Title and Abstract of Talks

Speaker: N. Andersson
Title: Modelling multifluid systems in general relativity.
Abstract: 
In this talk I will provide an overview of a powerful variational
description of relativistic fluid dynamics due to Brandon Carter.
I will compare the formulation to the "standard" approach, and
discuss how one can model systems with several independent
dynamical degrees of fluids. A typical example is provided by
a superfluid neutron star, and I will  discuss recent result in
that problem area. A key poit is the introduction of the entrainment
effect, by means of which the different fluids are coupled
and which can lead to velocities and momenta not being parallel.
Finally, I will discuss the challenges that have to be met in
the future, in particular ones associated with dissipation in relativistic fluids.

Speaker: I. Antoniadis
Title: Gravity modifications from extra dimensions.
Abstract: 
I will discuss possible modifications of Newton's law at short and 
large distance scales in models of extra dimensions and compare
with present experimental bounds.

Speaker: A. Avgoustidis
Title: Cosmic String Evolution in Brane Inflation.
Abstract:
There has been notable effort in recent years to obtain inflationary
models from string theory.  In the most well-studied scenario, brane
inflation, the inflationary phase typically ends with a phase transition,
leading to the production of a network of cosmic (super)strings.  In this
talk I will discuss the cosmological evolution of such string networks and
point out several differences to usual field theory strings arising in
more conventional theories.  The fact that these differences could in
principle be observed, renders cosmic strings an excellent probe for the
physics of the early universe.

Speaker: N. Batakis
Title: On a geometric alternative to the Higgs mass-generating mechanism.
Abstract: 
We will present the basics of a gauge-boson mass-generating mechanism in a
higher-dimensional (essentially Kaluza-Klein) setting, devoid of the
standard Higgs sector. We will also examine the possibility of  applying the
idea in D=4, as a realistic geometric alternative to the standard Higgs
mechanism.

Speaker: C. Bogdanos
Title: Exact Solutions in 5-D brane models with scalar fields.
Abstract: 
We consider the problem of a scalar field, non-minimally coupled to gravity
through a $-\xi\phi^{2}R$ term, in the presence of a Brane. Exact solutions,
for a wide range of values of the coupling parameter $\xi$, for both $\phi$-dependent
and $\phi$-independent Brane tension, are derived and their behaviour is studied.
In the case of a Randall-Sundrum geometry, a class of the resulting scalar field solutions
exhibits a folded-kink profile. We go beyond the Randall-Sundrum geometry
studying general warp factor solutions in the presence of a kink scalar. Analytic and
numerical results are provided for the case of a Brane or for smooth geometries, where
the scalar field acts as a thick Brane. It is shown that finite geometries with warp
factors that asymptotically decrease exponentially are realizable for a wide range
of parameter values.

Speaker: P. Boonserm
Title: Generating perfect fluid spheres in general relativity.
Abstract:
Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry
describing the interior of a particular idealized general relativistic star-a
static spherically symmetric blob of fluid with position-independent
density-the general relativity community has continued to devote considerable
time and energy to understanding the general-relativistic static perfect
fluid sphere. Over the last 90 years a tangle of specific perfect fluid
spheres has been discovered, with most of these specific examples seemingly
independent from each other. To bring some order to this collection,  we
develop several new transformation theorems that map perfect fluid spheres
into perfect fluid spheres. These transformation theorems sometimes lead to
unexpected connections between previously known perfect fluid spheres,
sometimes lead to new previously unknown perfect fluid spheres, and in
general can be used to develop a systematic way of classifying the set of all
perfect fluid spheres.

Speaker: C. Cattoen
Title: Necessary and sufficient conditions for big bangs, bounces, crunches,
rips, sudden singularities and extremality events.
Abstract:
Until recently, the physically relevant singularities occurring in FRW cosmologies
had traditionally been thought to be limited to the “big bang”, and possibly a
“big crunch”. However, over the last few years, the zoo of cosmological singularities
considered in the literature has become considerably more extensive, with “big rips”
and “sudden singularities” added to the mix, as well as renewed interest in non-singular
cosmological events such as “bounces” and “turnarounds”. In this talk, I will present
an extensive catalogue of such cosmological milestones, both at the kinematical and dynamical
level.First, using generalized power series, purely kinematical definitions of these cosmological
events are provided in terms of the behaviour of the scale factor a(t). The notion of a
“scale-factor singularity” is defined, and its relation to curvature singularities (polynomial
and differential) is explored. Second, dynamical information is extracted by using the Friedmann
equations (without assuming even the existence of any equation of state) to place constraints
on whether or not the classical energy conditions are satisfied at the cosmological milestones. 
Since the classification is extremely general, and modulo certain technical assumptions complete,
the corresponding results are to a high degree model-independent.

Speaker: M. Chichikina
Title: Group Analysis in Quantum Gravity.
Abstract:
New scheme of quantization of nonlinear systems is proposed.
We quantize bozon fields on nontrivial classical background.
Using of Bogoliubov group variables permits to avoid difficulties:
1. nonevident  conservation laws while perturbation theory is used.
2. zero-mode problem
The scheme permits to quantize, for example, gravitational field in the
neubourgood of exact solution of Einstein equations, taking into account
conservation laws explisitly in any order of perturbation theory.

