590 research outputs found
Hopf-algebra description of noncommutative-spacetime symmetries
In the study of certain noncommutative versions of Minkowski spacetime there
is still a large ambiguity concerning the characterization of their symmetries.
Adopting as our case study the kappaMinkowski noncommutative space-time, on
which a large literature is already available, we propose a line of analysis of
noncommutative-spacetime symmetries that relies on the introduction of a Weyl
map (connecting a given function in the noncommutative Minkowski with a
corresponding function in commutative Minkowski) and of a compatible notion of
integration in the noncommutative spacetime. We confirm (and we establish more
robustly) previous suggestions that the commutative-spacetime notion of
Lie-algebra symmetries must be replaced, in the noncommutative-spacetime
context, by the one of Hopf-algebra symmetries. We prove that in kappaMinkowski
it is possible to construct an action which is invariant under a Poincare-like
Hopf algebra of symmetries with 10 generators, in which the noncommutativity
length scale has the role of relativistic invariant. The approach here adopted
does leave one residual ambiguity, which pertains to the description of the
translation generators, but our results, independently of this ambiguity, are
sufficient to clarify that some recent studies (gr-qc/0212128 and
hep-th/0301061), which argued for an operational indistiguishability between
theories with and without a length-scale relativistic invariant, implicitly
assumed that the underlying spacetime would be classical.Comment: 20 pages, no figures, LaTex. This version has exactly the same
technical content as version 1, but the observation reported in Section VII
is discussed more pedagogicall
Dirac spinors for Doubly Special Relativity and -Minkowski noncommutative spacetime
We construct a Dirac equation that is consistent with one of the
recently-proposed schemes for a "doubly-special relativity", a relativity with
both an observer-independent velocity scale (still naturally identified with
the speed-of-light constant) and an observer-independent length/momentum scale
(possibly given by the Planck length/momentum). We find that the introduction
of the second observer-independent scale only induces a mild deformation of the
structure of Dirac spinors. We also show that our modified Dirac equation
naturally arises in constructing a Dirac equation in the kappa-Minkowski
noncommutative spacetime. Previous, more heuristic, studies had already argued
for a possible role of doubly-special relativity in kappa-Minkowski, but
remained vague on the nature of the consistency requirements that should be
implemented in order to assure the observer-independence of the two scales. We
find that a key role is played by the choice of a differential calculus in
kappa-Minkowski. A much-studied choice of the differential calculus does lead
to our doubly-special relativity Dirac equation, but a different scenario is
encountered for another popular choice of differential calculus.Comment: 26 pages, LaTex. v2: Alessandra Agostini (contributing some results
from her PhD thesis) is added to the list of authors. The results presented
in v1 remain unchanged and are contained in Section 2. Sections 3,4,5 add
results not present in v1, concerning the realization of the DSR-deformed
Dirac equation in kappa-Minkowski noncommutative spacetime. Title changed
accordingl
Accounting fraud, business failure and creative auditing: A microanalysis of the strange case of the Sunbeam Corporation
This article closely examines the Sunbeam Corporation's path to failure and explores the reasons for its singularity. From the analysis of US fraud cases included in the UCLA-LoPucki Bankruptcy Research Database, this corporate case appears as an outlier. For Sunbeam, the time-lapse between fraud disclosure and its final bankruptcy is the longest of the entire sample; it is unique because of its length. This article uses a historical microanalysis to evaluate different hypotheses about the Sunbeam Corporation's path to failure. The relationships between acquisitions and fraud, scapegoat dynamics' and creative auditing' are identified as the most relevant issues to be examined against a changing institutional context. The resulting reconstruction of the events provides unexpected insights and recommendations for future research on auditing and accounting fraud
A well resolved ODMR triplet minus singlet spectrum of P680 from PSII particles
AbstractAn ADMR T-S spectrum of the primary donor (P680) of photosystem II (PSII) was obtained from anaerobically photoreduced particles. The spectrum is the best resolved obtained so far having a main bleaching band at 684 nm with a linewidth of only 100 cmâ1. The view that this spectrum is produced by native homogeneous P680 unlike those obtained before is defended. A small bleaching observed at 678 nm is discussed in terms of the reaction center structure. One possible interpretation of the observations is that P680 is a very loose dimer with an exciton splitting of only 144 cmâ1 corresponding to a dimer center-to-center distance of roughly 11.5 Ă
Nanocrystalline TiO2 micropillar arrays grafted on conductive glass supports: Microscopic and spectroscopic studies
Dirac spinors for doubly special relativity and -Minkowski noncommutative spacetime
We construct a Dirac equation that is consistent with one of the recently-proposed schemes for a âdoubly-special relativityâ, a relativity with both an observer-independent velocity scale (still naturally identified with the speed-of-light constant) and an observer-independent length/momentum scale (possibly given by the Planck length/momentum). We find that the introduction of the second observer-independent scale only induces a mild deformation of the structure of Dirac spinors. We also show that our modified Dirac equation naturally arises in constructing a Dirac equation in the Îș-Minkowski noncommutative spacetime. Previous, more heuristic, studies had already argued for a possible role of doubly-special relativity in Îș-Minkowski, but remained vague on the nature of the consistency requirements that should be implemented in order to assure the observer-independence of the two scales. We find that a key role is played by the choice of a differential calculus in Îș-Minkowski. A much-studied choice of the differential calculus does lead to our doubly-special relativity Dirac equation, but a different scenario is encountered for another popular choice of differential calculus
A no-pure-boost uncertainty principle from spacetime noncommutativity
We study boost and space-rotation transformations in kappa-Minkowski
noncommutative spacetime, using the techniques that some of us had previously
developed (hep-th/0607221) for a description of translations in
kappa-Minkowski, which in particular led to the introduction of translation
transformation parameters that do not commute with the spacetime coordinates.
We find a similar description of boosts and space rotations, which allows us to
identify some associated conserved charges, but the form of the commutators
between transformation parameters and spacetime coordinates is incompatible
with the possibility of a pure boost.Comment: 8 pages, LaTe
Structureâreactivity relationship in Co3O4 promoted Au/CeO2 catalysts for the CH3OH oxidation reaction revealed by in situ FTIR and operando EXAFS studies
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