Abstract
We propose 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 postbang epochs comprise a universe-antiuniverse pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects a unique QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a remarkably 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 4.8×10^{8} GeV. Several other testable predictions follow: (i)the three light neutrinos are Majorana particles and allow neutrinoless double β decay; (ii)the lightest neutrino is massless; and (iii)there are no primordial long-wavelength gravitational waves. We mention connections to the strong CP problem and the arrow of time.
Highlights
We propose that the state of the Universe does not spontaneously violate CPT
Ignoring perturbations for the moment, the metric we see in our past is strikingly simple and analytic: gμν 1⁄4 a2ðτÞημν, where ημν is the flat Minkowski metric, and the scale factor aðτÞ is just proportional to the conformal time τ. If we take this metric seriously, and follow aðτÞ ∝ τ across the bang, we find that the analytically extended FRW background with −∞ < τ < ∞ suddenly exhibits a new isometry: time reversal symmetry τ → −τ
We find it yields a remarkably economical explanation of the cosmological dark matter: if the Universe is in its preferred CPT-symmetric vacuum, late-time observers see heavy sterile neutrinos emerging from the bang, for the same reason that distant observers see Hawking radiation emerging from a black hole
Summary
We propose 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. CPT symmetry selects a unique QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a remarkably economical explanation for the cosmological dark matter.
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