Speaker: D. Christodoulou
Title: The formation of shocks in 3-dimensional fluids.
Abstract:
In the lecture I shall present a summary of the contents of my recent 1100
page monograph with this title. The monograph considers the relativistic
Euler equations in three space dimensions for a perfect fluid with
an arbitrary equation of state. We consider regular initial data on a
spacelike hyperplane in Minkowski spacetime which
outside a sphere coincide with the data corresponding to a constant state.
We consider the restriction of the initial data to the exterior of a concentric
sphere  and we consider the maximal classical development of this data.
Then, under a suitable restriction on the size of the departure of the
initial data from those of the constant state, we prove certain theorems
which give a complete description of the maximal classical development.
In particular, the theorems give a detailed description of the geometry of
the boundary of the domain of the maximal classical development and a detailed
analysis of the behavior of the solution at this boundary.
A complete picture of shock formation in three-dimensional fluids is thereby
obtained. Also, sharp sufficient conditions on the initial data for the formation
of a shock in the evolution are established and  sharp upper and bounds for
the time required for the onset of shock formation are derived.

Speaker: C. Chryssomalakos
Title: Spacetime Nocommutativity the Canonical Way.
Abstract:
We present an ab initio approach to the problem of spacetime nocommutativity,
and show how fundamentally independent arguments seem to converge to one
particular type of it. On a second, parallel theme, we present a canonical
*-product, and the associated deformed integral, with simple, trace-like
properties.

Speaker: S. Cotsakis
Title: The Dominant Balance in Cosmology.
Abstract:
After a short discussion reviewing the basic issues of the
singularity vs completeness puzzle in general relativity, we introduce the
basic features of a new technique, the method of asymptotic splittings,
designed to deal with the nature of spacetimes near their singularities. We
focus on the more elementary parts, namely, the dominant balance and
asymptotic decompositions of vector fields, and then exploit the results to
discuss recent kinds of cosmological singularities including the so-called
sudden future singularities. Finally we remark on the general applicability
of the technique in general relativity.

Speaker: B.M. Cuadros-Melgar
Title: Stability and Thermodynamics of Brane Black Holes.
Abstract:
We consider scalar and axial gravitational perturbations of black hole
solutions in brane world scenarios. We show that perturbation
dynamics is surprisingly similar to the Schwarzschild case with strong
indications that the models are stable. Quasinormal modes and late-time
tails are discussed. We also study the thermodynamics of these scenarios
verifying the universality of Bekenstein's entropy bound as well as the
applicability of 't Hooft's brickwall method.

Speaker: H. Culetu.
Title: On a stationary spinning string spacetime.
Abstract:
The properties of a massless string endowed with intrinsic spin are discussed.
Even though the spacetime is Minkowskian geometrically, it has a
nontrivial topology due to a horizon located at r =0, similar with
the Rindler spacetime. The Sagnac time delay is calculated and proves
to be constant. We conjecture the spin of an elementary particle
originates in the frame dragging effect produced by the rotation
of the source. The radial acceleration of a rotating test particle
depends upon the sense of rotation due to the Planck length
entering the line element.

Speaker: S. Das
Title: Entanglement as a source of black hole entropy.
Abstract:
To investigate whether quantum entanglement between the inside and
outside of a black hole can give rise to Bekenstein-Hawking entropy, we
first compute the entanglement entropy of a quantum field, by tracing
over its degrees of freedom inside a spherical volume. We show that this
entropy is proportional to the area of the sphere when the field is in
its ground state, a generic coherent state or a class of squeezed
states. However, it is proportional to a power of area less than unity
when it is in an excited state. We discuss its generalisation to curved
spacetimes and implications of our results to black hole entropy. We
also identify the location of the degrees of freedom which give rise to
entanglement entropy.

Speaker: M. Delis
Title: The Close-Universe-Recollapse Conjecture and Asymptotic Decompositions
of Vector Fields. 
Abstract:
The closed-universe-recollapse conjecture for the existence of
all-encompassing future singularities in Bianchi IX vacuum, dust and perfect
fluid (P=kρ) space-times is shown to be correct using the method of
asymptotic decomposition of vector fields. Various physically relevant cases
for the ratio P/ρ are examined and analyzed and exact expressions for the
expansions of the dynamical variables detailing the nature of the universe
near the singularity are derived.


Speaker: N. Dimakis
Title: (2+1)-Cosmology with a general scalar field. 
Abstract:
The classical Einstein's equations for the two ``Bianchi types'' in
(2+1)-dimensions coupled to a general scalar field are laid down and
completely integrated. The corresponding Wheeler-DeWitt
equations are presented and solved for particular configurations.

