arXiv subjects

G. Yegorian

Publications and source records attributed to G. Yegorian.

30 records · Page 2Linked to original sources

arXiv2008

Hubble Diagram of Gamma-Rays Bursts calibrated with Gurzadyan-Xue Cosmology

Gamma-ray bursts (GRBs) being the most luminous among known cosmic objects carry an essential potential for cosmological studies if properly used as standard candles. In this paper we test with GRBs the cosmological predictions of the Gurzadyan-Xue (GX) model of dark energy, a novel theory that predicts, without any free parameters, the current vacuum fluctuation energy density close to the value inferred from the SNIa observations. We also compare the GX results with those predicted by the concordance scenario $Λ$-CDM. According to the statistical approach by Schaefer (2007), the use of several empirical relations obtained from GRBs observables, after a consistent calibration for a specific model, enables one to probe current cosmological models. Based on this recently introduced method, we use the 69 GRBs sample collected by Schaefer (2007); and the most recently released SWIFT satellite data (Sakamoto et al. 2007) together with the 41 GRBs sample collected by Rizzuto et al. (2007), which has the more firmly determined redshifts. Both data samples span a distance scale up to redshift about 7. We show that the GX models are compatible with the Hubble diagram of the Schaefer (2007) 69 GRBs sample. Such adjustment is almost identical to the one for the concordance $Λ$-CDM.

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arXiv2007

On Axial and Plane--Mirror Inhomogeneities in the WMAP3 Cosmic Microwave Background Maps

We study inhomogeneities in the distribution of the excursion sets in the Cosmic Microwave Background (CMB) temperature maps obtained by the three years survey of the Wilkinson Microwave Anisotropy Probe (WMAP). At temperature thresholds |T|<90 μK, the distributions of the excursion sets with over 200 pixels are concentrated in two regions, nearly at the antipodes, with galactic coordinates l= 94^\circ.7, b= 34^\circ.4 and l= 279^\circ.8, b= -29^\circ.2. The centers of these two regions drift towards the equator when the temperature threshold is increased. The centers are located close to one of the vectors of \ell =3 multipole. The two patterns of the substructures in the distribution of the excursion sets are mirrored, with χ^2=0.7-1.5. There is no obvious origin of this effect in the noise structure of WMAP, and there is no evidence for a dependence on the galactic cut. Would this effect be cosmological, it could be an indication of an anomalously large component of horizon-size density perturbations, independent of one of the spatial coordinates, and/or of a non-trivial slab-like spatial topology of the Universe.

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arXiv2007

On intrinsic symmetry in Gurzadyan-Xue cosmological models

Analysis of cosmological solutions of GX dark energy models shows the presence of a separatrix in the phase space of solutions which divides them into two classes: Friedmannian-like with initial singularity and non-Friedmannian solutions. The invariants are found, that reveal the intrinsic symmetry in GX models.

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arXiv2007

Luminosity distance in GX cosmological models

We derive luminosity distance equation in Gurzadyan-Xue cosmological models and compared it with available supernovae and radio galaxies data sets. We found that the luminosity distance does not depend explicitly the speed of light and the gravitation constant, and depends only on the matter parameter (GX-invariant) and curvature.

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arXiv2006

Ellipticity in Cosmic Microwave Background as a Tracer of Large-Scale Universe

Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data confirm the ellipticity of anisotropies of Cosmic Microwave Background (CMB) maps, found previously for Boomerang and WMAP 1-year high sensitivity maps. The low noise level of the WMAP latter data enable also to show that, the ellipticity is a property not described by the conventional cosmological model fitting the power spectrum of CMB. As a large scale anomaly, the ellipticity characteristics are consistent with the effect of geodesics mixing occurring in hyperbolic Universe. Its relation to other large scale effects, i.e. to suppressed low multipoles, as well as to dark energy if the latter is due to vacuum fluctuations, is then an arising issue.

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arXiv2006

Dynamics of perturbations in Gurzadyan-Xue cosmological models

Perturbation theory within Newtonian approximation is presented for cosmological models with varying physical constants. Analytical solutions for perturbations dynamics are obtained for each Gurzadyan-Xue model with pressureless matter and radiation. We found that perturbations grow during entire expansion within GX models, including curvature- and vacuum-dominated stage when they cease to grow in the standard cosmological model.

