Slides from the talk - CP3-Origins

The interesting case of Quasi-Single Field Inflation
k −3/2
3 ln k 3
,
k 1
QSF inflation predicts a family of models
parametrized by
α = 1 2 − ν ,
m 2
H 2 ≈ 9 (1)
4 ,
9 ν ≡ 4 − m2
H 2 . “isocurvaton” fields, i.e. field (2)
non-Gaussianity with intermediate and “shapes” is present between eventhe
if the non-Gaussianity is perfectly scaleheequilateral
inflaton requires and local m 2 ≥ 0, so α ≥−1. As m 2 /H 2 > 9/4, the isocurvatons
significant effects on density perturbations. So we are mainly interested in
a momentum dependence lies between that of the equilateral shape (α = 1)
large non-Gaussianity or its direct multifield generalization, and that of the
ultifield models with light isocurvatonssqueezed-limit
m H. (See [9–11] for reviews.)
n the isocurvaton masses may be model-dependent in more general situations,
dependence in the squeezed limit is a robust evidence for the existence of such
atively as follows [6, 7]. The fluctuations of the massive scalars decay after
y decay immediately after the horizon-exit, and for lighter scalars they decay
responsible for the large non-Gaussianities, are therefore generated between
n scales. The former
ν = 0.2
is responsible for the equilateral-like ν = 1 shapes, and the
cy check, if we look at the special limit of massless scalars, the superhorizon
over the characteristic local shape in the squeezed limit. This momentum
titatively as follows [8], at least for α close to −1 . Ignoring the physics within
ed limit of the three-point function can be regarded as the modulation of the
ngth modes from a long-wavelength mode. After horizon exit, we know that
ays as ∼ a −1−α • Inflationary phenomenology.
as a function of the scale factor a. So the amplitude of the
1+α
m is the mass of the
orthogonal to the inflaton
trajectory in field-space
Figure 1. Thisfigureillustratesamodelofquasi-singlefieldinflation in ter
The θ direction is the inflationary direction, with a slow-roll potential. The
isocurvature direction, which typically has mass of order H.
PHYSICAL REVIEW D 81, 063511 (2010)
larger than O(H), quasi-single field inflation makes the same predic
inflation. However, once large couplings exist and the mass are of orde
these massive isocurvatons can have important effects on density pert
In this paper, we shall study a simple model of quasi-single fiel
model, the coupling between the inflaton and the massive isocurvat
turning trajectory. The tangential direction of this turning trajector
direction, while the orthogonal direction is lifted by a mass oforderH
The motivations for investigating quasi-single field inflation are
• UV completion and fine-tuning in inflation models. To satisfy t
tion, fine-tunings or symmetries should generally be evoked. Atl
the case for models that have reasonable UV completion in string
ity [3, 4]. For slow-roll inflation, this means that, in the inflati
light fields will typically acquire mass of order the Hubble para
heavy to be the inflaton candidates. On the other hand, in a UV
tiple light fields arise naturally. Taking these facts into considera
of inflation emerges: There is one inflation direction with mass m
directions in the field space with m ∼ H. In contrast to the sl
higher order terms in the potential such as V ′′′ ∼ H and V ′′′′ ∼
these non-flat directions. To have more than one flat direction n
The above picture for inflation suggests the quasi-single field in
When Chen the & inflaton Wang trajectory (2010) tu
isocurvature perturbation is converted to curvature perturbation
ing the effect of such a conversion on density perturbations is in