62 research outputs found
Revealing modified gravity signal in matter and halo hierarchical clustering
We use a set of N-body simulations employing a modified gravity (MG) model
with Vainshtein screening to study matter and halo hierarchical clustering. As
test-case scenarios we consider two normal branch Dvali-Gabadadze-Porrati
(nDGP) gravity models with mild and strong growth rate enhancement. We study
higher-order correlation functions up to and associated
hierarchical amplitudes . We find that
the matter PDFs are strongly affected by the fifth-force on scales up to
Mpc, and the deviations from GR are maximised at . For reduced
cumulants , we find that at small scales Mpc the MG is
characterised by lower values, with the deviation growing from in the
reduced skewness up to even in . To study the halo clustering we
use a simple abundance matching and divide haloes into thee fixed number
density samples. The halo two-point functions are weakly affected, with a
relative boost of the order of a few percent appearing only at the smallest
pair separations (Mpc). In contrast, we find a strong MG signal
in 's, which are enhanced compared to GR. The strong model exhibits a
level signal at various scales for all halo samples and in all
cumulants. In this context, we find that the reduced kurtosis to be an
especially promising cosmological probe of MG. Even the mild nDGP model leaves
a imprint at small scales Mpc, while the stronger model
deviates from a GR-signature at nearly all scales with a significance of
. Since the signal is persistent in all halo samples and over a range
of scales, we advocate that the reduced kurtosis estimated from galaxy
catalogues can potentially constitute a strong MG-model discriminatory as well
as GR self-consistency test.Comment: 19 pages, 11 figures, comments are welcom
Kosmologia ciemnej materii z oddziaływaniem skalarnym
Niniejsza rozprawa jest zorganizowana następująco: w rozdziale pierwszym zawarliśmy wstępne podstawowe rozważania oraz dokładny opis Standardowego Modelu Kosmologicznego jak i badanego modelu ReBEL; w rozdziale drugim przedstawimy wyniki badań dotyczących wpływu oddziaływań skalarnych w CM na statystykę wielkoskalowych korelacji przestrzennych pola gęstości CM oraz gazu barionowego; w rozdziale trzecim zawarty został opis dokładnych badań wpływu sił ReBEL na wewnętrzne własności hal CM oraz na ich wzajemne korelacje przestrzenne. W ostatnim rozdziale rozprawy - rozdziale czwartym - zawarliśmy podsumowanie oraz wnioski końcowe. Do rozprawy dołączone zostały dwa dodatki, w których zawarto obszerny opis funkcji wygładzających stosowanych w kodzie GADGET2 (dodatek A) oraz wyprowadzenie wzoru na logarytmiczny wykładnik nachylenia widma mocy \ga_1 (dodatek B). Na końcu umieszczono szczegółowy wykaz literatury cytowanej w niniejszej pracy.Centrum Astronomiczne im. M. Kopernika PAN, Ministerstwo Nauki i Szkolnictwa WyższegoWojciech Hellwin
Improved analytical modeling of the non-linear power spectrum in modified gravity cosmologies
Reliable analytical modeling of the non-linear power spectrum (PS) of matter
perturbations is among the chief pre-requisites for cosmological analyses from
the largest sky surveys. This is especially true for the models that extend the
standard general-relativity paradigm by adding the fifth force, where numerical
simulations can be prohibitively expensive. Here we present a method for
building accurate PS models for two modified gravity (MG) variants: namely the
Hu-Sawicki , and the normal branch of the Dvali-Gabadadze-Porrati (nDGP)
braneworld. We start by modifying the standard halo model (HM) with respect to
the baseline Lambda-Cold-Dark-Matter (CDM) scenario, by using the HM
components with specific MG extensions. We find that our
retains 5% accuracy only up to mildly non-linear scales (
h/\,\mbox{Mpc}) when compared to PS from numerical simulations. At the same
time, our HM prescription much more accurately captures the ratio up to non-linear scales. We show
that using HM-derived together with a viable non-linear
CDM prescription (such as HALOFIT), we render a much better and
more accurate PS predictions in MG. The new approach yields considerably
improved performance, with modeled being now accurate to
within 5% all the way to non-linear scales of
h/\,\mbox{Mpc}. The magnitude of deviations from GR as fostered by these MG
models is typically in these regimes. Therefore reaching 5%
PS modeling is enough for forecasting constraints on modern-era cosmological
observables
Uneven flows: On cosmic bulk flows, local observers, and gravity
Using N-body simulations we study the impact of various systematic effects on
the bulk flow (BF) and the Cosmic Mach Number (CMN). We consider two types of
systematics: those related to survey properties and those induced by observer's
location in the Universe. In the former category we model sparse sampling,
velocity errors, and survey incompleteness. In the latter, we consider Local
Group (LG) analogue observers, placed in a specific location within the Cosmic
Web, satisfying various observational criteria. We differentiate such LG
observers from Copernican ones, who are at random locations. We report strong
systematic effects on the measured BF and CMN induced by sparse sampling,
velocity errors and radial incompleteness. For BF most of these effects exceed
10\% for scales Mpc. For CMN some of these systematics can be
catastrophically large () also on bigger scales. Moreover, we find that
the position of the observer in the Cosmic Web significantly affects the
locally measured BF (CMN), with effects as large as ( at
Mpc for a LG-like observer as compared to a random one. This
effect is comparable to the sample variance. To highlight the importance of
these systematics, we additionally study a model of modified gravity (MG) with
enhanced growth rate. We found that the systematic effects can mimic
the modified gravity signal. The worst-case scenario is realized for a case of
a LG-like observer, when the effects induced by local structures are degenerate
with the enhanced growth rate fostered by MG. Our results indicate that
dedicated constrained simulations and realistic mock galaxy catalogs will be
absolutely necessary to fully benefit from the statistical power of the
forthcoming peculiar velocity data from surveys such as TAIPAN, WALLABY, Cosmic
Flows-4 and SKA.Comment: 20 pages, 9+2 figures, comments are welcome
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