4,001 research outputs found
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 to the
Planckian spectrum. Thermality is preserved for black holes with . 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 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 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 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 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.
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