Spherically symmetric static spacetimes in vacuum f(T) gravity

We show that Schwarzschild geometry remains as a vacuum solution for those four-dimensional f(T) gravitational theories behaving as ultraviolet deformations of general relativity. In the gentler context of three-dimensional gravity, we also find that the infrared-deformed f(T) gravities, like the ones used to describe the late cosmic speed up of the Universe, have as the circularly symmetric vacuum solution a Deser-de Sitter or a BTZ-like spacetime with an effective cosmological constant depending on the infrared scale present in the function f(T).Comment: 8 pages. Some typos corrected and references updated. One additional typo corrected in Eq. (33). Accepted for publication in Physical Review D. Final versio

A type of Born-Infeld regular gravity and its cosmological consequences

Born-Infeld deformation strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of General Relativity. The equivalence between teleparallelism and General Relativity is exploited to obtain a deformed theory of gravity based on second order differential equations, since teleparallel Lagrangian is built just from first derivatives of the vierbein. We show that Born-Infeld teleparallelism cures the initial singularity in a spatially flat FRW universe; moreover, it provides a natural inflationary stage without resorting to an inflaton field. The Born-Infeld parameter bounds the dynamics of Hubble parameter H(t) and establishes a maximum attainable spacetime curvature.Comment: 3 pages. Talk given at the 7th Alexander Friedmann International Seminar on Gravitation and Cosmology, Joao Pessoa, Brazil, July 200

Born-Infeld Determinantal gravity and the taming of the conical singularity in 3-dimensional spacetime

In the context of Born-Infeld \emph{determinantal} gravity formulated in a n-dimensional spacetime with absolute parallelism, we found an exact 3-dimensional \emph{vacuum} circular symmetric solution without cosmological constant consisting in a rotating spacetime with non singular behavior. The space behaves at infinity as the conical geometry typical of 3-dimensional General Relativity without cosmological constant. However, the solution has no conical singularity because the space ends at a minimal circle that no freely falling particle can ever reach in a finite proper time. The space is curved, but no divergences happen since the curvature invariants vanish at both asymptotic limits. Remarkably, this very mechanism also forbids the existence of closed timelike curves in such a spacetime.Comment: 6 pages, 2 figures. References added, some discussions improved. Version accepted in Phys. Lett.

Remnant group of local Lorentz transformations in f(T) theories

It is shown that the extended teleparallel gravitational theories, known as f(T) theories, inherit some on shell local Lorentz invariance associated with the tetrad field defining the spacetime structure. We discuss some enlightening examples, such as Minkowski spacetime and cosmological (Friedmann-Robertson-Walker and Bianchi type I) manifolds. In the first case, we show that the absence of gravity reveals itself as an incapability in the selection of a preferred parallelization at a local level, due to the fact that the infinitesimal local Lorentz subgroup acts as a symmetry group of the frame characterizing Minkowski spacetime. Finite transformations are also discussed in these examples and, contrary to the common lore on the subject, we conclude that the set of tetrads responsible for the parallelization of these manifolds is quite vast and that the remnant group of local Lorentz transformations includes one and two dimensional Abelian subgroups of the Lorentz group.Comment: 10 pages. Minor changes. To appear in PR

Non trivial frames for f(T) theories of gravity and beyond

Some conceptual issues concerning $f(T)$ theories --a family of modified gravity theories based on absolute parallelism-- are analyzed. Due to the lack of local Lorentz invariance, the autoparallel frames satisfying the field equations are evasive to an \emph{a priori} physical understanding. We exemplify this point by working out the vierbein (tetrad) fields for closed and open Friedmann-Robertson-Walker cosmologies.Comment: 7 pages, 3 figures, some references added. Accepted for publication in Phys. Lett. B. Final Versio

The regular cosmic string in Born-Infeld gravity

It is shown that Born-Infeld gravity --a high energy deformation of Einstein gravity-- removes the singularities of a cosmic string. The respective vacuum solution results to be free of conical singularity and closed timelike curves. The space ends at a minimal circle where the curvature invariants vanish; but this circle cannot be reached in a finite proper time.Comment: 4 pages, submitted to Proceedings of Spanish Relativity Meeting 2010 (ERE2010, Granada, Spain

Resistencia a la compresión de un concreto f´c=210kg/cm2 con sustitución del agregado grueso por escoria de acería de horno de arco eléctrico.

Esta investigación tiene esencialmente el objetivo de sustituir el agregado grueso de una mezcla de concreto por escoria de acería de horno de arco eléctrico generada por la empresa Sider Perú - Chimbote, la sustitución será de un 50% y 60%, para así obtener un diseño de orden de un concreto convencional. Fueron realizados los siguientes ensayos: Granulometría, Peso Unitario, Contenido de Humedad, Gravedad específica, Absorción de los materiales y Ensayo de Abrasión en la máquina de Los Ángeles del agregado grueso y la escoria, así como ensayo de la resistencia a la compresión, estos resultados fueron procesados, examinados e interpretados con metodología estadística. Se elaboraron 09 probetas patrón, 09 probetas para el 50% de sustitución y 09 probetas para el 60% de sustitución, para obtener los resultados de la siguiente manera: en la muestra patrón a los 7 días se alcanzó una resistencia promedio de 163.49 kg/cm, a los 14 días 180.57 kg/cm 2 . Al sustituir al 50% de escoria se obtiene una resistencia promedio a los 7 días de 157.42 kg/cm 2 y a los 28 días 215.01 kg/cm 2 , a los 14 días 194.36 kg/cm2 2 y a los 28 días 231.43 kg/cm2. Asimismo, para la sustitución del 60% de escoria se alcanzó una resistencia promedio a los 7 días de 165.63 kg/cm , a los 14 días 181.52 kg/cm2 2 y a los 28 días 216.14 kg/cm2. Estos resultados obtenidos nos sirven para demostrar que el concreto experimental con 50% y 60% de sustitución del agregado grueso por escoria de acería de horno de arco eléctrico están dentro de los valores normales de orden de un concreto convencional, demostrando así nuestra hipótesis.Tesi

On Born-Infeld Gravity in Weitzenbock spacetime

Using the Teleparallel Equivalent of General Relativity formulated in Weitzenb\"{o}ck spacetime, we thoroughly explore a kind of Born-Infeld regular gravity leading to second order field equations for the vielbein components. We explicitly solve the equations of motion for two examples: the extended BTZ black hole, which results to exist even if the cosmological constant is positive, and a cosmological model with matter, where the scale factor results to be well behaved, giving so a singularity-free solution.Comment: 8 pages, 1 figure. Accepted for publication in Phys. Rev.

the role of premiums and discounts in business valuation evidence from the italian context

The valuation of a (non-totalitarian) shareholding in capital stock is characterized by some critical conditions, which are mainly related to the fact that the transfer or acquisition of the same can determine the transfer of control from one subject to another. It follows that the value of the investment can not simply be equal to the proportional value of the share capital, but should include premiums or discounts. Discounts and premiums do not just affect the value of a company; they play a crucial role in influencing a host of other factors and conditions that can make or break a deal. When it comes to business valuations, it is the business appraiser's responsibility to be intimately knowledgeable with every aspect of discounts and premiums: the different types, the situations when they may or may not apply, and how to quantify them. The paper has a twofold approach: on the one hand, it analyzes the main reference literature on the definition and characteristics of premiums and discounts and the recognition and quantification of the same; on the other, subsequently, it examines the behavior adopted by the Italian professional practice in recognition and appreciation of prizes and discounts