Session R8: Cosmology / Early Universe

Fundamental physics from the cosmological 21 cm radiation

New low frequency radio telescopes currently being built open up the possibility of observing the 21 cm radiation before the Epoch of Reionization in the future, in particular at redshifts $\sim 30< z <200$, also known as the dark ages. At these high redshifts, Cosmic Microwave Background (CMB) radiation is absorbed by neutral hydrogen at its 21 cm hyperfine transition. This redshifted 21 cm signal thus carries information about the state of the early Universe and can be used to test fundamental physics. We study two types of new physics which such observations can constrain. 1) We show that the 21 cm radiation is very sensitive to the variations in the fine structure constant and can in principle place constraints comparable to or better than the other astrophysical experiments. 2) Cosmic strings, if they exist, contribute to the anisotropies in the primordial gas leaving an imprint on the 21 cm radiation. We show that the 21 cm radiation can probe the entire parameter space predicted by the brane-inflation scenarios of superstring theory. Making such observations will require radio telescopes of collecting area $10^2-10^6\hspace{4 pt}\rm{km}^2$ compared to $\sim 1\hspace{4 pt}\rm{km}^2$ of current telescopes.   

The evolution of cosmic structure with coupled dark matter and dark energy

We examine how coupled dark matter and dark energy modify the development of structure in the universe. Specifically, we study how the various effects of these theories, such as a fifth force in the dark sector and a modified particle Hubble drag, produce variations in the redshifts of caustic formation and the present-day density profiles of Zel'dovich pancakes. We compare our results in direct simulation to a perturbation theory approach for the dark energy scalar field. We also examine whether models that have been tuned to match the constraints of current observations can produce new observable effects in the nonlinear structure of pancakes. Our results suggest that a fully realistic three-dimensional simulation will produce significant new observable features, such as modifications to the mass function and halo radial density profile shapes, that can be used to distinguish these models from standard concordance cosmology and from each other.   

Effects of structure formation on the apparent expansion rate of the universe

There are recent claims that back-reaction terms arise when the effective Friedmann equation is averaged over a spatial volume in a locally inhomogeneous cosmology. These terms are claimed to lead to a new average expansion rate of the universe. Many analytical methods for this averaging procedure have been proposed and investigated. In this talk, we discuss a numerical simulation approach in which we have derived a scheme to include general relativistic corrections for general three dimensional inhomogeneities in space. The volume averaged expansion rate is quantitatively calculated with an N-body simulation code for a matter dominated, structure forming era. We discuss current limits on the corrections to the standard expansion rate. The possible physical nature of the corrections and the impacts of this averaging on the cosmological observables will also be addressed.   

Large Scale Structure as a Probe of Gravitational Slip

Many modified gravity schemes predict a non-zero difference (``gravitational slip'') between the Newtonian and longitudinal perturbed metric potentials. Such a slip would affect the growth of large scale structure without altering the expansion history of the universe. We quantify the slip with a new parameter $\varpi$, show the effect of non-zero $\varpi$ on the growth of cosmic overdensities, and constrain its value using CMB and weak lensing data.   

Study of the Spectrum of Inflaton Fluctuations

We examine the spectrum of inflaton fluctuations resulting from a long period of inflation. Our objective is to determine the spectrum in a way that does not depend on regularization of the quantized inflaton fluctuations in curved spacetime. We summarize our results for the spectrum and its scale independence, and compare them to earlier results for the spectrum.   

Weak Gravitational Lensing Poisson Equation

To date, the observed gravitational shear has been related to the inferred projected mass density of the lens by an integral equation. Alternately, one can relate the observed shear to the gravitational potential by a partial differential equation. Using the Bianchi identity in the Newman Penrose spin coefficient formalism, we derive a new Poisson equation for the mass density where the source term is derivatives of the weak lensing shear. We examine the feasibility of integrating this Poisson equation for wide field ground based and space based telescopes.   

The Dark Side of Galactic Formation

Dark Matter and Dark Energy are both regarded as anomalies that must be solved by science. Each anomaly is being independently studied while numerous solutions are being suggested for each independent of the other. However, everyone either accepts or assumes that both anomalies must eventually conform to a single common solution. With a little imagination that single solution is not that hard to find. By assuming a real macroscopically extended fifth dimension, characterized by the extrinsic curvature of the four-dimensional portion of that space-time continuum, both DM and DE can be explained in a single model. CDM halos are a simple product of galactic formation and the DE that acts as a negative pressure to increase the expansion rate of the universe is a product of the maturity and old age of spiral galaxies. The extrinsic curvature of four-dimensional space-time, which is completely compatible with both general relativity and Kaluza's unification of general relativity and electromagnetism, can be identified directly with all forms of DM and DE. This model thus offers a starting point for the unification of relativity and the quantum.   

On the Geocentric Nature of the Big Bang Theory

An expanding universe with all heavenly bodies moving isotropically away from the earth seems to suggest a geocentric theory which is evidently false. To defend the Big Bang Theory (BBT) from falling into a geocentric theory, it is argued that if the universe is expanding linearly from the singularity, the heavenly bodies would appear to be leaving away from each other with isotropic velocity distribution with respect to any observer. In this presentation we will prove rigorously with both classical and relativistic analysis that even strict linearity of Hubble's law would not save the Big Bang from falling into a geocentric theory. The key of the analysis rests on the two crucial necessary conditions for the raisin-pudding model: 1) The velocities and the positions of the earth and the galaxies must be measured simultaneously; 2) The velocity transformation between the reference frame of the earth and that of the singularity must be linear. The first condition can not be satisfied due to the speed limit of light; and the second condition can not be satisfied due to non linear velocity transformation of relativity. The whole problem is originated from the Doppler shift explanation of the red shift. Wang's Dispersive Extinction Theory (DET), however, interprets the red shift as being caused by the dispersive extinction of the star light by the space medium, and therefore does not lead to a geocentric universe. This lends a strong support to DET over BBT.   

Hot Young Solution to Faint Sun and Supernova Problems

Results from three independent experiments involving the speed of light are presented. Luminosity of Type Ia supernovae depend upon constant fundamental parameters. Accurate measurements of c provide a valuable check on ``dark energy'' theories. One Theory states that scale R of Space/Time is related to age t by R = ct. Gravitation then requires that GM=tc$^3$. These expressions provide a simple solution to Einstein-Friedmann equations with k=0. Predicted change in c provides a close fit to observations of Type Ia supernova redshifts. The ``Faint Young Sun'' has been a paradox of astrophysics. According to standard models, when Earth was forming solar luminosity was only 75\% of today's value. Geology and the fossil record contradict this prediction. Because the Sun turns fuel to energy according to E=mc$^2$, change in c precisely accounts for the difference. If c had not changed in the amounts predicted, life would not have evolved on Earth. The Lunar Laser Ranging Experiment from 1969 measures the Moon's recession at 3.82 cm/yr, anomalously high. Geological evidence states that average recession is only 2.9 cm/yr. Change in c precisely accounts for the anomaly, indicating that c changes to this day. Corroborating evidence from three truly independent experiments distinguishes Theory from other DE models. Since M = R = t (Planck Units) leads to predictions not epicycles, Theory should be considered as an alternative to more cumbersome ideas.