8,420 research outputs found
Coulomb integrals and conformal blocks in the AdS3-WZNW model
We study spectral flow preserving four-point correlation functions in the
AdS3-WZNW model using the Coulomb gas method on the sphere. We present a
multiple integral realization of the conformal blocks and explicitly compute
amplitudes involving operators with quantized values of the sum of their spins,
i.e., requiring an integer number of screening charges of the first kind. The
result is given as a sum over the independent configurations of screening
contours yielding a monodromy invariant expansion in powers of the worldsheet
moduli. We then examine the factorization limit and show that the leading terms
in the sum can be identified, in the semiclassical limit, with products of
spectral flow conserving three-point functions. These terms can be rewritten as
the m-basis version of the integral expression obtained by J. Teschner from a
postulate for the operator product expansion of normalizable states in the
H3+-WZNW model. Finally, we determine the equivalence between the
factorizations of a particular set of four-point functions into products of two
three-point functions either preserving or violating spectral flow number
conservation. Based on this analysis we argue that the expression for the
amplitude as an integral over the spin of the intermediate operators holds
beyond the semiclassical regime, thus corroborating that spectral flow
conserving correlators in the AdS3-WZNW model are related by analytic
continuation to correlation functions in the H3+-WZNW model.Comment: 28 pages; references modified, published versio
Quantum critical point and superconducting dome in the pressure phase diagram of o-TaS3
We measure the electrical resistance of o-TaS3 between 1K and 300K under
pressures up to 20GPa. We observe a gradual decrease of the charge density wave
transition temperature with increasing pressure P following a mean-field
quantum fluctuation power law with a quantum critical point at a pressure Pc =
11.5GPa. Around the quantum critical point we observe a superconducting dome
with a maximum superconducting transition temperature Tc = 3.1K. Such dome is
similar to superconducting domes around other types of order suggesting that
the QCP is directly responsible for the enhancement of superconductivity
through a universal mechanism still not well understood.Comment: To be published in PRB as a Rapid Communication. 11 pages with 4
figure
High pressure effects in fluorinated HgBa2Ca2Cu3O(8+d)
We have measured the pressure sensitivity of Tc in fluorinated
HgBa2Ca2Cu3O(8+d) (Hg-1223) ceramic samples with different F contents, applying
pressures up to 30 GPa. We obtained that Tc increases with increasing pressure,
reaching different maximum values, depending on the F doping level, and
decreases for a further increase of pressure. A new high Tc record (166 K +/- 1
K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample
near the optimum doping level. Our results show that all our samples are at the
optimal doping, and that fluorine incorporation decreases the crystallographic
-parameter concomitantly increasing the maximum attainable Tc. This effect
reveals that the compression of the axes is one of the keys that controls
the Tc of high temperature superconductors.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
The Mexican intertemporal budget constraint: Persistent signals of an eventual collapse
This paper examines the sustainability of the Mexican current account deficit prior to the December 1994 crisis. It tests whether or not the Mexican economy was satisfying its intertemporal budget constraint, and finds that signals of possible trouble without a change in policies were present long before the crisis. The tests used are based on the Wickens-Uctum criterion for the sustainability of current account deficits, extended to include the case of possible interventions.intertemporal budget constraint, current account, sustainability of current account deficit, Mexico
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