Challenging the standard cosmological model

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The standard model of cosmology successfully explains a wide set of precise data, with a few simplifying assumptions and just seven free parameters. It has remained essentially unchanged for about 25 years. However, it is purely phenomenological and contains several unexplained aspects, e.g. there is no explanation for the nature of the dark matter or dark energy, or for the origin of the initial density perturbations. The model is far from being elegant, and additionally there is no expectation that it can be complete. Moreover, despite its successes, there are some apparent chinks in the armour of the standard cosmological model, variously called "anomalies", "curiosities" or "tensions" - it is currently unclear which of them may point the way towards new physics, which are caused by unidentified systematic effects, and which are just statistical fluctuations. Of course the obvious way to make progress is through obtaining much more sensitive data from future experiments with the goal of discovering that new parameters may be needed (such as a component of primordial gravitational waves, a non-trivial kind of dark energy, or observable effects from massive neutrinos). I am involved in such ambitious cosmic microwave background (CMB) experiments, but the results are not expected soon. For the 5 years of research proposed here, I will explore 4 separate ways to extend the cosmological model, each involving students in attempts to more immediately challenge the standard cosmology. First, some existing anomalies can be directly investigated with new data, e.g. probing large-scale curiosities using CMB polarization or lensing data.  Second, parameter tensions can be explored in the context of modified-gravity ideas or adding other novel physics ingredients to the model. Third, we can use cross-correlations between CMB "secondary" signals and other astrophysical survey data to extract additional cosmological information from existing data and confront this with the predictions of the standard model. Last, we can search for structures that would be difficult to explain within the standard picture, particularly proto-clusters of galaxies at high redshift. Through a combination of these interrelated research thrusts, this proposal will examine how the standard cosmological model needs to evolve to fully describe future cosmological data.