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arXiv2006

Cosmological models with Gurzadyan-Xue dark energy

The formula for dark energy density derived by Gurzadyan and Xue provides a value of density parameter of dark energy in remarkable agreement with current cosmological datasets, unlike numerous phenomenological dark energy scenarios where the corresponding value is postulated. This formula suggests the possibility of variation of physical constants such as the speed of light and the gravitational constant. Considering several cosmological models based on that formula and deriving the cosmological equations for each case, we show that, in all models source terms appear in the continuity equation. So, one one hand, GX models make up a rich set covering a lot of currently proposed models of dark energy, on the other hand, they reveal hidden symmetries, with a particular role of the separatrix $Ω_m=2/3$, and link with the issue of the content of physical constants.

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arXiv2006

Supernovae and Radio Galaxies Probing Gurzadyan-Xue Cosmological Models with Dark Energy

In the previous papers we derived cosmological equations for models with Gurzadyan-Xue dark energy, have performed their qualitative analysis and, particularly, have revealed a remarkable hidden invariance in the models with respect to the separatrix $Ω_{sep}$ in their phase portraits. Now, new analytic solutions for these models are obtained, showing additional symmetries at various curvatures. The likelihood analysis with supernovae and radio galaxies data and their characteristics (age, the deceleration parameter), again demonstrate the crucial role of the $Ω_{sep}$ for all models, in spite of the diversity of both, the initial equations and their solutions.

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arXiv2006

Hidden invariance in Gurzadyan-Xue cosmological models

The dark energy formula derived by Gurzadyan and Xue which leads to a value fitting the SN data, provides a scaling relation between the physical constants and cosmological parameters and defines a set of cosmological models. In previous works we have considered several of those models and derived the cosmological equations for each case. In this letter, we present the phase portrait analysis of those models. Surprisingly we found, first, that the separatrix in the phase space which determines the character of solutions depends solely on the value of the current matter density. Namely, at $Ω_m>2/3$ the equations describe Friedmannian Universe with the classical singularity at the beginning. While at $Ω_m<2/3$ all solutions for all models start with zero density and non vanishing scale factor. Secondly, more remarkable, the value $Ω_{sep}=2/3$ defining the separatrix is the same for all models, which reveales an underlying invariance hidden in the models, possibly, due to the basic nature of the GX-scaling.

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arXiv2005

Elliptic CMB Sky

The ellipticity of the anisotropy spots of the Cosmic Microwave Background measured by the Wilkinson Microwave Anisotropy Probe (WMAP) has been studied. We find an average ellipticity of about 2, confirming with a far larger statistics similar results found first for the COBE-DMR CMB maps, and then for the BOOMERanG CMB maps. There are no preferred directions for the obliquity of the anisotropy spots. The average ellipticity is independent of temperature threshold and is present on scales both smaller and larger than the horizon at the last scattering. The measured ellipticity characteristics are consistent with being the effect of geodesics mixing occurring in an hyperbolic Universe, and can mark the emergence of CMB ellipticity as a new observable constant describing the Universe. There is no way of simulating this effect. Therefore we cannot exclude that the observed behavior of the measured ellipticity can result from a trivial topology in the popular flat $Λ$-CDM model, or from a non-trivial topology.

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arXiv2004

WMAP confirming the ellipticity in BOOMERanG and COBE CMB maps

The recent study of BOOMERanG 150 GHz Cosmic Microwave Background (CMB) radiation maps have detected ellipticity of the temperature anisotropy spots independent on the temperature threshold. The effect has been found for spots up to several degrees in size, where the biases of the ellipticity estimator and of the noise are small. To check the effect, now we have studied, with the same algorithm and in the same sky region, the WMAP maps. We find ellipticity of the same average value also in WMAP maps, despite of the different sensitivity of the two experiments to low multipoles. Large spot elongations had been detected also for the COBE-DMR maps. If this effect is due to geodesic mixing and hence due to non precisely zero curvature of the hyperbolic Universe, it can be linked to the origin of WMAP low multipoles anomaly.

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arXiv2003

Is there a common origin for the WMAP low multipole and for the ellipticity in BOOMERanG CMB maps?

We have measured the ellipticity of several degree scale anisotropies in the BOOMERanG maps of the Cosmic Microwave Background (CMB) at 150 GHz. The average ellipticity is around 2.6-2.7. The biases of the estimator of the ellipticity and for the noise are small in this case. Large spot elongation had been detected also for COBE-DMR maps. If this effect is due to geodesic mixing, it would indicate a non precisely zero curvature of the Universe which is among the discussed reasons of the WMAP low multipole anomaly. Both effects are related to the diameter of the Universe: the geodesics mixing through hyperbolic geometry, low multipoles through boundary conditions.This common reason can also be related with the origin of the the cosmological constant: the modes of vacuum fluctuations conditioned by the boundary conditions lead to a value of the cosmological constant being in remarkable agreement with the supernovae observations.

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