4,040 research outputs found
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
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”.
A model of radiating black hole in noncommutative geometry
The phenomenology of a radiating Schwarzschild black hole is analyzed in a
noncommutative spacetime. It is shown that noncommutativity does not depend on
the intensity of the curvature. Thus we legitimately introduce noncommutativity
in the weak field limit by a coordinate coherent state approach. The new
interesting results are the following: i) the existence of a minimal non-zero
mass to which black hole can shrink; ii) a finite maximum temperature that the
black hole can reach before cooling down to absolute zero; iii) the absence of
any curvature singularity. The proposed scenario offers a possible solution to
conventional difficulties when describing terminal phase of black hole
evaporation.Comment: 10 pages, 4 figure
Relativistic kinetic theory of magnetoplasmas
Recently, an increasing interest in astrophysical as well as laboratory
plasmas has been manifested in reference to the existence of relativistic
flows, related in turn to the production of intense electric fields in
magnetized systems. Such phenomena require their description in the framework
of a consistent relativistic kinetic theory, rather than on relativistic MHD
equations, subject to specific closure conditions. The purpose of this work is
to apply the relativistic single-particle guiding-center theory developed by
Beklemishev and Tessarotto, including the nonlinear treatment of
small-wavelength EM perturbations which may naturally arise in such systems. As
a result, a closed set of relativistic gyrokinetic equations, consisting of the
collisionless relativistic kinetic equation, expressed in hybrid gyrokinetic
variables, and the averaged Maxwell's equations, is derived for an arbitrary
four-dimensional coordinate system.Comment: 6 pages, 1 figure. Contributed to the Proceedings of the 24th
International Symposium on Rarefied Gas Dynamics, July 10-16, 2004 Porto
Giardino Monopoli (Bari), Ital
A Methodological approach to estimating the Money Demand in Pre-Industrial Economies: Probate Inventories and Spain in the 18th century
The study of monetary phenomena and the understanding of price determination in Modern Europe are too often limited by the scarcity of good-quality data sets on the evolution across time of variables like money holdings, income, or wealth. In this paper we show that the information contained in probate inventories can be extremely useful to circumvent that problem. In particular, combining a data set of 114 inventories from Palencia (North of Spain) between 1750 and 1770 with census information (Catastro de Ensenada) we make a cross-section estimation of a money demand which is the first one ever produced for any period before the 19th century. The results provide meaningful insights about the relation between money demand and wealth, urbanization and structural change in a pre-industrial economy and highlight the potential of probate inventories to improve our knowledge of the monetary history of Modern Europe.
Generalized covariant gyrokinetic dynamics of magnetoplasmas
A basic prerequisite for the investigation of relativistic astrophysical
magnetoplasmas, occurring typically in the vicinity of massive stellar objects
(black holes, neutron stars, active galactic nuclei, etc.), is the accurate
description of single-particle covariant dynamics, based on gyrokinetic theory
(Beklemishev et al.,1999-2005). Provided radiation-reaction effects are
negligible, this is usually based on the assumption that both the space-time
metric and the EM fields (in particular the magnetic field) are suitably
prescribed and are considered independent of single-particle dynamics, while
allowing for the possible presence of gravitational/EM perturbations driven by
plasma collective interactions which may naturally arise in such systems. The
purpose of this work is the formulation of a generalized gyrokinetic theory
based on the synchronous variational principle recently pointed out (Tessarotto
et al., 2007) which permits to satisfy exactly the physical realizability
condition for the four-velocity. The theory here developed includes the
treatment of nonlinear perturbations (gravitational and/or EM) characterized
locally, i.e., in the rest frame of a test particle, by short wavelength and
high frequency. Basic feature of the approach is to ensure the validity of the
theory both for large and vanishing parallel electric field. It is shown that
the correct treatment of EM perturbations occurring in the presence of an
intense background magnetic field generally implies the appearance of
appropriate four-velocity corrections, which are essential for the description
of single-particle gyrokinetic dynamics.Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008
Minimal Scales from an Extended Hilbert Space
We consider an extension of the conventional quantum Heisenberg algebra,
assuming that coordinates as well as momenta fulfil nontrivial commutation
relations. As a consequence, a minimal length and a minimal mass scale are
implemented. Our commutators do not depend on positions and momenta and we
provide an extension of the coordinate coherent state approach to
Noncommutative Geometry. We explore, as toy model, the corresponding quantum
field theory in a (2+1)-dimensional spacetime. Then we investigate the more
realistic case of a (3+1)-dimensional spacetime, foliated into noncommutative
planes. As a result, we obtain propagators, which are finite in the ultraviolet
as well as the infrared regime.Comment: 16 pages, version which matches that published on CQ
Spinning Loop Black Holes
In this paper we construct four Kerr-like spacetimes starting from the loop
black hole Schwarzschild solutions (LBH) and applying the Newman-Janis
transformation. In previous papers the Schwarzschild LBH was obtained replacing
the Ashtekar connection with holonomies on a particular graph in a
minisuperspace approximation which describes the black hole interior. Starting
from this solution, we use a Newman-Janis transformation and we specialize to
two different and natural complexifications inspired from the complexifications
of the Schwarzschild and Reissner-Nordstrom metrics. We show explicitly that
the space-times obtained in this way are singularity free and thus there are no
naked singularities. We show that the transformation move, if any, the
causality violating regions of the Kerr metric far from r=0. We study the
space-time structure with particular attention to the horizons shape. We
conclude the paper with a discussion on a regular Reissner-Nordstrom black hole
derived from the Schwarzschild LBH and then applying again the Newmann-Janis
transformation.Comment: 18 pages, 18 figure
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