Speaker: V. . Dvoeglazov
Title: The Modified Bargmann-Wigner Formalism (Bosons of Spin 1 and 2).
Abstract:
On the basis of our recent modifications of the Dirac formalism we
generalize the Bargmann-Wigner formalism for higher spins to be compatible
with other formalisms for bosons. Relations with dual electrodynamics, with
the Ogievetskii-Polubarinov notoph  and the Weinberg 2(2J+1) theory are
found.  Next, we introduce  the dual analogues of the Riemann tensor and
derive corresponding dynamical equations in  the Minkowski space. Relations
with the Marques-Spehler chiral gravity theory are discussed.

Speaker: O. Efthimiou
Title: Graviton emission in the bulk from higher dimensional Schwarzschild black holes.
Abstract:
 In this talk we consider the evaporation of (4+n)-dimensional
non-rotating black holes into gravitons. We calculate the energy
emission rate for gravitons in the bulk obtaining analytical solutions
of the master equation satisfied by all three types (S,V,T) of
gravitational perturbations. Our results, valid in the low-energy
regime, show a vector radiation dominance for every value of n, while
the relative magnitude of the energy emission rate of the subdominant
scalar and tensor radiation depends on n.  The calculated low-energy
emission rate, for all types of degrees of freedom decreases with n,
although the full energy emission rate, integrated over all
frequencies, is expected to increase with n, as in the previously
studied case of a bulk scalar field.

Speaker: V. Frolov
Title: Gravitational Field of Gyratons.
Abstract: 
What is the gravitational field of a high energy photon in
a given state of its polarization? To attack this problem we consider
its classical analogue. Namely, we obtain exact solutions of the Einstein
equations for the gravitational field created by a beam-pulse of
spinning radiation (gyraton) in a D-dimensional spacetime. First we
demonstrate that these solutions belong to the class of metrics for
which all scalar invariants constructed from the curvature and its
covariant derivatives vanish. Next, we show that the vacuum Einstein
equations for a gyraton reduce to a linear problem in (D-2)-dimensional
Euclidean space. A general solution of these equations is obtained.
We construct gyraton-type solutions of the vacuum Einstein equations
and discuss their properties. We also discuss generalizations of the
gyraton metrics to the case when a gyraton is charges or  is moving
in the asymptotically AdS spacetime. Possible applications to the
problem of mini-black-hole production in the collision of highly
relativistic particles is briefly discussed.

Speaker: F. Girelli
Title: PHENOMENOLOGY OF QUANTUM GRAVITY: Quantum Reference Frames
and Modified Symmetries.
Abstract: 
I will first recall why quantum reference frames are of a key importance
in the understanding of the quantum gravity physics.
I will then study a toy model where one can construct quantum reference
frames, and show how in the semi classical limit they naturally imply a
deformation of the symmetries.
The toy model therfore provides another hint that in the semi classical
regime of quantum gravity one should have a deformation of the symmetries
such as met in Deformed Special Relativity.

Speaker: B. Hartmann
Title: Monopoles, sphalerons and the cosmological constant.
Abstract:
I will discuss the effects of a positive cosmological constant on the
nonperturbative solutions of gauge theories with spontaneous
symmetry breaking, namely monopoles and sphalerons.
Although the total mass within the cosmological horizon of these configurations is finite,
their mass evaluated at timelike infinity generically diverges for most values
of the cosmological constant. Thus, no finite energy monopoles and sphalerons
can exist for the currently accepted value of the cosmological constant.

Speaker: A. Herrera-Aguilar
Title: Localizing gravity on thick branes: a solution for massive KK modes of the Schoedinger equation.
Abstract:
We consider the generation of thick brane configurations in a 5D Riemannian
space time. In this framework, we show how 4D gravity can be localized on a
scalar thick brane which does not necessarily respect reflection symmetry,
generalizing in this way several previous models based on the Randall-Sundrum
(RS) system and avoiding both, the restriction to orbifold geometries and the
introduction of the branes in the action by hand. We first obtain a thick
brane solution that preserves 4D Poincare' invariance and breaks Z_2-symmetry
along the extra dimension which, indeed, can be either compact or extended. In
the non-compact case, this field configuration represents a thick brane with
positive energy density centered at y=c_2, whereas pairs of thick branes arise
in the compact case. We also recast the wave equations of the transverse
traceless modes of the linear fluctuations of the classical background into a
Schrodinger's equation form with a volcano potential of finite bottom. We
solve Schrodinger equation for the massless zero mode m^2=0 and obtain a
single bound wave function which represents a stable 4D graviton (without
tachyon modes). We also get a continuum gapless spectrum of KK states with
m^2>0 that are suppressed at y=c_2 and turn asymptotically into plane waves.
We found a particular case in which the Schrodinger equation can be solved
for all m^2>0, giving us the opportunity of studying analytically the massive
modes of the spectrum of KK states, a rare fact when considering thick brane
configurations.

Speaker: A. Kehagias
Title: On the cosmological constant problem.
Abstract:
A partial solution to the cosmological constant problem is presented
by using the simple observation that a three-brane  in a
six-dimensional bulk is flat.  A model is described  in which
Standard Model vacuum energy is always absorbed by the transverse
space. The latter is a tear-drop like space with a conical
singularity, which preserves bulk supersymmetry and gives rise to
conventional macroscopic 4D gravity with no cosmological constant.
Its cone acts like a drain depleting vacuum energy from the
three-brane to the tear drop increasing its volume. We stress that
although gravity is treated classically, Standard Model is handled
quantum-field theoretically and the model is robust against
Standard Model corrections and particular details.

