Strongly coupled perturbations in two-field inflationary models

Abstract:We analyze the signatures of inflationary models that are coupled to interacting field theories, a basic class of multifield models also motivated by their role in providing dynamically small scales. Near the squeezed limit of the bispectrum, we find a simple scaling behavior determined by operator dimensions, which are constrained by the appropriate unitarity bounds. Specifically, we analyze two simple and calculable classes of examples: conformal field theories (CFTs), and large-N CFTs deformed by relevant time-dependent double-trace operators. Together these two classes of examples exhibit a wide range of scalings and shapes of the bispectrum, including nearly equilateral, orthogonal and local non-Gaussianity in different regimes. Along the way, we compare and contrast the shape and amplitude with previous results on weakly coupled fields coupled to inflation. This signature provides a precision test for strongly coupled sectors coupled to inflation via irrelevant operators suppressed by a high mass scale up to ∼ 10 3 times the inflationary Hubble scale.

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“…Similar constraints arise in other models involving a linear mixing with the inflaton (e.g. [9][10][11][31][32][33][34]). …”

Section: Jhep10(2013)171supporting

confidence: 70%

Anomalous dimensions and non-gaussianity

Green

Lewandowski

Senatore

et al. 2013

J. High Energ. Phys.

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“…Although many authors noted the possible impact of the field space curvature on the inflationary dynamics (see, e.g., [11][12][13][14]), we argue that this physical effect can have much further reaching consequences than hitherto noticed. To give a simple and concrete example: in two-field models (in which the curvature tensor can be solely expressed in terms of the field space metric and the Ricci scalar R fs ) with hyperbolic geometry, i.e., with negative R fs , all inflationary trajectories, even those aligned with field space geodesics, tend to become unstable.…”

mentioning

confidence: 50%

“…Thanks to the slowing 2nd phase of inflation down of the inflaton field by a noncanonical normalization, this phase can last very long: in the numerical examples presented here its duration ranges from a few to over a thousand e-folds. Interestingly, this phase corresponds to a large value of η ⊥ and can be in certain situations described by an effective one-field model with a modified dispersion relation [23,24] or a model with transient tachyonic instability at the Hubble radius crossing [13]. Inflation then ends in a standard fashion by slowroll violation, = 1, before the fields rapidly converge to the stable potential minimum at (φ, χ) = (0, 0).…”

mentioning

confidence: 99%

Geometrical Destabilization of Inflation

2016

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We show the existence of a general mechanism by which heavy scalar fields can be destabilized during inflation, relying on the fact that the curvature of the field space manifold can dominate the stabilizing force from the potential and destabilize inflationary trajectories. We describe a simple and rather universal setup in which higher-order operators suppressed by a large energy scale trigger this instability. This phenomenon can prematurely end inflation, thereby leading to important observational consequences and sometimes excluding models that would otherwise perfectly fit the data. More generally, it modifies the interpretation of cosmological constraints in terms of fundamental physics. We also explain how the geometrical destabilization can lead to powerful selection criteria on the field space curvature of inflationary models.Introduction.-Recent cosmic microwave background data from the Planck and BICEP2/Keck collaborations [1, 2] constrain the tensor-to-scalar ratio r < 0.12 (95% C.L.) and the spectral index of primordial density perturbations n s = 0.968 ± 0.006 (68% C.L.). The simplest slow-roll single-field inflationary models are in perfect agreement with these data and the lack of measurable primordial non-Gaussianities [3,4]. Amongst them, models coming with a concave plateau potential, such as Starobinsky inflation [5] and its numerous variants (see, e.g., [6-8]), are observationally favored. Despite this phenomenological success, embedding inflation into a realistic high-energy context remains a highly nontrivial task (see Refs. [9, 10] for reviews), as inflation is an ultraviolet-sensitive phenomenon. One manifestation of these difficulties is the so-called η problem, i.e., the fact that even Planck-suppressed corrections to an otherwise flat enough potential generically ruin inflation. Another challenge is the ubiquitous presence of extra scalar fields in models constructed in supergravity or string theory. In general, these fields participate in the inflationary dynamics and can substantially modify the corresponding observable predictions. In this respect, the simplest theoretical hope is to stabilize these extra scalars by providing them with a large mass, exceeding the value of the Hubble parameter H during inflation.In this Letter, we show the existence of a very general geometrical mechanism by which the noninflationary degrees of freedom can be destabilized during inflation, even if they have large masses in the static vacuum. This mechanism relies on the fact that generic multifield inflationary models are nonlinear sigma models, i.e., the kinetic part of their action reads L kin = − 1 2 G IJ (φ K )∂ µ φ I ∂ µ φ J , where the manifold described by the field space metric G IJ is generally curved. It is well known that the curvature of space manifests itself in the geodesic deviation:

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“…1 These fields fluctuation quantum-mechanically during inflation and therefore have to be included in the computation of the primordial perturbations. The phenomenology of these models of quasisingle-field inflation [490] has been explored in [118,207,208,239,255,265,267,[491][492][493][494][495][496][497].…”

Section: Spectrum Of Statesmentioning

confidence: 99%