44 research outputs found
Three-form inflation and non-Gaussianity
We calculate the perturbed action, at second and third order, for a massive
three-form field minimally coupled to gravity, and use it to explore the
observational predictions of three-form inflation. One intriguing result is
that the value of the spectral index is nearly independent of the three-form
potential, being fixed solely by the number of e-folds of inflation, with
n_s=0.97 for the canonical number of 60. Considering the bispectrum, we employ
standard techniques to give explicit results for two models, one of which
produces a large non-Gaussianity. Finally, we confirm our results by employing
a duality relating the three-form theory to a non-canonical scalar field theory
and explicitly re-computing results in this dual picture.Comment: 23 pages, 6 figures. Typos corrected and addition of one appendix.
Accepted in JCA
Exploring Two-Field Inflation in the Wess-Zumino Model
We explore inflation via the effective potential of the minimal Wess-Zumino
model, considering both the real and imaginary components of the complex field.
Using transport techniques, we calculate the full allowed range of ,
and for different choices of the single free parameter, , and
present the probability distribution of these signatures given a simple choice
for the prior distribution of initial conditions. Our work provides a case
study of multi-field inflation in a simple but realistic setting, with
important lessons that are likely to apply more generally. For example, we find
that there are initial conditions consistent with observations of and
for values of that would be excluded if only evolutions in the real field
direction were to be considered, and that these may yield enhanced values of
. Moreover, we find that initial conditions fixed at high energy
density, where the potential is close to quartic in form, can still lead to
evolutions in a concave region of the potential during the observable number of
e-folds, as preferred by present data. The Wess-Zumino model therefore provides
an illustration that multi-field dynamics must be taken into account when
seeking to understand fully the phenomenology of such models of inflation.Comment: 19 pages, 6 figure
Multi-field inflation with large scalar fluctuations: non-Gaussianity and perturbativity
Recently multi-field inflation models that can produce large scalar
fluctuations on small scales have drawn a lot of attention, primarily because
they could lead to primordial black hole production and generation of large
second-order gravitational waves. In this work, we focus on models where the
scalar fields responsible for inflation live on a hyperbolic field space. In
this case, geometrical destabilisation and non-geodesic motion are responsible
for the peak in the scalar power spectrum. We present new results for scalar
non-Gaussianity and discuss its dependence on the model's parameters. On scales
around the peak, we typically find that the non-Gaussianity is large and close
to local in form. We validate our results by employing two different numerical
techniques, utilising the transport approach, based on full cosmological
perturbation theory, and the formalism, based on the separate
universe approximation. We discuss implications of our results for the
perturbativity of the underlying theory, focusing in particular on versions of
these models with potentially relevant phenomenology at interferometer scales.Comment: version accepted for publication in JCA
Moment transport equations for non-Gaussianity
We present a novel method for calculating the primordial non-Gaussianity
produced by super-horizon evolution during inflation. Our method evolves the
distribution of coarse-grained inflationary field values using a transport
equation. We present simple evolution equations for the moments of this
distribution, such as the variance and skewness. This method possesses some
advantages over existing techniques. Among them, it cleanly separates multiple
sources of primordial non-Gaussianity, and is computationally efficient when
compared with popular alternatives, such as the "delta N" framework. We adduce
numerical calculations demonstrating that our new method offers good agreement
with those already in the literature. We focus on two fields and the fNL
parameter, but we expect our method will generalize to multiple scalar fields
and to moments of arbitrarily high order. We present our expressions in a
field-space covariant form which we postulate to be valid for any number of
fields.Comment: 24 pages, 4 colour figures; uses iopart.cls. v2: Erroneous statements
about delta N method in Sec. 2 removed. Correction to gauge transformation in
Eq. (12) brings numerical results of Sec. 4 into better agreement with the
delta N formula. Conclusions remain the same. v3: minor change