Short distances, black holes, and TeV gravity

The Hawking effect can be rederived in terms of two-point functions and in such a way that it makes it possible to estimate, within the conventional semiclassical theory, the contribution of ultrashort distances at $I^+$ to the Planckian spectrum. Thermality is preserved for black holes with $\kappa l_P << 1$. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.Comment: 4 pages. Contribution to the MG11 Meeting (Berlin, July 2006

Zeno dynamics in wave-packet diffraction spreading

We analyze a simple and feasible practical scheme displaying Zeno, anti-Zeno, and inverse-Zeno effects in the observation of wave-packet spreading caused by free evolution. The scheme is valid both in spatial diffraction of classical optical waves and in time diffraction of a quantum wave packet. In the optical realization, diffraction spreading is observed by placing slits between a light source and a light-power detector. We show that the occurrence of Zeno or anti-Zeno effects depends just on the frequency of observations between the source and detector. These effects are seen to be related to the diffraction mode theory in Fabry-Perot resonators.Comment: 7 pages, 8 figure

A correspondence between modified gravity and General Relativity with scalar fields

We describe a novel procedure to map the field equations of nonlinear Ricci-based metric-affine theories of gravity, coupled to scalar matter described by a given Lagrangian, into the field equations of General Relativity coupled to a different scalar field Lagrangian. Our analysis considers examples with a single and $N$ real scalar fields, described either by canonical Lagrangians or by generalized functions of the kinetic and potential terms. In particular, we consider several explicit examples involving $f(R)$ theories and the Eddington-inspired Born-Infeld gravity model, coupled to different scalar field Lagrangians. We show how the nonlinearities of the gravitational sector of these theories can be traded to nonlinearities in the matter fields, and how the procedure allows to find new solutions on both sides of the correspondence. The potential of this procedure for applications of scalar field models in astrophysical and cosmological scenarios is highlighted.Comment: 14 pages; v2: section IIID extended, some minor corrections, references update

Nonsingular electrovacuum solutions with dynamically generated cosmological constant

We consider static spherically symmetric configurations in a Palatini extension of General Relativity including $R^2$ and Ricci-squared terms, which is known to replace the central singularity by a wormhole in the electrovacuum case. We modify the matter sector of the theory by adding to the usual Maxwell term a nonlinear electromagnetic extension which is known to implement a confinement mechanism in flat space. One feature of the resulting theory is that the non-linear electric field leads to a dynamically generated cosmological constant. We show that with this matter source the solutions of the model are asymptotically de Sitter and possess a wormhole topology. We discuss in some detail the conditions that guarantee the absence of singularities and of traversable wormholes.Comment: 7 double-column pages; v2: several changes in abstract and introductio

Mapping nonlinear gravity into General Relativity with nonlinear electrodynamics

We show that families of nonlinear gravity theories formulated in a metric-affine approach and coupled to a nonlinear theory of electrodynamics can be mapped into General Relativity (GR) coupled to another nonlinear theory of electrodynamics. This allows to generate solutions of the former from those of the latter using purely algebraic transformations. This correspondence is explicitly illustrated with the Eddington-inspired Born-Infeld theory of gravity, for which we consider a family of nonlinear electrodynamics and show that, under the map, preserve their algebraic structure. For the particular case of Maxwell electrodynamics coupled to Born-Infeld gravity we find, via this correspondence, a Born-Infeld-type nonlinear electrodynamics on the GR side. Solving the spherically symmetric electrovacuum case for the latter, we show how the map provides directly the right solutions for the former. This procedure opens a new door to explore astrophysical and cosmological scenarios in nonlinear gravity theories by exploiting the full power of the analytical and numerical methods developed within the framework of GR.Comment: 11 pages. v2: next discussions inserted, refs added; matches the version accepted for publication in EPJ

Defaults and Returns in the High Yield Bond Market: The Year 2003 in Review and Market Outlook

High yield bond defaults in 2003 declined significantly from record 2002 levels closing the year at $38.5 billion for a default rate of 4.66improvement from the 25companies had issues that were investment grade sometime prior to default. These fallen angels accounted for 33The high-yield bond market returned an impressive 30.62near record level of$137.4 billion; the vast majority was used for refinancing existing loan and bond issues. Based on our mortality rate methodology and assuming different measures of credit risk of recent new issuance, we expect default rates to continue their decline in 2004 to between 3.2% - 3.8%, with rates increasing in 2005 to above 4.0%

Agency Problems in the Solutions of Banking Crises

This paper examines the agency problems that arise when a Central Bank rescues a failing bank. Specifically, the objectives of this paper are to determine: (1) the agency problems that derive from the mechanism of the purchase of risky loans and (2) the response of the banks to the incentives that they face when the Central Bank purchased their risky loans. The empirical evidence from the Chilean banking crisis of the 1980s shows that the rescued banks had higher levels of risk and they were less efficient. However, it is not clear that the higher level of risks were due to moral hazard behavior. I also found that some additional measures mitigated the agency problems. These mitigating factors included limiting the amount of financial assistance per bank, the closing or selling of the banks with more serious solvency problems and, the designation of Provisional Administrator in some banks.

Chilean Banking Crisis of the 1980s: Solutions and estimation of the costs

This paper reviews the solutions to the Chilean banking crisis of the 1980s and analyzes their effects on banks, deriving policy lessons from this analysis. This paper also estimates the cost of the rescue of each institution. The three main solutions to the crisis were the following: (i) foreclosure of insolvent institutions or transfer of their assets and liabilities to the solvent institutions; (ii) acquisition of high-risk portfolio (bad loans) under condition of repurchase without provision of fresh funds; and (iii) acquisition of high-risk portfolio under condition of repurchase through future profits with provision of fresh funds. The results showed that the third alternative as the most efficient for the recovery of a significant number of financial institutions with solvency problems. Supporting bank re-capitalization and creating incentives for recovering bad loans helped to accelerate the recovery of the banking industry. The total cost was significant. The cost of foreclosure of insolvent institutions was 10.6 % of the GDP and the cost of portfolio purchase under conditions of repurchase reached 6.7 % of the GDP.