7 research outputs found
Regularization ambiguity and van der Waals black hole in 2 + 1 dimensions
Charged black holes in a (2+1
)-dimensional anti-de Sitter space-time suffer from some limitations such as the ambiguity in the definition of the mass and the bad short distance behavior. In this paper we present a way to resolve such issues. By extending the parameter space of the BTZ geometry, we properly identify the integration constants in order to remove the conical singularity sitting at the origin. In such a way we obtain a well defined Minkowski limit and horizons also in the case of de Sitter background space. On the thermodynamic side, we obtain a proper internal energy, by invoking the consistency with the Area Law, even if the mass parameter does not appear in the metric coefficients. As a further improvement, we show that it is sufficient to assume a finite size of the electric charge to obtain a short scale regular geometry. The resulting solution, generalizing the charged BTZ metric, is dual to a van der Waals gas
Confinement effects from interacting chromo-magnetic and axion fields
We study a non-Abelian gauge theory with a pseudo scalar coupling \phi
\epsilon ^{\mu \nu \alpha \beta} F_{\mu \nu}^a F_{\alpha \beta}^a in the case
where a constant chromo-electric, or chromo-magnetic, strength expectation
value is present. We compute the interaction potential within the framework of
gauge-invariant, path-dependent, variables formalism. While in the case of a
constant chromo-electric field strength expectation value the static potential
remains Coulombic, in the case of a constant chromo-magnetic field strength the
potential energy is the sum of a Coulombic and a linear potentials, leading to
the confinement of static charges.Comment: 12 pages, no figures, published versio
Remarks on confinement driven by axion-like particles in Yang-Mills theories
Features of screening and confinement are studied for a non-Abelian gauge
theory with a mixture of pseudoscalar and scalar coupling, in the case where a
constant chromo-electric, or chromo-magnetic, strength expectation value is
present. Our discussion is carried out using the gauge-invariant but
path-dependent variables formalism. We explicitly show that the static
potential profile is the sum of a Yukawa and a linear potential, leading to the
confinement of static probe charges. Interestingly, similar results have been
obtained in the context of gluodynamics in curved space-time. For only
pseudoscalar coupling, the results are radically different.Comment: 8 pages, Latex; typos corrected; presentation improved; 2 references
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Finite axionic electrodynamics from a new noncommutative approach
Using the gauge-invariant but path-dependent variables formalism, we compute
the static quantum potential for noncommutative axionic electrodynamics (or
axionic electrodynamics in the presence of a minimal length). Accordingly, we
obtain an ultraviolet finite static potential which is the sum of a Yukawa-type
and a linear potential, leading to the confinement of static charges.
Interestingly, it should be noted that this calculation involves no theta
expansion at all. The present result makes manifest the key role played by the
new quantum of length in our analysis.Comment: 14 pages, 2 figures, final version to appear in J.Phys.A, added
comments, reference list update
Hawking emission from quantum gravity black holes
We address the issue of modelling quantum gravity effects in the evaporation
of higher dimensional black holes in order to go beyond the usual
semi-classical approximation. After reviewing the existing six families of
quantum gravity corrected black hole geometries, we focus our work on
non-commutative geometry inspired black holes, which encode model independent
characteristics, are unaffected by the quantum back reaction and have an
analytical form compact enough for numerical simulations. We consider the
higher dimensional, spherically symmetric case and we proceed with a complete
analysis of the brane/bulk emission for scalar fields. The key feature which
makes the evaporation of non-commutative black holes so peculiar is the
possibility of having a maximum temperature. Contrary to what happens with
classical Schwarzschild black holes, the emission is dominated by low frequency
field modes on the brane. This is a distinctive and potentially testable
signature which might disclose further features about the nature of quantum
gravity.Comment: 36 pages, 18 figures, v2: updated reference list, minor corrections,
version matching that published on JHE
Predictions for Nongaussianity from Nonlocal Inflation
In our previous work the nonlinearity parameter f_NL, which characterizes
nongaussianity in the cosmic microwave background, was estimated for a class of
inflationary models based on nonlocal field theory. These models include p-adic
inflation and generically have the remarkable property that slow roll inflation
can proceed even with an extremely steep potential. Previous calculations found
that large nongaussianity is possible; however, the technical complications
associated with studying perturbations in theories with infinitely many
derivatives forced us to provide only an order of magnitude estimate for f_NL.
We reconsider the problem of computing f_NL in nonlocal inflation models,
showing that a particular choice of field basis and recent progress in
cosmological perturbation theory makes an exact computation possible. We
provide the first quantitatively accurate computation of the bispectrum in
nonlocal inflation, confirming our previous claim that it can be observably
large. We show that the shape of the bispectrum in this class of models makes
it observationally distinguishable from Dirac-Born-Infeld inflation models.Comment: 26 pages, 5 figures; references added, sign convention for f_NL
clarified, minor correction
Un-graviton corrections to the Schwarzschild black hole.
We introduce an effective action smoothly extending the standard Einstein-Hilbert action to include un-gravity effects. The improved field equations are solved for the un-graviton corrected Schwarzschild geometry reproducing the Mureika result. This is an important test to confirm the original ``guess'' of the form of the Un-Schwarzschild metric. Instead of working in the weak field approximation and ``dressing'' the Newtonian potential with un-gravitons, we solve the ``effective Einstein equations'' including all order un-gravity effects. An unexpected ``bonus'' of accounting un-gravity effects is the fractalisation of the event horizon. In the un-gravity dominated regime the event horizon thermodynamically behaves as fractal surface of dimensionality twice the scale dimension d_U