1,370 research outputs found
Future constraints on variations of the fine structure constant from combined CMB and weak lensing measurements
We forecast the ability of future CMB and galaxy lensing surveys to constrain
variations of the fine structure constant. We found that lensing data, as those
expected from satellite experiments as Euclid could improve the constraint from
future CMB experiments leading to a \Delta \alpha / \alpha = 8*10^{-4}
accuracy. A variation of the fine structure constant \alpha is strongly
degenerate with the Hubble constant H_0 and with inflationary parameters as the
scalar spectral index n_s. These degeneracies may cause significant biases in
the determination of cosmological parameters if a variation in \alpha as large
as \sim 0.5 % is present at the epoch of recombination.Comment: 6 pages, 6 figures, improved text and few typos correcte
Including birefringence into time evolution of CMB: current and future constraints
We introduce birefringence effects within the propagation history of CMB,
considering the two cases of a constant effect and of an effect that increases
linearly in time, as the rotation of polarization induced by birefringence
accumulates during photon propagation. Both cases result into a mixing of E and
B modes before lensing effects take place, thus leading to the fact that
lensing is acting on spectra that are already mixed because of birefringence.
Moreover, if the polarization rotation angle increases during propagation,
birefringence affects more the large scales that the small scales. We put
constraints on the two cases using data from WMAP 9yr and BICEP 2013 and
compare these results with the constraints obtained when the usual procedure of
rotating the final power spectra is adopted, finding that this dataset
combination is unable to distinguish between effects, but it nevertheless hints
for a non vanishing value of the polarization rotation angle. We also forecast
the sensitivity that will be obtained using data from Planck and PolarBear,
highlighting how this combination is capable to rule out a vanishing
birefringence angle, but still unable to distinguish the different scenarios.
Nevertheless, we find that the combination of Planck and PolarBear is sensitive
enough to highlight the existence of degeneracies between birefringence
rotation and gravitational lensing of CMB photons, possibly leading to false
detection of non standard lensing effects if birefringence is neglected.Comment: 20 pages, 10 figures. New version matching the one accepted by JCAP.
Corrected typos in equations 2.17-2.1
Does Quartessence Ease Tensions?
Tensions between cosmic microwave background observations and the growth of
the large-scale structure inferred from late-time probes pose a serious
challenge to the concordance CDM cosmological model. State-of-the-art
data from the Planck satellite predicts a higher rate of structure growth than
what preferred by low-redshift observables. Such tension has hitherto eluded
conclusive explanations in terms of straightforward modifications to
CDM, e.g. the inclusion of massive neutrinos or a dynamical dark
energy component. Here, we investigate models of 'quartessence' -- a single
dark component mimicking both dark matter and dark energy -- whose
non-vanishing sound speed inhibits structure growth at late times on scales
smaller than its corresponding Jeans' length. In principle, this could
reconcile high- and low-redshift observations. We put this hypothesis to test
against temperature and polarisation spectra from the latest Planck release,
SDSS DR12 measurements of baryon acoustic oscillations and redshift-space
distortions, and cosmic shear correlation functions from KiDS. This the first
time that any specific model of quartessence is applied to actual data. We show
that, if we naively apply CDM nonlinear prescription to quartessence,
the combined data sets allow for tight constraints on the model parameters.
Apparently, quartessence alleviates the tension between the total matter
fraction and late-time structure clustering, although in fact the tension is
transferred from the latter to the quartessence sound speed parameter. However,
we found that this strongly depends upon information from nonlinear scales.
Indeed, if we relax this assumption, quartessence models appear still viable.
For this reason, we argue that the nonlinear behaviour of quartessence deserves
further investigation and may lead to a deeper understanding of the physics of
the dark Universe.Comment: 8 pages, 6 figures, 1 table; matching published versio
Reconstruction of the Dark Energy equation of state from latest data: the impact of theoretical priors
We reconstruct the Equation of State of Dark Energy (EoS) from current data
using a non-parametric approach where, rather than assuming a specific time
evolution of this function, we bin it in time. We treat the transition between
the bins with two different methods, i.e. a smoothed step function and a
Gaussian Process reconstruction, investigating whether or not the two
approaches lead to compatible results. Additionally, we include in the
reconstruction procedure a correlation between the values of the EoS at
different times in the form of a theoretical prior that takes into account a
set of viability and stability requirements that one can impose on models
alternative to CDM. In such case, we necessarily specialize to broad,
but specific classes of alternative models, i.e. Quintessence and Horndeski
gravity. We use data coming from CMB, Supernovae and BAO surveys. We find an
overall agreement between the different reconstruction methods used; with both
approaches, we find a time dependence of the mean of the reconstruction, with
different trends depending on the class of model studied. The constant EoS
predicted by the CDM model falls anyway within the bounds of
our analysis.Comment: 17 pages, 5 figures. Prepared for submission to JCA
Constraints on cosmological parameters from future cosmic microwave background experiments
The Planck satellite experiment will soon let cosmologists to determine most of the cosmological parameters with unprecedented accuracy. In particular a strong improvement is expected in many parameters of interest, including neutrino mass, the amount of relativistic particles at recombination, the primordial Helium abundance and the injection of extra ionizing photon by dark matter self-annihilation. Here we review the constraints achievable by future experiments and discuss the implications for fundamental physics. © 2010 IOP Publishing Ltd
E-ELT constraints on runaway dilaton scenarios
We use a combination of simulated cosmological probes and astrophysical tests
of the stability of the fine-structure constant , as expected from the
forthcoming European Extremely Large Telescope (E-ELT), to constrain the class
of string-inspired runaway dilaton models of Damour, Piazza and Veneziano. We
consider three different scenarios for the dark sector couplings in the model
and discuss the observational differences between them. We improve previously
existing analyses investigating in detail the degeneracies between the
parameters ruling the coupling of the dilaton field to the other components of
the universe, and studying how the constraints on these parameters change for
different fiducial cosmologies. We find that if the couplings are small (e.g.,
) these degeneracies strongly affect the constraining
power of future data, while if they are sufficiently large (e.g.,
, as in agreement with current
constraints) the degeneracies can be partially broken. We show that E-ELT will
be able to probe some of this additional parameter space.Comment: 16 pages, 8 figures. Updated version matching the one accepted by
JCA
Latest evidence for a late time vacuum -- geodesic CDM interaction
We perform a reconstruction of the coupling function between vacuum energy
and geodesic cold dark matter using the latest observational data. We bin the
interaction in seventeen redshift bins but use a correlation prior to prevent
rapid, unphysical oscillations in the coupling function. This prior also serves
to eliminate any dependence of the reconstruction on the binning method. We use
two different forms of the correlation prior, finding that both give similar
results for the reconstruction of the dark matter -- dark energy interaction.
Calculating the Bayes factor for each case, we find no meaningful evidence for
deviation from the null interacting case, i.e. CDM, in our
reconstruction.Comment: 14 pages, 7 figures. Version 2 matches published version in Physics
of the Dark Universe (Figure 2 updated to better show H0 and sigma 8
tensions, additional discussion of results added in section 4.1
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