On Schwinger Pair Creation in Gravity and in Closed Superstring Theory

We investigate the Schwinger pair creation process in the context of gravitational models with the back reaction of the electric field included in the geometry. The background is also an exact solution of type II superstring theory, where the electric field arises by Kaluza-Klein reduction. We obtain a closed formula for the pair creation rate that incorporates the gravitational back reaction. At weak fields it has the same structure as the general Schwinger formula, albeit pairs are produced by a combination of Schwinger and Unruh effect, the latter due to the presence of a Rindler horizon. In four spacetime dimensions, the rate becomes constant at strong electric fields. For states with mass of Kaluza-Klein origin, the rate has a power-like dependence in the electric field, rather than the familiar (non-perturbative) exponential dependence. We also reproduce the same formula from the string partition function for winding string states. Finally, we comment on the generalization to excited string states.Comment: 21 page

Determinants of the development of corporate bond markets in Argentina: One size does not fit all

Conventional theory leads to expect bonds to be a financing vehicle for large firms because of economies of scale and contracting costs. We find both in our econometric evidence for firms quoted on Latin American stock exchanges, and in our survey results for Argentina, that size of assets is a robust determinant of the use of bond finance. This result, together with the fact that there are few firms that are large in terms of market value, can help understand why Argentina, as well as Latin America, has small bond markets in terms of the ratio of the stock of bonds to GDP. Since firm value represents the present value of the cash flows against which the firm borrows, the outstanding stock of corporate bonds is as small as the size of Argentine firms.debt structure, leverage, short term debt, corporate bonds, firm size, firm value

Loan and bond finance in Argentina, 1985-2005

Loan and bond finance during 1985-2005 can be divided into three sub-periods. After the 1982 debt crisis, which mainly involved domestic and foreign bank loans to both the corporate and government sectors, there was practically no credit. This situation of lack of credit persisted until the domestic economy was stabilized in 1991 with the Convertibility Plan, and foreign debt renegotiation was completed in 1993 with the Brady Plan. Loan finance recovered to unprecedented levels since the 1950s, and bond finance became for the first time an important financing vehicle for both the national government and large firms in the corporate sector. Credit came to a sudden stop in 2001, with widespread default on both corporate and government bonds. The 2001 debt crisis was not followed by runaway domestic inflation, and by 2005 Argentina was able to return to foreign capital markets.bank loans, sovereign bonds, provincial bonds, central bank bonds, corporate bonds, pension funds, yields, liquidity

A proposal for a generalized canonical osp(1,2) quantization of dynamical systems with constraints

The aim of this paper is to consider a possibility of constructing for arbitrary dynamical systems with first-class constraints a generalized canonical quantization method based on the osp(1,2) supersymmetry principle. This proposal can be considered as a counterpart to the osp(1,2)-covariant Lagrangian quantization method introduced recently by Geyer, Lavrov and M\"ulsch. The gauge dependence of Green's functions is studied. It is shown that if the parameter m^2 of the osp(1,2) superalgebra is not equal to zero then the vacuum functional and S-matrix depend on the gauge. In the limit $m\to 0$ the gauge independence of vacuum functional and S - matrix are restored. The Ward identities related to the osp(1,2) symmetry are derived.Comment: Revised version. To appear in Mod.Phys.Lett.

Effects of Vacancies on Properties of Relaxor Ferroelectrics: a First-Principles Study

A first-principles-based model is developed to investigate the influence of lead vacancies on the properties of relaxor ferroelectric Pb(Sc1/2Nb1/2)O3 (PSN). Lead vacancies generate large, inhomogeneous, electric fields that reduce barriers between energy minima for different polarization directions. This naturally explains why relaxors with significant lead vacancy concentrations have broadened dielectric peaks at lower temperatures, and why lead vacancies smear properties in the neighborhood of the ferroelectric transition in PSN. We also reconsider the conventional wisdom that lead vacancies reduce the magnitude of dielectric response.Comment: 11 pages, 1 figur

Molecular diagnosis and typing of Trypanosoma cruzi populations and lineages in cerebral Chagas disease in a patient with AIDS

