Clustering evolution between z=1 and today

We present results of an investigation of clustering evolution of field galaxies between a redshift of z ∼ 1 and the present epoch. The current analysis relies on a sample of ∼ 14000 galaxies in two fields of the COMBO 17 survey. The redshift distribution extends to z ∼ 1. The amplitude of the three-dimensional correlation function can be estimated by means of the projected correlation function w(r _p ). The validity of the deprojection was tested on the Las Campanas Redshift Survey (LCRS). In a flat cosmology with non-zero cosmological constant for bright galaxies (M _B ≤-18) the clustering growth is proportional to (1+z) ^-2. However, the measured clustering evolution clearly depends on Hubble type. While locally the clustering strength of early type galaxies is equal to that of the bright galaxies, at high redshifts they are much stronger clustered, and thus the clustering has to evolve much more slowly. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Peak Luminosity of Type Ia Supernovae and its Implications for the Cosmic Expansion Rate

1 IN~DUCTIONInterest in take la supernovae (SNe la) has risen dramatically with their application to thecosmological problems since Kowal (1968). Their powerful capabilities as distance indicatorson the cosmic scale have pushed them into the limelight of cosmology. They now provide themain route to the current eXPansion rate and the deceleration of the adverse. (see Branch1998; Perlmutter et al. 1999; mess et al. 1998).SNe la are reversally accepted as the result of thermonuclear eXPlo…     

The Hubble Flow: Why Does the Cosmological Expansion Preserve Its Kinematical Identity from a Few Mpc Distance to the Observation Horizon?

The problem of the physical nature of the Hubble flow in the Local Volume (D < 10 Mpc) stated by Sandage is studied. New observational data on galaxy motions and matter distribution around the Local Group and nearby similar systems are described. Dynamical models are discussed on the basis of the recent data on cosmic vacuum or dark energy.     

Non-circular beam correction to the CMB power spectrum

In the era of high precision CMB measurements, systematic effects are beginning to limit the ability to extract subtler cosmological information. The non-circularity of the experimental beam has become progressively important as CMB experiments strive to attain higher angular resolution and sensitivity. The effect of non-circular beam on the power spectrum is important at multipoles larger than the beam-width. For recent experiments with high angular resolution, optimal methods of power spectrum estimation are computationally prohibitive and sub-optimal approaches, such as the Pseudo-C_l method are used. We provide an analytic framework for correcting the power spectrum for the effect of beam non-circularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. We advocate that when the non-circular beams are important, it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transforms die down fast with m.     

Modeling repulsive gravity with creation

There is a growing interest among cosmologists for theories with negative energy scalar fields and creation, in order to model a repulsive gravity. The classical steady state cosmology proposed by Bondi, Gold & Hoyle in 1948, was the first such theory which used a negative kinetic energy creation field to invoke creation of matter. We emphasize that creation plays a very crucial role in cosmology and provides a natural explanation to the various explosive phenomena occurring in local (z < 0.1) and extra galactic universe. We exemplify this point of view by considering the resurrected version of this theory — the quasi-steady state theory, which tries to relate creation events directly to the large scale dynamics of the universe and supplies more natural explanations of the observed phenomena. Although the theory predicts a decelerating universe at the present era, it explains successfully the recent SNe Ia observations (which require an accelerating universe in the standard cosmology), as we show in this paper by performing a Bayesian analysis of the data.     

Time Variation of Cosmic and Quantum Masses in Dirac’s Cosmology

It is shown that the expressions of five fundamental masses appearing in physics and cosmology can be written in terms of the constants of nature. We study the time variation of them in the context of a generalized Dirac’s cosmology based on the large number hypothesis (LNH). This generalization allows one to have the gravitational constant not depending upon time contrary to Dirac’s original theory. It also allows the rest mass of the particle to vary with cosmological time. Further, we show that there exist simple algebraic relations between them and that their ratios can be expressed as powers of the large dimensionless number 10⁴⁰.     

Astronomical measurements and constraints on the variability of fundamental constants

We review the present status of how astronomical observations allow to constrain the evolution of fundamental constants of nature. The main observational constraints on the variation of the gravitational constant, on the fine structure constant and on the proton-to-electron mass ratio are reviewed. We also elaborate on some theoretical schemes which naturally lead to such variations.     

Some critiques of the big bang cosmology

Still more shocking than the metaphysical assumption of some initial singularity, is the constant insistence upon the so-called cosmological principle of “homogeneity” and “isotropy” of the Universe. Observations do contradict this principle. And to me, the inhomogeneous, fractal at least on a certain scale range, of the distribution of matter is in itself an important cosmological fact, hitherto almost neglected. Moreover difficultties as to the applicability of the second principle of thermodynamics, observations of abnormal redshifts, etc., are casting large doubts not only upon the standard cosmological models, but even on the interpretation of the observed redshift as due solely to a universal expansion.     

MOND—theoretical aspects

I discuss open theoretical questions pertaining to the modified dynamics (MOND)—a proposed alternative to dark matter, which posits a breakdown of Newtonian dynamics in the limit of small accelerations. In particular, I point the reasons for thinking that MOND is an effective theory—perhaps, despite appearance, not even in conflict with GR. I then contrast the two interpretations of MOND as modified gravity and as modified inertia. I describe two mechanical models that are described by potential theories similar to (non-relativistic) MOND: a potential-flow model, and a membrane model. These might shed some light on a possible origin of MOND. The possible involvement of vacuum effects is also speculated on.