Rapid-Turn Inflationary Attractors

We study how both the swampland distance conjecture and the Lyth bound affect the parameter space of multi-field models of inflation. A generic feature of multi-field inflation is that the geodesic distance [∆φ] G separating any two points laying along the inflationary trajectory differs from the non-geodesic distance [∆φ] NG traversed by the inflaton between those points. These distances must respect a relation of the formwhere f is a function determined by the specific multi-field model under scrutiny. We show that this relation leads to important constraints on the parameter space characterizing the multi-field dynamics. Indeed, the swampland distance conjecture implies an upper bound on [∆φ] G set by the details of the ultraviolet completion of inflation, whereas the Lyth bound implies a lower bound on [∆φ] NG determined by the value of the tensor-to-scalar ratio. If future observations confirm the existence of primordial tensor perturbations, these two bounds combined lead to tight constraints on the possible values of the entropy mass of the isocurvature fields orthogonal to the inflationary trajectory and the rate of turn of the inflationary trajectory in multi-field space. We analyze the emerging constraints in detail for the particular case of two-field inflation in hyperbolic field spaces.

Section: Perturbationssupporting

confidence: 76%

A tip for landscape riders: multi-field inflation can fulfill the swampland distance conjecture

Bravo

Palma

Riquelme

2020

“…Let us also point out that when more than two fields are present, one can define a turning rate associated to every normal direction and they will contribute to the total turning rate 10 Recent multifield inflation investigations have pointed out that small turning rates are not necessary for a successful period of slow-roll inflation [23][24][25][26][27][28], as we showed explicitly above. Most of these studies focus on the case of non-zero negative curvature of the scalar manifold.…”

Section: Slow-roll Fat Inflation and Large Turnsmentioning

confidence: 90%

“…The adiabatic mass squared m 2 T is given by 26) and the entropy mass M is given by 27) where V N N = N i N j ∇ i ∇ j V and R is the scalar manifold's Ricci scalar. At superhorizon scales, (2.24) becomesQ 28) and one can define an effective entropy mass as M 2 ef f = M 2 + 4Ω 2 .…”

Section: Dynamics Of the Linear Perturbationsmentioning

confidence: 99%

Fat inflatons, large turns and the η-problem

Chakraborty

Chiovoloni

Loaiza-Brito

et al. 2020

It is commonly believed that a successful period of inflation driven by a single or several scalar fields requires a specific hierarchy of masses given by M inf H M heavy , where M inf can correspond to several or a single light field and M heavy corresponds to any heavy field that might be integrated out if it satisfies suitable conditions. This is at the heart of the so called η-problem in inflation, since large contributions to the masses of the inflatons might spoil the slow-roll conditions required for inflation. We show that, while this is an unavoidable conclusion in single field inflation, in multifield inflation, heavy fields as defined above, may be fully responsible for a successful period of what we call fat slow-roll inflation. Moreover we show that in this scenario, the turning rate of the inflationary trajectory, Ω/H, is larger than one. Thus, the η-problem is evaded with large turns in fat inflation. Depending on the perturbations' mass spectra, cosmological predictions will differ either slightly or largely with respect to those of the single field case. We illustrate this scenario in a concrete example in Type IIB string flux compactifications, where a probe D5-brane moving along the angular and radial directions in a warped throat drives fat D5-brane natural inflation. An instantaneous superplanckian decay constant can be defined, consistent with our low energy approximations, thanks to the strong warping of the geometry. We compute the cosmological observables, which differ from the single field case. We also discuss fat inflation in the context of recently proposed swampland de Sitter conjectures.

“…Over the last few years there has been much interest in two-field inflation models with strongly non-geodesic motion . These models have been studied under various names (such as spinflation, hyperinflation, side-tracked inflation, angular inflation, and effective single-field theories with a reduced speed of sound from heavy fields), but have recently been shown to belong to a general class of solutions known as 'rapid-turn attractors' [4]. Intriguingly, inflation models with rapidly turning fields can be realised in potentials that are much too steep for standard slow-roll inflation [22,30], and may thereby ameliorate the so-called inflationary 'η-problem' [31,32].…”

Section: Introductionmentioning

confidence: 99%

Mild non-Gaussianities under perturbative control from rapid-turn inflation models

Bjorkmo

Ferreira

Marsh

2019

Self Cite

Inflation can be supported in very steep potentials if it is generated by rapidly turning fields, which can be natural in negatively curved field spaces. The curvature perturbation, ζ, of these models undergoes an exponential, transient amplification around the time of horizon crossing, but can still be compatible with observations at the level of the power spectrum. However, a recent analysis (based on a proposed single-field effective theory with an imaginary speed of sound) found that the trispectrum and other higher-order, non-Gaussian correlators also undergo similar exponential enhancements. This arguably leads to 'hyper-large' non-Gaussianities in stark conflict with observations, and even to the loss of perturbative control of the calculations. In this paper, we provide the first analytic solution of the growth of the perturbations in two-field rapid-turn models, and find it in good agreement with previous numerical and single-field EFT estimates. We also show that the nested structure of commutators of the in-in formalism has subtle and crucial consequences: accounting for these commutators, we show analytically that the naively leading-order piece (which indeed is exponentially large) cancels exactly in all relevant correlators. The remaining non-Gaussianities of these models are modest, and there is no problem with perturbative control from the exponential enhancement of ζ. Thus, rapidturn inflation with negatively curved field spaces remains a viable and interesting class of candidate theories of the early universe.