MR. SANTANU DAS

Using a new line of sight CMB code, called CMBAns, that allow us to modify H(z) for any given feature at any redshift we study the effect of changes in the expansion history of the Universe on the CMB power spectrum. Motivated by the detailed analytical calculations of the effects of the changes in H(z) on ISW plateau and CMB low multipoles, we study two phenomenological parametric form of the expansion history using WMAP data and through MCMC analysis. Our MCMC analysis shows that the standard LCDM cosmological model is consistent with the CMB data allowing the expansion history of the Universe vary around this model at different redshifts. However, our analysis also show that a decaying dark energy model proposed in A. Sha¿eloo, V. Sahni & A. A. Starobinsky - 2009 has in fact a marginally better fit than the standard cosmological constant model to CMB data. Considering the fact that the analysis with Baryon Acoustic Oscillation (BAO) and supernovae data mildly prefer the decaying dark energy model to LCDM, makes this finding interesting and worth further investigation.