50,651 research outputs found
Quantum Corrections to the Two-dimensional Gravity with External Field
We introduce an external field to calculate the quantum corrections of the 2d
gravity, via trace anomaly. We show that there are black hole type solution
even in the absence of matter field and cosmological constant. We also see that
these solutions are similar to the ones obtained from dilaton two-dimensional
gravity.Comment: 12 pages, Latex, revised versio
Non-Declarative Sentences and Communication in Husserl’s Logical Investigations: contributions to a theory on communicative acts in the light of Husserl and Austin
Theses towards a new natural philosophy
In this paper I address some philosophical questions regarding the impact quantum
mechanics has in the classical conceptions about reality and knowledge. I stress that
onto-gnosiological realism still is an option to the issues regarding the relationship
between knowledge and reality. Rejecting some radical aspects of Copenhagen
interpretation of quantum formalism, I emphasize the advantages of de Broglie’s
realistic and causal model. To finish with, I discuss the limits of the Cartesian concept
of matter and the split between matter and mind
On the trace anomaly and the energy-momentum conservation of quantum fields at D=2 in classical curved backgrounds
We study the conformal symmetry and the energy-momentum conservation of
scalar field interacting with a curved background at D=2. We avoid to
incorporate the metric determinant into the measure of the scalar field to
explain the conformal anomaly and the consequent energy-momentum conservation.
Contrarily, we split the scalar field in two other fields, in such a way that
just one of them can be quantized. We show that the same usual geometric
quantities of the anomaly are obtained, which are accompanied by terms
containing the new field of the theory.Comment: 5 pages, no figure
Acceleration field of a Universe modeled as a mixture of scalar and matter fields
A model of the Universe as a mixture of a scalar (inflaton or rolling tachyon
from the string theory) and a matter field (classical particles) is analyzed.
The particles are created at the expense of the gravitational energy through an
irreversible process whereas the scalar field is supposed to interact only with
itself and to be minimally coupled with the gravitational field. The
irreversible processes of particle creation are related to the non-equilibrium
pressure within the framework of the extended (causal or second-order)
thermodynamic theory. The scalar field (inflaton or tachyon) is described by an
exponential potential density added by a parameter which represents its
asymptotic value and can be interpreted as the vacuum energy. This model can
simulate three phases of the acceleration field of the Universe, namely,(a) an
inflationary epoch with a positive acceleration followed by a decrease of the
acceleration field towards zero, (b) a past decelerated period where the
acceleration field decreases to a maximum negative value followed by an
increase towards zero, and (c) a present accelerated epoch. For the energy
densities there exist also three distinct epochs which begin with a scalar
field dominated period followed by a matter field dominated epoch and coming
back to a scalar field dominated phase.Comment: 9 pages, 2 figures, to be published in General Relativity and
Gravitatio
Hipparcos distances of Ophiuchus and Lupus cloud complexes
We combine extinction maps from the Two Micron All Sky Survey (2MASS) with
Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates
of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based
on a rigorous maximum-likelihood approach, shows that the rho-Ophiuchi cloud is
located at (119 +/- 6) pc and the Lupus complex is located at (155 +/- 8) pc;
in addition, we are able to put constraints on the thickness of the clouds and
on their orientation on the sky (both these effects are not included in the
error estimate quoted above). For Ophiuchus, we find some evidence that the
streamers are closer to us than the core. The method applied in this paper is
currently limited to nearby molecular clouds, but it will find many natural
applications in the GAIA-era, when it will be possible to pin down the distance
and three-dimensional structure of virtually every molecular cloud in the
Galaxy.Comment: A&A in press - Corrected typo (Lupus distance) in the electronic
abstrac
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