@jefsART: I have no idea how far you are in your studies, but if still at the very beginning you might like to have a look at this free online course which starts next Monday, 9 May 2016: https://www.futurelearn.com/courses/gravity/2.
I have recently completed this fascinating online course by Paris Diderot University: Gravity! From Big Bang to Black Holes. Knew absolutely nothing about the subject - still know only the bare minimum. But as I'm now hooked I am determined to progress. I fear some of my questions may be too...
Since the very rapid expansion of the Universe, ie Inflation, caused curvature to be smoothed out, the assumption must be that curvature existed between the time of the Big Bang and the start of Inflation. If that is correct, is this borne out by the Planck or any other theory?