6,799 research outputs found
Topological Equivalence between the Fibonacci Quasicrystal and the Harper Model
One-dimensional quasiperiodic systems, such as the Harper model and the
Fibonacci quasicrystal, have long been the focus of extensive theoretical and
experimental research. Recently, the Harper model was found to be topologically
nontrivial. Here, we derive a general model that embodies a continuous
deformation between these seemingly unrelated models. We show that this
deformation does not close any bulk gaps, and thus prove that these models are
in fact topologically equivalent. Remarkably, they are equivalent regardless of
whether the quasiperiodicity appears as an on-site or hopping modulation. This
proves that these different models share the same boundary phenomena and
explains past measurements. We generalize this equivalence to any
Fibonacci-like quasicrystal, i.e., a cut and project in any irrational angle.Comment: 7 pages, 2 figures, minor change
Softly broken supersymmetric Yang-Mills theories: Renormalization and non-renormalization theorems
We present a minimal version for the renormalization of softly broken
Super-Yang-Mills theories using the extended model with a local gauge coupling.
It is shown that the non-renormalization theorems of the case with unbroken
supersymmetry are valid without modifications and that the renormalization of
soft-breaking parameters is completely governed by the renormalization of the
supersymmetric parameters. The symmetry identities in the present context are
peculiar, since the extended model contains two anomalies: the Adler-Bardeen
anomaly of the axial current and an anomaly of supersymmetry in the presence of
the local gauge coupling. From the anomalous symmetries we derive the exact
all-order expressions for the beta functions of the gauge coupling and of the
soft-breaking parameters. They generalize earlier results to arbitrary
normalization conditions and imply the NSVZ expressions for a specific
normalization condition on the coupling.Comment: 24 pages, LaTeX, v2: one reference adde
On Critical Massive (Super)Gravity in adS3
We review the status of three-dimensional "general massive gravity" (GMG) in
its linearization about an anti-de Sitter (adS) vacuum, focusing on critical
points in parameter space that yield generalizations of "chiral gravity". We
then show how these results extend to N=1 super-GMG, expanded about a
supersymmetric adS vacuum, and also to the most general `curvature-squared' N=1
supergravity model.Comment: 10 pages, Proceedings of ERE 2010, Granada, 6-10 september 2010;
reference adde
Physical renormalization condition for the quark-mixing matrix
We investigate the renormalization of the quark-mixing matrix in the
Electroweak Standard Model. We show that the corresponding counterterms must be
gauge independent as a consequence of extended BRS invariance. Using rigid
SU(2)_L symmetry, we proof that the ultraviolet-divergent parts of the
invariant counterterms are related to the field renormalization constants of
the quark fields. We point out that for a general class of renormalization
schemes rigid SU(2)_L symmetry cannot be preserved in its classical form, but
is renormalized by finite counterterms. Finally, we discuss a genuine physical
renormalization condition for the quark-mixing matrix that is gauge independent
and does not destroy the symmetry between quark generations.Comment: 20 pages, LaTeX, minor changes, references adde
Large Charge Four-Dimensional Extremal N=2 Black Holes with R^2-Terms
We consider N=2 supergravity in four dimensions with small R^2 curvature
corrections. We construct large charge extremal supersymmetric and
non-supersymmetric black hole solutions in all space, and analyze their
thermodynamic properties.Comment: 18 pages. v2,3: minor fixe
Pauli's Theorem and Quantum Canonical Pairs: The Consistency Of a Bounded, Self-Adjoint Time Operator Canonically Conjugate to a Hamiltonian with Non-empty Point Spectrum
In single Hilbert space, Pauli's well-known theorem implies that the
existence of a self-adjoint time operator canonically conjugate to a given
Hamiltonian signifies that the time operator and the Hamiltonian possess
completely continuous spectra spanning the entire real line. Thus the
conclusion that there exists no self-adjoint time operator conjugate to a
semibounded or discrete Hamiltonian despite some well-known illustrative
counterexamples. In this paper we evaluate Pauli's theorem against the single
Hilbert space formulation of quantum mechanics, and consequently show the
consistency of assuming a bounded, self-adjoint time operator canonically
conjugate to a Hamiltonian with an unbounded, or semibounded, or finite point
spectrum. We point out Pauli's implicit assumptions and show that they are not
consistent in a single Hilbert space. We demonstrate our analysis by giving two
explicit examples. Moreover, we clarify issues sorrounding the different
solutions to the canonical commutation relations, and, consequently, expand the
class of acceptable canonical pairs beyond the solutions required by Pauli's
theorem.Comment: contains corrections to minor typographical errors of the published
versio
Boojums in Rotating Two-Component Bose-Einstein Condensates
A boojum is a topological defect that can form only on the surface of an
ordered medium such as superfluid He and liquid crystals. We study
theoretically boojums appearing between two phases with different vortex
structures in two-component BECs where the intracomponent interaction is
repulsive in one phase and attractive in the other. The detailed structure of
the boojums is revealed by investigating its density distribution, effective
superflow vorticity and pseudospin texture.Comment: 4 pages, 4 figure
Adolescents' life plans in the city of Madrid. Are immigrant origins of any importance?
Identities formed during adolescence are known to be crucial in shaping future life decisions in multiple domains, including not only the educational and work careers but also partnership arrangements, fertility trajectories, residential choices, even civic and political attitudes. In this article we examine in a very simple and mostly descriptive way the main differences and similarities between the daily life of adolescents of immigrant and non-immigrant origin, and their wishes and expectations for their future, utilizing data from the Chances Survey, collected in 30 secondary schools in the city of Madrid in 2011. Our methods combine a comparison of means, the ANOVA test, multivariate regressions and factor analysis, in order to identify when adolescents of immigrant origin reveal wishes and expectations significantly different from those of their classmates of native origin; and the extent to which they expect higher frustration of their wishes in their future life, or not. Differences by gender are also explored. Our findings suggest similarities and differences between both groups depending on the particular aspect examined, and discard a systematic pattern of greater optimism or pessimism among immigrant adolescents compared to their non-immigrant classmates. Differences by origin tend to be larger when respondents are asked about the immediate future instead of the more distant one, and immigrant girls seem to be the most pessimistic about their future.
5D Attractors with Higher Derivatives
We analyze higher derivative corrections to attractor geometries in five
dimensions. We find corrected AdS_3xS^2 geometries by solving the equations of
motion coming from a recently constructed four-derivative supergravity action
in five dimensions. The result allows us to explicitly verify a previous
anomaly based derivation of the AdS_3 central charges of this theory. Also, by
dimensional reduction we compare our results with those of the 4D higher
derivative attractor, and find complete agreement.Comment: 18 pages, harvma
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