31 research outputs found
Large Scale Structure Forecast Constraints on Particle Production During Inflation
Bursts of particle production during inflation provide a well-motivated
mechanism for creating bump like features in the primordial power spectrum.
Current data constrains these features to be less than about 5% the size of the
featureless primordial power spectrum at wavenumbers of about 0.1 h Mpc^{-1}.
We forecast that the Planck cosmic microwave background experiment will be able
to strengthen this constraint to the 0.5% level. We also predict that adding
data from a square kilometer array (SKA) galaxy redshift survey would improve
the constraint to about the 0.1% level. For features at larger wave-numbers,
Planck will be limited by Silk damping and foregrounds. While, SKA will be
limited by non-linear effects. We forecast for a Cosmic Inflation Probe (CIP)
galaxy redshift survey, similar constraints can be achieved up to about a
wavenumber of 1 h Mpc^{-1}.Comment: 10 pages. Matches PRD accepted versio
Asymmetric Gravitational Lenses in TeVeS and Application to the Bullet Cluster
Aims: We explore the lensing properties of asymmetric matter density
distributions in Bekenstein's Tensor-Vector-Scalar theory (TeVeS). Methods:
Using an iterative Fourier-based solver for the resulting non-linear scalar
field equation, we numerically calculate the total gravitational potential and
derive the corresponding TeVeS lensing maps. Results: Considering variations on
rather small scales, we show that the lensing properties significantly depend
on the lens's extent along the line of sight. Furthermore, all simulated TeVeS
convergence maps strongly track the dominant baryonic components, non-linear
effects, being capable of counteracting this trend, turn out to be very small.
Setting up a toy model for the cluster merger 1E0657-558, we infer that TeVeS
cannot explain observations without assuming an additional dark mass component
in both cluster centers, which is in accordance with previous work.Comment: LaTex, 14 pages, 10 figures, references added, 2 figures removed,
minor text changes to fit accepted version (A&A
Extreme Mass-Ratio Inspirals in the Effective-One-Body Approach: Quasi-Circular, Equatorial Orbits around a Spinning Black Hole
We construct effective-one-body waveform models suitable for data analysis
with LISA for extreme-mass ratio inspirals in quasi-circular, equatorial orbits
about a spinning supermassive black hole. The accuracy of our model is
established through comparisons against frequency-domain, Teukolsky-based
waveforms in the radiative approximation. The calibration of eight high-order
post-Newtonian parameters in the energy flux suffices to obtain a phase and
fractional amplitude agreement of better than 1 radian and 1 % respectively
over a period between 2 and 6 months depending on the system considered. This
agreement translates into matches higher than 97 % over a period between 4 and
9 months, depending on the system. Better agreements can be obtained if a
larger number of calibration parameters are included. Higher-order mass ratio
terms in the effective-one-body Hamiltonian and radiation-reaction introduce
phase corrections of at most 30 radians in a one year evolution. These
corrections are usually one order of magnitude larger than those introduced by
the spin of the small object in a one year evolution. These results suggest
that the effective-one-body approach for extreme mass ratio inspirals is a good
compromise between accuracy and computational price for LISA data analysis
purposes.Comment: 21 pages, 8 figures, submitted to Phys. Rev.
Statistical Characterization of Temperature Patterns in Anisotropic Cosmologies
We consider the issue of characterizing the coherent large-scale patterns
from CMB temperature maps in globally anisotropic cosmologies. The methods we
investigate are reasonably general; the particular models we test them on are
the homogeneous but anisotropic relativistic cosmologies described by the
Bianchi classification. Although the temperature variations produced in these
models are not stochastic, they give rise to a "non-Gaussian" distribution of
temperature fluctuations over the sky that is a partial diagnostic of the
model. We explore two methods for quantifying non-Gaussian and/or
non-stationary fluctuation fields in order to see how they respond to the
Bianchi models.We first investigate the behavior of phase correlations between
the spherical harmonic modes of the maps. Then we examine the behavior of the
multipole vectors of the temperature distribution which, though defined in
harmonic space, can indicate the presence of a preferred direction in real
space, i.e. on the 2-sphere. These methods give extremely clear signals of the
presence of anisotropy when applied to the models we discuss, suggesting that
they have some promise as diagnostics of the presence of global asymmetry in
the Universe.Comment: 14 pages, 10 figures, 4 tables, accepted by MNRA
Graviton Spectra in String Cosmology
We propose to uncover the signature of a stringy era in the primordial
Universe by searching for a prominent peak in the relic graviton spectrum. This
feature, which in our specific model terminates an increase and
initiates an decrease, is induced during the so far overlooked
bounce of the scale factor between the collapsing deflationary era (or pre-Big
Bang) and the expanding inflationary era (or post-Big Bang). We evaluate both
analytically and numerically the frequency and the intensity of the peak and we
show that they may likely fall in the realm of the new generation of
interferometric detectors. The existence of a peak is at variance with
ordinarily monotonic (either increasing or decreasing) graviton spectra of
canonical cosmologies; its detection would therefore offer strong support to
string cosmology.Comment: 14 pages, RevTex source and 6 figures.p
Probing the inflaton: Small-scale power spectrum constraints from measurements of the CMB energy spectrum
In the early Universe, energy stored in small-scale density perturbations is
quickly dissipated by Silk-damping, a process that inevitably generates mu- and
y-type spectral distortions of the cosmic microwave background (CMB). These
