On the Locality of the No Hair Conjecture and the Measure of the Universe

We reanalize the recently proposed proof by Jensen and Stein-Schabes [1] of the No Hair Theorem for inhomogeneous spacetimes, putting a special emphasis on the asymptotic behaviour of the shear and curvature. We conclude that the theorem only holds locally and estimate the minimum size a region should be in order for it to inflate. We discuss in some detail the assumptions used in the theorem. In the last section we speculate about the possible measure of the set of spacetimes that would undergo inflation.     

Influence of the size,geometry and temporal response of the finite piezoelectric sensor on the photoacoustic signal: the case of the point-like source

Most photoacoustic (PA) work assumes a point-like detection of generated pressure waves; this assumption results in important differences between predicted and experimental signals, as shown in this paper. We used the geometry of a real sensor in the theoretical signal generation through the discretization of the sensing surface, considering each element as a point-like sensor. We modeled the interaction between the wavefront and the real sensor, starting from a well-known PA pressure relation for a point-like source and punctual detection. We obtained the electrical response of the real sensor experimentally and modeled it as a summation of Gaussian functions. The impulse response was convolved with the total PA pressure to obtain the theoretical PA signal. We analyzed the dependence of the source-sensor distance on the discretization size. Then the predicted signal and experimental data were compared for two different frequency response transducers. We found differences in shape and temporal width of simulated PA signals for point-like-source/punctual-detection model and for point-like-source/finite-sensor model.     

Four-forms and the vanishing of the cosmological constant

We show that the dynamics (and statics) of a four-form are more subtle than previously appreciated, especially when used in conjuction with the Baum-Hawking-Coleman mechanism. We investigate the properties of the four-forms on closed euclidean, open euclidean, and lorentzian manifolds. We find that only under special conditions is their behaviour such that the cosmological constant vanishes.     

Identifying the community structure of the international-trade multi-network

We study the community structure of the multi-network of commodity-specific trade relations among world countries over the 1992-2003 period. We compare structures across commodities and time by means of the normalized mutual information index (NMI). We also compare them with exogenous community structures induced by geography and regional trade agreements. We find that commodity-specific community structures are very heterogeneous and much more fragmented than that characterizing the aggregate ITN. This shows that the aggregate properties of the ITN may result (and be very different) from the aggregation of very diverse commodity-specific layers of the multi-network. We also show that commodity-specific community structures, especially those related to the chemical sector, are becoming more and more similar to the aggregate one. Finally, our findings suggest that geography-induced partitions of our set of countries are much more correlated with observed community structures than partitions induced by regional-trade agreements. This result strengthens previous findings from the empirical literature on trade.     

Analysis of the effects of the global financial crisis on the Turkish economy, using hierarchical methods

We have analyzed the topology of 50 important Turkish companies for the period 2006-2010 using the concept of hierarchical methods (the minimal spanning tree (MST) and hierarchical tree (HT)). We investigated the statistical reliability of links between companies in the MST by using the bootstrap technique. We also used the average linkage cluster analysis (ALCA) technique to observe the cluster structures much better. The MST and HT are known as useful tools to perceive and detect global structure, taxonomy, and hierarchy in financial data. We obtained four clusters of companies according to their proximity. We also observed that the Banks and Holdings cluster always forms in the centre of the MSTs for the periods 2006-2007, 2008, and 2009-2010. The clusters match nicely with their common production activities or their strong interrelationship. The effects of the Automobile sector increased after the global financial crisis due to the temporary incentives provided by the Turkish government. We find that Turkish companies were not very affected by the global financial crisis.     

On the logarithmic solutions of the WDVV equations

We consider restrictions and subsystems in the ∨-systems corresponding to the logarithmic solutions of the WDVV equations. We present certain solutions through restrictions of the Coxeter systems.     

Fluctuations of the Increment of the Argument for the Gaussian Entire Function

The Gaussian entire function is a random entire function, characterised by a certain invariance with respect to isometries of the plane. We study the fluctuations of the increment of the argument of the Gaussian entire function along planar curves. We introduce an inner product on finite formal linear combinations of curves (with real coefficients), that we call the signed length, which describes the limiting covariance of the increment. We also establish asymptotic normality of fluctuations.     

On the propagation of a fissioning system across the barrier towards scission

We describe the motion of a fissioning nuclear system from the potential minimum across the saddle region to scission by means of a Fokker-Planck type equation. We pay particular attention to the problems associated with the motion of broad distributions in phase space. We introduce propagators to obtain global solutions. The results are compared with Kramers' stationary solution for all friction and with simplified dynamical calculations which start behind or on top of the barriers. We are able to find stationary solutions numerically for all finite friction values. We compare the corresponding decay rates with Kramers' formulae for large and small friction.     

Calculations of the propagator within the tomographic-probability framework

We show that the ambiguity in choosing the tomographic propagator for an evolving linear quantum system is related to the homogeneity properties of the system symplectic tomogram. We study in detail an example of the driven harmonic oscillator. We prove that two formally different propagators of the quantum kinetic equation for the oscillator are identical on the domain of homogeneous tomographic probability distributions.     

