38,421 research outputs found
B0bar decays to D(*)0 eta and D(*)0 eta'
We consider the hadronic B decays B0bar -> D0 eta, B0bar -> D*0 eta, B0bar ->
D0 eta', B0bar -> D*0 eta' in the framework of a quark-flavour basis and
factorization. The formalism allows to compute the decays to the eta meson and
to relate them to those of the eta'. Measuring the branching ratios of these
processes may shed light on the nature of the eta-eta' mixing. On the
experimental side, only upper limits on the branching ratios are known at
present.Comment: 12 pages, 2 figures, 2 tables (LaTeX, revtex), minor revision: note
added at the end concerning new data and few reference
A note on classical and quantum unimodular gravity
We discuss unimodular gravity at a classical level, and in terms of its
extension into the UV through an appropriate path integral representation.
Classically, unimodular gravity is simply a gauge fixed version of General
Relativity (GR), and as such it yields identical dynamics and physical
predictions. We clarify this and explain why there is no sense in which it can
"bring a new perspective" to the cosmological constant problem. The quantum
equivalence between unimodular gravity and GR is more of a subtle question, but
we present an argument that suggests one can always maintain the equivalence up
to arbitrarily high momenta. As a corollary to this, we argue that whenever
inequivalence is seen at the quantum level, that just means we have defined two
different quantum theories that happen to share a classical limit.Comment: 5 pages; v2: Some clarifying comments added. Version to appear in
European Physical Journal
Stability analysis of electric power systems for âmore electricâ aircraft
This paper presents a comprehensive assessment of small-signal stability for a âmore-electricâ
aircraft power system consisting of a synchronous variable-frequency generator which supplies several power
electronic controlled loads via an 18-pulse autotransformer rectifier unit (ATRU) for AC-DC conversion.
Functional models for key power system components and loads are derived. Numerical tools employed for the
automatic calculation of linearized equations and operating points are described, and the influence of leading
design and operational parameter on system stability is evaluated
Jet Shapes in Opaque Media
We present general arguments, based on medium-induced radiative energy loss,
which reproduce the non-gaussian shapes of away-side di-jet azimuthal
correlations found in nucleus-nucleus collisions at RHIC. A rather simple
generalization of the Sudakov form factors to opaque media allowing an
effective description of the experimental data is proposed.Comment: 4 pages, 2 ps figure
Status of background-independent coarse-graining in tensor models for quantum gravity
A background-independent route towards a universal continuum limit in
discrete models of quantum gravity proceeds through a background-independent
form of coarse graining. This review provides a pedagogical introduction to the
conceptual ideas underlying the use of the number of degrees of freedom as a
scale for a Renormalization Group flow. We focus on tensor models, for which we
explain how the tensor size serves as the scale for a background-independent
coarse-graining flow. This flow provides a new probe of a universal continuum
limit in tensor models. We review the development and setup of this tool and
summarize results in the 2- and 3-dimensional case. Moreover, we provide a
step-by-step guide to the practical implementation of these ideas and tools by
deriving the flow of couplings in a rank-4-tensor model. We discuss the
phenomenon of dimensional reduction in these models and find tentative first
hints for an interacting fixed point with potential relevance for the continuum
limit in four-dimensional quantum gravity.Comment: 28 pages, Review prepared for the special issue "Progress in Group
Field Theory and Related Quantum Gravity Formalisms" in "Universe
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