1,721,054 research outputs found
The effect of interacting dark energy on local measurements of the Hubble constant
Full text linkIn the current state of cosmology, where cosmological parameters are being measured to percent accuracy, it is essential to understand all sources of error to high precision. In this paper we present the results of a study of the local variations in the Hubble constant measured at the distance scale of the Coma Cluster, and test the validity of correcting for the peculiar velocities predicted by gravitational instability theory. The study is based on N-body simulations, and includes models featuring a coupling between dark energy and dark matter, as well as two ΛCDM simulations with different values of σ8. It is found that the variance in the local flows is significantly larger in the coupled models, which increases the uncertainty in the local measurements of the Hubble constant in these scenarios. By comparing the results from the different simulations, it is found that most of the effect is caused by the higher value of σ8 in the coupled cosmologies, though this cannot account for all of the additional variance. Given the discrepancy between different estimates of the Hubble constant in the universe today, cosmological models causing a greater cosmic variance is something that we should be aware of
Efficient implementation of the time renormalization group
No full textThe time renormalization group (TRG) is an effective method for accurate calculations of the matter power spectrum at the scale of the first baryonic acoustic oscillations. By using a particular variable transformation in the TRG formalism, we can reduce the 2D integral in the source term of the equations of motion for the power spectrum into a series of 1D integrals. The shape of the integrand allows us to precompute only 13 antiderivatives numerically, which can then be reused when evaluating the outer integral. While this introduces a few challenges to keep numerical noise under control, we find that the computation time for nonlinear corrections to the matter power spectrum decreases by a factor of 50. This opens up the possibility to use TRG for mass production as in Markov chain Monte Carlo methods. A FORTRAN code demonstrating this new algorithm is publicly available
Constraining the growth of perturbations with lensing of supernovae
Full text linkA recently proposed technique allows one to constrain both the background and perturbation cosmological parameters through the distribution function of Type Ia supernova apparent magnitudes. Here we extend this technique to alternative cosmological scenarios, in which the growth of structure does not follow the Λ cold dark matter prescription. We apply the method first to the supernova data provided by the JLA catalogue combined with all the current independent redshift distortion data and with low-redshift cluster data from Chandra and show that although the supernovae alone are not very constraining, they help in reducing the confidence regions. Then we apply our method to future data from Large Synoptic Survey Telescope (LSST) and from a survey that approximates the Euclid satellite mission. In this case we show that the combined data are nicely complementary and can constrain the normalization σ8 and the growth rate index γ to within 0.6 per cent and 7 per cent, respectively. In particular, the LSST supernova catalogue is forecast to give the constraint γ(σ8/0.83)6.7 = 0.55 ± 0.1. We also report on constraints relative to a step-wise parametrization of the growth rate of structures. These results show that supernova lensing serves as a good cross-check on the measurement of perturbation parameters from more standard techniques
Idrocarburi alogenati nelle acque da bere
No full textViene fatta una valutazione critica della metodologia LLE-GC-ECD prevista dalla normativa vigente per l’analisi degli idrocarburi clorurati volatili e dei trialometani nelle acque da bere.
La LLE-GC-ECD risulta per alcune sostanze, quali cloroformio e metilcloroformio, poco accurata.
Come tecnica alternativa viene proposta una versione dedicata della tecnica combinata Purge and Trap-GC-MS in modalità SIM che risulta accurata per tutte le sostanze di interesse e di maggiore selettività rispetto alla LLE-GC-ECD.Here it is reported a critical evaluation of LLE-GC-ECD methodology that is provided by laws in force, for the analysis of volatile chlorinated
hydrocarbons and trihalomethanes in drinking waters. LLE-GC-ECD is not very accurate for some substances like chloroform and
methylchloroform. Purge and Trap-GC-MS in SIM mode, an improved combined technique, is suggested as alternative method, it is accurate
and more selective than LLE-GC-ECD for all examined compounds
Fitting and forecasting coupled dark energy in the non-linear regime
No full textWe consider cosmological models in which dark matter feels a fifth force mediated by the dark energy scalar field, also known as coupled dark energy. Our interest resides in estimating forecasts for future surveys like Euclid when we take into account non-linear effects, relying on new fitting functions that reproduce the non-linear matter power spectrum obtained from N-body simulations. We obtain fitting functions for models in which the dark matter-dark energy coupling is constant. Their validity is demonstrated for all available simulations in the redshift range 0z=-1.6 and wave modes below 0k=1 h/Mpc. These fitting formulas can be used to test the predictions of the model in the non-linear regime without the need for additional computing-intensive N-body simulations. We then use these fitting functions to perform forecasts on the constraining power that future galaxy-redshift surveys like Euclid will have on the coupling parameter, using the Fisher matrix method for galaxy clustering (GC) and weak lensing (WL). We find that by using information in the non-linear power spectrum, and combining the GC and WL probes, we can constrain the dark matter-dark energy coupling constant squared, β2, with precision smaller than 4% and all other cosmological parameters better than 1%, which is a considerable improvement of more than an order of magnitude compared to corresponding linear power spectrum forecasts with the same survey specifications
Fisher matrix for the one-loop galaxy power spectrum: measuring expansion and growth rates without assuming a cosmological model
No full textWe introduce a methodology to extend the Fisher matrix forecasts to mildly
non-linear scales without the need of selecting a cosmological model. We make
use of standard non-linear perturbation theory for biased tracers complemented
by counterterms, and assume that the cosmological distances can be measured
accurately with standard candles. Instead of choosing a specific model, we
parametrize the linear power spectrum and the growth rate in several and
bins. We show that one can then obtain model-independent constraints of the
expansion rate and the growth rate , besides the bias
functions. We apply the technique to both Euclid and DESI public specifications
in the range and show that the gain in precision when going
from to /Mpc is around two- to threefold, while it
reaches four- to ninefold when extending to /Mpc. In
absolute terms, with Mpc, one can reach high precision on
at each -shell: 8-10% for DESI with , 5-6% for Euclid
with . This improves to 1-2% if the growth rate is taken
to be -independent. The growth rate itself has in general much weaker
constraints, unless assumed to be -independent, in which case the gain is
similar to the one for and uncertainties around 5-15% can be reached at
each -bin. We also discuss how neglecting the non-linear corrections can
have a large effect on the constraints even for Mpc,
unless one has independent strong prior information on the non-linear
parameters.Comment: v3: new appendix E discussing the AP effect under binning of mu and
k; code upgraded to include non-diagonal beta(k) entries; accepted for
publication in JCAP v2: corrected bug affecting high-k results; included
extra FoG-related nuisance parameters; extended discussion and analysis; new
Appendix D; 12 new reference
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