Theory HEP Seminar

Isotropisation in cyclic universe cosmologies

Chandrima Ganguly

DAMTP, Cambridge

tandard models of cosmology use inflation as a mechanism to resolve the isotropy and homogeneity problem of the universe as well as the flatness problem. However, due to various well known problems with the inflationary paradigm, there has been an ongoing search for alternatives. Perhaps the most famous among these is the cyclic universe scenario or scenarios which incorporate bounces. As these scenarios have a contracting phase in the evolution of the universe, it is reasonable to ask whether the problems of homogeneity and isotropy can still be resolved in these scenarios. In my talk, I will focus on the problem of the resolution of isotropy. In the contracting phase of the evolution, the mechanism of ekpyrosis is used in most cosmological scenarios which incorporate a contracting phase to mitigate the problem of anisotropies blowing up on approaching the bounce. I will start by studying anisotropic universes and I shall examine the effect of the addition of ultra-stiff anisotropic pressures on the ekpyrotic phase. I will then consider evolving such anisotropic universes through several cycles with increasing expansion maxima at each successive bounce. This eventually leads to flatness in the isotropic case. My aim will be to see if the resolution of the flatness problem also leads to a simultaneous resolution of the isotropy problem. In the last section of my talk, I will briefly consider the effect of non comoving velocities on the shape of this anisotropic bouncing universe.