635 research outputs found
Quaternionic and Poisson-Lie structures in 3d gravity: the cosmological constant as deformation parameter
Each of the local isometry groups arising in 3d gravity can be viewed as the
group of unit (split) quaternions over a ring which depends on the cosmological
constant. In this paper we explain and prove this statement, and use it as a
unifying framework for studying Poisson structures associated with the local
isometry groups. We show that, in all cases except for Euclidean signature with
positive cosmological constant, the local isometry groups are equipped with the
Poisson-Lie structure of a classical double. We calculate the dressing action
of the factor groups on each other and find, amongst others, a simple and
unified description of the symplectic leaves of SU(2) and SL(2,R). We also
compute the Poisson structure on the dual Poisson-Lie groups of the local
isometry groups and on their Heisenberg doubles; together, they determine the
Poisson structure of the phase space of 3d gravity in the so-called
combinatorial description.Comment: 34 pages, minor corrections, references adde
A Chern-Simons approach to Galilean quantum gravity in 2+1 dimensions
We define and discuss classical and quantum gravity in 2+1 dimensions in the
Galilean limit. Although there are no Newtonian forces between massive objects
in (2+1)-dimensional gravity, the Galilean limit is not trivial. Depending on
the topology of spacetime there are typically finitely many topological degrees
of freedom as well as topological interactions of Aharonov-Bohm type between
massive objects. In order to capture these topological aspects we consider a
two-fold central extension of the Galilei group whose Lie algebra possesses an
invariant and non-degenerate inner product. Using this inner product we define
Galilean gravity as a Chern-Simons theory of the doubly-extended Galilei group.
The particular extension of the Galilei group we consider is the classical
double of a much studied group, the extended homogeneous Galilei group, which
is also often called Nappi-Witten group. We exhibit the Poisson-Lie structure
of the doubly extended Galilei group, and quantise the Chern-Simons theory
using a Hamiltonian approach. Many aspects of the quantum theory are determined
by the quantum double of the extended homogenous Galilei group, or Galilei
double for short. We study the representation theory of the Galilei double,
explain how associated braid group representations account for the topological
interactions in the theory, and briefly comment on an associated
non-commutative Galilean spacetime.Comment: 38 pages, 1 figure, references update
transition form factors in Quenched and QCD
Calculations of the magnetic dipole, electric quadrupole and Coulomb
quadrupole amplitudes for the transition are presented
both in quenched QCD and with two flavours of degenerate dynamical quarks.Comment: Lattice2003(Matrix), 3 page
Calculation of the N to Delta electromagnetic transition matrix element
We present results on the ratio of electric quadrupole to magnetic dipole
amplitudes, , for the transition from lattice QCD. We consider both the quenched and the 2-flavor
theory.Comment: 3 pages, 4 figures, talk presented at Lattice2002(matrixel); Layout
of figures adjuste
Boundary conditions and symplectic structure in the Chern-Simons formulation of (2+1)-dimensional gravity
We propose a description of open universes in the Chern-Simons formulation of
(2+1)-dimensional gravity where spatial infinity is implemented as a puncture.
At this puncture, additional variables are introduced which lie in the
cotangent bundle of the Poincar\'e group, and coupled minimally to the
Chern-Simons gauge field. We apply this description of spatial infinity to open
universes of general genus and with an arbitrary number of massive spinning
particles. Using results of [9] we give a finite dimensional description of the
phase space and determine its symplectic structure. In the special case of a
genus zero universe with spinless particles, we compare our result to the
symplectic structure computed by Matschull in the metric formulation of
(2+1)-dimensional gravity. We comment on the quantisation of the phase space
and derive a quantisation condition for the total mass and spin of an open
universe.Comment: 44 pages, 3 eps figure
Meson decay constants from Nf=2 clover fermions
We present recent results for meson decay constants calculated on
configurations with two flavours of O(a)-improved Wilson fermions.
