Research

Large Scale Universe and the Cosmic Microwave Background

1. Non-Gaussianities in cosmic microwave background maps

The increasing angular resolution and the low noise-to-signal ratio of the cosmic microwave background (CMB) observations enable one to undertake the study of tiny non-Gaussian signals. Among such signals, we continue the investigation the distribution of excursion sets in CMB temperature anisotropy maps, using Wilkinson Microwave Anisotropy Probe’s (WMAP, NASA) data. The particular aim is to probe whether the properties of symmetries are compatible with the Sachs-Wolfe effect in the presence of an anomalously large component of horizon-size density perturbations, independent of one of the spatial coordinates, and/or a slab-like spatial topology of the Universe. We apply the Kolmogorov’s parameter and other descriptors to further reveal the properties of this and other non-Gaussianities.

2. The CMB vs large scale structure cross-correlations

The Kolmogorov stochasticity parameter, the K-statistic and other descriptors are used to reveal the voids via the temperature anomalies of the CMB maps. This includes the already detected about 30 Mpc scale voids at the galaxy surveys, in future also possibly to study the proposed 100 Mpc and even larger ones, up to the Hubble scale. The latter is related with the currently discussed possibility of our location near a center of a large void. The predicted stratification of the degree of the randomness close to the walls of the void can act as a signature for the voids. Therefore the Kolmogorov map technique not only enables one to study the large scale filaments from a new viewpoint but also can be a tool to separate various signals, both of cosmological and non-cosmological origin.

3. High redshift Hubble diagram

According to the recently developed statistical approach, the use of several empirical relations obtained from gamma burst source observables, after a consistent calibration for a specific model, can probe cosmological models. The use of the increasing amount of data of the SWIFT and other satellites together with other samples with firmly determined redshifts up to over seven has proved the efficiency of the approach. Together with the data of the high redshift supernovae this enables one the construction of the Hubble diagram sensitive to various dark energy models. The latter is particularly useful for the determination of the critical redshift value when the dark energy had started to dominate over the matter density.

Galaxy clusters and galactic halo

The detection of clusters of galaxies in large surveys plays an important part in extragalactic astronomy, and particularly in cosmology, since cluster counts can give strong constraints on cosmological parameters. X-ray imaging is in particular a reliable means to discover new clusters, and large X-ray surveys are now available. Considering XMM-Newton satellite data for a sample of 40 Abell clusters, we show that their analysis with a Kolmogorov distribution can provide a distinctive signature for galaxy clusters. The Kolmogorov method is sensitive to the correlations in the cluster X-ray properties and can therefore be used for their identification, thus allowing to search reliably for clusters in a simple way.

We studied the 7-year data obtained by the WMAP satellite to trace the halo of the nearby giant spiral galaxy M31. We detected a temperature asymmetry in the M31 halo along the rotation direction up to about 120 kpc. This could be the first detection of a galactic halo in microwaves and may open a new way to probe hidden baryons in these relatively less studied galactic objects using high accuracy CMB measurements. Although baryons constitute about 4 per cent of the content of the universe, most of them are still not detected and can be hidden in galactic halo.

Complex systems

1. Dynamical chaos

The geometrical i.e. of  Maupertuis parametrization, stochastic differential equation (of Van Kampen type)  approaches is used to continue the study of chaotic properties of gravitating systems. The technique has probed with the results of parallel numerical simulations of N-body systems. The results then will be applied to the observational data on star clusters and elliptical galaxies.

2. Composite signals

The technique of degree of randomness is used to model the correlations in sequences containing various subsignals and noise. Kolmogorov stochasticity parameter enables to quantify the randomness in number sequences and hence appears as an efficient tool to distinguish the signals. Numerical experiments for a broad class of composite signals of regular and random properties enable to obtain the qualitative and quantitative criteria for the behavior of the descriptor depending on the input parameters typical to astrophysical signals.

A new limit on the light speed isotropy from the GRAAL experiment at the European Synchrotron Radiation Facility (Grenoble)

When the electrons stored in the ring of the European Synchrotron Radiation Facility (ESRF) scatter on a laser beam, the lower energy of the scattered electron spectra, the Compton Edge (CE), is given by the two body photon-electron relativistic kinematics and depends on the velocity of light. A precision measurement of the position of this CE as a function of the daily variations of the direction of the electron beam in an absolute reference frame of the cosmic microwave background provides a one-way test of relativistic kinematics and the isotropy of the velocity of light, as was originally suggested by Gurzadyan and Margarian (1996). The results of GRAAL-ESRF measurements improve the previously existing one-way limits, up to 10^-14, thus showing the efficiency of this method and the interest of further studies in this direction.

Testing General Relativity: participation in LARES satellite project

The recently launched LAser RElativity Satellite (LARES) is expected to provide high precision constraints to the General Relativity, the frame dragging Lense-Thirring effect, as well as to the extensions of General Relativity such as the Chern-Simons gravity with metric coupled to a scalar field.

The correspondence between geodesic motion in General Relativity and the motion of an extended body by means of the Ehlers-Geroch theorem was studied in the context of LARES. It was shown that being possibly the highest mean density orbiting body in the Solar system, LARES provides the best realization of a test particle ever reached experimentally and provides a unique possibility for testing the predictions of General Relativity.

The Kolmogorov analysis of the residual data of two LAGEOS satellites on General Relativistic Lense-Thirring effect reveals a tiny difference in the properties of the satellites, explained by Yarkovsky-Rubincam effect of thermal thrust. This is the first detection of the latter effect for artificial satellites.