CONFERENCE

Exterior Calculus on the Computer and the Application to the Quadratic Poincare Gauge Theory of Gravity
Muzaffer Adak
Pamukkale University

Abstract: In the first half of my talk I will introduce some basics of the computer algebra system, REDUCE, and one package of its, EXCALC. The EXCALC package has the capability of doing exterior calculus symbolically [1]. As a simple application I will obtain the Reisner-Norstrom solution to the Einstein equation [2]. In the second part I will introduce the quadratic Poincare Gauge Theory of Gravity. The next step is to generalize the results of the paper by M Gurses et al [3]. This step is ongoing...
[1] E Schrufer, http://www.reduce-algebra.com/docs/excalc.pdf
[2] E Schrufer, F W Hehl and J D McCrea, Gen. Rel. Grav. 19 (1987) 197
[3] P Baekler, M Gurses, F W Hehl and J D McCrea, Phys. Lett. A 128 (1988) 245.

Higher dimensional thin-shell wormholes in Einstein-Yang-Mills-Gauss-Bonnet gravity
S Habib Mazharimousavi
Eastern Mediterranean University

Abstract: We present thin-shell wormhole solutions in Einstein-Yang-Mills-Gauss-Bonnet (EYMGB) theory in higher dimensions $d\geq 5$. Exact black hole solutions are employed for this purpose where the radius of thin-shell lies outside the event horizon. For some reasons the cases $d=5$ and $d>5$ are treated separately. The surface energy-momentum of the thin-shell creates surface pressures to resist against collapse and rendering stable wormholes possible. We test the stability of the wormholes against spherical perturbations through a linear energy-pressure relation and plot stability regions. Apart from this restricted stability we investigate the possibility of normal (i.e. non-exotic) matter which satisfies the energy conditions. For negative values of the Gauss-Bonnet (GB) parameter we obtain such physical wormholes.
Based on: S Habib Mazharimousavi, M Halilsoy and Z Amirabi, Class. Quantum Grav. 28 (2011) 025004.

A Tribute to Brian Edgar: His Recent Work on Solution Generation Techniques
Ayse Hümeyra Bilge
Kadir Has University

Abstract: We review the contributions of late Brian Edgar to general relativity, with emphasis on his recent work on the solution generation technique with "complete tables". In this technique, the Newman-Penrose equations are arranged as an integrable maximally overdetermined system, called a "complete table" and an appropriate change of variable where the Weyl scalars play the role of independent variables leads to an exact solution.

Relativity prospects and ventures at EMU
M. Halilsoy
Eastern Mediterranean University

Abstract: General introduction on Cyprus; memories with John A. Wheeler and Y. Nutku. Plane waves, their interaction and holography. Anisotropy of the Universe, my own way. Stability of Magnetic Universe and black p-braes. Particle Model from Black Holes, ...

Quantum singularities in (2+1) dimensional matter coupled black hole spacetimes
OZLEM UNVER
Middle East Technical University

Abstract: Quantum singularities considered in the 3D BTZ spacetime by Pitelli and Letelier (Phys. Rev.
D77: 124030, 2008) is extended to charged BTZ and 3D Einstein-Maxwell-dilaton gravity spacetimes. We analyze the occurence of naked singularities in the Einstein-Maxwell extension of the BTZ spacetime both in linear and non-linear electrodynamics as well as in the Einstein-Maxwell-dilaton gravity spacetimes with the quantum test fields obeying the Klein-Gordon and Dirac equations. We show that with the inclusion of the matter fields; the conical geometry near r = 0 is removed and restricted classes of solutions are admitted for the Klein-Gordon and Dirac equations. Hence, the classical central singularity at r = 0 turns out to be quantum mechanically singular for quantum particles obeying Klein-Gordon equation but nonsingular for fermions obeying Dirac equation. Explicit calculations reveal that the occurrence of the timelike naked singularities in the considered spacetimes do not violate the cosmic censorship hypothesis as far as the Dirac fields are concerned. The role of horizons that clothes the singularity in the black hole cases is replaced by repulsive potential barrier against the propagation of Dirac fields.
Based on: O. Unver and O. Gurtug, Phys. Rev. D82: 084016, (2010), [arXiv: 1004.2572 [gr-gc]].

Axion inflation from string theory
Heeseung Zoe
Middle East Technical University

Abstract:

Quasi-coherent states for time dependent harmonic oscillator
Nuri UNAL
Akdeniz University

Abstract: In this study we construct the coherent states for harmonic oscillator with time dependent mass and frequency by solving the Schrdinger equation. We discuss the uncertainities in these states. They do not satisfy the minimum uncertainity condition. However, these states do not disperse.

No new "simple" perfect fluid black holes
Ibrahim Semiz
Bogaziçi University

Abstract: Considering the standard ''static" spherically symmetric ansatz $ds^{2} = -B(r) dt^{2} + A(r) dr^{2} + r^{2} d\Omega^{2}$ for Einstein's Equations with perfect fluid source, we ask how we can interpret solutions where $A(r)$ {\em and} $B(r)$ are not positive, as they must be for the static matter source interpretation to be valid.
Noting that the requirement of Lorentzian signature implies $A(r) B(r) >0$, we find two possible interpretations:
(i) The nonzero component of the source four-velocity does {\em not} have to be $u^{0}$. This provides a connection from the above ansatz to the Kantowski-Sachs (KS) spacetimes.
(ii) Regions with negative $A(r)$ and $B(r)$ of "static" solutions in the literature must be interpreted as corresponding to tachyonic source.
The combinations of source type and four-velocity direction result in four possible cases. One is the standard case, one is identical to the KS case, and two are tachyonic. The dynamic tachyonic case was anticipated in the literature, but the static tachyonic case seems to be new. We derive Oppenheimer-Volkoff-like equations for each case, and find some simple solutions. We conclude that new "simple" black hole solutions of the above form, supported by a perfect fluid, do not exist.

Unitarity analysis of general Born-Infeld gravity theories
Tahsin Çagri Sisman
Middle East Technical University

Abstract: We develop techniques of analyzing the unitarity of general Born-Infeld (BI) gravity actions in D-dimensional spacetimes. Determinantal form of the action allows us to find a compact expression quadratic in the metric fluctuations around constant curvature backgrounds. This is highly nontrivial since for the BI actions, in principle, infinitely many terms in the curvature expansion should contribute to the quadratic action in the metric fluctuations around constant curvature backgrounds, which would render the unitarity analysis intractable. Moreover in even dimensions, unitarity of the theory depends only on finite number of terms built from the powers of the curvature tensor. We apply our techniques to some four-dimensional examples.
Based on: I. Gullu, T. C. Sisman and B. Tekin, Phys. Rev. D 82, 124023 (2010).

New Cubic Curvature Theories in D Dimensions
Bayram Tekin
Middle East Technical University

Abstract: We will construct all the unitary cubic curvature gravity theories in anti-de Sitter spaetimes. Along the way, we will discuss the recent critical gravity theory.
Based on: I. Gullu, T.C. Sisman and B. Tekin, work to appear and S.Deser, H.Liu, H.Lu, C.N.Pope, T.C.Sisman and B.Tekin, arXiv:1101.4009 [hep-th].

Axi-Dilaton Fields Coupled to Born-Infeld Electrodynamics
Tekin Dereli
Koc University

Abstract:We will give a generalization of Born-Infeld electrodynamics with axion and dilaton field couplings that are determined by
electric-magnetic duality and SL(2,R) symmetries. Static,spherically symmetric solutions in the Minkowski background will be discussed.
(This is joint work with D.Burton and R.W.Tucker.)