1,033 research outputs found
The modular S-matrix as order parameter for topological phase transitions
We study topological phase transitions in discrete gauge theories in two
spatial dimensions induced by the formation of a Bose condensate. We analyse a
general class of euclidean lattice actions for these theories which contain one
coupling constant for each conjugacy class of the gauge group. To probe the
phase structure we use a complete set of open and closed anyonic string
operators. The open strings allow one to determine the particle content of the
condensate, whereas the closed strings enable us to determine the matrix
elements of the modular -matrix, also in the broken phase. From the measured
broken -matrix we may read off the sectors that split or get identified in
the broken phase, as well as the sectors that are confined. In this sense the
modular -matrix can be employed as a matrix valued non-local order parameter
from which the low-energy effective theories that occur in different regions of
parameter space can be fully determined.
To verify our predictions we studied a non-abelian anyon model based on the
quaternion group of order eight by Monte Carlo simulation. We
probe part of the phase diagram for the pure gauge theory and find a variety of
phases with magnetic condensates leading to various forms of (partial)
confinement in complete agreement with the algebraic breaking analysis. Also
the order of various transitions is established.Comment: 37 page
Tensor product representations of the quantum double of a compact group
We consider the quantum double D(G) of a compact group G, following an
earlier paper. We use the explicit comultiplication on D(G) in order to build
tensor products of irreducible *-representations. Then we study their behaviour
under the action of the R-matrix, and their decomposition into irreducible
*-representations. The example of D(SU(2)) is treated in detail, with explicit
formulas for direct integral decomposition (`Clebsch-Gordan series') and
Clebsch-Gordan coefficients. We point out possible physical applications.Comment: LaTeX2e, 27 pages, corrected references, accepted by Comm.Math.Phy
More on core instabilities of magnetic monopoles
In this paper we present new results on the core instability of the 't Hooft
Polyakov monopoles we reported on before. This instability, where the spherical
core decays in a toroidal one, typically occurs in models in which charge
conjugation is gauged. In this paper we also discuss a third conceivable
configuration denoted as ``split core'', which brings us to some details of the
numerical methods we employed. We argue that a core instability of 't Hooft
Polyakov type monopoles is quite a generic feature of models with charged Higgs
particles.Comment: Latex, 15 pages, 6 figures; published versio
On Sibling and Exceptional W Strings
We discuss the physical spectrum for strings based on the algebras ,
, , and . For a simply-laced string, we find a
connection with the unitary Virasoro minimal model, where is the
dual Coxeter number of the underlying Lie algebra. For the string based on
, we find a connection with the unitary super-Virasoro
minimal model.Comment: 16 page
Spinor field realizations of the non-critical string based on the linear algebra
In this paper, we investigate the spinor field realizations of the
algebra, making use of the fact that the algebra can be linearized
through the addition of a spin-1 current. And then the nilpotent BRST charges
of the spinor non-critical string were built with these realizations.Comment: 10 pages, no figures, revtex4 style, accepted by Commun.Theor.Phy
Nested Topological Order
We introduce the concept of nested topological order in a class of exact
quantum lattice Hamiltonian models with non-abelian discrete gauge symmetry.
The topological order present in the models can be partially destroyed by
introducing a gauge symmetry reduction mechanism. When symmetry is reduced in
several islands only, this imposes boundary conditions to the rest of the
system giving rise to topological ground state degeneracy. This degeneracy is
related to the existence of topological fluxes in between islands or,
alternatively, hidden charges at islands. Additionally, island deformations
give rise to an extension of topological quantum computation beyond
quasiparticles.Comment: revtex4, 4 page
Manipulating electronic states at oxide interfaces using focused micro X-rays from standard lab-sources
Recently, x-ray illumination, using synchrotron radiation, has been used to
manipulate defects, stimulate self-organization and to probe their structure.
Here we explore a method of defect-engineering low-dimensional systems using
focused laboratory-scale X-ray sources. We demonstrate an irreversible change
in the conducting properties of the 2-dimensional electron gas at the interface
between the complex oxide materials LaAlO3 and SrTiO3 by X-ray irradiation. The
electrical resistance is monitored during exposure as the irradiated regions
are driven into a high resistance state. Our results suggest attention shall be
paid on electronic structure modification in X-ray spectroscopic studies and
highlight large-area defect manipulation and direct device patterning as
possible new fields of application for focused laboratory X-ray sources.Comment: 12 pages, 4 figure
Fourier transform and the Verlinde formula for the quantum double of a finite group
A Fourier transform S is defined for the quantum double D(G) of a finite
group G. Acting on characters of D(G), S and the central ribbon element of D(G)
generate a unitary matrix representation of the group SL(2,Z). The characters
form a ring over the integers under both the algebra multiplication and its
dual, with the latter encoding the fusion rules of D(G). The Fourier transform
relates the two ring structures. We use this to give a particularly short proof
of the Verlinde formula for the fusion coefficients.Comment: 15 pages, small errors corrected and references added, version to
appear in Journal of Physics
Assessing the environmental impacts of production- and consumption-side measures in sustainable agriculture intensification in the European Union
Sustainable agricultural intensification (SI) is an important strategy to respond to the combined challenge of achieving food security and providing public goods and ecosystem services to society, including mitigation and adaptation of climate change. Sustainable intensification includes a wide range of measures at both the supply and demand-side of agricultural production. However, currently, it is unclear what are the most effective and priority measures. This study assesses the potential of different SI measures for reducing GHG (greenhouse gas) emissions and increasing land use efficiency in the European Union's agriculture sector. A scenario approach was combined with life cycle analysis to quantify the environmental impacts of a number of different SI measures. The sustainable intensification measures assessed in this study are: 1) changing human diet; 2) using food waste in livestock diets; 3) shifting from monoculture cropping to crop rotation, and, 4) incorporating crop residues into the soil. The results reveal that the studied SI measures have the potential to increase land use savings, ranging from 0.06 to 3.32 m2/person/day, while GHG emission savings ranging from 71 to 1872 g CO2-eq/person/day can be achieved at EU level. Among these SI measures, changing human diet showed a remarkably high reduction of environmental impacts. On the contrary, increased GHG emission savings in the other SI measures (i.e. crop residue incorporation in the field and replacing soybean meal in conventional feed by food waste-based feed) are counter effected by increased GHG emissions in the energy sector due to reduction of feedstock availability for bioenergy production. The approach used in this study allows the assessment of both the production and consumption-side SI measures and allows the identification of the most effective SI measures and their potential trade-offs
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