Speaker: G S Khadekar
Title: Higher Dimensional String Cosmological Model With
Dynamical Cosmological Term Lambda.
Abstract:
We have analysed Kaluza Klein type five dimensional
string cosmological model by considering three different forms of
dynamical variable $\Lambda$: $\Lambda \sim \left
(\frac{\dot{R}}{R}\right)^2,$ $\Lambda \sim
\left(\frac{\ddot{R}}{R}\right)$ and $\Lambda \sim \rho$. It is
found that, the connecting free parameters of the models with
cosmic matter and vacuum energy density parameters are equivalent,
in the context of higher dimensional space time.

Speaker: I. Klaoudatou
Title: Cosmological singularities, closed trapped surfaces and Bel-Robinson energy.
Abstract:
We provide a complete classification of the spacetime singularities possible in an isotropic
universe by exploiting the behaviours of three functions, namely, the Hubble expansion
rate, the scale factor and the Bel-Robinson energy of these universes. We use the Bel-Robinson
energy to test whether the character of the singularity present in any particular exact solution
of the field equations describing such universes depends on the given spatial geometry.
We further examine the relation between the existence of closed trapped surfaces and possible
bounds on the Bel-Robinson energy in these types of universes. 

Speaker: K. Kokkotas
Title: Spacetime modes of relativistic stars.
Abstract:
We will present recent progress in the study of spacetime modes of
relativistic stars. The study involves spacetime modes of fast rotating
stars and stars in scalar-tensor theory of gravity.

Speaker: A. Kouretsis
Title: FRW-metric and Friedman Equations in generalized cosmological model.
Abstract:
A generalized model of space-time is given, taking into consideration the
anisotropic structure of fields which are depended on the position and the
direction (velocity).In this framework the generalized FRW-metric,Friedman
and Raychadouri equations are studied. In some cases a cosmological magnetic
field is considered in relation with the physical geometry of space-time
in which Cartan connection has a fundamental role. As well a corelation with the
inflation is examined on the basis of the aforementioned metric structure. 

Speaker: M. Leclerc
Title: Hermitian Dirac Hamiltonian in time dependent gravitational field.
Abstract:
It is shown by a straightforward argument that the Hamiltonian
generating the time evolution of the Dirac wave function
in relativistic quantum mechanics is not hermitian with respect to
the covariantly defined inner product whenever the background
metric is time dependent. An alternative, hermitian, Hamiltonian is
found and is shown to be directly related to the canonical
field energy.  Further, the relation of the Hamiltonian to the generator of
time translations in the second quantized theory is  established.

Speaker: JJ. M.T. Louko
Title: Excited by a quantum field: Does shape matter?
Abstract:
We analyse the instantaneous excitation rate of an accelerated
Unruh-DeWitt particle detector whose coupling to a scalar field on
Minkowski space is regularised by a finite spatial profile. We show,
under mild technical assumptions, that the zero size limit of the
detector response is well defined, independent of the choice of the
profile function, and given by a manifestly finite integral formula
that no longer involves epsilon-regulators or limits. The thermal result
for uniform acceleration is recovered as a special case. Applications to
quotients of Minkowski space are discussed, with a view to probing the
topology of quantum black holes by particle detectors.

Speaker:  R. Maartens
Title: Acceleration without dark energy.
Abstract:
There is increasingly strong evidence for the acceleration of the late-time
universe from observations. A satisfactory explanation of this acceleration is
perhaps the greatest theoretical challenge in cosmology. Within the
framework of general relativity, the acceleration typically originates from a
dark energy field with effectively negative pressure. Alternatively, it is
possible that there is no dark energy, but instead an infrared modification of
general relativity on very large scales that accounts for late-time
acceleration. I will review various models of modified gravity that have been
proposed, looking at their dynamics and perturbations and how they
compare against observational data. 

Speaker:  P. Martinetti
Title: The thermal time hypothesis.
Abstract:
We shall present an overview on the thermal time hypothesis (TTH) of Connes and
Rovelli which proposes a intrinsic definition of the notion of "physical flow of time" that
may be interesting in a quantum gravity context.  Here we shall illustrate the TTH by  emphasizing some
applications to general relativity and quantum field theories in curved spacetimes. Especially we
will present our adaptation of the Unruh effect (i.e. the fact that the vacuum state of a quantum
field theory on Minkovski spacetime is viewed as a thermal state for an eternal observer with constant
acceleration) to observers with finite lifetime. Also we aim at discussing some recent application of the TTH
to de Sitter space.

Speaker:  J. Miritzis
Title: Singularity analysis of varying light-speed models.
Abstract:
We study the finite time singularities of isotropic cosmological models with
varying speed of light using the method of asymptotic splittings.

