arXiv subjects

Elias C. Vagenas

Publications and source records attributed to Elias C. Vagenas.

At least 73 records · Page 4Linked to original sources

arXiv2008

Universality of Quantum Gravity Corrections

We show that the existence of a minimum measurable length and the related Generalized Uncertainty Principle (GUP), predicted by theories of Quantum Gravity, influence all quantum Hamiltonians. Thus, they predict quantum gravity corrections to various quantum phenomena. We compute such corrections to the Lamb Shift, the Landau levels and the tunnelling current in a Scanning Tunnelling Microscope (STM). We show that these corrections can be interpreted in two ways: (a) either that they are exceedingly small, beyond the reach of current experiments, or (b) that they predict upper bounds on the quantum gravity parameter in the GUP, compatible with experiments at the electroweak scale. Thus, more accurate measurements in the future should either be able to test these predictions, or further tighten the above bounds and predict an intermediate length scale, between the electroweak and the Planck scale.

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arXiv2008

Area spectrum of rotating black holes via the new interpretation of quasinormal modes

Motivated by the recent work on a new physical interpretation of quasinormal modes by Maggiore, we utilize this new proposal to the interesting case of Kerr black hole. In particular, by modifying Hod's idea, the resulting black hole horizon area is quantized and the resulting area quantum is in full agreement with Bekenstein's result. Furthermore, in an attempt to show that the area spectrum is equally spaced, we follow Kunstatter's method. We propose a new interpretation as a result of Maggiore's idea, for the frequency that appears in the adiabatic invariant of a black hole. The derived area spectrum is similar to that of the quantum-corrected Kerr black hole but it is not equally spaced.

gr-qc↗

arXiv2008

Thermodynamical Interpretation of the Interacting Holographic Dark Energy Model in a non-flat Universe

Motivated by the recent work of Wang, Lin, Pavon, and Abdalla [1], we generalize their work to the non-flat case. In particular, we provide a thermodynamical interpretation for the holographic dark energy model in a non-flat universe. For this case, the characteristic length is no more the radius of the event horizon (R_E) but the event horizon radius as measured from the sphere of the horizon (L). Furthermore, when interaction between the dark components of the holographic dark energy model in the non-flat universe is present its thermodynamical interpretation changes by a stable thermal fluctuation. A relation between the interaction term of the dark components and this thermal fluctuation is obtained. In the limiting case of a flat universe, i.e. k=0, all results given in [1] are obtained.

hep-th↗

arXiv2008

The Cosmological Dynamics of Interacting Holographic Dark Energy Model

Motivated by the recent observations for the cosmic acceleration and the suitable evolution of the Universe provided an interaction (decay of dark energy to matter) is incorporated in a cosmological model, we study the cosmological evolution of the Interacting Holographic Dark Energy scenario. Critical points are derived and their corresponding cosmological models are presented. The dynamical character of these models is revealed.

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arXiv2008

Gravitational anomalies: a recipe for Hawking radiation

We explore the method of Robinson and Wilczek for deriving the Hawking temperature of a black hole. In this method, the Hawking radiation restores general covariance in an effective theory of near-horizon physics which otherwise exhibits a gravitational anomaly at the quantum level. The method has been shown to work for broad classes of black holes in arbitrary spacetime dimensions. These include static black holes, accreting or evaporating black holes, charged black holes, rotating black holes, and even black rings. In the case of charged and rotating black holes, the expected super-radiant current is also reproduced.

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arXiv2008

Energy-momentum complexes in f(R) theories of gravity

Despite the fact that modified theories of gravity, in particular the f(R) gravity models have attracted much attention in the last years, the problem of the energy localization in the framework of these models has not been addressed. In the present work the concept of energy-momentum complexes is presented in this context. We generalize the Landau-Lifshitz prescription of calculating the energy-momentum complex to the framework of f(R) gravity. As an important special case, we explicitly calculate the energy-momentum complex for the Schwarzschild-de Sitter metric for a general f(R) theory as well as for a number of specific, popular choices of f(R).

gr-qc↗

arXiv2006

Gravitational Anomalies, Hawking Radiation, and Spherically Symmetric Black Holes

Motivated by the recent work of Robinson and Wilczek, we evaluate the gravitational anomaly of a chiral scalar field in a Vaidya spacetime of arbitrary mass function, and thus the outgoing flux from the time-dependent horizon in that spacetime. We show that this flux differs from that of a perfect blackbody at a fixed temperature. When this flux is taken into account, general covariance in that spacetime is restored. We also generalize their results to the most general static, and spherically symmetric spacetime.

