Stability of a two-sublattice spin-glass model

We study the stability of the replica-symmetric solution of a two-sublattice infinite-range spin-glass model, which can describe the transition from antiferromagnetic to spin glass state. The eigenvalues associated with replica-symmetric perturbations are in general complex. The natural generalization of the usual stability condition is to require the real part of these eigenvalues to be positive. The necessary and sufficient conditions for all the roots of the secular equation to have positive real parts is given by the Hurwitz criterion. The generalized stability condition allows a consistent analysis of the phase diagram within the replica-symmetric approximation.Comment: 21 pages, 5 figure

Reference Frames and the Physical Gravito-Electromagnetic Analogy

The similarities between linearized gravity and electromagnetism are known since the early days of General Relativity. Using an exact approach based on tidal tensors, we show that such analogy holds only on very special conditions and depends crucially on the reference frame. This places restrictions on the validity of the "gravito-electromagnetic" equations commonly found in the literature.Comment: 9 Pages, 1 figure. To appear in the Proceedings of the IAU Symposium 261 "Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis", Virginia Beach, USA, 27 April - 1 May 200

Liberalization of trade in services: A CGE analysis for Argentina, Brazil and Uruguay

In this paper we use two computable general equilibrium models to evaluate gains of liberalization of trade in services for Argentina, Brazil and Uruguay. We employ two CGE models for the calculations. For the Argentine and Uruguayan cases, we apply a model built by the authors (see Chisari (2009)) based on the MPSGE. For Brazil, our study uses the GTAP model – adapted by Rutherford (2005) that also works on an MPSGE platform. We also consider two basic cases of liberalization of trade in services: 1) mobility of goods, in which there is mobility of services across borders, as it is the traditional case of exports and imports of goods, and 2) trade presence, that is location in the domestic country of new operators with a new technology for producing services. We estimate the gains from improvements in efficiency, quality and productivity of the industries of services, due to more intense competition in the domestic market as well as from reductions in the implicit mark up on domestic services due to barriers to trade. Quality advancements lead to gains in welfare of a similar order, or even higher than expected in the case of productivity improvements. To address the case of trade presence, a latent technology is defined in situ, operative or not depending on relative prices (its market share in the overall equilibrium of the economy is endogenous). This is especially relevant for the case of telecommunications. We also observe that: 1) the economy’s specific endowment of factors will limit the expected gains of the liberalization if the latent technology is unsuitable or incompatible with them, 2) governments can face some dilemmas regarding domestic market regulations, if the liberalization of trade in financial services called for a change in regulations so that the domestic demand for government bonds were to fall.Computable general equilibrium; liberalization of trade; trade in services

Quasi-Local Linear Momentum in Black-Hole Binaries

We propose a quasi-local formula for the linear momentum of black-hole horizons inspired by the formalism of quasi-local horizons. We test this formula using two complementary configurations: (i) by calculating the large orbital linear momentum of the two black holes in an unequal-mass, zero-spin, quasi-circular binary and (ii) by calculating the very small recoil momentum imparted to the remnant of the head-on collision of an equal-mass, anti-aligned-spin binary. We obtain results consistent with the horizon trajectory in the orbiting case, and consistent with the net radiated linear momentum for the much smaller head-on recoil velocity.Comment: 5 pages, 3 figures, revtex

The Casimir spectrum revisited

We examine the mathematical and physical significance of the spectral density sigma(w) introduced by Ford in Phys. Rev. D38, 528 (1988), defining the contribution of each frequency to the renormalised energy density of a quantum field. Firstly, by considering a simple example, we argue that sigma(w) is well defined, in the sense of being regulator independent, despite an apparently regulator dependent definition. We then suggest that sigma(w) is a spectral distribution, rather than a function, which only produces physically meaningful results when integrated over a sufficiently large range of frequencies and with a high energy smooth enough regulator. Moreover, sigma(w) is seen to be simply the difference between the bare spectral density and the spectral density of the reference background. This interpretation yields a simple `rule of thumb' to writing down a (formal) expression for sigma(w) as shown in an explicit example. Finally, by considering an example in which the sign of the Casimir force varies, we show that the spectrum carries no manifest information about this sign; it can only be inferred by integrating sigma(w).Comment: 10 pages, 4 figure