Speaker:  I. Moss
Title: Radiating Branes (or New light on moving mirrors).
Abstract:
A general framework is described for classical and quantum radiation reaction
on a body of $m$ dimensions in a space of $n$ dimensions. Early work on
moving mirrors is generalised to cosmological branes moving in higher
dimensions. This raises the question-can branes radiate away their
cosmological constant? (Answer=no)

Speaker:  W.  Natorf
Title: Symmetries of the Robinson-Trautman equation.
Abstract:
I will discuss the symmetries of the Robinson-
-Trautman equation and give its possible symmetric
solutions and symmetry reductions.

Speaker: JS. Nesseris
Title: Constraints on Dark Energy Models from the Legacy and Gold SnIa Datasets.
Abstract:
A comparative analysis of three recent and reliable SnIa datasets available in the
literature was made: the Full Gold (FG) dataset (157 data points 0 < z < 1.75), a
Truncated Gold (TG) dataset (140 data points 0 < z < 1) and the most recent Supernova
Legacy Survey (SNLS) dataset (115 data points 0 < z < 1). It was found that the best fit
dynamical w(z) obtained from the SNLS dataset does not cross the PDL w = -1 and
remains above and close to the w = -1 line for the whole redshift range 0 < z < 1 showing
no evidence for phantom behaviour.  In contrast, the best fit dynamical w(z) obtained
from the Gold datasets (FG and TG) clearly crosses the PDL and departs significantly
from the PDL w = -1 line while the LCDM parameter values are about 2 \sigma away
from the best fit w(z). Also for the Gold dataset a scalar-tensor theory was reconstructed,
for which the best fit form of w(z) was also found to cross the phantom divide line.

Speaker: JA. Papazoglou
Title: Scalar mode analysis of the warped Salam-Sezgin model.
Abstract:
We study the scalar perturbation sector of the general axisymmetric
warped Salam-Sezgin  model with codimension-2 branes. We focus on the
perturbations which mix with the dilaton. We show that the scalar
fluctuations analysis can be reduced to studying two scalar modes
of constant wavefunction, plus modes of non-constant wavefunction which
obey a single Schrodinger equation. From the obtained explicit solution of
the scalar modes, we point out the importance of the non-constant modes in
describing the four dimensional effective theory. This observation remains
true for the unwarped case and was neglected in the relevant literature.
Furthermore, we show that due to these modes, the warped solutions can be
unstable for a certain region of the parameter space.

Speaker: JG.O. Papadopoulos
Title: An Algorithm for detecting absorbable constants in Riemannian Spaces.
Abstract:
The problem of distinguishing between essential and non essential constants
contained in a metric tensor field is addressed. The codification of the problem leads to
a criterion, which in turn, reduces the initial problem to that of solving a system of partial
differential equations of the first order.

Speaker: JP. Pasipoularides
Title: Brane world scenario in the presence of a non-minimally coupled scalar field.
Abstract:
We consider the case of brane world models in the presence of a bulk scalar field which
interacts non-minimally with gravity, via a possible interaction term of the form -(1/2) \xi R \phi^2.
By solving numerically the corresponding Einstein equations with the scalar field, in the case of
a \phi^4 potential, we obtain three classes of solutions with different features, in appropriate
regions of the non-minimal coupling \xi. As a possible implication, we examine the possibility
to construct brane models which incorporate a layer-phase mechanism for the localization of
ordinary particles on the brane.

Speaker: JA. Passamonti
Title: Nonlinear effects in Pulsations of Compact Stars and Gravitational Waves.
Abstract:
Nonlinear stellar oscillations can be studied by using a multiparameter
perturbative approach, which is appropriate for investigating the low
and mild nonlinear dynamical regimes.  In this talk, we present the
perturbative framework to describe, in the time domain, the nonlinear
coupling between the radial and nonradial perturbations of spherically
symmetric and perfect fluid compact  stars.  This particular coupling
can be described by gauge invariant quantities that obeys a system of
partial differential equations with source terms, which are made up of
product of first order radial and nonradial perturbations.  We report
the results of numerical simulations that exhibit in the stellar dynamics
and in the related gravitational wave signal some interesting nonlinear
effects, such as combination harmonics and resonances.

Speaker: JL. Perivolaropoulos
Title: Accelerating Universe from Scalar-Tensor Theories.
Abstract:
There is accumulating observational evidence (based on SnIa data)
that the dark energy equation of state parameter $w$ may be
evolving with time and crossing the phantom divide barrier $w=-1$
at recent times. The confirmation of these indications by future
data would indicate that minimally coupled quintessence can not
reproduce the observed expansion rate $H(z)$ for any scalar field
potential. Here we explicitly demonstrate that scalar tensor
theories of gravity (extended quintessence) can predict crossing
of the phantom divide barrier. We reconstruct phenomenologically
viable scalar-tensor potentials $F(\Phi)$ and $U(\Phi)$ that can
reproduce a polynomial best fit expansion rate $H(z)$ and the
corresponding dark energy equation of state parameter $w(z)$
crossing the $w=-1$ line. The form of the reconstructed scalar
tensor potentials is severely constrained but is not uniquely
determined. This is due to observational uncertainties in the form
of $H(z)$ and also because a single observed function $H(z)$ does
not suffice for the reconstruction of the two potential functions
$F(\Phi)$ and $U(\Phi)$.

