39,320 research outputs found
Recent results in Euclidean dynamical triangulations
We study a formulation of lattice gravity defined via Euclidean dynamical
triangulations (EDT). After fine-tuning a non-trivial local measure term we
find evidence that four-dimensional, semi-classical geometries are recovered at
long distance scales in the continuum limit. Furthermore, we find that the
spectral dimension at short distance scales is consistent with 3/2, a value
that is also observed in the causal dynamical triangulation (CDT) approach to
quantum gravity.Comment: 7 pages, 3 figures. Proceedings for the 3rd conference of the Polish
society on relativit
Lattice Quantum Gravity and Asymptotic Safety
We study the nonperturbative formulation of quantum gravity defined via
Euclidean dynamical triangulations (EDT) in an attempt to make contact with
Weinberg's asymptotic safety scenario. We find that a fine-tuning is necessary
in order to recover semiclassical behavior. Such a fine-tuning is generally
associated with the breaking of a target symmetry by the lattice regulator; in
this case we argue that the target symmetry is the general coordinate
invariance of the theory. After introducing and fine-tuning a nontrivial local
measure term, we find no barrier to taking a continuum limit, and we find
evidence that four-dimensional, semiclassical geometries are recovered at long
distance scales in the continuum limit. We also find that the spectral
dimension at short distance scales is consistent with 3/2, a value that could
resolve the tension between asymptotic safety and the holographic entropy
scaling of black holes. We argue that the number of relevant couplings in the
continuum theory is one, once symmetry breaking by the lattice regulator is
accounted for. Such a theory is maximally predictive, with no adjustable
parameters. The cosmological constant in Planck units is the only relevant
parameter, which serves to set the lattice scale. The cosmological constant in
Planck units is of order 1 in the ultraviolet and undergoes renormalization
group running to small values in the infrared. If these findings hold up under
further scrutiny, the lattice may provide a nonperturbative definition of a
renormalizable quantum field theory of general relativity with no adjustable
parameters and a cosmological constant that is naturally small in the infrared.Comment: 69 pages, 25 figures. Revised discussion of target symmetry
throughout paper. Numerical results unchanged and main conclusions largely
unchanged. Added references and corrected typos. Conforms with version
published in Phys. Rev.
Charmless two-body B decays: A global analysis with QCD factorization
In this paper, we perform a global analysis of and decays
with the QCD factorization approach. It is encouraging to observe that the
predictions of QCD factorization are in good agreement with experiment. The
best fit is around . The penguin-to-tree ratio of decays is preferred to be larger than 0.3.
We also show the confidence levels for some interesting channels: , and , . For decays, they are expected to have smaller branching ratios with
more precise measurements.Comment: 20 pages, 4 figures, version to appear in Phys. Rev.
First radius measurements of very low mass stars with the VLTI
e present 4 very low mass stars radii measured with the VLTI using the 2.2
microns VINCI test instrument. The observations were carried out during the
commissioning of the 104-meter-baseline with two 8-meter-telescopes. We measure
angular diameters of 0.7-1.5 mas with accuracies of 0.04-0.11 mas, and for
spectral type ranging from M0V to M5.5V. We determine an empirical mass-radius
relation for M dwarfs based on all available radius measurements. The observed
relation agrees well with theoretical models at the present accuracy level,
with possible discrepancy around 0.5-0.8 Msolar that needs to be confirmed. In
the near future, dozens of M dwarfs radii will be measured with 0.1-1%
accuracy, with the VLTI, thanks to the improvements expected from the near
infrared instrument AMBER. This will bring strong observational constraints on
both atmosphere and interior physics.Comment: Accepted for publication in Astronomy and Astrophysics Letters, 4
pages, 3 figure
Terminologiebestuur in Suid- Afrika: 'n Ideaalmodel *
Die nuwe taalbestel in Suid-Afrika het tot gevolg gehad dat die ontwikkeling, die uitbouing, die bestuur en ook die verspreiding van terminologiese inligting in elf amptelike tale gedoen moet word. 'n Veranderde terminologiebestuursprogram moet derhalwe daargestel word om aan die behoeftes van 'n nuwe terminologiegemeenskap te voldoen. So 'n model sou ideaal gesien binne die Nasionale Taaldiens se terminologiekoördineringsafdeling geïmplementeer kon word. In die eerste gedeelte van hierdie artikel word 'n model voorgestel van hoe terminologiebestuur suksesvol binne 'n terminologiebestuursentrum aangepak kan word. In die tweede gedeelte van die artikel word die implikasies van die model in die Suid-Afrikaanse situasie verreken om vas te stel hoe die terminologiebestuursprogram aangepas sou kon word om aan die eise van die nuwe taalbestel te voldoen en om die nuwe teikengroep(e) voldoende te bereik.
Sleutelwoorde: Amptelike Tale, Beplanning En Koördinering, Disseminering, Evaluering, Gemarginaliseerde Tale, Inheemse Tale, Implementering, Meertalige Terminologiebestuursisteem, Navorsing, Ontwikkelende Tale, Ontwikkelde Tale, Opleiding, Standaardisering, Termbank, Terminologie, Terminologiebestuursentrum, Terminologiebestuursprogram, Terminologieontwikkeling, Terminologiewer
Coexistence of localized and itinerant electrons in BaFe2X3 (X = S and Se) revealed by photoemission spectroscopy
We report a photoemission study at room temperature on BaFe2X3 (X = S and Se)
and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p
core-level peaks of BaFe2X3 are broad and exhibit two components, indicating
that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe
2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a
charge-transfer satellite. The insulating ground state of CsFe2Se3 can be
viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The
itinerant versus localized behaviors can be associated with the stability of
chalcogen p holes in the two-leg ladder structure.Comment: 5 pages, 5 figures, Accepted in publication for Physical Review
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