Trypanosoma cruzi DNA was amplified from an intracranial biopsy and peripheral blood of an HIV patient with encephalitis; this episode was indicative of AIDS and congenital Chagas disease. The analysis of a microsatellite locus revealed a multiclonal parasite population at the brain lesion with a more complex minicircle signature than that profiled in blood using restriction fragment length polymorphism (RFLP)-PCR and low stringency single primer (LSSP) PCR. Interestingly, different sublineages of T. cruzi II were detected in blood and brain by means of spliced-leader and 24s ribosomal-DNA amplifications. Quantitative-competitive PCR monitored the decrease of parasitic load during treatment and secondary prophylaxis with benznidazole. The synergy between parasiticidal plus antiretroviral treatments probably allowed the patient a longer survival than usually achieved in similar episodes. This is the first case report demonstrating a differential distribution of natural parasite populations and sublineages in Chagas disease reactivation, showing the proliferation of cerebral variants not detectable in peripheral blood.Fil: Burgos, Juan Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Bergher, Sandra B.. Gobierno de la Ciudad de Buenos Aires. Hospital "Ignacio Pirovano"; ArgentinaFil: Freitas, Jorge M.. Universidade Federal de Minas Gerais; BrasilFil: Bisio, Margarita María Catalina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Altcheh, Jaime Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Gobierno de la Ciudad de Buenos Aires. Hospital General de Niños "Ricardo Gutiérrez"; ArgentinaFil: Teijeiro, Ricardo. Gobierno de la Ciudad de Buenos Aires. Hospital "Ignacio Pirovano"; ArgentinaFil: Begher, Sandra B.. Gobierno de la Ciudad de Buenos Aires. Hospital "Ignacio Pirovano"; ArgentinaFil: Freilij, Hector León. Gobierno de la Ciudad de Buenos Aires. Hospital General de Niños "Ricardo Gutiérrez"; ArgentinaFil: Deccarlini, Florencia. Gobierno de la Ciudad de Buenos Aires. Hospital "Ignacio Pirovano"; ArgentinaFil: Levalle, Jorge. Gobierno de la Ciudad de Buenos Aires. Hospital "Ignacio Pirovano"; ArgentinaFil: Lopez Alcoba, Horacio. Gobierno de la Ciudad de Buenos Aires. Hospital "Ignacio Pirovano"; ArgentinaFil: Burgos, Juan Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisiología, Biología Molecular y Celular; ArgentinaFil: Levin, Mariano Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Duffy, Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Macedo, Andrea M.. Universidade Federal de Minas Gerais; BrasilFil: Schijman, Alejandro Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentin

Effects of quark family nonuniversality in SU(3)_c X SU(4)_L X U(1)_x models

Flavour changing neutral currents arise in the $SU(3)_c\otimes SU(4)_L\otimes U(1)_X$ extension of the standard model because anomaly cancellation among the fermion families requires one generation of quarks to transform differently from the other two under the gauge group. In the weak basis the distinction between quark families is meaningless. However, in the mass eigenstates basis, the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify left-handed quarks in families. In this sense there are, in principle, three different assignments of quark weak eigenstates into mass eigenstates. In this work, by using measurements at the Z-pole, atomic parity violation data and experimental input from neutral meson mixing, we examine two different models without exotic electric charges based on the 3-4-1 symmetry, and address the effects of quark family nonuniversality on the bounds on the mixing angle between two of the neutral currents present in the models and on the mass scales $M_{Z_2}$ and $M_{Z_3}$ of the new neutral gauge bosons predicted by the theory. The heaviest family of quarks must transform differently in order to keep lower bounds on $M_{Z_2}$ and $M_{Z_3}$ as low as possible without violating experimental constraints.Comment: 27 pages, 10 tables, 2 figures. Equation (19) and typos corrected. Matches version to appear in Phys. Rev.

Removing zero Lyapunov exponents in volume-preserving flows

Baraviera and Bonatti proved that it is possible to perturb, in the c^1 topology, a volume-preserving and partial hyperbolic diffeomorphism in order to obtain a non-zero sum of all the Lyapunov exponents in the central direction. In this article we obtain the analogous result for volume-preserving flows.Comment: 10 page