Speaker: JN. Pidokrajt
Title: Application of Information Geometry to Black Hole Thermodynamics.
Abstract:
We study thermodynamics of various black hole families by means of
Ruppeiner geometry which is a one particular type of information geometry.
The Ruppeiner metric is defined as the negative of the Hessian of the thermodynamic
entropy function of the system with respect to the mechanically conserved parameters,
like mass, charge and spin in the case of black holes.  The Ruppeiner metric has a
conformal counterpart called the Weinhold metric. We find that for many black hole
families, one or the other of  these metrics is flat. The Ruppeiner metric, when it is
curved, tends to behave in a way that suggests that it is physically meaningful. Most
recent findings from the Ruppeiner information geometry in black hole thermodynamics
include the prediction of the thermodynamic stabilities of the Kerr black holes in all dimensions.

Speaker: JJ.M. Pons
Title: Dimensional reductions, truncations, constraints and the issue of consistency.
Abstract:
I discuss the ideas concerning dimensional reduction (Kaluza-Klein theory)
and truncation (elimination of most of KK modes) as a way to formulate
lower dimensional theories starting from higher dimensional ones. Then
one can get solutions of the higher dimensional theories through the
uplifting of solutions of the lower dimensional ones. I discuss also the
role of contraints to further reduce the degrees of freedom and I show its
connection with Dirac approach to gauge systems. Examples of succesfull
truncations will be given, as well as of solutions obtained by uplifting.

Speaker: G. Rigopoulos
Title: Non-Gaussianity as a new observable in multifield inflation?
Abstract:
Inflation is the currently accepted explanation for the origin of
large-scale structure in the Universe by naturally providing a nearly
scale-invariant density perturbation at early times. In conventional
single-field inflationary models this perturbation is a Gaussian random
field to very high accuracy. I will discuss the possibility of enhanced
non-Gaussianity from multi-field models at a level possibly observable in
the near future. Hence, non-Gaussianity emerges as an additional probe of
the physics of the early Universe.

Speaker: M. Ryan
Title: Quantum collapse of dust shells in 2+1 gravity.
Abstract:
The minisuperspace canonical quantization of the collapse of dust shells is
a toy model of the quantum collapse of more complicated objects.  In 3+1 gravity
the possible Hamiltonians that describe this collapse (generated from the Israel
equation for shell motion) are so complicated that only numerical solutions are
possible.  Even in the Newtonian analogue of this problem, where an analytic
solution exists, it is impossible to find analytic wave packets whose evolution
can tell us something about horizon formation.  In 2+1 gravity, one possible
Hamiltonian is simple enough to allow us to carry out the entire canonical
quantization program analytically and allows us to study horizon formation.

Speaker: Gerhard Sch\"afer
Title: Analytical solution of the Einstein field equations for binary
black holes under conformal-flat condition.
Abstract:
In any physical field theory the two-body problem is of utmost
importance. This particularly applies to Einstein's theory of gravity.
In my talk an analytical solution of the two-body problem will be
presented within a conformally truncated version of the Einstein field
equations. The solution represents a stationary gravitational field and
related herewith a conservative dynamics of two black holes with
Brill-Lindquist initial data. Various limiting cases of the solution
will be discussed including post-Newtonian expansion.
The ISCO will be given and it will be shown that for
circular orbits the ADM and Komar masses coincide.

Speaker: Y. Shnir
Title: Axially symmetric solutions of Einstein-Yang-Mills theory and Einstein-Yang-Mills-Higgs theory.
Abstract:
We discuss properties of the axially symmetric static saddle point
solutions of SU(2) Yang-Mills-Higgs theory which represent composite
states of monopoles and antimonopoles and/or vortex rings. They are either
deformations of the topologically trivial sector or deformations of the
axially symmetric charge n multimonopole. The energy of these
configurations exceeds the Bogomol'nyi bound even in the limit of
vanishing scalar coupling. When the theory is coupled with gravity new
branches of the graviting monopoles/vortices emerges smoothly from these
flat space configurations. We discuss interpretation of the upper branche
configuration as a composite system consisting of Bartnik-McKinnon
solution of EYM theory and an outer multimonopole/vortex solution of the
EYMH theory.

Speaker: H. Sotani
Title: Possibility to determine the radius of accretion disk by gravitational waves.
Abstract:
We investigate gravitational waves from a dust disk around a
Schwarzschild black hole to focus on whether we can extract any of its
physical properties from a direct detection of gravitational waves. We
adopt a black hole perturbation approach in a time domain, which is a
satisfactory approximation to illustrate a dust disk in a supermassive
black hole. We find that we can determine the radius of the disk by
using the power spectrum of gravitational waves and that our method to
extract the radius works for a disk of arbitrary density distribution.
Therefore we believe a possibility exists for determining the radius of
the disk from a direct observation of gravitational waves detected by
the Laser Interferometer Space Antenna.