Non-perturbative renormalisation is applied and quark mass dependencies as well
as finite volume and discretisation effects are investigated. In this work we
also present a computation of the coupling of the light vector mesons to the
tensor current using dynamical fermions.Comment: 6 pages, contribution to Lattice2005(Hadron spectrum and quark
masses
Distribution Amplitudes of Pseudoscalar Mesons
We present results for the first two moments of the distribution amplitudes
of pseudoscalar mesons. Using two flavors of non-perturbatively improved clover
fermions and non-perturbative renormalization of the matrix elements we perform
both chiral and continuum extrapolations and compare with recent results from
models and experiments.Comment: 7 pages, 4 figures, based on presentation at Lattice 200
Flavour singlet pseudoscalar masses in N_f = 2 QCD
We perform a lattice mass analysis in the flavour singlet pseudoscalar
channel on the SESAM and TXL full QCD vacuum configurations, with 2 active
flavours of dynamical Wilson fermions at beta = 5.6. At our inverse lattice
spacing, a^-1 = 2.3 GeV, we retrieve by a chiral extrapolation to the physical
light quark masses the value m_eta' = 3.7(+8)(-4) m_pi. A crude extrapolation
from (N_f = 3) phenomenology would suggest m_eta' \approx 5.1 m_pi for N_f = 2
QCD. we verify that the mass gap between the singlet state eta' and the pi
flavour triplt state is due to gauge configurations with non-trivial topology.Comment: 8 pages, 10 figure
Microcyclospora and Microcyclosporella: novel genera accommodating epiphytic fungi causing sooty blotch on apple
Recent studies have found a wide range of ascomycetes to be associated with sooty blotch and flyspeck (SBFS) blemishes on the surfaces of pomaceous fruits, specifically apples. Based on collections of such fungi from apple orchards in Germany and Slovenia we introduce two novel genera according to analyses of morphological characters and nuclear ribosomal DNA sequences (large subunit and internal transcribed spacer regions). Microcyclosporella is represented by a single species, M. mali, and is presently known from Germany and Slovenia. Microcyclosporella is Pseudocercosporella-like in morphology, but genetically and morphologically distinct from Pseudocercosporella s.str., for which an epitype is designated based on a fresh collection of P. bakeri from Laos. Furthermore, Pseudocercosporella is shown to be paraphyletic within the Capnodiales. Microcyclospora gen. nov. is Pseudocercospora-like in morphology, but is genetically and morphologically distinct from Pseudocercospora s.str., which is based on P. vitis. Three species, Microcyclospora malicola, M. pomicola (both collected in Germany), and M. tardicrescens (collected in Slovenia) are described. Finally, a new species of Devriesia, D. pseudoamericana, is described from pome fruit surfaces collected in Germany. Devriesia is shown to be paraphyletic, and to represent several lineages of which only Devriesia s.str. is thermotolerant. Further collections are required, however, before the latter generic complex can be resolved
Nucleon Electromagnetic Form Factors from Lattice QCD using 2+1 Flavor Domain Wall Fermions on Fine Lattices and Chiral Perturbation Theory
We present a high-statistics calculation of nucleon electromagnetic form
factors in lattice QCD using domain wall quarks on fine lattices, to
attain a new level of precision in systematic and statistical errors. Our
calculations use lattices with lattice spacing a=0.084 fm for
pion masses of 297, 355, and 403 MeV, and we perform an overdetermined analysis
using on the order of 3600 to 7000 measurements to calculate nucleon electric
and magnetic form factors up to 1.05 GeV. Results are shown
to be consistent with those obtained using valence domain wall quarks with
improved staggered sea quarks, and using coarse domain wall lattices. We
determine the isovector Dirac radius , Pauli radius and
anomalous magnetic moment . We also determine connected contributions
to the corresponding isoscalar observables. We extrapolate these observables to
the physical pion mass using two different formulations of two-flavor chiral
effective field theory at one loop: the heavy baryon Small Scale Expansion
(SSE) and covariant baryon chiral perturbation theory. The isovector results
and the connected contributions to the isoscalar results are compared with
experiment, and the need for calculations at smaller pion masses is discussed.Comment: 44 pages, 40 figure
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