hep-th↗

arXiv2006

Energy distribution in the dyadosphere of a Reissner-Nordstrom black hole in Moller's prescription

The energy and momentum distributions in the dyadosphere of a Reissner-Nordstrom black hole are evaluated. The Moller's energy-momentum complex is employed for this computation. The spacetime under study is modified due to the effects of vacuum fluctuations in the dyadosphere. Therefore, the corrected Reissner-Nordstrom black hole metric takes into account the first contribution of the weak field limit of one-loop QED. Furthermore, a comparison and a consequent connection between our results that those already existing in the literature is provided. We hypothesize that when the energy distribution is of specific form there is a relation that connects the coefficients in the Einstein's prescription with those in the Moller's prescription.

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arXiv2005

Hawking Radiation as Tunneling through the Quantum Horizon

Planck-scale corrections to the black-hole radiation spectrum in the Parikh-Wilczek tunneling framework are calculated. The corrective terms arise from modifications in the expression of the surface gravity in terms of the mass-energy of the black hole-emitted particle system. The form of the new spectrum is discussed together with the possible consequences for the fate of black holes in the late stages of evaporation.

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arXiv2005

On Hawking Radiation as Tunneling with Logarithmic Corrections

There has been recent speculation that the tunneling paradigm for Hawking radiation could -- after quantum-gravitational effects have suitably been incorporated -- provide a means for resolving the (black hole) information loss paradox. A prospective quantum-gravitational effect is the logarithmic-order correction to the Bekenstein-Hawking entropy/area law. In this letter, it is demonstrated that, even with the inclusion of the logarithmic correction (or, indeed, the quantum correction up to any perturbative order), the tunneling formalism is still unable to resolve the stated paradox. Moreover, we go on to show that the tunneling framework effectively constrains the coefficient of this logarithmic term to be non-negative. Significantly, the latter observation implies the necessity for including the canonical corrections in the quantum formulation of the black hole entropy.

gr-qc↗

arXiv2005

On Hawking Radiation as Tunneling with Back-Reaction

Recently, Angheben et.al. [hep-th/0503081] have presented a refined method for calculating the (tree-level) black hole temperature by way of the tunneling paradigm. In the current letter, we demonstrate how their formalism can be suitably adapted to accommodate the (higher-order) effects of the gravitational back-reaction.

gr-qc↗

arXiv2005

Area Spectrum of Kerr and extremal Kerr Black Holes from Quasinormal Modes

Motivated by the recent interest in quantization of black hole area spectrum, we consider the area spectrum of Kerr and extremal Kerr black holes. Based on the proposal by Bekenstein and others that the black hole area spectrum is discrete and equally spaced, we implement Kunstatter's method to derive the area spectrum for the Kerr and extremal Kerr black holes. The real part of the quasinormal frequencies of Kerr black hole used for this computation is of the form $mΩ$ where $Ω$ is the angular velocity of the black hole horizon. The resulting spectrum is discrete but not as expected uniformly spaced. Thus, we infer that the function describing the real part of quasinormal frequencies of Kerr black hole is not the correct one. This conclusion is in agreement with the numerical results for the highly damped quasinormal modes of Kerr black hole recently presented by Berti, Cardoso and Yoshida. On the contrary, extremal Kerr black hole is shown to have a discrete area spectrum which in addition is evenly spaced. The area spacing derived in our analysis for the extremal Kerr black hole area spectrum is not proportional to $\ln 3$. Therefore, it does not give support to Hod's statement that the area spectrum $A_{n}=(4l^{2}_{p}ln 3)n$ should be valid for a generic Kerr-Newman black hole.

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arXiv2004

When conceptual worlds collide: The GUP and the BH entropy

Recently, there has been much attention devoted to resolving the quantum corrections to the Bekenstein--Hawking (black hole) entropy. In particular, many researchers have expressed a vested interest in fixing the coefficient of the sub-leading logarithmic term. In the current paper, we are able to make some substantial progress in this direction by utilizing the generalized uncertainty principle (GUP). Notably, the GUP reduces to the conventional Heisenberg relation in situations of weak gravity but transcends it when gravitational effects can no longer be ignored. Ultimately, we formulate the quantum-corrected entropy in terms of an expansion that is consistent with all previous findings. Moreover, we demonstrate that the logarithmic prefactor (indeed, any coefficient of the expansion) can be expressed in terms of a single parameter that should be determinable via the fundamental theory.