Speaker: T. Sotiriou
Title: The metric-affine formalism of  f(R) gravity.
Abstract:
Recently an class of alternative theories of gravity which goes under the name
f(R) gravity, has received considerable attention, mainly due to its
interesting applications in cosmology. However, the phenomenology of such
theories is not only relevant to cosmological scales,  especially when it is
treated within the framework of the so called Palatini variation, an
independent variation with respect to the metric and the connection, which is
not considered a priopi to be the Levi-Civita connection of the metric. If this
connection has its standard geometrical meaning the resulting theory will be a
metric-affine theory of gravity, as will be discussed in this talk. The general
formalism will be presented and several aspects of the theory will be covered,
mainly focusing on the enriched phenomenology that such theories exhibit with
respect to General Relativity, relevant not only to large scales (cosmology)
but also to small scales (e.g. torsion).

Speaker: N. Stergioulas
Title: Supermassive Black Hole Formation through Rotational Instabilities.
Abstract:
We investigate new paths to black hole formation by considering the
general relativistic evolution of a differentially rotating supermassive star with toroidal
shape. We find that a large number of such models are unstable to nonaxisymmetric modes, which
leads to a fragmentation into self-gravitating, collapsing components. In the case
of one such fragment, we apply a simplified adaptive mesh refinement technique to follow the
evolution to the formation of an apparent horizon centered on the fragment. This is the first study
of the one-armed instability in full general relativity.

Speaker: D. Sudarsky
Title: A signature of Quantum Gravity at the source of the seeds for cosmic  structure?
Abstract:
The remarkable agreement between the observations of  the spectrum of 
temperature fluctuations in the CMB and the corresponding predictions coming from inflationary models 
are taken as confirmation of the quantum fluctuation origin of the seeds of cosmic structure.   This 
talk focuses on the transmutation of the original quantum fluctuations, which are essentially homogeneous and 
isotropic-- arising as they do from an homogeneous and isotropic vacuum state--  into  the classical 
inhomogeneities and anisotropies that correspond to the observations.  We argue  that the standard accounts 
of this aspect of the problem are not fully satisfactory and that there  is a need for New Physics.  This 
New Physics would  be presumably tied to some Quantum aspects of Gravitation,  as suggested by  R. Penrose, and we 
show that a simple generalization of his ideas seems to  be  able to account for that  transformation, and 
have the features required for a successful phenomenology. 

Speaker: J. Tafel
Title: Reductions of self-dual Einstein equations.
Abstract:
In this talk I give a short review of formulations of self-duality
conditions in the Einstein theory. Self-dual metrics are meaningful for
description of gravitational instantons, nonlinear gravitons and completely
integrable equations. I make some historical remarks with an emphasis on
little known results of  physicists from the Hiroshima University in 1935.
I discuss relations between equations obtained by Plebanski, Husain or
Grant. In particular, I find the Backlund transformation between
the Plebanski and the Husain equations.  I also show that the self-duality
conditions are equivalent to a pair of equations describing canonical
transformations in 2-dimensional phase spaces. Examples of solutions are
presented.

Speaker: P. Terzis
Title: Automorphisms, a new symmetry and the cartography of Bianchi Type Cosmologies.
Abstract:
The theory of symmetries of systems of coupled, ordinary
differential equations (ODE's) is used to develop a concise
algorithm for cartographing the space of solutions to vacuum Bianchi
Einstein's Field Equations (EFE). The symmetries used are the well
known automorphisms of the Lie algebra for the corresponding
isometry group of each Bianchi Type, as well as the scaling and the
time reparameterization symmetry. Application of the method to Type
III results in: a) the recovery of all known solutions without prior
assumption of any extra symmetry, b) the enclosure of the entire
unknown part of the solution space into a single, second order ODE
in terms of one dependent variable and c) a partial solution to this
ODE, i.e. a new Type III vacuum solution. It is also
worth-mentioning the fact that the solution space is seen to be
naturally partitioned into three distinct, disconnected pieces: one
consisting of the known Siklos (pp-wave) solution, another occupied
by the Type III member of the known Ellis-MacCallum family and the
third described by the aforementioned ODE in which the new solution
resides. Lastly, preliminary results reported show that the unknown
part of the solution space for other Bianchi Types is described by a
strikingly similar ODE, pointing to a natural operational
unification as far as the problem of solving the cosmological EFE's
is concerned.

Speaker: N. Tetradis
Title: Brane cosmology in a bulk with arbitrary matter content.
Abstract:
We study the cosmological evolution on a brane within a bulk with arbitrary
matter content. We consider a Friedmann-Robertson-Walker brane, invariantly
characterized by a six-dimensional group of isometries. We derive the
effective Friedmann and Raychaudhuri equations. We show that the Hubble
expansion rate on the brane depends on the covariantly defined integrated
mass in the bulk, which determines the energy density of the generalized
dark radiation. We present particular examples, some of which (such as the
radiating brane) describe energy exchange between the brane and the bulk.
We also consider the possibility of an induced gravity term on the brane.
The Friedmann equation has a branch characterized by an effective
cosmological constant and accelerated  expansion. Another remarkable feature
is that the contribution from the generalized dark radiation appears with a
negative sign. As a result, the presence of the bulk corresponds to an
effective negative energy density on the brane, without violation of the
weak energy condition. The transition from a period of domination of the
matter energy density by non-relativistic brane matter to domination by the
generalized dark radiation corresponds to a crossing of the phantom divide w=-1.

