9,838 research outputs found
Homotheties and topology of tangent sphere bundles
We prove a Theorem on homotheties between two given tangent sphere bundles
of a Riemannian manifold of , assuming different
variable radius functions and weighted Sasaki metrics induced by the
conformal class of . New examples are shown of manifolds with constant
positive or with constant negative scalar curvature, which are not Einstein.
Recalling results on the associated almost complex structure and
symplectic structure on the manifold , generalizing the
well-known structure of Sasaki by admitting weights and connections with
torsion, we compute the Chern and the Stiefel-Whitney characteristic classes of
the manifolds and .Comment: 15 pages, to appear in Journal of Geometr
Natural SU(2)-structures on tangent sphere bundles
We define and study natural -structures, in the sense of
Conti-Salamon, on the total space of the tangent sphere bundle of any
given oriented Riemannian 3-manifold . We recur to a fundamental exterior
differential system of Riemannian geometry. Essentially, two types of
structures arise: the contact-hypo and the non-contact and, for each, we study
the conditions for being hypo, nearly-hypo or double-hypo. We discover new
double-hypo structures on , of which the well-known
Sasaki-Einstein are a particular case. Hyperbolic geometry examples also
appear. In the search of the associated metrics, we find a theorem, useful for
explicitly determining the metric, which applies to all
-structures in general. Within our application to tangent
sphere bundles, we discover a whole new class of metrics specific to
3d-geometry. The evolution equations of Conti-Salamon are considered; leading
to a new integrable -structure on
associated to any flat .Comment: 27 pages, 1 figure, final version, accepted in The Asian Journal of
Mathematic
Pass-through from exchange rate to prices in Brazil:an analysis using time-varying parameters for the 1980 â 2002 period
The aim of the present paper is to analyze the pass-through from exchange rate to inflation in Brazil from 1980 to 2002. Initially, we developed a model of a profit-maximizing firm based on the pricing-to-market approach presented by FEENSTRA and KENDAL (1997). In order to adapt the model to the Brazilian reality, we considered the following aspects: (i) the firm sells its product both in the domestic market â where it has some pricing power â and in the foreign market â where it is a price-taker; (ii) costs are a function of the exchange rate; (iii) the degree of openness is included in the demand equation. Results show that the Kalman Filter yields better results than linear models with time-invariant parameters and that the inflationary environment and the exchange rate regime perceived by the agents affect the degree of pass-through. We can observe a reduction in the pass-through to consumer price indices (IPCA and IGP-DI) after the implementation of the Real plan, and a more intense reduction after the adoption of the floating exchange rate regime in 1999. These results are in line with other estimates presented in the literature. The pass-through to wholesale prices, however, is relatively constant and its levels are close to one throughout the period. This also seems to be a consistent result if we consider a small (price-taking) economy in the foreign marketexchange rate, pass-through, Kalman filter
Erratum: QCD sum rules study of the charmonium mesons
We correct a mistake in the analytical expression given in
Nucl. Phys. {\bf A} 815, 53 (2009) [arXiv:0804.4817] for the
and molecular currents. As a consequence,
the mass obtained for the molecular current:
GeV is no longer compatible with the
experimental mass of the meson Y(4260).Comment: 1 pag
Comment on ``Casimir force in compact non-commutative extra dimensions and radius stabilization''
We call attention to a series of mistakes in a paper by S. Nam [JHEP 10
(2000) 044, hep-th/0008083].Comment: 6 pages, LaTeX, uses JHEP.cl
Nature of the X(5568) : a critical Laplace sum rule analysis at N2LO
We scrutinize recent QCD spectral sum rules (QSSR) results to lowest order
(LO) predicting the masses of the BK molecule and (su)\bar(bd) four-quark
states. We improve these results by adding NLO and N2LO corrections to the PT
contributions giving a more precise meaning on the b-quark mass definition used
in the analysis. We extract our optimal predictions using Laplace sum rule
(LSR) within the standard stability criteria versus the changes of the external
free parameters (\tau-sum rule variable, t_c continuum threshold and
subtraction constant \mu). The smallness of the higher order PT corrections
justifies (a posteriori) the LO order results + the uses of the ambiguous heavy
quark mass to that order. However, our predicted spectra in the range (5173\sim
5226) MeV, summarized in Table 7, for exotic hadrons built with four different
flavours (buds), do not support some previous interpretations of the D0
candidate[1], X(5568), as a pure molecule or a four-quark state. If
experimentally confirmed, it could result from their mixing with an angle: sin
2\theta\approx 0.15. One can also scan the region (2327~ 2444) MeV (where the
D*_{s0}(2317) might be a good candidate) and the one (5173~ 5226) MeV for
detecting these (cuds) and (buds) unmixed exotic hadrons (if any) via,
eventually, their radiative or \pi+hadrons decays.Comment: Version matching with the publised version : some references added
and updated, comments added, misprint corrected (51 pages, 66 figures, 7
tables
Production of the Y(4260) State in B Meson Decay
We calculate the branching ratio for the production of the meson in
the decay . We use QCD sum rules approach and we consider
the to be a mixture between charmonium and exotic tetraquark,
, states with . Using the value of the
mixing angle determined previously as: , we get the
branching ratio , which
allows us to estimate an interval on the branching fraction in agreement with the experimental
upper limit reported by Babar Collaboration.Comment: 5 pages, 2 figures, 1 table. arXiv admin note: text overlap with
arXiv:1105.134
Testing Nonlinearities Between Brazilian Exchange Rate and Inflation Volatilities
There are few studies directly addressing exchange rate and inflation volatilities, and lack of consensus among them. However, this kind of study is necessary, especially because they can help monetary authorities to know price behavior better. This article analyses the relation between exchange rate and inflation volatilities using a bivariate GARCH model, and therefore modeling conditional volatilities, fact largely unexplored by the literature. We find a semi-concave relation between those series, and this nonlinearity may explain their apparently disconnection under a floating exchange rate system. The article also shows that traditional tests, with non-conditional volatilities, are not robust.
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