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We analyze the ability of galaxy and CMB lensing surveys to constrain massive neutrinos and new models of dark radiation. We present a Fisher forecast analysis for neutrino mass constraints with the LSST galaxy survey and the CMB S4 survey. A joint analysis of the three galaxy and shear 2-point functions, along with key systematics parameters and Planck priors, constrains the neutrino masses to $sum m_ u = 0.041,$eV at 1-$sigma$ level, comparable to constraints expected from Stage 4 CMB lensing. If low redshift information from upcoming spectroscopic surveys like DESI is included, the constraint becomes $sum m_ u = 0.032,$eV. These constraints are derived having marginalized over the number of relativistic species ($N_{rm eff}$), which is somewhat degenerate with the neutrino mass. We also explore the gain by combining LSST and CMB S4, that is, using the five relevant auto- and cross-correlations of the two datasets. We conclude that advances in modeling the nonlinear regime and the measurements of other parameters are required to ensure a neutrino mass detection. Using the same datasets, we explore the ability of LSST-era surveys to test nonstandard models with dark radiation. We find that if evidence for dark radiation is found from $N_{rm eff}$ measurements, the mass of the dark radiation candidate can be measured at a 1-$sigma$ level of $0.162,$eV for fermionic dark radiation, and $0.137,$eV for bosonic dark radiation, for $Delta N_{rm eff} = 0.15$. We also find that the NNaturalness model of Arkani-Hamed et al 2016, with extra light degrees of freedom, has a sub-percent effect on the power spectrum: even more ambitious surveys than the ones considered here will be needed to test such models.
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We perform a thorough examination of the neutrino mass ($M_ u$) constraints achievable by combining future spectroscopic galaxy surveys with cosmic microwave background (CMB) experiments, focusing on the contribution of CMB lensing and galaxy-CMB lensing. CMB lensing can help by breaking the $M_ u$-curvature degeneracy when combined with baryon acoustic oscillation (BAO)-only measurements, but we demonstrate this combination wastes a great deal of constraining power, as the broadband shape of the power spectrum contributes significantly to constraints. We also expand on previous work to demonstrate how cosmology-independent constraints on $M_ u$ can be extracted by combining measurements of the scale-dependence in the power spectrum caused by neutrino free-streaming with the full power of future CMB surveys. These free-streaming constraints are independent of the optical depth to the CMB ($tau$) and competitive with constraints from BAOs for extended cosmologies, even when both are combined with CMB lensing and galaxy-CMB lensing.
Tests of gravity on large-scales in the universe can be made using both imaging and spectroscopic surveys. The former allow for measurements of weak lensing, galaxy clustering and cross-correlations such as the ISW effect. The latter probe galaxy dynamics through redshift space distortions. We use a set of basic observables, namely lensing power spectra, galaxy-lensing and galaxy-velocity cross-spectra in multiple redshift bins (including their covariances), to estimate the ability of upcoming surveys to test gravity theories. We use a two-parameter description of gravity that allows for the Poisson equation and the ratio of metric potentials to depart from general relativity. We find that the combination of imaging and spectroscopic observables is essential in making robust tests of gravity theories. The range of scales and redshifts best probed by upcoming surveys is discussed. We also compare our parametrization to others used in the literature, in particular the gamma parameter modification of the growth factor.
Measuring the total neutrino mass is one of the most exciting opportunities available with next-generation cosmological data sets. We study the possibility of detecting the total neutrino mass using large-scale clustering in 21cm intensity mapping and photometric galaxy surveys, together with CMB information. We include the scale-dependent halo bias contribution due to the presence of massive neutrinos, and use a multi-tracer analysis in order to reduce cosmic variance. The multi-tracer combination of an SKAO-MID 21cm intensity map with Stage~4 CMB lensing dramatically shrinks the uncertainty on total neutrino mass to $sigma(M_ u) simeq 45,$meV, using only linear clustering information ($k_{rm max} = 0.1, h/$Mpc) and without a prior on optical depth. When we add to the multi-tracer the clustering information expected from LSST, the forecast is $sigma(M_ u) simeq 12,$meV.
Cosmic Microwave Background (CMB) is a powerful probe to study the early universe and various cosmological models. Weak gravitational lensing affects the CMB by changing its power spectrum, but meanwhile, it also carries information about the distribution of lensing mass and hence, the large scale structure (LSS) of the universe. When studies of the CMB is combined with the tracers of LSS, one can constrain cosmological models, models of LSS development and astrophysical parameters simultaneously. The main focus of this project is to study the cross-correlations between CMB lensing and the galaxy matter density to constrain the galaxy bias ($b$) and the amplitude scaling parameter ($A$), to test the validity of $Lambda$CDM model. We test our approach for simulations of the Planck CMB convergence field and galaxy density field, which mimics the density field of the Herschel Extragalactic Legacy Project (HELP). We use maximum likelihood method to constrain the parameters.
Measurements of cosmic microwave background (CMB) anisotropies provide strong evidence for the existence of dark matter and dark energy. They can also test its composition, probing the energy density and particle mass of different dark-matter and dark-energy components. CMB data have already shown that ultra-light axions (ULAs) with mass in the range $10^{-32}~{rm eV} to 10^{-26}~{rm eV}$ compose a fraction $< 0.01$ of the cosmological critical density. Here, the sensitivity of a proposed CMB-Stage IV (CMB-S4) experiment (assuming a 1 arcmin beam and $< 1~mu K{rm-arcmin}$ noise levels over a sky fraction of 0.4) to the density of ULAs and other dark-sector components is assessed. CMB-S4 data should be $sim 10$ times more sensitive to the ULA energy-density than Planck data alone, across a wide range of ULA masses $10^{-32}< m_{a}< 10^{-23}~{rm eV}$, and will probe axion decay constants of $f_{a}approx 10^{16}~{rm GeV}$, at the grand unified scale. CMB-S4 could improve the CMB lower bound on the ULA mass from $sim 10^{-25}~{rm eV}$ to $10^{-23}~{rm eV}$, nearing the mass range probed by dwarf galaxy abundances and dark-matter halo density profiles. These improvements will allow for a multi-$sigma$ detection of percent-level departures from CDM over a wide range of masses. Much of this improvement is driven by the effects of weak gravitational lensing on the CMB, which breaks degeneracies between ULAs and neutrinos. We also find that the addition of ULA parameters does not significantly degrade the sensitivity of the CMB to neutrino masses. These results were obtained using the axionCAMB code (a modification to the CAMB Boltzmann code), presented here for public use.
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