Cosmology

The universe has turned out to be simpler than expected on both very small and very large scales. We propose a minimal, highly predictive framework connecting particle physics to cosmology. Instead of introducing an ``attractor” phase such as inflation we extrapolate the observed universe all the way back to the initial singularity where we impose a CPT symmetric boundary condition via a generalization of the method of images. If the hot plasma in the early universe is perfectly conformal, so is the singularity. The cosmos may then be analytically extended to a ``mirror image” universe prior to the bang. Using this new boundary condition we calculate the gravitational entropy for cosmologies with radiation, matter, Lambda and space curvature, finding it favours spatially flat, homogeneous and isotropic universes with a small positive cosmological constant in accord with observation. To maintain conformal symmetry, we include unusual Dim-0 (dimension zero) fields. They improve the SM’s coupling to gravity, cancelling the vacuum energy and two local “Weyl” anomalies, without introducing additional propagating modes. They also cancel pathologies introduced into the graviton propagator by loops of SM particles. Cancellation requires precisely 3 generations of SM fermions, each with a RH neutrino. It also requires a composite Higgs, presumably built with the Dim-0 fields. One of the RH neutrinos, if stable, is a viable candidate for the dark matter which will be tested soon. The Dim-0 fields source scale-invariant curvature perturbations in the early universe. Subject to two simple but crucial theoretical assumptions, the amplitude and spectral tilt match the observations with remarkable accuracy. (See arXiv:2302.00344 and references therein).

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