spectral distortions depend on the shape and amplitude of the primordial power
spectrum at wavenumbers k < 10^4 Mpc^{-1}. Here we study constraints on the
primordial power spectrum derived from COBE/FIRAS and forecasted for PIXIE. We
show that measurements of mu and y impose strong bounds on the integrated
small-scale power, and we demonstrate how to compute these constraints using
k-space window functions that account for the effects of thermalization and
dissipation physics. We show that COBE/FIRAS places a robust upper limit on the
amplitude of the small-scale power spectrum. This limit is about three orders
of magnitude stronger than the one derived from primordial black holes in the
same scale range. Furthermore, this limit could be improved by another three
orders of magnitude with PIXIE, potentially opening up a new window to early
Universe physics. To illustrate the power of these constraints, we consider
several generic models for the small-scale power spectrum predicted by
different inflation scenarios, including running-mass inflation models and
inflation scenarios with episodes of particle production. PIXIE could place
very tight constraints on these scenarios, potentially even ruling out
running-mass inflation models if no distortion is detected. We also show that
inflation models with sub-Planckian field excursion that generate detectable
tensor perturbations should simultaneously produce a large CMB spectral
distortion, a link that could potentially be established by PIXIE.Comment: 13 pages, 10 figures, submitted to Ap
The stochastic gravitational-wave background in the absence of horizons
Gravitational-wave astronomy has the potential to explore one of the deepest and most puzzling aspects of Einstein's theory: the existence of black holes. A plethora of ultracompact, horizonless objects have been proposed to arise in models inspired by quantum gravity. These objects may solve Hawking's information-loss paradox and the singularity problem associated with black holes, while mimicking almost all of their classical properties. They are, however, generically unstable on relatively short timescales. Here, we show that this 'ergoregion instability' leads to a strong stochastic background of gravitational waves, at a level detectable by current and future gravitational-wave detectors. The absence of such background in the first observation run of Advanced LIGO already imposes the most stringent limits to date on black-hole alternatives, showing that certain models of 'quantum-dressed' stellar black holes can be at most a small percentage of the total population. The future LISA mission will allow for similar constraints on supermassive black-hole mimickers
Complementarity of Future Dark Energy Probes
In recent years a plethora of future surveys have been suggested to constrain
the nature of dark energy. In this paper we adapt a binning approach to the
equation of state factor ``w'' and discuss how future weak lensing, galaxy
cluster counts, Supernovae and baryon acoustic oscillation surveys constrain
the equation of state at different redshifts. We analyse a few representative
future surveys, namely DES, PS1, WFMOS, PS4, EUCLID, SNAP and SKA, and perform
a principal component analysis for the ``w'' bins. We also employ a prior from
Planck cosmic microwave background measurements on the remaining cosmological
parameters. We study at which redshifts a particular survey constrains the
equation of state best and how many principal components are significantly
determined. We then point out which surveys would be sufficiently
complementary. We find that weak lensing surveys, like EUCLID, would constrain
the equation of state best and would be able to constrain of the order of three
significant modes. Baryon acoustic oscillation surveys on the other hand
provide a unique opportunity to probe the equation of state at relatively high
redshifts.Comment: 22 pages, 20 figure
Planck 2015 results. XVIII. Background geometry and topology of the Universe
Maps of cosmic microwave background (CMB) temperature and polarization from the 2015 release of Planck data provide the highestquality full-sky view of the surface of last scattering available to date. This enables us to detect possible departures from a globally isotropic cosmology. We present the first searches using CMB polarization for correlations induced by a possible non-trivial topology with a fundamental domain that intersects, or nearly intersects, the last-scattering surface (at comoving distance Ïrec), both via a direct scan for matched circular patterns at the intersections and by an optimal likelihood calculation for specific topologies. We specialize to flat spaces with cubic toroidal (T3) and slab (T1) topologies, finding that explicit searches for the latter are sensitive to other topologies with antipodal symmetry. These searches yield no detection of a compact topology with a scale below the diameter of the last-scattering surface. The limits on the radius âi of the largest sphere inscribed in the fundamental domain (at log-likelihood ratio Îlnâ > â5 relative to a simply-connected flat Planck best-fit model) are: âi > 0.97 Ïrec for the T3 cubic torus; and âi > 0.56 Ïrec for the T1 slab. The limit for the T3 cubic torus from the matched-circles search is numerically equivalent, âi > 0.97 Ïrec at 99% confidence level from polarization data alone. We also perform a Bayesian search for an anisotropic global Bianchi VIIh geometry. In the non-physical setting, where the Bianchi cosmology is decoupled from the standard cosmology, Planck temperature data favour the inclusion of a Bianchi component with a Bayes factor of at least 2.3 units of log-evidence. However, the cosmological parameters that generate this pattern are in strong disagreement with those found from CMB anisotropy data alone. Fitting the induced polarization pattern for this model to the Planck data requires an amplitude of â0.10 ± 0.04 compared to the value of + 1 if the model were to be correct. In the physically motivated setting, where the Bianchi parameters are coupled and fitted simultaneously with the standard cosmological parameters, we find no evidence for a Bianchi VIIh cosmology and constrain the vorticity of such models to (Ï/H)0 < 7.6 Ă 10-10 (95% CL)