87 research outputs found
Assessing non-linear models for galaxy clustering III: Theoretical accuracy for Stage IV surveys
We provide in depth MCMC comparisons of two different models for the halo
redshift space power spectrum, namely a variant of the commonly applied
Taruya-Nishimichi-Saito (TNS) model and an effective field theory of large
scale structure (EFTofLSS) inspired model. Using many simulation realisations
and Stage IV survey-like specifications for the covariance matrix, we check
each model's range of validity by testing for bias in the recovery of the
fiducial growth rate of structure formation. The robustness of the determined
range of validity is then tested by performing additional MCMC analyses using
higher order multipoles, a larger survey volume and a more highly biased tracer
catalogue. We find that under all tests, the TNS model's range of validity
remains robust and is found to be much higher than previous estimates. The
EFTofLSS model fails to capture the spectra for highly biased tracers as well
as becoming biased at higher wavenumbers when considering a very large survey
volume. Further, we find that the marginalised constraints on for all
analyses are stronger when using the TNS model.Comment: 25 pages, 19 figures. Accepted version for publication in JCA
COLA with massive neutrinos
The effect of massive neutrinos on the growth of cold dark matter
perturbations acts as a scale-dependent Newton's constant and leads to
scale-dependent growth factors just as we often find in models of gravity
beyond General Relativity. We show how to compute growth factors for
CDM and general modified gravity cosmologies combined with massive
neutrinos in Lagrangian perturbation theory for use in COLA and extensions
thereof. We implement this together with the grid-based massive neutrino method
of Brandbyge and Hannestad in and compare COLA simulations
to full -body simulations of CDM and gravity with
massive neutrinos. Our implementation is computationally cheap if the
underlying cosmology already has scale-dependent growth factors and it is shown
to be able to produce results that match -body to percent level accuracy
for both the total and CDM matter power-spectra up to Mpc.Comment: 29 pages, 15 figures, 1 table, version accepted for publication in
JCAP, added frame-lagging terms in 2LPT sections (results unaffected) and
appendix on comparison to SP
ISIS: a new N-body cosmological code with scalar fields based on RAMSES. Code presentation and application to the shapes of clusters
Several extensions of the standard cosmological model include scalar fields
as new degrees of freedom in the underlying gravitational theory. A particular
class of these scalar field theories include screening mechanisms intended to
hide the scalar field below observational limits in the solar system, but not
on galactic scales, where data still gives freedom to find possible signatures
of their presence. In order to make predictions to compare with observations
coming from galactic and clusters scales (i.e. in the non-linear regime of
cosmological evolution), cosmological N-body simulations are needed, for which
codes that can solve for the scalar field must be developed. We present a new
implementation of scalar-tensor theories of gravity which include screening
mechanisms. The code is based in the already existing code RAMSES, to which we
have added a non-linear multigrid solver that can treat a large class of scalar
tensor theories of modified gravity. We present details of the implementation
and the tests that we made to it. As application of the new code, we have
studied the influence that two particular modified gravity theories, the
symmetron and gravity, have on the shape of cluster sized dark matter
halos and found consistent results with previous estimations made with a static
analysis.Comment: 13 pages, 6 figures, matches version accepted for publication in A&
Hydrodynamic Effects in the Symmetron and -gravity Models
In this paper we present the first results from implementing two
scalar-tensor modified gravity theories, the symmetron and the Hu-Sawicki
-gravity model, into a hydrodynamic N-body code with dark matter
particles and a baryonic ideal gas. The study is a continuation of previous
work where the symmetron and have been successfully implemented in the
RAMSES code, but for dark matter only. By running simulations, we show that the
deviation from CDM in these models for the gas density profiles are
significantly lower than the dark matter equivalents. When it comes to the
matter power-spectrum we find that hydrodynamic simulations agree very well
with dark matter only simulations as long as we consider scales larger than
h/Mpc. In general the effects of modified gravity on the baryonic
gas is found to not always mirror the effects it has on the dark matter. The
largest signature is found when considering temperature profiles. We find that
the gas temperatures in the modified gravity model studied here show
deviations, when compared to CDM, that can be a factor of a few larger
than the deviations found in density profiles and power spectra.Comment: 11 pages, 10 figures, submitted to MNRA
Investigating the degeneracy between modified gravity and massive neutrinos with redshift-space distortions
There is a well known degeneracy between the enhancement of the growth of
large-scale structure produced by modified gravity models and the suppression
due to the free-streaming of massive neutrinos at late times. This makes the
matter power-spectrum alone a poor probe to distinguish between modified
gravity and the concordance CDM model when neutrino masses are not
strongly constrained. In this work, we investigate the potential of using
redshift-space distortions (RSD) to break this degeneracy when the modification
to gravity is scale-dependent in the form of Hu-Sawicki . We find that if
the linear growth rate can be recovered from the RSD signal, the degeneracy can
be broken at the level of the dark matter field. However, this requires
accurate modelling of the non-linearities in the RSD signal, and we here
present an extension of the standard perturbation theory-based model for
non-linear RSD that includes both Hu-Sawicki modified gravity and
massive neutrinos.Comment: 24 pages, 12 figures, 1 table; corrected typo in prefactors of the
'13'-type 1-loop SPT term
Dark matter haloes in modified gravity and dark energy: interaction rate, small-, and large-scale alignment
We study the properties of dark matter haloes in a wide range of modified
gravity models, namely, , DGP, and interacting dark energy models. We
study the effects of modified gravity and dark energy on the internal
properties of haloes, such as the spin and the structural parameters. We find
that gravity enhance the median value of the Bullock spin parameter, but
could not detect such effects for DGP and coupled dark energy. also
yields a lower median sphericity and oblateness, while coupled dark energy has
the opposite effect. However, these effects are very small. We then study the
interaction rate of haloes in different gravity, and find that only strongly
coupled dark energy models enhance the interaction rate. We then quantify the
enhancement of the alignment of the spins of interacting halo pairs by modified
gravity. Finally, we study the alignment of the major axes of haloes with the
large-scale structures. The alignment of the spins of interacting pairs of
haloes in DGP and coupled dark energy models show no discrepancy with GR, while
shows a weaker alignment. Strongly coupled dark energy shows a stronger
alignment of the halo shape with the large-scale structures.Comment: 11 pages, 6 figures, MNRAS Accepte
Spatial variations of the fine-structure constant in symmetron models
We investigate the variation of the fine-structure constant, {\alpha}, in
symmetron models using N-body simulations in which the full spatial
distribution of {\alpha} at different redshifts has been calculated. In
particular, we obtain simulated sky maps for this variation, and determine its
power spectrum. We find that in high-density regions of space (such as deep
inside dark matter halos) the value of {\alpha} approaches the value measured
on Earth. In the low-density outskirts of halos the scalar field value can
approach the symmetry breaking value and leads to significantly different
values of {\alpha}. If the scalar-photon coupling strength {\beta}{\gamma} is
of order unity we find that the variation of {\alpha} inside dark matter halos
can be of the same magnitude as the recent claims by Webb et al. of a dipole
variation. Importantly, our results also show that with low-redshift symmetry
breaking these models exhibit some dependence of {\alpha} on lookback time (as
opposed to a pure spatial dipole) which could in principle be detected by
sufficiently accurate spectroscopic measurements, such as those of ALMA and the
ELT-HIRES.Comment: 11 pages, 9 figure
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