2,284 research outputs found
Abelian Hall Fluids and Edge States: a Conformal Field Theory Approach
We show that a Coulomb gas Vertex Operator representation of 2D Conformal
Field Theory gives a complete description of abelian Hall fluids: as an
euclidean theory in two space dimensions leads to the construction of the
ground state wave function for planar and toroidal geometry and characterizes
the spectrum of low energy excitations; as a Minkowski theory gives the
corresponding dynamics of the edge states. The difference between a generic
Hall fluid and states of the Jain's sequences is emphasized and the presence,
in the latter case, of of an extended algebra
and the consequent propagation on the edges of a single charged mode and
neutral modes is discussed.Comment: Latex, 22 page
Knizhnik-Zamolodchikov equation and extended symmetry for stable Hall states
We describe a component abelian Hall fluid as a system of {\it composite
bosons} moving in an average null field given by the external magnetic field
and by the statistical flux tubes located at the position of the particles. The
collective vacuum state, in which the bosons condense, is characterized by a
Knizhnik-Zamolodchikov differential equation relative to a
Wess-Zumino model. In the case of states belonging to Jain's sequences the
Knizhnik-Zamolodchikov equation naturally leads to the presence of an
\hat{U}(1)\ot \hat{SU}(n) extended algebra. Only the mode is
charged while the modes are neutral, in agreement with recent
results obtained in the study of the edge states.Comment: 11 pages, Late
2+1 Einstein Gravity as a Deformed Chern-Simons Theory
The usual description of 2+1 dimensional Einstein gravity as a Chern-Simons
(CS) theory is extended to a one parameter family of descriptions of 2+1
Einstein gravity. This is done by replacing the Poincare' gauge group symmetry
by a q-deformed Poincare' gauge group symmetry, with the former recovered when
q-> 1. As a result, we obtain a one parameter family of Hamiltonian
formulations for 2+1 gravity. Although formulated in terms of noncommuting
dreibeins and spin-connection fields, our expression for the action and our
field equations, appropriately ordered, are identical in form to the ordinary
ones. Moreover, starting with a properly defined metric tensor, the usual
metric theory can be built; the Christoffel symbols and space-time curvature
having the usual expressions in terms of the metric tensor, and being
represented by c-numbers. In this article, we also couple the theory to
particle sources, and find that these sources carry exotic angular momentum.
Finally, problems related to the introduction of a cosmological constant are
discussed.Comment: Latex file, 26 pages, no figure
Comments on the Non-Commutative Description of Classical Gravity
We find a one-parameter family of Lagrangian descriptions for classical
general relativity in terms of tetrads which are not c-numbers. Rather, they
obey exotic commutation relations. These noncommutative properties drop out in
the metric sector of the theory, where the Christoffel symbols and the Riemann
tensor are ordinary commuting objects and they are given by the usual
expression in terms of the metric tensor. Although the metric tensor is not a
c-number, we argue that all measurements one can make in this theory are
associated with c-numbers, and thus that the common invariant sector of our
one--parameter family of deformed gauge theories (for the case of zero torsion)
is physically equivalent to Einstein's general relativity.Comment: Latex file, 13 pages, no figure
Comment on "Quantitative wave-particle duality in multibeam interferometers"
In a recent paper [Phys. Rev. {\bf A64}, 042113 (2001)] S. D\"urr proposed an
interesting multibeam generalization of the quantitative formulation of
interferometric wave-particle duality, discovered by Englert for two-beam
interferometers. The proposed generalization is an inequality that relates a
generalized measure of the fringe visibility, to certain measures of the
maximum amount of which-way knowledge that can be stored in a which-way
detector. We construct an explicit example where, with three beams in a pure
state, the scheme proposed by D\"{u}rr leads to the possibility of an ideal
which-way detector, that can achieve a better path-discrimination, at the same
time as a better fringe visibility. In our opinion, this seems to be in
contrast with the intuitive idea of complementarity, as it is implemented in
the two-beams case, where an increase in path discrimination always implies a
decrease of fringe visibility, if the beams and the detector are in pure
states.Comment: 4 pages, 1 encapsulated figure. In press on Phys. Rev.
Evidence on the Efficacy of School-Based Incentives for Healthy Living
We analyze the effects of a school-based incentive program on children's exercise habits. The program offers children an opportunity to win prizes if they walk or bike to school during prize periods. We use daily child-level data and individual fixed effects models to measure the impact of the prizes by comparing behavior during prize periods with behavior during non-prize periods. Variation in the timing of prize periods across different schools allows us to estimate models with calendardate fixed effects to control for day-specific attributes, such as weather and proximity to holidays. On average, we find that being in a prize period increases riding behavior by sixteen percent, a large impact given that the prize value is just six cents per participating student. We also find that winning a prize lottery has a positive impact on ridership over subsequent weeks; consider heterogeneity across prize type, gender, age, and calendar month; and explore differential effects on the intensive versus extensive margins.health; exercise; children; school; incentives; active commuting
XAI.it 2021 - Preface to the Second Italian Workshop on Explainable Artificial Intelligence
Artificial Intelligence systems are increasingly playing an increasingly important role in our daily lives. As their importance in our everyday lives grows, it is fundamental that the internal mechanisms that guide these algorithms are as clear as possible. It is not by chance that the recent General Data Protection Regulation (GDPR) emphasized the users' right to explanation when people face artificial intelligencebased technologies. Unfortunately, the current research tends to go in the opposite direction, since most of the approaches try to maximize the effectiveness of the models (e.g., recommendation accuracy) at the expense of the explainability and the transparency. The main research questions which arise from this scenario is straightforward: how can we deal with such a dichotomy between the need for effective adaptive systems and the right to transparency and interpretability? Several research lines are triggered by this question: building transparent intelligent systems, analyzing the impact of opaque algorithms on final users, studying the role of explanation strategies, investigating how to provide users with more control in the behavior of intelligent systems. XAI.it, the Italian workshop on Explainable AI, tries to address these research lines and aims to provide a forum for the Italian community to discuss problems, challenges and innovative approaches in the various sub-fields of XAI
XAI.it 2022 - Preface to the Third Italian Workshop on Explainable Artificial Intelligence
Artificial Intelligence systems are increasingly playing an increasingly important role in our daily lives. As their importance in our everyday lives grows, it is fundamental that the internal mechanisms that guide these algorithms are as clear as possible. It is not by chance that the recent General Data Protection Regulation (GDPR) emphasized the usersâ right to explanation when people face artificial intelligence-based technologies. Unfortunately, the current research tends to go in the opposite direction, since most of the approaches try to maximize the effectiveness of the models (e.g., recommendation accuracy) at the expense of the explainability and the transparency. The main research questions which arise from this scenario is straightforward: how can we deal with such a dichotomy between the need for effective adaptive systems and the right to transparency and interpretability? Several research lines are triggered by this question: building transparent intelligent systems, analyzing the impact of opaque algorithms on final users, studying the role of explanation strategies, investigating how to provide users with more control in the behavior of intelligent systems. XAI.it, the Italian workshop on Explainable AI, tries to address these research lines and aims to provide a forum for the Italian community to discuss problems, challenges and innovative approaches in the various sub-fields of XAI
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