Cosmology with time-varyingG

It is shown that a Universe with a time-varying gravitational constantG necessarily implies creation if the rest mass of matter particlesm _p is constant. In this case, from Einstein's field equations, the conditions for energy-momentum propagation are ·(GT ^v ) from which matter and photon propagation equations are derived. Free matter particle propagation is not affected by creation that is given byGN _pm_p=const, whereN _p is the number of matter particles within a proper volume. This relation introduces explicitly the rest mass of the Universe into the field equations. Free photon propagation is affected by creation that is given byGT v R=const, whereN is the number of photons within a proper volume, which is the cosmic red shift law. Conservation of the cosmic background photon distribution determines photon creation asG ³ N ⁴ . The results are applied to the caseG t ^–1 equivalent toN _p ÷ t.It is found that at an aget=1, 0^–40 t _o, of the order light takes to travel a proton size, Planck's units become of the order of the proton's massm _p, sizer _p, and timer _p/c. Hence, matter particles at this age are quantum black holes. Evaporation of these quantum black holes at this age gives a background blackbody radiation that, red shifted to present timet ₀, gives the present cosmic microwave background.A cosmological model of the Friedmann type is constructed. The red shift versus distance relation is derived taking into account creation. Using a Hubble's constantH _obs=50 km sec^–1 Mpc^–1 and a deceleration parameterq _obs=1.0 the model is of the typek=1 and gives a present aget ₀=6.81×10⁹ yr, consistent with Uranium model ages. Thus, the three results for the age of the Universe, i.e., radioactive decay, Hubble's constant, and stellar evolution are brought together in this creation model. The matter-dominated era occurs fort>7.6×10^–3 t ₀, while the radiation-dominated era occurs for 7.6×10^–3 t _o>t>10^–40 t _o. The origin of the Universe is placed at this last limit, which is Planck's time at the corresponding G, consisting of quantum black holes at a temperature T_i=3×10¹¹K.     

Cosmology with cluster surveys

Surveys of clusters of galaxies provide us with a powerful probe of the density and nature of the dark energy. The red-shift distribution of detected clusters is highly sensitive to the dark energy equation of state parameterw. Upcoming Sunyaev-Zel’dovich (SZ) surveys would provide us large yields of clusters to very high red-shifts. Self-calibration of cluster scaling relations, possible for such a huge sample, would be able to constrain systematic biases on mass estimators. Combining cluster red-shift abundance with limited mass follow-up and cluster mass power spectrum can then give constraints onw, as well as onσ ₈ and Ω_M to a few per cents.     

Cosmology with rolling tachyon

We examine the possibility of rolling tachyon to play the dual role of inflaton at early epochs and dark matter at late times. We argue that enough inflation can be generated with the rolling tachyon either by invoking the large number of branes or brane world assisted inflation. However, reheating is problematic in this model. On leave from Jamia Millia Islamia, New Delhi 110 025, India     

Cosmology with a Shock-Wave

We construct the simplest solution of the Einstein equations that incorporates a shock-wave into a standard Friedmann-Robertson-Walker metric whose equation of state accounts for the Hubble constant and the microwave background radiation temperature. This produces a new solution of the Einstein equations from which we are able to show that the distance from the shock-wave to the center of the explosion at present time is comparable to the Hubble distance. We are motivated by the idea that the expansion of the universe as measured by the Hubble constant might be accounted for by an event more similar to a classical explosion than by the well-accepted scenario of the Big Bang.     

Cosmology with the intergalactic medium

We discuss a few new results which points out the importance of the intergalactic medium as a diagnostic for the formation and evolution of galaxies in the Universe. We discuss the recent studies to determine the power spectrum of fluctuation from QSO-absorption line studies, and then some feedback processes from early galaxies which influence the intergalactic medium.     

Cosmology

Precise astronomical observations of the cosmic expansion and the anisotropies of the cosmic microwave background have confirmed the simple cosmological “big bang” models. They have also produced evidence for a strange composition of the cosmic matter and energy density. The known baryons contribute only 5 percent to the cosmic substrate, while 25 percent are due to unknown dark matter particles, and 70 percent seem to come from a mysterious dark energy component which presently acts like a cosmological constant accelerating the cosmic expansion.     

Cosmology with inhomogeneous magnetic fields

We review spacetime dynamics in the presence of large-scale electromagnetic fields and then consider the effects of the magnetic component on perturbations to a spatially homogeneous and isotropic universe. Using covariant techniques, we refine and extend earlier work and provide the magnetohydrodynamic equations that describe inhomogeneous magnetic cosmologies in full general relativity. Specialising this system to perturbed Friedmann–Robertson–Walker models, we examine the effects of the field on the expansion dynamics and on the growth of density inhomogeneities, including non-adiabatic modes. We look at scalar perturbations and obtain analytic solutions for their linear evolution in the radiation, dust and inflationary eras. In the dust case we also calculate the magnetic analogue of the Jeans length. We then consider the evolution of vector perturbations and find that the magnetic presence generally reduces the decay rate of these distortions. Finally, we examine the implications of magnetic fields for the evolution of cosmological gravitational waves.     

