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 $a$-parameter concomitantly increasing the maximum attainable Tc. This effect reveals that the compression of the $a$ 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