CPT-Symmetric Universe

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I will introduce our recent proposal that the state of the universe does *not* spontaneously violate CPT. Instead, the universe after the big bang is the CPT image of the universe before it, both classically and quantum mechanically. The pre- and post-bang epochs comprise a universe/anti-universe pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects the QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a particularly economical explanation for the cosmological dark matter. Requiring only the standard three-generation model of particle physics (with right-handed neutrinos), a Z_2 symmetry suffices to render one of the right-handed neutrinos stable. We calculate its abundance from first principles: matching the observed dark matter density requires its mass to be 4.8 x 10^{8} GeV. Several other testable predictions immediately follow: e.g. (i) the lightest neutrino is massless; (ii) neutrinoless double beta decay occurs at a specific rate; and (iii) there are no primordial long-wavelength gravitational waves. The proposal also has interesting things to say about the strong CP problem, the observed electrodynamic arrow of time, cosmological boundary conditions, and the wave-function of the universe. (Based on arXiv:1803.08928, arXiv:1803.08930, and forthcoming work.)