Session A13: Cosmological Tests of General Relativity and Supersymmetry

Numerical Cosmology: Building a Dynamical Universe

In this talk I discuss an often over-looked aspect of most cosmological models, dynamical interactions caused by gravitational waves. Did gravitational waves interacting with the primordial plasma field result in a chaotic system? What impact would such a system have on cosmic structure formation? I begin by reviewing our current state of knowledge involving gravitational waves in the early universe. Then, I review work done to understand the physics of turbulent plasmas. Finally, I show the results of computer simulations of gravitational wave/plasma interactions in the early universe. This work seeks to explain what role gravitational waves played in the early universe when interacting with the primordial plasma field, primordial seed magnetic fields and cold dark matter.   

Extending the validity of Lagrangian Perturbation Theory

Lagrangian Perturbation Theory (LPT) has been widely used to model the non-linear growth of large-scale structure analytically. However, it is known that the Lagrangian series fails to converge when applied to spherical voids. The work to be presented discusses the convergence properties for homogeneous spherical top-hats with arbitrary initial density and velocity perturbations. For this special class of problems, we derive the time of validity of the series and demonstrate how to extend the range of validity. The conclusion is that LPT should be viewed as a finite difference approximation, which, similar to the Euler-Poisson system can diverge prior to shell crossings and it requires a time-step condition to assure stability and yield convergent results.   

Supersymmetric Hybrid Inflation Redux

We discuss the important role played during inflation by one of the soft supersymmetry breaking terms in the inflationary potential of supersymmetric hybrid inflation models. With minimal Kahler potential, the inclusion of this term allows the prediction for the scalar spectral index to agree with the value $n_{s}$ = 0.963$^{+0.014}$ $_{-0.015}$ found by WMAP5. In the absence of this soft term, and by taking into account only radiative and supergravity corrections, it is well known that $n_{s} \quad \ge $ 0.985. This same soft term has previously been shown to play a key role in resolving the MSSM \textit{$\mu $} problem. The tensor to scalar ratio $r$ is quite small in these models, taking on values $r \quad \le $ 10$^{-5}$ in the WMAP5 2$\sigma $ range of $n_{s}$.   

Astrophysical Searches for Extra Spatial Dimensions

Extra spatial dimensions have been employed in theoretical physics for quite some time now. Earth-bound experimental tests for the existence of extra spatial dimensions are currently limited. Astrophysical tests are also possible. I will review some of the basic conceptual ideas that underlie the theories. Then I will discuss some astrophysical observations that could test for the existence of extra spatial dimensions.   

Cosmological Constraints on Moduli from Cosmic Strings

Cosmological constraints on moduli, whose coupling to matter is stronger than Planck mass suppressed coupling, are derived. In particular, moduli are considered to be produced by oscillating loops of cosmic strings and constraints are obtained from their effects on big bang nucleosynthesis and their contribution to diffuse gamma ray background and dark matter. Large volume and warped Type-IIB flux compactifications are taken as examples where strongly coupled moduli are present. Finally, the constraints on cosmic string tension, modulus mass and modulus coupling constant are obtained and it is shown that the constraints are relaxed significantly when the coupling constant is large enough. In addition, the effect of thermal production of moduli are considered and the corresponding constraints are derived.   

Combining Shear Statistics to Constrain Cosmological Parameters

Weak gravitational lensing causes shear in the images of distant galaxies. Shear statistics can be measured from high-quality astronomical images and then fit to theoretical expectations. Thus constraints can be made on dark matter structures and on dark energy. Code to measure the two-point correlation function (2PCF) including tomography (redshift information) is modified and developed. Code to measure the signal-to-noise peak counts is adapted. The 2PCF and peak counts are measured on a shear catalog derived from the Hubble Space Telescope COSMOS survey. Constraints on cosmological parameters are then derived from the measured 2PCF and from the peak counts. These constraints are combined to break the degeneracy between the matter mass density ($\Omega _m$) and the amplitude of density fluctuations ($\sigma _8$), making the overall set of constraints tighter.   

Testing General Relativity on Cosmological Scales with Weak Gravitational Lensing

Weak gravitational lensing is a powerful probe of modifications of General Relativity on cosmological scales, since such modifications can affect both how matter produces gravitational potential wells and how photons move within these wells. I will discuss alternative theories of gravitation and how we may constrain such theories using weak lensing observables, including those that could be obtained with the balloon-borne High Altitude Lensing Observatory (HALO). I will also discuss the ``parametrized-post-Friedmannian'' approach for obtaining model-independent constraints, in which new parameters are introduced to characterize the departure from General Relativity on large scales.   

Cosmological Tests of General Relativity with tomographic surveys

Future cosmological surveys, combining galaxy counts and weak lensing measurements, will map the evolution of matter perturbations and gravitational potentials from the matter dominated epoch until today. In addition to tightening the constraints on allowed expansion histories, the combination of these measurements will test the relationships between matter overdensities, local curvature, and the Newtonian potential. These relation- ships can be modi?ed in alternative theories of gravity and by exotic forms of Dark Energy. I will present a study of the potential of upcoming and future tomographic surveys, such as DES and LSST, with the aid of CMB and supernovae data, to detect departures from the growth of perturbations expected within General Relativity with a cosmological constant.   

Parameter Estimation Forecasts in Cosmology

In the current era of precision cosmology, new extremely well planned observational missions are being designed to study cosmology to unprecedented detail. Such missions will not only allow us to constrain the free parameters in the standard model of cosmology, but also to test the possible departures in this model. In order to optimize the scientific impact of these surveys, it is therefore essential to forecast the constraints from these surveys, and also study different ways in which this data can be used to study cosmology. We discuss forecasts, in particular those pertaining to dark energy studies from the planned surveys.