Prediction of the physical response for the two-photon photorefractive effect

We present a new model for the two-photon photorefractive recording process. We solved the resulting set of nonlinear coupled partial differential equations of the model within a linear approximation of the steady state. We found very good agreement with experimental results.     

Inhomogeneous Cosmologies, the Copernican Principle and the Cosmic Microwave Background: More on the EGS Theorem

We discuss inhomogeneous cosmological models which satisfy the Copernican principle. We construct some inhomogeneous cosmological models starting from the ansatz that the all the observers in the models view an isotropic cosmic microwave background. We discuss multi-fluid models, and illustrate how more general inhomogeneous models may be derived, both in General Relativity and in scalar-tensor theories of gravity. Thus we illustrate that the cosmologicalprinciple, the assumption that the Universe we live in is spatially homogeneous, does not necessarily follow from the Copernican principle and the high isotropy of the cosmic microwave background. We also present some new conformally flat two-fluid solutions of Einstein's field equations.     

Primordial superstrings and the origin of the universe

We discuss some of the cosmological implications of superstring theories. We pay particular attention to the issue of the initial state and its relationship withR-duality.     

Detecting the standard model Higgs bosonin the WW decay channel using forward proton tagging at the LHC

We present a detailed study of the central exclusive production of the standard model Higgs boson in the WW decay channel at the LHC. We include estimates of the experimental acceptance, including that of the proposed proton tagging detectors at 220 m and 420 m around either ATLAS and/or CMS, and the level 1 trigger acceptances. We give first estimates of the photon-photon and glue-glue background processes in the semi-leptonic and fully leptonic decay channels. We find that there will be a detectable signal for Higgs masses between 140 GeV and 200 GeV, and that the backgrounds should be controllable. Arrival of the final proofs: 1 December 2005     

Influence of temperature gradient at the reflectors on the bit-error rate in periscope laser communication systems in the presence of platform vibrations

We propose a reflector back-fixing method for substantially improving the pointing accuracy in comparison with the around-fixing method. We use the developed model for analyzing the bit-error rate (BER) in the presence of the satellite??s platform vibration. We consider the relationship between the BER and temperature gradient at elliptical reflectors, in view of the two fixing methods mentioned above. We also analyze the effect of beam wavelength and truncation ratio on the BER. We find that the back-fixing of the reflectors can reduce substantially the BER, thus, providing stabler performance of periscope laser-communication systems.     

Non-stationary effects in the coupled quantum dots influenced by the electron-phonon interaction

We analyzed time evolution of the localized charge in the system of two interacting single level quantum dots coupled with the continuous spectrum states in the presence of electron-phonon interaction. We demonstrated that electron-phonon interaction leads to an increase in localized charge relaxation rate. We also found that several time scales with different relaxation rates appear in the system in the case of non-resonant tunneling between the dots. We revealed the formation of oscillations in the filling numbers time evolution caused by the emission and adsorption processes of phonons.     

On the calculation of the Berry phase in a solvable model

We study fermions defined on a one-dimensional interval, for which the interaction is given by a four-parameter family of boundary conditions. We compare the full solution to the adiabatic approximation and determine the Berry phase for a number of typical orbits in parameter space. We observe the occurrence of a non-trivial fundamental group and discuss the possibilities of avoided crossings and apparent crossings.     

Constraining the topology of the universe

The first year data from the Wilkinson Microwave Anisotropy Probe are used to place stringent constraints on the topology of the Universe. We search for pairs of circles on the sky with similar temperature patterns along each circle. We restrict the search to back-to-back circle pairs, and to nearly back-to-back circle pairs, as this covers the majority of the topologies that one might hope to detect in a nearly flat universe. We do not find any matched circles with radius greater than 25 degrees. For a wide class of models, the nondetection rules out the possibility that we live in a universe with topology scale smaller than 24 Gpc.     

Simulations of the Hubbard model

We discuss results of simulations of the Hubbard model of interacting electrons on a lattice. We start with a brief discussion of methodology and point out some of the outstanding problems. We then discuss results of simulations of the model in three, two, and one dimension, particularly in connection with its magnetic and superconducting properties. We conclude with a brief discussion of future directions.     

Barriers in the p-spin interacting spin-glass model: the dynamical approach

We investigate the barriers separating metastable states in the spherical p-spin glass model using the instanton method. We show that the problem of finding the barrier heights can be reduced to the causal two-real-replica dynamics. We find the probability for the system to escape one of the highest energy metastable states and the energy barrier corresponding to this process.     

From the Sky to the Fundamental Physics

We discuss the relation between string theory/supergravity and the observational data in cosmology, as well as at LHC, past and future. We pay particular attention to the possibility of the future detection of primordial gravitational waves and how this might affect our understanding of fundamental physics.