Abstract
In the standard approach to deriving inflationary predictions, we evolve a vacuum state in time according to the rules of a given model. Since the only observables are the future values of correlators and not their time evolution, this brings about a large degeneracy: a vast number of different models are mapped to the same minute number of observables. Furthermore, due to the lack of time-translation invariance, even tree-level calculations require an increasing number of nested integrals that quickly become intractable. Here we ask how much of the final observables can be “bootstrapped” directly from locality, unitarity and symmetries.To this end, we introduce two new “boostless” bootstrap tools to efficiently compute tree-level cosmological correlators/wavefunctions without any assumption about de Sitter boosts. The first is a Manifestly Local Test (MLT) that any n-point (wave)function of massless scalars or gravitons must satisfy if it is to arise from a manifestly local theory. When combined with a sub-set of the recently proposed Bootstrap Rules, this allows us to compute explicitly all bispectra to all orders in derivatives for a single scalar. Since we don’t invoke soft theorems, this can also be extended to multi-field inflation. The second is a partial energy recursion relation that allows us to compute exchange correlators. Combining a bespoke complex shift of the partial energies with Cauchy’s integral theorem and the Cosmological Optical Theorem, we fix exchange correlators up to a boundary term. The latter can be determined up to contact interactions using unitarity and manifest locality. As an illustration, we use these tools to bootstrap scalar inflationary trispectra due to graviton exchange and inflaton self-interactions.
Highlights
In the standard approach to deriving inflationary predictions, we evolve a vacuum state in time according to the rules of a given model
Since the only observables are the future values of correlators and not their time evolution, this brings about a large degeneracy: a vast number of different models are mapped to the same minute number of observables
We begin by reviewing aspects of a scalar quantum field in de Sitter space including the formalism of the wavefunction of the universe and the recently derived Cosmological Optical Theorem (COT) [32] which will be used throughout this work
Summary
We begin by reviewing aspects of a scalar quantum field in de Sitter (dS) space including the formalism of the wavefunction of the universe and the recently derived Cosmological Optical Theorem (COT) [32] which will be used throughout this work. For a contact 3-point function we require three independent variables and these are already provided by the three external energies and so there is no need to introduce any inner products. Under a limited number of assumptions, it was shown in [32] that perturbative unitarity implies a set of powerful constraints on both contact and exchange contributions to the wavefunction coefficients in the form of a Cosmological Optical Theorem (COT) (see [35] for a complementary derivation of the COT and [46,47,48] for analogous statements in anti-de Sitter (AdS) space).
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