99 research outputs found
In search of an observational quantum signature of the primordial perturbations in slow-roll and ultra slow-roll inflation
In the standard inflationary paradigm, cosmological density perturbations are
generated as quantum fluctuations in the early Universe, but then undergo a
quantum-to-classical transition. A key role in this transition is played by
squeezing of the quantum state, which is a result of the strong suppression of
the decaying mode component of the perturbations. Motivated by ever improving
measurements of the cosmological perturbations, we ask whether there are
scenarios where this decaying mode is nevertheless still observable in the late
Universe, ideally leading to a ``smoking gun'' signature of the quantum nature
of the perturbations. We address this question by evolving the quantum state of
the perturbations from inflation into the post-inflationary Universe. After
recovering the standard result that in slow-roll (SR) inflation the decaying
mode is indeed hopelessly suppressed by the time the perturbations are observed
(by orders of magnitude), we turn to ultra slow-roll (USR)
inflation, a scenario in which the usual decaying mode actually grows on
super-horizon scales. Despite this drastic difference in the behavior of the
mode functions, we find also in USR that the late-Universe decaying mode
amplitude is dramatically suppressed, in fact by the same orders of
magnitude. We finally explain that this large suppression is a general result
that holds beyond the SR and USR scenarios considered and follows from a
modified version of Heisenberg's uncertainty principle and the observed
amplitude of the primordial power spectrum. The classical behavior of the
perturbations is thus closely related to the classical behavior of macroscopic
objects drawing an analogy with the position of a massive particle, the
curvature perturbations today have an enormous effective mass of order , making them highly classical.Comment: 27 pages, 7 figures. Comments welcom
To Bin or Not To Bin: Decorrelating the Cosmic Equation of State
The physics behind the acceleration of the cosmic expansion can be elucidated
through comparison of the predictions of dark energy equations of state to
observational data. In seeking to optimize this, we investigate the advantages
and disadvantages of using principal component analysis, uncorrelated
bandpowers, and the equation of state within redshift bins. We demonstrate that
no one technique is a panacea, with tension between clear physical
interpretation from localization and from decorrelated errors, as well as model
dependence and form dependence. Specific lessons include the critical role of
proper treatment of the high redshift expansion history and the lack of a
unique, well defined signal-to-noise or figure of merit.Comment: 26 pages, 28 figure
Calibrating Dark Energy
Exploring the diversity of dark energy dynamics, we discover a calibration
relation, a uniform stretching of the amplitude of the equation of state time
variation with scale factor. This defines homogeneous families of dark energy
physics. The calibration factor has a close relation to the standard time
variation parameter w_a, and we show that the new, calibrated w_a describes
observables, i.e. distance and Hubble parameter as a function of redshift,
typically to an accuracy level of 10^{-3}. We discuss implications for figures
of merit for dark energy science programs.Comment: 9 pages, 10 figure
Primordial physics from large-scale structure beyond the power spectrum
We study constraints on primordial mode-coupling from the power spectrum,
squeezed-limit bispectrum and collapsed trispectrum of matter and halos. We
describe these statistics in terms of long-wavelength -point functions
involving the matter/halo density and position-dependent power spectrum. This
allows us to derive simple, analytic expression for the information content,
treating constraints from scale-dependent bias in the halo power spectrum on
the same footing as those from higher order statistics. In particular, we
include non-Gaussian covariance due to long-short mode-coupling from non-linear
evolution, which manifests itself as long-mode cosmic variance in the
position-dependent power spectrum. We find that bispectrum forecasts that
ignore this cosmic variance may underestimate by up to a
factor for the matter density (at ) and commonly a factor for the halo bispectrum. Constraints from the bispectrum can be improved by
combining it with the power spectrum and trispectrum. The reason is that, in
the position-dependent power spectrum picture, the bispectrum and trispectrum
intrinsically incorporate multitracer cosmic variance cancellation, which is
optimized in a joint analysis. For halo statistics, we discuss the roles of
scale-dependent bias, matter mode-coupling, and non-linear, non-Gaussian
biasing (). While scale-dependent bias in the halo power spectrum
is already very constraining, higher order halo statistics are competitive in
the regime where stochastic noise in the position-dependent halo power spectrum
is low enough for cosmic variance cancellation to be effective, i.e.~for large
halo number density and large . This motivates exploring this
regime observationally.Comment: 48 pages, 20 figures. Comments welcom
CMB Lensing Constraints on Neutrinos and Dark Energy
Signatures of lensing of the cosmic microwave background radiation by
gravitational potentials along the line of sight carry with them information on
the matter distribution, neutrino masses, and dark energy properties. We
examine the constraints that Planck, PolarBear, and CMBpol future data,
including from the B-mode polarization or the lensing potential, will be able
to place on these quantities. We simultaneously fit for neutrino mass and dark
energy equation of state including time variation and early dark energy
density, and compare the use of polarization power spectra with an optimal
quadratic estimator of the lensing. Results are given as a function of
systematics level from residual foreground contamination. A realistic CMBpol
experiment can effectively constrain the sum of neutrino masses to within 0.05
eV and the fraction of early dark energy to 0.002. We also present a
surprisingly simple prescription for calculating dark energy equation of state
constraints in combination with supernova distances from JDEM.Comment: 18 pages, 14 figures. Small changes made to match version to be
published in Phys. Rev.
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