26,346 research outputs found
Three-dimensional quantum electrodynamics as an effective interaction
We obtain a Quantum Electrodynamics in 2+1 dimensions by applying a
Kaluza--Klein type method of dimensional reduction to Quantum Electrodynamics
in 3+1 dimensions rendering the model more realistic to application in
solid-state systems, invariant under translations in one direction. We show
that the model obtained leads to an effective action exhibiting an interesting
phase structure and that the generated Chern--Simons term survives only in the
broken phase.Comment: 10 pages in Plain Te
phi-fourth model on a circle
The four dimensional critical scalar theory at equilibrium with a thermal
bath at temperature is considered. The thermal equilibrium state is labeled
by the winding number of the vacua around the compact imaginary-time
direction which compactification radius is 1/T. The effective action for zero
modes is a three dimensional scalar theory in which the mass of the
the scalar field is proportional to resembling the Kaluza-Klein
dimensional reduction. Similar results are obtained for the theory at zero
temperature but in a one-dimensional potential well. Since parity is violated
by the vacua with odd vacuum number , in such cases there is also a cubic
term in the effective potential. The -term contribution to the vacuum
shift at one-loop is of the same order of the contribution from the
-term in terms of the coupling constant of the four dimensional theory
but becomes negligible as tends to infinity. Finally, the relation between
the scalar classical vacua and the corresponding SU(2) instantons on
in the 't Hooft ansatz is studied.Comment: 9 pages, revtex4, to appear in Phys.Lett.
Endurant Types in Ontology-Driven Conceptual Modeling: Towards OntoUML 2.0
For over a decade now, a community of researchers has contributed
to the development of the Unified Foundational Ontology (UFO)
- aimed at providing foundations for all major conceptual modeling constructs.
This ontology has led to the development of an Ontology-Driven
Conceptual Modeling language dubbed OntoUML, reflecting the ontological
micro-theories comprising UFO. Over the years, UFO and OntoUML
have been successfully employed in a number of academic, industrial and
governmental settings to create conceptual models in a variety of different
domains. These experiences have pointed out to opportunities of
improvement not only to the language itself but also to its underlying
theory. In this paper, we take the first step in that direction by revising
the theory of types in UFO in response to empirical evidence. The
new version of this theory shows that many of the meta-types present
in OntoUML (differentiating Kinds, Roles, Phases, Mixins, etc.) should
be considered not as restricted to Substantial types but instead should
be applied to model Endurant Types in general, including Relator types,
Quality types and Mode types. We also contribute a formal characterization
of this fragment of the theory, which is then used to advance a
metamodel for OntoUML 2.0. Finally, we propose a computational support
tool implementing this updated metamodel
The incidence of reserve requirements in Brazil: Do bank stockholders share the burden?
There is consensus in the economic literature that reserve requirements are a tax levied upon financial intermediation, yet the incidence of the tax remains controversial. In this paper, we test whether changes in reserve requirements in Brazil impact the stock returns of the Brazilian financial system distinctly from the rest of the economy. We show that Brazilian bank stock returns may have been affected by changes in reserve requirements on both time deposits and transaction accounts, which implies that the tax burden of required reserves has not been fully passed through to banksâ borrowers or clients. Stock returns of non-financial firms may also have been affected by changes in reserve requirements, suggesting that in some cases, reserve requirements on time deposits and transaction accounts served as a non-neutral instrument of monetary or fiscal policy in Brazil.tax incidence, reserve requirements, event studies
Continuity properties of a factor of Markov chains
Starting from a Markov chain with a finite alphabet, we consider the chain
obtained when all but one symbol are undistinguishable for the practitioner. We
study necessary and sufficient conditions for this chain to have continuous
transition probabilities with respect to the past
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