# User:Søren Bertil F. Dorch/Proposed/Lambda cold dark matter

Dr. Jeremiah P. Ostriker accepted the invitation on 30 September 2007 (self-imposed deadline: 30 February 2008).

Co-author: Tarun Souradeep, IUCAA, Pune, India (email: tarun@iucaa.ernet.in)

Figure 1: Our place on the Cosmic triangle

Concordant $$\Lambda$$-Cold dark matter cosmology

The observational status of the emerging Lambda Cold dark matter ($$\Lambda$$-CDM) cosmology that has emerged as the `concordance' model of the universe over the past decade.

## Abstract

Observational Cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spearheaded by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. More recently,observations of the Large scale structure in the distribution of galaxies, High redshift supernova have provided the required complementary information. We review the current status cosmological parameter estimates from joint analysis of CMB anisotropy and Large scale structure (LSS) data. We also sound a note of caution on over stating the successes achieved thus far.

## Introduction

Recent developments in Cosmology have been largely driven by huge improvement in quality, quantity and the scope of cosmological observations. The measurement of temperature anisotropy in the Cosmic Microwave Background (CMB) is arguably been the most influential of these recent observational success stories. A glorious decade of CMB anisotropy measurements has been topped off by the data from the Wilkinson Microwave Anisotropy Probe (WMAP) of NASA.Observational success has set off an intense interplay between theory and observations. While on one hand, the observations have constrained theoretical scenarios and models more precisely, some of these observations have thrown up new challenges to theoretical understanding and others that have brought issues from the realm of theoretical speculation to observational verification. The results the WMAP mission on CMB anisotropy~\cite{ben_wmap03} and the power spectrum of density perturbations from the SDSS survey of galaxies\cite{sdss}, have allowed very precise estimation of cosmological parameters~\cite{maxsdss,sel04}.

These results have been widely heralded as the dawn of precision cosmology. To a casual science observer, the unprecedented precision in determining the parameters of the standard cosmological model often conveys the false impression that we actually know and understand the components that make up the universe, we know its primal history (including the theoretical scenarios of baryogenesis and inflation), evolution including growth of large scale structures. The reality is that our understanding of some of the components is limited to very rudimentary characterization, eg., in terms their cosmic energy density, velocity dispersion and equation of state etc.. Besides the obvious need for direct detection, we are not quite in a position to even rule out equally viable non-standard alternatives.