Cosmology with weak lensing surveys

Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening matter. The distortions are due to fluctuations in the gravitational potential, and are directly related to the distribution of matter and to the geometry and dynamics of the Universe. As a consequence, weak gravitational lensing offers unique possibilities for probing the Dark Matter and Dark Energy in the Universe. In this review, we summarise the theoretical and observational state of the subject, focussing on the statistical aspects of weak lensing, and consider the prospects for weak lensing surveys in the future.     

Cosmology with non-minimally coupled k-field

We consider a non-minimally coupled (with gravity) scalar field with non-canonical kinetic energy. The form of the kinetic term is of Dirac–Born–Infeld form. We study the early evolution of the universe when it is sourced only by the k-field, as well as late time evolution when both the matter and k-field are present. For the k-field, we have considered constant potential as well as potential inspired from boundary string field theory. We show that it is possible to have an inflationary solution in early time as well as late time accelerating phases. The solutions also exhibit attractor properties in a sense that they do not depend on the initial conditions for certain values of the parameters.     

Quantum Cosmology with Hyperbolic Potential

For an FRW model with a minimally coupled scalar field having hyperbolic(exponential) potential we evaluate the wave function both by solving theWheeler-Dewitt (WD) equation and by evaluating the path integral. The WDequation is solved in configuration as well as in momentum space, while thepath integral is evaluated by dividing the lapse integral into a number of pieces.     

Cosmology with a variable Chaplygin gas

We consider a new generalized Chaplygin gas model that includes the original Chaplygin gas model as a special case. In such a model the generalized Chaplygin gas evolves as from dust to quiescence or phantom. We show that the background evolution for the model is equivalent to that for a coupled dark energy model with dark matter. The constraints from the current type Ia supernova data favour a phantom-like Chaplygin gas model.     

Extra-Dimensional Cosmology with a Traversable Wormhole

We discuss many interesting and attractive features of a higher-dimensional cosmology with a static traversable wormhole dominated by a variable effective cosmological constant depending on the scale factor aft） as Aeffective =Ca^-2 ＋ A0, where C and A0 are positive constants.     

Cosmology with the Nearby Supernova Factory

The Nearby Supernova Factory (SNfactory) is currently finishing its first survey of low redshift (0.03<z<0.08) type Ia supernovae. These data add to the understanding of the expansion history of the universe. Observations are performed using the Supernova Integral Field Spectrograph (SNIFS), an integral field spectrograph delivering full spectro-photometric information of the target. The corresponding dataset aims at the inference of the Hubble diagram zero point with unprecedented accuracy. Moreover, the data offers a variety of related physical studies such as the understanding of progenitor systems, explosion scenarios and host galaxy characteristics. The SNfactory is also working on novel methods accessible with spectro-photometric measurements, reducing systematic uncertainties and improving the statistical power of the SN data.     

Cosmology with light axions from technicolor

We consider cosmological consequences of the spontaneous breaking of a global symmetry that is anomalous under technicolor interactions, leading to the emergence of a light axion-like particle. Avoiding overclosure of the universe by such axions yields the upper bound fa?¹⁰¹⁰ GeV$f_a?{10}^{10}\text{GeV}$ on the symmetry breaking scale, corresponding to keV-scale axions. However, diffuse X-ray background data typically require larger values of fa$f_a$. The overclosure and X-ray bounds can be reconciled if the axion initial amplitude of oscillations Ai∼fa/10$A_i\sim f_a/10$. In this case, a viable axionic dark matter candidate with a mass in the 50–100 eV range emerges. The detection of this type of dark matter may pose a challenge.     

Cosmology with cosmic microwave background anisotropy

Measurements of CMB anisotropy and, more recently, polarization have played a very important role in allowing precise determination of various parameters of the ‘standard’ cosmological model. The expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early Universe have also been established — ‘acausally’ correlated initial perturbations in a flat, statistically isotropic Universe, adiabatic nature of primordial density perturbations. Direct evidence for gravitational instability mechanism for structure formation from primordial perturbations has been established. In the next decade, future experiments promise to strengthen these deductions and uncover the remaining crucial signature of inflation — the primordial gravitational wave background.     

Post-Newtonian Cosmology

Newtonian Cosmology is commonly used in astrophysical problems, because of its obvious simplicity when compared with general relativity. However it has inherent difficulties, the most obvious of which is the non-existence of a well-posed initial value problem. In this paper we investigate how far these problems are met by using the post-Newtonian approximation in cosmology.     

Scaling Cosmology

We show that with the help of a suitable coupling between dark energy and cold dark matter it is possible to reproduce any scaling solution _{X M} a , where _X and _M are the densities of dark energy and dark matter, respectively. We demonstrate how the case = 1 alleviates the coincidence problem. Future observations of supernovae at high redshift as well as quasar pairs which are planned to discriminate between different cosmological models will also provide direct constraints on the coupling between dark matter and dark energy.