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Register a new userSuperCool Inflation: A Graceful Exit from Eternal Inflation at LHC Scales and Below
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Authors
Douglas Spolyar
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In SuperCool Inflation (SCI), a technically natural and thermal effect gives a graceful exit to old inflation. The Universe starts off hot and trapped in a false vacuum. The Universe supercools and inflates solving the horizon and flatness problems. The inflaton couples to a set of QCD like fermions. When the fermions non-Abelian gauge group freezes, the Yukawa terms generate a tadpole for the inflaton, which removes the barrier. Inflation ends, and the Universe rapidly reheats. The thermal effect is technically natural in the same way that the QCD scale is technically natural. In fact, Witten used a similar mechanism to drive the Electro-Weak (EW) phase transition; critically, no scalar field drives inflation, which allows SCI to avoid eternal inflation and the measure problem. SCI also works at scales, which can be probed in the lab, and could be connected to EW symmetry breaking. Finally, we introduce a light spectator field to generate density perturbations, which match the CMB. The light field does not affect the inflationary dynamics and can potentially generate non-Gaussianities and isocurvature perturbations observable with Planck.
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Two qualitatively different modes of ending superluminal expansion are possible in extended inflation. One mode, different from the one envoked in most extended models to date, easily avoids making big bubbles that distort the cosmic microwave background radiation (CMBR). In this mode, the spectrum of density fluctuations is found to be scale-free, $P(k) propto k^n$, where $n$ might lie anywhere between 0.5 and 1.0 (whereas, previously, it appeared that the range $1.0> n gtsim 0.84$ was disallowed).
A seemingly simple question, how does warm inflation exit gracefully?, has a more complex answer than in a cold paradigm. It has been highlighted here that whether warm inflation exits gracefully depends on three independent choices: The form of the potential, the choice of the warm inflation model (i.e., on the form of its dissipative coefficient) and the regime, of weak or strong dissipation, characterizing the warm inflation dynamics. Generic conditions on slow-roll parameters and several constraints on the different model parameters required for warm inflation to exit gracefully are derived.
Current data from the Planck satellite and the BICEP2 telescope favor, at around the $2 sigma$ level, negative running of the spectral index of curvature perturbations from inflation. We show that for negative running $alpha < 0$, the curvature perturbation amplitude has a maximum on scales larger than our current horizon size. A condition for the absence of eternal inflation is that the curvature perturbation amplitude always remain below unity on superhorizon scales. For current bounds on $n_{rm S}$ from Planck, this corresponds to an upper bound of the running $alpha < - 4 times 10^{-5}$, so that even tiny running of the scalar spectral index is sufficient to prevent eternal inflation from occurring, as long as the running remains negative on scales outside the horizon. In single-field inflation models, negative running is associated with a finite duration of inflation: we show that eternal inflation may not occur even in cases where inflation lasts as long as $10^4$ e-folds.
We forecast the ability of cosmic microwave background (CMB) temperature and polarization datasets to constrain theories of eternal inflation using cosmic bubble collisions. Using the Fisher matrix formalism, we determine both the overall detectability of bubble collisions and the constraints achievable on the fundamental parameters describing the underlying theory. The CMB signatures considered are based on state-of-the-art numerical relativistic simulations of the bubble collision spacetime, evolved using the full temperature and polarization transfer functions. Comparing a theoretical cosmic-variance-limited experiment to the WMAP and Planck satellites, we find that there is no improvement to be gained from future temperature data, that adding polarization improves detectability by approximately 30%, and that cosmic-variance-limited polarization data offer only marginal improvements over Planck. The fundamental parameter constraints achievable depend on the precise values of the tensor-to-scalar ratio and energy density in (negative) spatial curvature. For a tensor-to-scalar ratio of $0.1$ and spatial curvature at the level of $10^{-4}$, using cosmic-variance-limited data it is possible to measure the width of the potential barrier separating the inflating false vacuum from the true vacuum down to $M_{rm Pl}/500$, and the initial proper distance between colliding bubbles to a factor $pi/2$ of the false vacuum horizon size (at three sigma). We conclude that very near-future data will have the final word on bubble collisions in the CMB.
We present an interpretation of the physics of space-times undergoing eternal inflation by repeated nucleation of bubbles. In many cases the physics can be interpreted in terms of the quantum mechanics of a system with a finite number of states. If this interpretation is correct, the conventional picture of these space-times is misleading.
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