2 research outputs found
Non-gaussianity from the bispectrum in general multiple field inflation
We study the non-gaussianity from the bispectrum in multi-field inflation
models with a general kinetic term. The models include the multi-field
K-inflation and the multi-field Dirac-Born-Infeld (DBI) inflation as special
cases. We find that, in general, the sound speeds for the adiabatic and entropy
perturbations are different and they can be smaller than 1. Then the
non-gaussianity can be enhanced. The multi-field DBI-inflation is shown to be a
special case where both sound speeds are the same due to a special form of the
kinetic term. We derive the exact second and third order actions including
metric perturbations. In the small sound speed limit and at leading order in
the slow-roll expansion, we derive the three point function for the curvature
perturbation which depends on both adiabatic and entropy perturbations. The
contribution from the entropy perturbations has a different momentum dependence
if the sound speed for the entropy perturbations is different from the
adiabatic one, which provides a possibility to distinguish the multi-field
models from single field models. On the other hand, in the multi-field DBI
case, the contribution from the entropy perturbations has the same momentum
dependence as the pure adiabatic contributions and it only changes the
amplitude of the three point function. This could help to ease the constraints
on the DBI-inflation models.Comment: 16 pages, no figur
On the Issue of the \zeta Series Convergence and Loop Corrections in the Generation of Observable Primordial Non-Gaussianity in Slow-Roll Inflation. Part I: the Bispectrum
We show in this paper that it is possible to attain very high, {\it including
observable}, values for the level of non-gaussianity f_{NL} associated with the
bispectrum B_\zeta of the primordial curvature perturbation \zeta, in a
subclass of small-field {\it slow-roll} models of inflation with canonical
kinetic terms. Such a result is obtained by taking care of loop corrections
both in the spectrum P_\zeta and the bispectrum B_\zeta. Sizeable values for
f_{NL} arise even if \zeta is generated during inflation. Five issues are
considered when constraining the available parameter space: 1. we must ensure
that we are in a perturbative regime so that the \zeta series expansion, and
its truncation, are valid. 2. we must apply the correct condition for the
(possible) loop dominance in B_\zeta and/or P_\zeta. 3. we must satisfy the
spectrum normalisation condition. 4. we must satisfy the spectral tilt
constraint. 5. we must have enough inflation to solve the horizon problem.Comment: LaTeX file, 40 pages, 6 figures, Main body: 26 pages, Appendix: 8
pages, References: 6 pages. v2: minor grammatical changes, references added
and updated, a few changes reflecting the fact that = 0, conclusions
unchanged. Version accepted for publication in Journal of Cosmology and
Astroparticle Physic