750 research outputs found
Influence of heavy modes on perturbations in multiple field inflation
We investigate linear cosmological perturbations in multiple field
inflationary models where some of the directions are light while others are
heavy (with respect to the Hubble parameter). By integrating out the massive
degrees of freedom, we determine the multi-dimensional effective theory for the
light degrees of freedom and give explicitly the propagation matrix that
replaces the effective sound speed of the one-dimensional case. We then examine
in detail the consequences of a sudden turn along the inflationary trajectory,
in particular the possible breakdown of the low energy effective theory in case
the heavy modes are excited. Resorting to a new basis in field space, instead
of the usual adiabatic/entropic basis, we study the evolution of the
perturbations during the turn. In particular, we compute the power spectrum and
compare with the result obtained from the low energy effective theory.Comment: 24 pages, 13 figures; v2 substantial changes in sec.V; v3 matching
the published version on JCA
A general proof of the equivalence between the \delta N and covariant formalisms
Recently, the equivalence between the \delta N and covariant formalisms has
been shown (Suyama et al. 2012), but they essentially assumed Einstein gravity
in their proof. They showed that the evolution equation of the curvature
covector in the covariant formalism on uniform energy density slicings
coincides with that of the curvature perturbation in the \delta N formalism
assuming the coincidence of uniform energy and uniform expansion (Hubble)
slicings, which is the case on superhorizon scales in Einstein gravity. In this
short note, we explicitly show the equivalence between the \delta N and
covariant formalisms without specifying the slicing condition and the
associated slicing coincidence, in other words, regardless of the gravity
theory.Comment: 7 pages,a reference added, to be published in EP
P33. Design and evaluation of an Escherichia coli biomarker for indication of pH
Measuring pH is one of the most commonly used techniques in both the laboratory as well as the field due to its importance in a multitude of biochemical processes. Traditional methods of measuring pH may be highly developed in accuracy and precision but often involve disruption of the environment. Biological markers offer an alternative that allows for long-term pH monitoring. This innovative approach allows for vast applications such as in the manufacturing, food processing and research industries. Under moderate acidic conditions, the asr (acid shock RNA) gene is highly inducible and has been demonstrated to be crucial for growth at high acidities. The alx locus in E. coli contains a putative transporter preceded by a pH-induced riboregulator that operates under moderately alkaline conditions. In this study, vivid blue/purple and green/blue chromoproteins, cJBlue and amilCP respectively, were used as visual indicators. DH5α competent E. coli cells were transformed with recombinant plasmids containing either amilCP downstream the asr promoter or cjBlue downstream the alx promoter and 5’UTR, giving rise to the alx-cjBlue and asr-amilCP cell lines. Through this methodology, we were able to create strains of E. coli that expressed either a blue or blue-green chromoprotein under low or high pHs respectively
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
Non-Gaussianity from Lifshitz Scalar
A Lifshitz scalar with the dynamical critical exponent z = 3 obtains
scale-invariant, super-horizon field fluctuations without the need of an
inflationary era. Since this mechanism is due to the special scaling of the
Lifshitz scalar and persists in the presence of unsuppressed self-couplings,
the resulting fluctuation spectrum can deviate from a Gaussian distribution. We
study the non-Gaussian nature of the Lifshitz scalar's intrinsic field
fluctuations, and show that primordial curvature perturbations sourced from
such field fluctuations can have large non-Gaussianity of order f_NL = O(100),
which will be detected by upcoming CMB observations. We compute the bispectrum
and trispectrum of the fluctuations, and discuss their configurations in
momentum space. In particular, the bispectrum is found to take various shapes,
including the local, equilateral, and orthogonal shapes. Intriguingly, all
integrals in the in-in formalism can be performed analytically.Comment: 17 pages, 15 figures, v2: published in JCA
A Statistical Approach to Multifield Inflation: Many-field Perturbations Beyond Slow Roll
We study multifield contributions to the scalar power spectrum in an ensemble
of six-field inflationary models obtained in string theory. We identify
examples in which inflation occurs by chance, near an approximate inflection
point, and we compute the primordial perturbations numerically, both exactly
and using an array of truncated models. The scalar mass spectrum and the number
of fluctuating fields are accurately described by a simple random matrix model.
During the approach to the inflection point, bending trajectories and
violations of slow roll are commonplace, and 'many-field' effects, in which
three or more fields influence the perturbations, are often important. However,
in a large fraction of models consistent with constraints on the tilt the
signatures of multifield evolution occur on unobservably large scales. Our
scenario is a concrete microphysical realization of quasi-single-field
inflation, with scalar masses of order , but the cubic and quartic couplings
are typically too small to produce detectable non-Gaussianity. We argue that
our results are characteristic of a broader class of models arising from
multifield potentials that are natural in the Wilsonian sense.Comment: 39 pages, 17 figures. References added. Matches version published in
JCA
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
Trispectrum from Ghost Inflation
Ghost inflation predicts almost scale-invariant primordial cosmological
perturbations with relatively large non-Gaussianity. The bispectrum is known to
have a large contribution at the wavenumbers forming an equilateral triangle
and the corresponding nonlinear parameter is typically of
order . In this paper we calculate trispectrum from ghost inflation
and show that the corresponding nonlinear parameter is typically of
order . We investigate the shape dependence of the trispectrum and see
that it has some features different from DBI inflation. Therefore, our result
may be useful as a template to distinguish ghost inflation from other models of
inflation by future experiments.Comment: 25 pages, 10 figure
Non-Gaussianity from false vacuum inflation: Old curvaton scenario
We calculate the three-point correlation function of the comoving curvature
perturbation generated during an inflationary epoch driven by false vacuum
energy. We get a novel false vacuum shape bispectrum, which peaks in the
equilateral limit. Using this result, we propose a scenario which we call "old
curvaton". The shape of the resulting bispectrum lies between the local and the
false vacuum shapes. In addition we have a large running of the spectral index.Comment: 13 pages, 3 figures; v2 with minor revison; v3 final version to
appear on JCA
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