kinematic approach to off-diagonal geometric phases for
pure and mixed states. We further extend the mixed state concept proposed in
[Phys. Rev. Lett. {\bf 90}, 050403 (2003)] to degenerate density operators. The
first and second order off-diagonal geometric phases are analyzed for unitarily
evolving pairs of pseudopure states.Comment: New section IV, new figure, journal ref adde
Vortex Strings and Four-Dimensional Gauge Dynamics
We study the low-energy quantum dynamics of vortex strings in the Higgs phase
of N=2 supersymmetric QCD. The exact BPS spectrum of the stretched string is
shown to coincide with the BPS spectrum of the four-dimensional parent gauge
theory. Perturbative string excitations correspond to bound W-bosons and quarks
while the monopoles appear as kinks on the vortex string. This provides a
physical explanation for an observation by N. Dorey relating the quantum
spectra of theories in two and four dimensions.Comment: 23 pages, 1 figure. v2: Two extra appendices included: one on the
brane construction, the other describing the potential on the vortex moduli
space. Two figures added. Typos corrected and references added. v3: BPS
nature of quarks correcte
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