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Register a new userBreaking the Dark Degeneracy with the Drifting Coefficient of the Field Cluster Mass Function
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We present a numerical analysis supporting the evidence that the redshift evolution of the drifting coefficient of the field cluster mass function is capable of breaking several cosmic degeneracies. This evidence is based on the data from the CoDECS and DUSTGRAIN-pathfinder simulations performed separately for various non-standard cosmologies including coupled dark energy, $f(R)$ gravity and combinations of $f(R)$ gravity with massive neutrinos as well as for the standard $Lambda$CDM cosmology. We first numerically determine the field cluster mass functions at various redshifts in the range of $0le zle 1$ for each cosmology. Then, we compare the analytic formula developed in previous works with the numerically obtained field cluster mass functions by adjusting its drifting coefficient, $beta$, at each redshift. It is found that the analytic formula with the best-fit coefficient provides a good match to the numerical results at all redshifts for all of the cosmologies. The empirically determined redshift evolution of the drifting coefficient, $beta(z)$, turns out to significantly differ among different cosmologies. It is also shown that even without using any prior information on the background cosmology the drifting coefficient, $beta(z)$, can discriminate with high statistical significance the degenerate non-standard cosmologies not only from the $Lambda$CDM but also from one another. It is concluded that the evolution of the departure from the Einstein-de Sitter state and spherically symmetric collapse processes quantified by $beta(z)$ is a powerful probe of gravity and dark sector physics.
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Future large-scale spectroscopic astronomical surveys, e.g. Euclid, will enable the compilation of vast new catalogues of clusters and voids in the galaxy distribution. By combining the constraining power of both cluster and void number counts, such surveys could place stringent simultaneous limits on the sum of neutrino masses $M_ u$ and the dark energy equation of state $w(z) = w_0 + w_a z/(1+z)$. For minimal normal-hierarchy neutrino masses, we forecast that Euclid clusters + voids ideally could reach uncertainties $sigma(M_ u) lesssim 15$ meV, $sigma(w_0) lesssim~0.02$, $sigma(w_a) lesssim 0.07$, independent of other data. Such precision is competitive with expectations for e.g. galaxy clustering and weak lensing in future cosmological surveys, and could reject an inverted neutrino mass hierarchy at $gtrsim 99%$ confidence.
We provide the first direct lifting of the mass/anisotropy degeneracy for a cluster of galaxies, by jointly fitting the line of sight velocity dispersion and kurtosis profiles of the Coma cluster, assuming an NFW tracer density profile, a generalized-NFW dark matter profile and a constant anisotropy profile. We find that the orbits in Coma must be quasi-isotropic, and find a mass consistent with previous analyses, but a concentration parameter 50% higher than expected in cosmological N-body simulations. We then test the accuracy of our method on realistic non-spherical systems with substructure and streaming motions, by applying it to the ten most massive structures in a cosmological N-body simulation. We find that our method yields fairly accurate results on average (within 20%), although with a wide variation (factor 1.7 at 1 sigma) for the concentration parameter, with decreased accuracy and efficiency when the projected mean velocity is not constant with radius.
The mass-sheet degeneracy is a well-known problem in gravitational lensing which limits our capability to infer astrophysical lens properties or cosmological parameters from observations. As the number of gravitational wave observations grows, detecting lensed events will become more likely, and to assess how the mass-sheet degeneracy may affect them is crucial. Here we study both analytically and numerically how the lensed waveforms are affected by the mass-sheet degeneracy computing the amplification factor from the diffraction integral. In particular, we differentiate between the geometrical optics, wave optics and interference regimes, focusing on ground-based gravitational waves detectors. In agreement with expectations of gravitational lensing of electromagnetic radiation, we confirm how, in the geometrical optics scenario, the mass-sheet degeneracy cannot be broken with only one lensed image. However, we find that in the interference regime, and in part in the wave-optics regime, the mass-sheet degeneracy can be broken with only one lensed waveform thanks to the characteristic interference patterns of the signal. Finally, we quantify, through template matching, how well the mass-sheet degeneracy can be broken. We find that, within present GW detector sensitivities and considering signals as strong as those which have been detected so far, the mass-sheet degeneracy can lead to a $1sigma$ uncertainty on the lens mass of $sim 12%$. With these values the MSD might still be a problematic issue. But in case of signals with higher signal-to-noise ratio, the uncertainty can drop to $sim 2%$, which is less than the current indeterminacy achieved by dynamical mass measurements.
We study cosmological models with interaction between dark energy (DE) and dark matter (DM). For the interaction term $Q$ in cosmic evolution equations, there is a model-independent degeneracy-breaking (D-B) point when $Q_{1}$ (a part of $Q$) equals to zero, where the interaction can be probed without degeneracy between the constant DE equation of state (EoS).
We use the relations between aperture stellar velocity dispersion (sigma_ap), stellar mass (M_sps), and galaxy size (R_e) for a sample of sim 150,000 early-type galaxies from SDSS/DR7 to place constraints on the stellar initial mass function (IMF) and dark halo response to galaxy formation. We build LCDM based mass models that reproduce, by construction, the relations between galaxy size, light concentration and stellar mass, and use the spherical Jeans equations to predict sigma_ap. Given our model assumptions (including those in the stellar population synthesis models), we find that reproducing the median sigma_ap vs M_sps relation is not possible with {it both} a universal IMF and a universal dark halo response. Significant departures from a universal IMF and/or dark halo response are required, but there is a degeneracy between these two solutions. We show that this degeneracy can be broken using the strength of the correlation between residuals of the velocity-mass (Delta log sigma_ap) and size-mass (Delta log R_e) relations. The slope of this correlation, d_vr equiv Delta log sigma_ap/Delta log R_e, varies systematically with galaxy mass from d_vr simeq -0.45 at M_sps sim 10^{10}M_sun, to d_vr simeq -0.15 at M_sps sim 10^{11.6} M_sun. The virial fundamental plane (FP) has d_vr=-1/2, and thus we find the tilt of the observed FP is mass dependent. Reproducing this tilt requires {it both} a non-universal IMF and a non-universal halo response. Our best model has mass-follows-light at low masses (Msps < 10^{11.2}M_sun) and unmodified NFW haloes at M_sps sim 10^{11.5} M_sun. The stellar masses imply a mass dependent IMF which is lighter than Salpeter at low masses and heavier than Salpeter at high masses.
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