1,970 research outputs found
Multifield Reheating after Modular -Inflation
In the inflationary framework of cosmology the initial phase of rapid
expansion has to be followed by a reheating stage, which is envisioned to end
in a radiation dominated big bang. Key parameters that characterize this big
bang state are the temperature at the end of the reheating stage and the baryon
asymmetry. For general interacting theories these parameters are difficult to
obtain analytically because of the involved structure of the potential. In this
paper multifield reheating is considered for interacting theories in which the
inflaton trajectory is weakly curved. This scenario is realized in the model of
-inflation, a particular example of modular inflation, allowing an estimate
of the reheat temperature.Comment: 15 pages, improved approximation, added reference
Single-Field Inflation and the Local Ansatz: Distinguishability and Consistency
The single-field consistency conditions and the local ansatz have played
separate but important roles in characterizing the non-Gaussian signatures of
single- and multifield inflation respectively. We explore the precise
relationship between these two approaches and their predictions. We demonstrate
that the predictions of the single-field consistency conditions can never be
satisfied by a general local ansatz with deviations necessarily arising at
order . This implies that there is, in principle, a minimum
difference between single- and (fully local) multifield inflation in
observables sensitive to the squeezed limit such as scale-dependent halo bias.
We also explore some potential observational implications of the consistency
conditions and its relationship to the local ansatz. In particular, we propose
a new scheme to test the consistency relations. In analogy with delensing of
the cosmic microwave background, one can deproject the coupling of the long
wavelength modes with the short wavelength modes and test for residual
anomalous coupling.Comment: 17 page
Modular Inflation Observables and -Inflation Phenomenology
Modular inflation is the restriction to two fields of automorphic inflation,
a general group based framework for multifield scalar field theories with
curved target spaces, which can be parametrized by the comoving curvature
perturbation and the isocurvature perturbation tensor . This
paper describes the dynamics and observables of these perturbations and
considers in some detail the special case of modular inflation as an extensive
class of two-field inflation theories with a conformally flat target space. It
is shown that the nonmodular nature of derivatives of modular forms leads to
CMB observables in modular invariant inflation theories that are in general
constructed from almost holomorphic modular forms. The phenomenology of the
model of -inflation is compared to the recent observational constraints from
the Planck satellite and the BICEP2/Keck Array data.Comment: 39 pages, 3 figures. This extended version includes a detailed
discussion of the almost holomorphic nature of the physical observables in
modular invariant inflation theorie
The Strong Multifield Slowroll Condition and Spiral Inflation
We point out the existing confusions about the slowroll parameters and
conditions for multifield inflation. If one requires the fields to roll down
the gradient flow, we find that only articles adopting the Hubble slowroll
expansion are on the right track, and a correct condition can be found in a
recent book by Liddle and Lyth. We further analyze this condition and show that
the gradient flow requirement is stronger than just asking for a slowly
changing, quasi-de Sitter solution. Therefore it is possible to have a
multifield slowroll model that does not follow the gradient flow. Consequently,
it no longer requires the gradient to be small. It even bypasses the first
slowroll condition and some related no-go theorems from string theory. We
provide the "spiral inflation" as a generic blueprint of such inflation model
and show that it relies on a monodromy locus---a common structure in string
theory effective potentials.Comment: 12 pages, version 4, cosmetic changes recommended by referee,
resubmitting to PR
Testing Multi-Field Inflation: A Geometric Approach
We develop an approach for linking the power spectra, bispectrum, and
trispectrum to the geometric and kinematical features of multifield
inflationary Lagrangians. Our geometric approach can also be useful in
determining when a complicated multifield model can be well approximated by a
model with one, two, or a handful of fields. To arrive at these results, we
focus on the mode interactions in the kinematical basis, starting with the case
of no sourcing and showing that there is a series of mode conservation laws
analogous to the conservation law for the adiabatic mode in single-field
inflation. We then treat the special case of a quadratic potential with
canonical kinetic terms, showing that it produces a series of mode sourcing
relations identical in form to that for the adiabatic mode. We build on this
result to show that the mode sourcing relations for general multifield
inflation are extension of this special case but contain higher-order covariant
derivatives of the potential and corrections from the field metric. In
parallel, we show how these interactions depend on the geometry of the
inflationary Lagrangian and on the kinematics of the associated field
trajectory. Finally, we consider how the mode interactions and effective number
of fields active during inflation are reflected in the spectra and introduce a
multifield consistency relation, as well as a multifield observable that can
potentially distinguish two-field scenarios from scenarios involving three or
more effective fields.Comment: 21 pages, 4 figures + tables. Revised to clarify several points and
reorganized Section III for pedagogical reasons. Error in one equation and
typos were corrected, as well as additional references adde
Multifield DBI Inflation and Non-Gaussianities
We analyze the trajectories for multifield DBI inflation, which can arise in
brane inflation models, and show that the trajectories are the same as in
typical slow roll inflation. We calculate the power spectrum and find that the
higher derivative terms of the DBI action lead to a suppression of the
contribution from the isocurvature perturbations. We also calculate the
bispectrum generated by the isocurvature perturbation, and find that it leads
to distinctive features.Comment: 7 pages, 4 figures; v2. references added; v3. typos corrected,
matches published versio
Combined local and equilateral non-Gaussianities from multifield DBI inflation
We study multifield aspects of Dirac-Born-Infeld (DBI) inflation. More
specifically, we consider an inflationary phase driven by the radial motion of
a D-brane in a conical throat and determine how the D-brane fluctuations in the
angular directions can be converted into curvature perturbations when the
tachyonic instability arises at the end of inflation. The simultaneous presence
of multiple fields and non-standard kinetic terms gives both local and
equilateral shapes for non-Gaussianities in the bispectrum. We also study the
trispectrum, pointing out that it acquires a particular momentum dependent
component whose amplitude is given by . We show that
this relation is valid in every multifield DBI model, in particular for any
brane trajectory, and thus constitutes an interesting observational signature
of such scenarios.Comment: 38 pages, 11 figures. Typos corrected; references added. This version
matches the one in press by JCA
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