arXiv subjects

Elias C. Vagenas

Publications and source records attributed to Elias C. Vagenas.

81 records · Page 5Linked to original sources

arXiv2003

2d Stringy Black Holes and Varying Constants

Motivated by the recent interest on models with varying constants and whether black hole physics can constrain such theories, two-dimensional charged stringy black holes are considered. We exploit the role of two-dimensional stringy black holes as toy models for exploring paradoxes which may lead to constrains on a theory. A two-dimensional charged stringy black hole is investigated in two different settings. Firstly, the two-dimensional black hole is treated as an isolated object and secondly, it is contained in a thermal environment. In both cases, it is shown that the temperature and the entropy of the two-dimensional charged stringy black hole are decreased when its electric charge is increased in time. By piecing together our results and previous ones, we conclude that in the context of black hole thermodynamics one cannot derive any model independent constraints for the varying constants. Therefore, it seems that there aren't any varying constant theories that are out of favor with black hole thermodynamics.

hep-th↗

arXiv2003

Cardy-Verlinde Formula and Achucarro-Ortiz Black Hole

In this paper it is shown that the entropy of the black hole horizon in the Achucarro-Ortiz spacetime, which is the most general two-dimensional black hole derived from the three-dimensional rotating BTZ black hole, can be described by the Cardy-Verlinde formula. The latter is supposed to be an entropy formula of conformal field theory in any dimension.

hep-th↗

arXiv2003

Energy Distribution in 2d Stringy Black Hole Backgrounds

We utilize Moller's and Einstein's energy-momentum complexes in order to explicitly evaluate the energy distributions associated with the two-dimensional "Schwarzschild" and "Reissner-Nordstrom" black hole backgrounds. While Moller's prescription provides meaningful physical results, Einstein's prescription fails to do so in the aforementioned gravitational backgrounds. These results hold for all two-dimensional static black hole geometries. The results obtained within this context are exploited in order Seifert's hypothesis to be investigated.

gr-qc↗

arXiv2003

Casimir Effect, Achucarro-Ortiz Black Hole and the Cosmological Constant

We treat the two-dimensional Achucarro-Ortiz black hole (also known as (1+1) dilatonic black hole) as a Casimir-type system. The stress tensor of a massless scalar field satisfying Dirichlet boundary conditions on two one-dimensional "walls" ("Dirichlet walls") is explicitly calculated in three different vacua. Without employing known regularization techniques, the expression in each vacuum for the stress tensor is reached by using the Wald's axioms. Finally, within this asymptotically non-flat gravitational background, it is shown that the equilibrium of the configurations, obtained by setting Casimir force to zero, is controlled by the cosmological constant.

hep-th↗

arXiv2003

Generalization of the KKW Analysis for Black Hole Radiation

An extension of the Keski-Vakuri, Kraus and Wilczek (KKW) analysis to black hole spacetimes which are not Schwarzschild-type is presented. Preserving the regularity at the horizon and stationarity of the metric in order to deal with the across-horizon physics, a more general coordinate transformation is introduced. In this analysis the Hawking radiation is viewed as a tunnelling process which emanates from the non-Schwarzschild-type black hole. Expressions for the temperature and entropy of these non-Schwarzschild-type black holes are extracted. As a paradigm, in the context of this generalization, we consider the Garfinkle-Horowitz-Strominger (GHS) black hole as a dynamical background and we derive the modified temperature and entropy of GHS black hole. Deviations are eliminated and corresponding standard results are recovered to the lowest order in the emitted shell of energy. The extremal GHS black hole is found to be non-``frozen'' since it is characterized by a constant non-zero temperature. Furthermore, the modified extremality condition forbids naked singularities to form from the collapse of the GHS black hole.

hep-th↗

arXiv2003

Complex Paths and Covariance of Hawking Radiation in 2D Stringy Black Holes

Hawking radiation is computed in different coordinate systems using the method of complex paths. In this procedure the event horizon of the 2D Schwarzschild stringy black hole is treated as a singularity for the semiclassical action functional. After the regularization of the event horizon's singularity the emission/absorption probabilities and the Hawking temperature in the different coordinate representations are derived. The identical results obtained indicate the covariance of the Hawking radiation.

hep-th↗

arXiv2002

Two-Dimensional Dilatonic Black Holes and Hawking Radiation

Hawking radiation emanating from two-dimensional charged and uncharged dilatonic black holes - dimensionally reduced from (2+1) spinning and spinless, respectively, BTZ black holes - is viewed as a tunnelling process. Two dimensional dilatonic black holes (AdS(2) included) are treated as dynamical backgrounds in contrast to the standard methodology where the background geometry is fixed when evaluating Hawking radiation. This modification to the geometry gives rise to a nonthermal part in the radiation spectrum. Nonzero temperature of the extremal two-dimensional charged black hole is found. The Bekenstein-Hawking area formula is easily derived for these dynamical geometries.

hep-th↗

arXiv2002

Semiclassical Corrections to the Bekenstein-Hawking entropy of the BTZ Black Hole via Self-Gravitation

Hawking radiation is viewed as a tunnelling process. In this way the effect of self-gravitation gives rise to semiclassical corrections to the entropy of the (2+1) BTZ black hole. The modified entropy, due to specific modelling of the self-gravitation effect, of the (2+1) BTZ black hole is evaluated. To first order in $ω$ which is a shell of energy radiated outwards the event horizon of the BTZ black hole, modified entropy is proportional to the horizon. In this semiclassical analysis, corrections to the Bekenstein-Hawking formula $S_{BH}=\mathcal{A}_{H} / 4l_{P}^{2}$ are found to be negative and the proportionality factor connecting the modified entropy, $S_{bh}$, of the (2+1) BTZ black hole to the Bekenstein-Hawking entropy, $S_{BH}$, is evaluated to first order in $ω$.

hep-th↗

arXiv2001

Are Extremal 2D Black Holes Really Frozen ?

In the standard methodology for evaluating the Hawking radiation emanating from a black hole, the background geometry is fixed. Trying to be more realistic we consider a dynamical geometry for a two-dimensional charged black hole and we evaluate the Hawking radiation as tunneling process. This modification to the geometry gives rise to a nonthermal part in the radiation spectrum. We explore the consequences of this new term for the extremal case.

hep-th↗