history-universe-08The early universe was so extremely hot, that it passed through the transition of forming nucleons from quarks about 10 microseconds after the big bang. This transition could have left an impact on cosmological observables today, if the transition was of first order. Lattice gauge calculations within quantum chromodynamics  QCD indicate that such a first order transition could only happen at a nonvanishing baryon density, if at all. In the scenario of the so called ‘little inflation’, an initial high baryon density is assumed which is diluted to the presently observed value by a short inflationary period due to a first order (chiral) phase transition. Cosmological signals include a gravitational wave background, production of dark matter perturbations and a modified power spectrum of primordial fluctuations at small mass scales.