21,787 research outputs found
An Observational Test of Two-field Inflation
We study adiabatic and isocurvature perturbation spectra produced by a period
of cosmological inflation driven by two scalar fields. We show that there
exists a model-independent consistency condition for all two-field models of
slow-roll inflation, despite allowing for model-dependent linear processing of
curvature and isocurvature perturbations during and after inflation on
super-horizon scales. The scale-dependence of all spectra are determined solely
in terms of slow-roll parameters during inflation and the dimensionless
cross-correlation between curvature and isocurvature perturbations. We present
additional model-dependent consistency relations that may be derived in
specific two-field models, such as the curvaton scenario.Comment: 6 pages, latex with revtex, no figures; v2, minor changes, to appear
in Physical Review
The Detectability of Departures from the Inflationary Consistency Equation
We study the detectability, given CMB polarization maps, of departures from
the inflationary consistency equation, r \equiv T/S \simeq -5 n_T, where T and
S are the tensor and scalar contributions to the quadrupole variance,
respectively. The consistency equation holds if inflation is driven by a
slowly-rolling scalar field. Departures can be caused by: 1) higher-order terms
in the expansion in slow-roll parameters, 2) quantum loop corrections or 3)
multiple fields. Higher-order corrections in the first two slow-roll parameters
are undetectably small. Loop corrections are detectable if they are nearly
maximal and r \ga 0.1. Large departures (|\Delta n_T| \ga 0.1) can be seen if r
\ga 0.001. High angular resolution can be important for detecting non-zero
r+5n_T, even when not important for detecting non-zero r.Comment: 7 pages, 4 figures, submitted to PR
Calculating the local-type fNL for slow-roll inflation with a non-vacuum initial state
Single-field slow-roll inflation with a non-vacuum initial state has an
enhanced bispectrum in the local limit. We numerically calculate the local-type
fNL signal in the CMB that would be measured for such models (including the
full transfer function and 2D projection). The nature of the result depends on
several parameters, including the occupation number N_k, the phase angle
\theta_k between the Bogoliubov parameters, and the slow-roll parameter
\epsilon. In the most conservative case, where one takes \theta_k \approx
\eta_0 k (justified by physical reasons discussed within) and \epsilon\lesssim
0.01, we find that 0 < fNL < 1.52 (\epsilon/0.01), which is likely too small to
be detected in the CMB. However, if one is willing to allow a constant value
for the phase angle \theta_k and N_k=O(1), fNL can be much larger and/or
negative (depending on the choice of \theta_k), e.g. fNL \approx 28
(\epsilon/0.01) or -6.4 (\epsilon/0.01); depending on \epsilon, these scenarios
could be detected by Planck or a future satellite. While we show that these
results are not actually a violation of the single-field consistency relation,
they do produce a value for fNL that is considerably larger than that usually
predicted from single-field inflation.Comment: 8 pages, 1 figure. v2: Version accepted for publication in PRD. Added
greatly expanded discussion of the phase angle \theta_k; this allows the
possibility of enhanced fNL, as mentioned in abstract. More explicit
comparisons with earlier wor
Parity breaking signatures from a Chern-Simons coupling during inflation: the case of non-Gaussian gravitational waves
Considering high-energy modifications of Einstein gravity during inflation is
an interesting issue. We can constrain the strength of the new gravitational
terms through observations of inflationary imprints in the actual universe. In
this paper we analyze the effects on slow-roll models due to a Chern-Simons
term coupled to the inflaton field through a generic coupling function
. A well known result is the polarization of primordial gravitational
waves (PGW) into left and right eigenstates, as a consequence of parity
breaking. In such a scenario the modifications to the power spectrum of PGW are
suppressed under the conditions that allow to avoid the production of ghost
gravitons at a certain energy scale, the so-called Chern-Simons mass .
In general it has been recently pointed out that there is very little hope to
efficiently constrain chirality of PGW on the basis solely of two-point
statistics from future CMB data, even in the most optimistic cases. Thus we
search if significant parity breaking signatures can arise at least in the
bispectrum statistics. We find that the tensor-tensor-scalar bispectra for each polarization state are the only ones that
are not suppressed. Their amplitude, setting the level of parity breaking
during inflation, is proportional to the second derivative of the coupling
function and they turn out to be maximum in the squeezed limit. We
comment on the squeezed-limit consistency relation arising in the case of
chiral gravitational waves, and on possible observables to constrain these
signatures.Comment: 31 pages, 1 figure. V3: references added; typos correcte
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