4,751 research outputs found
First order parent formulation for generic gauge field theories
We show how a generic gauge field theory described by a BRST differential can
systematically be reformulated as a first order parent system whose spacetime
part is determined by the de Rham differential. In the spirit of Vasiliev's
unfolded approach, this is done by extending the original space of fields so as
to include their derivatives as new independent fields together with associated
form fields. Through the inclusion of the antifield dependent part of the BRST
differential, the parent formulation can be used both for on and off-shell
formulations. For diffeomorphism invariant models, the parent formulation can
be reformulated as an AKSZ-type sigma model. Several examples, such as the
relativistic particle, parametrized theories, Yang-Mills theory, general
relativity and the two dimensional sigma model are worked out in details.Comment: 36 pages, additional sections and minor correction
Symmetry Protected Topological phases and Generalized Cohomology
We discuss the classification of SPT phases in condensed matter systems. We
review Kitaev's argument that SPT phases are classified by a generalized
cohomology theory, valued in the spectrum of gapped physical systems. We
propose a concrete description of that spectrum and of the corresponding
cohomology theory. We compare our proposal to pre-existing constructions in the
literature.Comment: 27 pages, 10 figures. v2: citation updat
General Covariance in Algebraic Quantum Field Theory
In this review we report on how the problem of general covariance is treated
within the algebraic approach to quantum field theory by use of concepts from
category theory. Some new results on net cohomology and superselection
structure attained in this framework are included.Comment: 61 pages, 3 figures, LaTe
A subsystem-independent generalization of entanglement
We introduce a generalization of entanglement based on the idea that
entanglement is relative to a distinguished subspace of observables rather than
a distinguished subsystem decomposition. A pure quantum state is entangled
relative to such a subspace if its expectations are a proper mixture of those
of other states. Many information-theoretic aspects of entanglement can be
extended to the general setting, suggesting new ways of measuring and
classifying entanglement in multipartite systems. By going beyond the
distinguishable-subsystem framework, generalized entanglement also provides
novel tools for probing quantum correlations in interacting many-body systems.Comment: 5 pages, 1 encapsulated color figure, REVTeX4 styl
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