Disformally coupled inflation

Bruck, Carsten van de; Koivisto, Tomi S.; Longden, Chris

doi:10.1088/1475-7516/2016/03/006

Cited by 26 publications

(22 citation statements)

References 98 publications

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“…This action encompasses a wide range of models, including coupled and uncoupled two-field models [11,12], those with Diract Born Infeld (DBI) kinetic terms [13], disformally coupled inflation [14], and even many theories with non-standard gravity following a transformation of the action (such as Starobinsky inflation after conformal transformation [15,16]).…”

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confidence: 99%

Running of the running and entropy perturbations during inflation

Bruck

Longden

2016

Phys. Rev. D

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In single field slow-roll inflation, one expects that the spectral index n s − 1 is first order in slow-roll parameters. Similarly, its running α s ¼ dn s =d log k and the running of the running β s ¼ dα s =d log k are second and third order and therefore expected to be progressively smaller, and usually negative. Hence, such models of inflation are in considerable tension with a recent analysis hinting that β s may actually be positive, and larger than α s . Motivated by this, in this work we ask the question of what kinds of inflationary models may be useful in achieving such a hierarchy of runnings, particularly focusing on twofield models of inflation in which the late-time transfer of power from isocurvature to curvature modes allows for a much more diverse range of phenomenology. We calculate the runnings due to this effect and briefly apply our results to assess the feasibility of finding jβ s j ≳ jα s j in some specific models. DOI: 10.1103/PhysRevD.94.021301 Constraining models of inflation is one of the most important goals of cosmology. By constraining or even ruling out models of inflation, cosmologists learn a great deal about model building in theories beyond the standard model. Even with the latest cosmological observations [1,2], there is still a plethora of inflationary models compatible with data [3]. It was recently pointed out that observations of the cosmic microwave background (CMB) radiation are consistent with a rather large running of the running of the spectral index, 1 [4,5]. The constraints on α s and β s given in [5] are α s ¼ 0.011 AE 0.010 and β s ¼ 0.027 AE 0.013 (fixing the pivot scale at k ¼ 0.05 Mpc −1 ), which implies β s > 0 at the 2σ confidence level and hints that the running of the running may be larger than the running itself. The running α s also appears to be positive (although less significantly), which leads to a slight tension with a wide range of inflationary models that predict a negative running [6]. Future CMB experiments are needed to determine these parameters more precisely, but given this first hint of what is potentially a powerful piece of evidence in early universe cosmology, it is interesting and worthwhile to consider the theoretical viability for such a hierarchy of runnings to be realized in inflation.In standard single field slow-roll models, the running is of second order in slow-roll parameters and the running of the running is third order [see Eqs. (5)- (7) below]. Thus, in such models of inflation, one would quite generally expect β s to be smaller than α s . These observational hints motivate the current work, in which we study predictions of α s and β s in single and two-field inflationary scenarios with the intention of understanding what kinds of inflationary models could be consistent with such a hierarchy of runnings.While almost all investigations of inflationary models make predictions for the spectral index, relatively few study the running [6][7][8][9], and almost none discuss the running of the running [4,10]. This is largely underst...

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confidence: 99%

Running of the running and entropy perturbations during inflation

Bruck

Longden

2016

Phys. Rev. D

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“…These terms appear although the field χ has no contribution to the dynamics of the universe. Hence, these terms could largely alter the oscillation behaviour of the inflaton field during preheating compared with our case, and could modify the feature of inflation compared with that in [26]. However, in this work, we concentrate on the preheating process of model based upon the disformal inflationary scenario investigated in [26], so that we will not consider this situation.…”

Section: Scalar-tensor Theory With the Disformal Couplingmentioning

confidence: 92%

Preheating in an inflationary model with disformal coupling

Karwan

Channuie

2017

Phys. Rev. D

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In this work, we investigate the preheating mechanism in a disformally-coupled inflationary model where the scalar field $\phi$ (which is the inflaton field) naturally coupled to another matter field $\chi$ induced by the disformal transformation. In the present scenario, novel derivative interactions mixing the kinetic terms of the two fields emerge inherently. We start by deriving the evolution of the background system when the back reaction on the background field is neglected. We examine the particle production due to parametric resonances in the models and find in Minkowski space that the stage of parametric resonances can be described by the Mathieu equation. Interestingly, we discover that broad resonances in our models can be typically achieved. Finally, we compare our results with previously studied model with derivative couplings.Comment: v2: 17 pages, 2 figures, texts modified, more references added, version accepted for publication by Physical Rev.

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“…(3.26) contain factors of the transfer function T RS , we need a way of computing this. Fortunately, this can be obtained from our numerical simulations of the perturbed equations of motion carried out in section 2 and our previous paper [30], by comparing the final value of P R to its value at horizon-crossing.…”

Section: Non-gaussianitiesmentioning

confidence: 99%

Non-Gaussianity in multi-sound-speed disformally coupled inflation

Bruck

Koivisto

Longden

2017

J. Cosmol. Astropart. Phys.

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Abstract. Most, if not all, scalar-tensor theories are equivalent to General Relativity with a disformally coupled matter sector. In extra-dimensional theories such a coupling can be understood as a result of induction of the metric on a brane that matter is confined to. This article presents a first look at the non-Gaussianities in disformally coupled inflation, a simple two-field model that features a novel kinetic interaction. Cases with both canonical and Dirac-Born-Infeld (DBI) kinetic terms are taken into account, the latter motivated by the possible extra-dimensional origin of the disformality. The computations are carried out for the equilateral configuration in the slow-roll regime, wherein it is found that the non-Gaussianity is typically rather small and negative. This is despite the fact that the new kinetic interaction causes the perturbation modes to propagate with different sounds speeds, which may both significantly deviate from unity during inflation.arXiv:1608.08801v2 [astro-ph.CO]

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Disformally coupled inflation

Cited by 26 publications

References 98 publications

Running of the running and entropy perturbations during inflation

Running of the running and entropy perturbations during inflation

Preheating in an inflationary model with disformal coupling

Non-Gaussianity in multi-sound-speed disformally coupled inflation

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