102 research outputs found
Multi-field open inflation model and multi-field dynamics in tunneling
We consider a multi-field open inflation model, in which one of the fields
dominates quantum tunneling from a false vacuum while the other field governs
slow-roll inflation within the bubble nucleated from false vacuum decay. We
call the former the tunneling field and the latter the inflaton field. In the
limit of a negligible interaction between the two fields, the false vacuum
decay is described by a Coleman-De Luccia instanton. Here we take into account
the coupling between the two fields and construct explicitly a multi-field
instanton for a simple quartic potential model. We also solve the evolution of
the scalar fields within the bubble. We find our model realizes open inflation
successfully. This is the first concrete, viable model of open inflation
realized with a simple potential. We then study the effect of the multi-field
dynamics on the false vacuum decay, specifically on the tunneling rate. We find
the tunneling rate increases in general in comparison with the single field
case, though the increase is small unless the inflaton affects the instanton
solution substantially.Comment: 13 pages, 4 figure
Enhanced local-type inflationary trispectrum from a non-vacuum initial state
We compute the primordial trispectrum for curvature perturbations produced
during cosmic inflation in models with standard kinetic terms, when the initial
quantum state is not necessarily the vacuum state. The presence of initial
perturbations enhances the trispectrum amplitude for configuration in which one
of the momenta, say , is much smaller than the others, . For those squeezed configurations the trispectrum acquires the
so-called local form, with a scale dependent amplitude that can get values of
order . This amplitude can be larger than the
prediction of the so-called Maldacena consistency relation by a factor ,
and can reach the sensitivity of forthcoming observations, even for
single-field inflationary models.Comment: 11 pages, 1 figure. References added, typos corrected, minor change
Effects of Nonlinear Dispersion Relations on Non-Gaussianities
We investigate the effect of non-linear dispersion relations on the
bispectrum. In particular, we study the case were the modified relations do not
violate the WKB condition at early times, focusing on a particular example
which is exactly solvable: the Jacobson-Corley dispersion relation with quartic
correction with positive coefficient to the squared linear relation. We find
that the corrections to the standard result for the bispectrum are suppressed
by a factor where is the scale where the modification
to the dispersion relation becomes relevant. The modification is {\it mildly}
configuration-dependent and equilateral configurations are more suppressed with
respect to the local ones, by a factor of one percent. There is no
configuration leading to enhancements. We then analyze the results in the
framework of particle creation using the approximate gluing method of
Brandenberger and Martin, which relates more directly to the modeling of the
trans-Planckian physics via modifications of the vacuum at a certain cutoff
scale. We show that the gluing method overestimates the leading order
correction to the spectrum and bispectrum by one and two orders, respectively,
in . We discuss the various approximation and conclude that for
dispersion relations not violating WKB at early times the particle creation is
small and does not lead to enhanced contributions to the bispectrum. We also
show that in many cases enhancements do not occur when modeling the
trans-Planckian physics via modifications of the vacuum at a certain cutoff
scale. Most notably they are only of order O(1) when the Bogolyubov
coefficients accounting for particle creation are determined by the Wronskian
condition and the minimization of the uncertainty between the field and its
conjugate momentum.Comment: v1: 11 pages, 2 figures; v2: references update
Holographic Non-Gaussianity
We investigate the non-Gaussianity of primordial cosmological perturbations
within our recently proposed holographic description of inflationary universes.
We derive a holographic formula that determines the bispectrum of cosmological
curvature perturbations in terms of correlation functions of a holographically
dual three-dimensional non-gravitational quantum field theory (QFT). This
allows us to compute the primordial bispectrum for a universe which started in
a non-geometric holographic phase, using perturbative QFT calculations.
Strikingly, for a class of models specified by a three-dimensional
super-renormalisable QFT, the primordial bispectrum is of exactly the
factorisable equilateral form with f_nl^eq=5/36, irrespective of the details of
the dual QFT. A by-product of this investigation is a holographic formula for
the three-point function of the trace of the stress-energy tensor along general
holographic RG flows, which should have applications outside the remit of this
work.Comment: 42 pages, 2 figs, published versio
Large non-Gaussian Halo Bias from Single Field Inflation
We calculate Large Scale Structure observables for non-Gaussianity arising
from non-Bunch-Davies initial states in single field inflation. These scenarios
can have substantial primordial non-Gaussianity from squeezed (but observable)
momentum configurations. They generate a term in the halo bias that may be more
strongly scale-dependent than the contribution from the local ansatz. We also
discuss theoretical considerations required to generate an observable
signature.Comment: 30 pages, 14 figures, typos corrected and minor changes to match
published version JCAP09(2012)00
Galilean symmetry in the effective theory of inflation: new shapes of non-Gaussianity
We study the consequences of imposing an approximate Galilean symmetry on the
Effective Theory of Inflation, the theory of small perturbations around the
inflationary background. This approach allows us to study the effect of
operators with two derivatives on each field, which can be the leading
interactions due to non-renormalization properties of the Galilean Lagrangian.
In this case cubic non-Gaussianities are given by three independent operators,
containing up to six derivatives, two with a shape close to equilateral and one
peaking on flattened isosceles triangles. The four-point function is larger
than in models with small speed of sound and potentially observable with the
Planck satellite.Comment: 23 pages, 6 figures. v2: minor changes to match JCAP published
versio
Phenomenology of a Pseudo-Scalar Inflaton: Naturally Large Nongaussianity
Many controlled realizations of chaotic inflation employ pseudo-scalar
axions. Pseudo-scalars \phi are naturally coupled to gauge fields through c
\phi F \tilde{F}. In the presence of this coupling, gauge field quanta are
copiously produced by the rolling inflaton. The produced gauge quanta, in turn,
source inflaton fluctuations via inverse decay. These new cosmological
perturbations add incoherently with the "vacuum" perturbations, and are highly
nongaussian. This provides a natural mechanism to generate large nongaussianity
in single or multi field slow-roll inflation. The resulting phenomenological
signatures are highly distinctive: large nongaussianity of (nearly) equilateral
shape, in addition to detectably large values of both the scalar spectral tilt
and tensor-to-scalar ratio (both being typical of large field inflation). The
WMAP bound on nongaussianity implies that the coupling, c, of the pseudo-scalar
inflaton to any gauge field must be smaller than about 10^{2} M_p^{-1}.Comment: 45 pages, 7 figure
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