The critical geometry of a thermal big bang
  We explore the space of scalar-tensor theories containing two
non-conformalmetrics, and find a discontinuity pointing to a "critical"
cosmological solution. Due to the different maximal speeds of propagation for
matter and gravity,the cosmological fluctuations start off inside the horizon
even without inflation, and will more naturally have a thermal origin (since
there is never vacuum domination). The critical model makes an unambiguous,
non-tuned prediction for the spectral index of the scalar fluctuations: $n_S=
0.96478(64)$. Considering also that no gravitational waves are produced, we
have unveiled the most predictive model on offer. The model has a simple
geometrical interpretation as a probe 3-brane embedded in an $EAdS_2\times E_3$
geometry.
