Charged rotating noncommutative black holes

In this paper we complete the program of the noncomutative geometry inspired black holes, providing the richest possible solution, endowed with mass, charge and angular momentum. After providing a prescription for employing the Newman-Janis algorithm in the case of nonvanishing stress tensors, we find regular axisymmetric charged black holes in the presence of a minimal length. We study also the new thermodynamics and we determine the corresponding higher-dimensional solutions. As a conclusion we make some consideration about possible applications.Comment: 13 pages, 3 figures, correction of a typesetting inattention, updated reference list, version accepted for publication on Physical Review

Noncommutative nonsingular black holes

Adopting noncommutative spacetime coordinates, we determined a new solution of Einstein equations for a static, spherically symmetric matter source. The limitations of the conventional Schwarzschild solution, due to curvature singularities, are overcome. As a result, the line element is endowed of a regular DeSitter core at the origin and of two horizons even in the considered case of electrically neutral, nonrotating matter. Regarding the Hawking evaporation process, the intriguing new feature is that the black hole is allowed to reach only a finite maximum temperature, before cooling down to an absolute zero extremal state. As a consequence the quantum back reaction is negligible.Comment: 10 pages, 2 figures, to appear in Proceedings to the 8th Workshop `What Comes Beyond the Standard Model', July 19-29, 2005, Bled, Slovenia, edited by C.D. Froggatt (Glasgow U.), N. Mankoc Borstnik (Ljubljana U.) and H.B. Nielsen (Bohr Inst.

Spectral dimension of a quantum universe

In this paper, we calculate in a transparent way the spectral dimension of a quantum spacetime, considering a diffusion process propagating on a fluctuating manifold. To describe the erratic path of the diffusion, we implement a minimal length by averaging the graininess of the quantum manifold in the flat space case. As a result we obtain that, for large diffusion times, the quantum spacetime behaves like a smooth differential manifold of discrete dimension. On the other hand, for smaller diffusion times, the spacetime looks like a fractal surface with a reduced effective dimension. For the specific case in which the diffusion time has the size of the minimal length, the spacetime turns out to have a spectral dimension equal to 2, suggesting a possible renormalizable character of gravity in this regime. For smaller diffusion times, the spectral dimension approaches zero, making any physical interpretation less reliable in this extreme regime. We extend our result to the presence of a background field and curvature. We show that in this case the spectral dimension has a more complicated relation with the diffusion time, and conclusions about the renormalizable character of gravity become less straightforward with respect to what we found with the flat space analysis.Comment: 5 pages, 1 figure, references added, typos corrected, title changed, final version published in Physical Review

Adult mortality and investment: a new explanation of the English agricultural productivity in the 18th century

We claim that the exogenous decline of adult mortality at the end of the seventeenth century can be one of the causes driving both the decline of interest rate and the increase in agricultural production per acre in preindustrial England. Following the intuition of the life-cycle hypothesis, we show that the increase in adult life expectancy must have implied less farmer impatience and it could have caused more investment in nitrogen stock and land fertility, and higher production per acre. We analyse this dynamic interaction using an overlapping generation model and show that the evolution of agricultural production and capital rates of return predicted by the model coincide fairly well with their empirical pattern

Was malthus right? a var analysis of economic and demographic interactions in pre-industrial England

This paper shows that the interaction between economic and demographic variables in England before the onset of modern economic growth did not fit some crucial assumptions of the Malthusian model. I estimated a vector autoregression for data on fertility, nuptiality, mortality and real wages over the period 1541-1840 applying a well-known identification strategy broadly used in macroeconomics. The results show that endogenous adjustment of population to real wages functioned as Malthus assumed only until the 17th century: positive checks disappeared during the 17th century and preventive checks disappeared before 1740. This implies that the endogenous adjustment of population levels to changes in real wages -one of the cornerstones of the Malthusian model- did not work during an important part of the period usually considered within the "Malthusian regime"

Black holes in an ultraviolet complete quantum gravity

In this Letter we derive the gravity field equations by varying the action for an ultraviolet complete quantum gravity. Then we consider the case of a static source term and we determine an exact black hole solution. As a result we find a regular spacetime geometry: in place of the conventional curvature singularity extreme energy fluctuations of the gravitational field at small length scales provide an effective cosmological constant in a region locally described in terms of a de Sitter space. We show that the new metric coincides with the noncommutative geometry inspired Schwarzschild black hole. Indeed, we show that the ultraviolet complete quantum gravity, generated by ordinary matter is the dual theory of ordinary Einstein gravity coupled to a noncommutative smeared matter. In other words we obtain further insights about that quantum gravity mechanism which improves Einstein gravity in the vicinity of curvature singularities. This corroborates all the existing literature in the physics and phenomenology of noncommutative black holes.Comment: 5 pages, 2 figures, minor corrections, version matching that published by Physics Letters

Local Agglomerations and Trade: an Empirical Investigation

This paper proposes an empirical investigation of a few outcomes of economic geography models. First, we intend to assess the role of the home market effect and of the level of transport costs on the outgoing trade flows. For this purpose we refer to a regional context looking at a chosen sample of European regions. In the second part, we focus on the analysis of the trade flows of a sample for Italian industrial districts. In addition, in this last part, attention is drawn to state the benefits that the common sharing of services provide to the firms that belong to a district, above all in terms of their international competitiveness.Agglomerations; Industrial Districts; Home Market; Transport Costs; Trade Flows

Labor Productivity in Spain: 1977-2002

This study examines the evolution of labor productivity across Spanish regions during the period from 1977 to 2002. By applying the kernel technique, we estimate the effects of the Transition process on labor productivity and its main sources. We find that Spanish regions experienced a major convergence process in labor productivity and in human capital in the 1977-1993 period. We also pinpoint the existence of a transition co-movement between labor productivity and human capital. Conversely, the dynamics of investment in physical capital seem unrelated to the transition dynamics of labor productivity. The lack of co-evolution can be addressed as one of the causes of the current slowdown in productivity. Classification-JEL: J24, N34, N940, O18, O52, R10Labor productivity, employment, human capital, physical capital, Spanish regions.