327 research outputs found
Strongly Scale-dependent Non-Gaussianity
We discuss models of primordial density perturbations where the
non-Gaussianity is strongly scale-dependent. In particular, the non-Gaussianity
may have a sharp cut-off and be very suppressed on large cosmological scales,
but sizeable on small scales. This may have an impact on probes of
non-Gaussianity in the large-scale structure and in the cosmic microwave
background radiation anisotropies.Comment: 4 page
On the one loop corrections to inflation and the CMB anisotropies
We investigate the one loop effective potential of inflation in a standard model of chaotic inflation. The leading one loop corrections to the effective inflaton potential are evaluated in the quasi de Sitter background, and we estimate the one loop correction to the two-point function of the inflaton perturbations in the Hartree approximation. In this approximation, the one loop corrections depends on the total number of e-foldings of inflation and the maximal effect is estimated to be a correction to the power spectrum of a few percent. However, such a correction may be difficult to disentangle from the background in the simplest scenario
The Matrix Reloaded - on the Dark Energy Seesaw
We propose a novel mechanism for dark energy, based on an extended seesaw for scalar fields, which does not require any new physics at energies below the TeV scale. A very light quintessence mass is usually considered to be technically unnatural, unless it is protected by some symmetry broken at the new very light scale. We propose that one can use an extended seesaw mechanism to construct technically natural models for very light fields, protected by SUSY softly broken above a TeV
de Sitter limit of inflation and nonlinear perturbation theory
We study the fourth order action of the comoving curvature perturbation in an
inflationary universe in order to understand more systematically the de Sitter
limit in nonlinear cosmological perturbation theory. We derive the action of
the curvature perturbation to fourth order in the comoving gauge, and show that
it vanishes sufficiently fast in the de Sitter limit. By studying the de Sitter
limit, we then extrapolate to the n'th order action of the comoving curvature
perturbation and discuss the slow-roll order of the n-point correlation
function.Comment: 14 pages, 1 figure; typos corrected and discussion of tensor modes
adde
Cosmological diagrammatic rules
A simple set of diagrammatic rules is formulated for perturbative evaluation
of ``in-in" correlators, as is needed in cosmology and other nonequilibrium
problems. These rules are both intuitive, and efficient for calculational
purposes.Comment: 7 pages, 3 figure
Nonlocality vs. complementarity: a conservative approach to the information problem
A proposal for resolution of the information paradox is that "nice slice"
states, which have been viewed as providing a sharp argument for information
loss, do not in fact do so as they do not give a fully accurate description of
the quantum state of a black hole. This however leaves an information
*problem*, which is to provide a consistent description of how information
escapes when a black hole evaporates. While a rather extreme form of
nonlocality has been advocated in the form of complementarity, this paper
argues that is not necessary, and more modest nonlocality could solve the
information problem. One possible distinguishing characteristic of scenarios is
the information retention time. The question of whether such nonlocality
implies acausality, and particularly inconsistency, is briefly addressed. The
need for such nonlocality, and its apparent tension with our empirical
observations of local quantum field theory, may be a critical missing piece in
understanding the principles of quantum gravity.Comment: 11 pages of text and figures, + references. v2 minor text. v3 small
revisions to match final journal versio
On the divergences of inflationary superhorizon perturbations
We discuss the infrared divergences that appear to plague cosmological
perturbation theory. We show that within the stochastic framework they are
regulated by eternal inflation so that the theory predicts finite fluctuations.
Using the formalism to one loop, we demonstrate that the infrared
modes can be absorbed into additive constants and the coefficients of the
diagrammatic expansion for the connected parts of two and three-point functions
of the curvature perturbation. As a result, the use of any infrared cutoff
below the scale of eternal inflation is permitted, provided that the background
fields are appropriately redefined. The natural choice for the infrared cutoff
would of course be the present horizon; other choices manifest themselves in
the running of the correlators. We also demonstrate that it is possible to
define observables that are renormalization group invariant. As an example, we
derive a non-perturbative, infrared finite and renormalization point
independent relation between the two-point correlators of the curvature
perturbation for the case of the free single field.Comment: 12 page
Enhancing the tensor-to-scalar ratio in simple inflation
We show that in theories with a nontrivial kinetic term the contribution of
the gravitational waves to the CMB fluctuations can be substantially larger
than that is naively expected in simple inflationary models. This increase of
the tensor-to-scalar perturbation ratio leads to a larger B-component of the
CMB polarization, thus making the prospects for future detection much more
promising. The other important consequence of the considered model is a higher
energy scale of inflation and hence higher reheating temperature compared to a
simple inflation.Comment: 9 pages, 1 figure and references are added, discussion is slightly
extended, published versio
MSSM curvaton in the gauge-mediated SUSY breaking
We study the curvaton scenario using the MSSM flat directions in the
gauge-mediated SUSY breaking model. We find that the fluctuations in the both
radial and phase directions can be responsible for the density perturbations in
the universe through the curvaton mechanism. Although it has been considered
difficult to have a successful curvaton scenario with the use of those flat
directions, it is overcome by taking account of the finite temperature effects,
which induce a negative thermal logarithmic term in the effective potential of
the flat direction.Comment: 12 page
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