Speaker: C. Tsagas
Title: Superadiabatic Magnetic Amplification in Conformally Flat Universes.
Abstract:
We consider the evolution of cosmological magnetic fields in FRW models
and outline a geometrical mechanism for their large-scale superadiabatic
amplification. Contrary to the widespread perception of the opposite,
this is possible within standard electromagnetic theory. We discuss the
general relativistic nature of the effect, how it modifies the adiabatic
magnetic evolution and estimate the main features of the
superadiabatically amplified residual B-field.

Speaker: M. Tsamparlis
Title: General Relativity and Collineations.
Abstract:
The symmetries in General Relativity are applied either to the
Physics or the Geometry via relations of the form L_{X}A_{ab}=B_{ab} 
where A_{ab} is a metric geometric object, that is, \Gamma^a_{bc},R_{ab},\ldots.
These later symmetries are called collineations.
This talk is a general talk which explains why and how collineations
are defined, how they are interrelated in a collineation tree, what is their
effect on the kinematics and the dynamics of spacetime and finally
we describe briefly how they are applied in certain situations.
We explain the tools used in their study and show their utilization
by means of examples. The subject of collineations is an ever open
subject where one can find interesting and fundamental applications to all branches of Physics.

Speaker: A. Tsokaros
Title: New numerical method for binary black hole/neutron star data.
Abstract:
New numerical method to construct binary black hole/neutron star initial
data is presented.  The new method uses three spherical coordinate
patches; two of them are centered at the binary compact objects, and
the one at the center of mass extends to the asymptotics. Detail convergence
tests for the essential part of the code are performed for a few types of selected
Green's functions to treat different boundary conditions.  Test problems are
the calculation of gravitational potential of a fluid source, as well as the toy
model for binary black hole field. 

Speaker: D. Tsoubelis
Title: Lie point symmetry reductions of  Bondi's radiating metric.
Abstract:
The Lie point symmetries of the Einstein vacuum equations
corresponding to the Bondi form of the line element are presented.
Using these symmetries, we study reductions of the field equations,
which might lead to new asymptotically flat solutions,
representing gravitational waves emitted by an isolated source.

Speaker: P. Wallden
Title: Effective Topology through Spacetime Tomography.
Abstract:
In this talk we recover the effective topology of spacetime using certain
concepts of the decoherent histories approach to Quantum Theory and
in particular the notion of records. From a series of (gedanken) experiments,
we obtain the set of possible events, grouped into sub-sets that corresponds
to histories, but with no other information such as (causal) order or any notion of
proximity. This corresponds to tomography of the `effective' spacetime, that is
done in an operational way. Making certain assumptions about these records,
and using the existence of upper bound in the speed of transfer of matter and information, we
recover the full partial (causal) order up to certain ambiguities that are then classified.
The partially ordered set of events corresponds to an `effective' causal set which
is a discretized version of spacetime with the causal relation as defining feature.
We conclude with a derivation of the topology of this effective discretized spacetime.

Speaker: R. Woodard
Title: Leading Log Solutions for SQED and Yukawa during Inflation.
Abstract:
During inflation the quantum effects of massless, minimally
coupled scalars and gravitons are vastly enhanced. In perturbative
loop corrections this enhancement manifests as factors of the
logarithm of the inflationary scale factor, which are known as
``infrared logarithms.'' No matter how small the coupling constant,
the continued expansion of spacetime must eventually increase the
infrared logarithms to the point that perturbation theory breaks
down. A reasonable approach for evolving past this breakdown is to
resume the series of leading infrared logarithms. Alexei Starobinskii
has developed a technique for accomplishing this for any minimally
coupled scalar with non-derivative interactions. In this talk I
generalize Starobinskii's technique to two more complicated theories
which also show infrared logarithms: scalar quantum electrodynamics
and Yukawa theory. In SQED the result is that the photon develops a
mass of order the inflationary Hubble constant, and that the scalar
evolves to a non-perturbatively large amplitude of the Hubble
constant over the electric charge. In Yukawa the result is even more
interesting: the scalar causes the fermion to develop a mass which
grows without bound, and the resulting negative vacuum energy must
eventually cancel the cosmological constant, no matter how large.

Speaker: V. Zamarias
Title: Geometrical Tachyon Dynamics in the Background of a Bulk Tachyon Field.
Abstract:
The dynamics of a D3-brane in the background of a bulk tachyon field of a
D3-brane solution of Type-0 string theory is studied. It has been shown that
these dynamics can be described by a geometrical tachyon field rolling down
its potential which is modified by a function of the bulk tachyon and
inflation occurs at weak string coupling, where the bulk tachyon condenses,
near the top of the geometrical tachyon potential. Moreover a late
accelerating phase has been found when the bulk tachyon asymptotes to zero
and the geometrical tachyon field reaches the minimum of the potential.