Abstract:We explore the cosmological consequences of having the fluctuations of the inflaton field entangled with those of another scalar, within the context of a toy model consisting of non-interacting, minimally coupled scalars in a fixed de Sitter background. We find that despite the lack of interactions in the Lagrangian, the initial state entanglement modifies the mode equation for the inflaton fluctuations and thus can induce changes in cosmological observables. These effects are examined for a variety of choices of masses and we find that they can be consistent with the requirement that the back reaction of the modified state not affect the inflationary phase while still giving rise to observable effects in the power spectrum. Our results suggest that more realistic extensions of the ideas explored here beyond the simple toy model may lead to interesting observable effects.

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To what extent can the Planck satellite observations be interpreted as confirmation of the quantum part of the inflationary paradigm? Has it “seen” the Bunch-Davies state? We compare and contrast the Bunch-Davies interpretation with one using a so-called entangled state in which the fluctuations of a spectator scalar field are entangled with those of the metric perturbations ζ. We first show how a spectator scalar field Σ, with an expectation value σ(t) that evolves in time, will generically generate such a state. We then use this state to compute the power spectrum P ζ(k) and thence the temperature anisotropies Cl in the Cosmic Microwave Background (CMB). We find interesting differences from the standard calculations using the Bunch-Davies (BD) state. We argue that existing data may already be used to place interesting bounds on this class of deviations from the BD state and that, for some values of the parameters of the state, the power spectra may be consistent with the Planck satellite data.

The minimal theory of massive gravity (MTMG) has two branches of stable cosmological solutions: a self-accelerating branch, which, except for the mass of tensor modes has exactly the same behavior of linear perturbations as ΛCDM in general relativity (GR), and a normal branch with nontrivial behavior. We explore the influence of the integrated Sachs-Wolfe-galaxy correlation constraints on the normal branch of MTMG, which, in its simplest implementation, has one free parameter more than ΛCDM in GR (or the self-accelerating branch of MTMG): θ. This parameter is related to the graviton mass and only affects the behavior of the cosmological linear perturbation dynamics. Using 2d-mass and SDSS data, we check which values of θ lead to a positive or negative crosscorrelation. We find that positive cross-correlation is achieved for a large parameter-space interval. Within this allowed region of parameter space, we perform a χ 2 analysis in terms of the parameter θ, while keeping the other background parameters fixed to the best-fit values of Planck. We then infer that the normal branch of MTMG fits the data well in a nontrivial portion of the parameter space, and future experiments should be able to distinguish such a model from ΛCDM in GR (or the self-accelerating branch of MTMG).