Primordial density perturbations with running spectral index: impact on non-linear cosmic structures

Abstract

We explore the statistical properties of non-linear cosmic structures in a flat cold dark matter ( CDM) cosmology in which the index n S of the primordial power spectrum for scalar perturbations is allowed to depend on the scale. Within the inflationary paradigm, the running of the scalar spectral index can be related to the properties of the inflation potential, and it is hence of critical importance to test it with all kinds of observations, which cover the linear and non-linear regime of gravitational instability. We focus on the amount of running α S,0 (≡ dn S /d ln(k/k p )) allowed by an updated combination of cosmic microwave background (CMB) anisotropy data and the 2dF Galaxy Redshift Survey. Our analysis constrains α S,0 = −0.051 +0.047 −0.053 (−0.034 +0.039 −0.040 ) at 95 per cent Confidence Level when (not) taking into account primordial gravitational waves in a ratio as predicted by canonical single field inflation, in agreement with other works. For the cosmological models best fitting the data both with and without running we studied the abundance of galaxy clusters and of rare objects, the halo bias, the concentration of dark matter haloes, the Baryon Acoustic Oscillation, the power spectrum of cosmic shear and the Integrated Sachs-Wolfe effect. We find that counting galaxy clusters in future X-ray and Sunyaev-Zel'dovich surveys could discriminate between the two models, more so if broad redshift information about the cluster samples will be available. Likewise, measurements of the power spectrum of cosmological weak lensing as performed by planned all-sky optical surveys such as EUCLID could detect a running of the primordial spectral index, provided the uncertainties about the source redshift distribution and the underlying matter power spectrum are well under control.

The bahamas project: effects of a running scalar spectral index on large-scale structure

“…Whereas at the low-mass end (M 2 × 10 13 M ), the negative running cosmologies tend to predict slightly lower concentrations, the effect on these scales is small compared to the high-mass end. A similar result was found by Fedeli et al (2010), who predicted low-mass halos to have a lower concentration value in a negative running cosmology, but high-mass halos to have a slightly higher concentration.…”

“…This makes sense when looking at the HMF, or the comoving halo space density, which showed that a negative running cosmology led to an increase in the number of halos in this higher mass bin, and therefore one can expect them to be a less biased tracer of the underlying matter distribution, which as a result will lead to a lower clustering signal compared to the no-running cosmology's result. This result agrees with that predicted by Fedeli et al (2010), who showed that in a negative running cosmology dark matter halos in the cluster regime are less biased compared with the standard model (see figure 10 in Fedeli et al 2010). The other two negative running cosmologies see a similar trend, but not to the same level.…”

“…A qualitatively similar result was found by Fedeli et al (2010), who showed using semi-analytic methods that the concentration of low-mass halos in a negative running cosmology is lower than in the standard ΛCDM model. They also showed that to a small extent this effect was reversed at the high-mass end, with these objects being slightly more concentrated.…”

“…Although a systematic exploration of the effects a running scalar spectral index on LSS in the Universe using large cosmological hydrodynamic simulations has not been conducted, research has went into the effects of running using semi-analytic models (e.g. Fedeli et al (2010)). Here, we explore how well these approximate methods work in reproducing the HMF, and the redshift evolution of dark matter halos.…”

Probing small-scale cosmological fluctuations with the 21 cm forest: Effects of neutrino mass, running spectral index, and warm dark matter

“…On the other hand, these effects can also alter the dark matter profile within individual halos and hence the gas profile as well, potentially affecting the 21 cm absorption sig- nal. Consequences for the halo dark matter profile of massive neutrinos [60], RSI [61] and WDM [8,62] have been studied to some extent for galaxy-to cluster-scale halos at low redshifts, indicating that they are affected mainly in the central regions with r/r vir 0.1. Although no corresponding work exists for high-redshift minihalos, we may speculate that the impact is less than that due to the mass function with regard to our results, for which the outer regions of the halo are more relevant (Fig.2).…”