hep-th↗

arXiv2004

Energy distribution in a BTZ black hole spacetime

We evaluate the energy distribution associated with the (2+1)-dimensional rotating BTZ black hole. The energy-momentum complexes of Landau-Lifshitz and Weinberg are employed for this computation. Both prescriptions give exactly the same form of energy distribution. Therefore, these results provide evidence in support of the claim that, for a given gravitational background, different energy-momentum complexes can give identical results in three dimensions, as it is the case in four dimensions.

hep-th↗

arXiv2004

Self-Gravitational Corrections to the Cardy-Verlinde Formula and the FRW Brane Cosmology in SdS_5 Bulk

The semiclassical corrections to the Cardy-Verlinde entropy of a five-dimensional Schwarzschild de-Sitter black hole (SdS_5) are explicitly evaluated. These corrections are considered within the context of KKW analysis and arise as a result of the self-gravitation effect. In addition, a four-dimensional spacelike brane is considered as the boundary of the SdS_5 bulk background. It is already known that the induced geometry of the brane is exactly given by that of a radiation-dominated FRW universe. By exploiting the CFT/FRW-cosmology relation, we derive the self-gravitational corrections to the first Friedmann-like equation which is the equation of the brane motion. The additional term that arises due to the semiclassical analysis can be viewed as stiff matter where the self-gravitational corrections act as the source for it. This result is contrary to standard analysis that regards the charge of SdS_5 bulk black hole as the source for stiff matter. Furthermore, we rewrite the Friedmann-like equation in a such way that it represents the conservation equation of energy of a point particle moving in a one-dimensional effective potential. The self-gravitational corrections to the effective potential and, consequently, to the point particle's motion are obtained. A short analysis on the asymptotic behavior of the 4-dimensional brane is presented.

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arXiv2004

Self-Gravitational Corrections to the Cardy-Verlinde Formula of Achucarro-Ortiz Black Hole

Recently, it was shown that the entropy of the black hole horizon in the Achucarro-Ortiz spacetime can be described by the Cardy-Verlinde formula. In this paper, we compute the self-gravitational corrections to the Cardy-Verlinde formula of the two-dimensional Achucarro-Ortiz black hole. These corrections stem from the effect of self-gravitation and they are derived in the context of Keski-Vakkuri, Kraus and Wilczek (KKW) analysis. The black hole under study is therefore treated as a dynamical background. The self-gravitational corrections to the entropy as given by the Cardy-Verlinde formula of Achucarro-Ortiz black hole, are found to be positive. This result provides evidence in support of the claim that the holographic bound is not universal in the framework of two-dimensional gravity models.

hep-th↗

arXiv2003

Effective mass of a radiating charged particle in Einstein's universe

The effective gravitational mass as well as the energy and momentum distributions of a radiating charged particle in Einstein's universe are evaluated. The Moller's energy-momentum complex is employed for this computation. The spacetime under study is a generalization of Bonnor and Vaidya spacetime in the sense that the metric is described in the cosmological background of Einstein's universe in lieu of the flat background. Several spacetimes are limiting cases of the one considered here. Particularly for the Reissner-Nordstrom black hole background, our results are exactly the same with those derived by Cohen and Gautreau using Whittaker's theorem and by Cohen and de Felice using Komar's mass. Furthermore, the power output for the spacetime under consideration is obtained.

hep-th↗

arXiv2003

Energy and Momentum Distributions of a (2+1)-dimensional black hole background

Using Einstein, Landau-Lifshitz, Papapetrou and Weinberg energy-momentum complexes we explicitly evaluate the energy and momentum distributions associated with a non-static and circularly symmetric three-dimensional spacetime. The gravitational background under study is an exact solution of the Einstein's equations in the presence of a cosmological constant and a null fluid. It can be regarded as the three-dimensional analogue of the Vaidya metric and represents a non-static spinless (2+1)-dimensional black hole with an outflux of null radiation. All four above-mentioned prescriptions give exactly the same energy and momentum distributions for the specific black hole background. Therefore, the results obtained here provide evidence in support of the claim that for a given gravitational background, different energy-momentum complexes can give identical results in three dimensions. Furthermore, in the limit of zero cosmological constant the results presented here reproduce the results obtained by Virbhadra who utilized the Landau-Lifshitz energy-momentum complex for the same (2+1)-dimensional black hole background in the absence of a cosmological constant.

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