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Spherical collapse in Galileon gravity : fifth force solutions, halo mass function and halo bias.

Barreira, A. and Li, B. and Baugh, C. M. and Pascoli, S. (2013) 'Spherical collapse in Galileon gravity : fifth force solutions, halo mass function and halo bias.', Journal of cosmology and astroparticle physics., 11 (2013). 056.


We study spherical collapse in the Quartic and Quintic Covariant Galileon gravity models within the framework of the excursion set formalism. We derive the nonlinear spherically symmetric equations in the quasi-static and weak-field limits, focusing on model parameters that fit current CMB, SNIa and BAO data. We demonstrate that the equations of the Quintic model do not admit physical solutions of the fifth force in high density regions, which prevents the study of structure formation in this model. For the Quartic model, we show that the effective gravitational strength deviates from the standard value at late times (zlesssim1), becoming larger if the density is low, but smaller if the density is high. This shows that the Vainshtein mechanism at high densities is not enough to screen all of the modifications of gravity. This makes halos that collapse at zlesssim1 feel an overall weaker gravity, which suppresses halo formation. However, the matter density in the Quartic model is higher than in standard ΛCDM, which boosts structure formation and dominates over the effect of the weaker gravity. In the Quartic model there is a significant overabundance of high-mass halos relative to ΛCDM. Dark matter halos are also less biased than in ΛCDM, with the difference increasing appreciably with halo mass. However, our results suggest that the bias may not be small enough to fully reconcile the predicted matter power spectrum with LRG clustering data.

Item Type:Article
Keywords:Galaxy clusters, Modified gravity, Dark energy theory, Cosmological parameters from CMBR.
Full text:(NA) Not Applicable
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Publisher statement:This is an author-created, un-copyedited version of an article accepted for publication in Journal of Cosmology and Astroparticle Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
Date accepted:No date available
Date deposited:No date available
Date of first online publication:November 2013
Date first made open access:No date available

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