# UMICH-2015: Dark Energy / Gravity / Dark Matter Summary

## Contents

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**S4 offers unique potential as a probe of cosmic acceleration and growth of structure:**

**Observations with S4 have the potential to falsify the Lambda model which makes predictions for the expansion history and growth of structure.**

**Unique CMB-S4 windows on linear regime, large scales and high redshift**

1) **CMB lensing measures integrated structure and sensitive to both expansion history and growth of structure (hopefully covered in neutrino session in depth).**

2) **Galaxy Clusters are the most massive collapsed structures and their abundance as a function of redshift is are extremely sensitive to expansion and growth.** Key to realizing the potential of this method is a precise cluster mass calibration. At z < ~1, strong synergy with next-generation optical surveys (like LSST) which will be able to calibrate masses from stacked optical weak lensing. At z > ~1, CMB cluster lensing can potentially calibrate mass at ~1% accuracy, however this level will require ~arcminute resolution.

- Plot of N(M,z) cluster counts for different S4 configurations. (Left) N(z) per 4000 deg^2 survey. S4 would find roughly 19,000, 9,500, or 6,200 clusters for a 1,2,3 arcmin angular resolution survey, respectively, at a S/N ~ 4.5 (approximately a 99% purity threshold). (Right) the 50% completeness level of the S4 cluster survey

- CMB cluster lensing. S/N of detection for different CMB S4 configurations. Translate to mass calibration vs mass and redshift. For ~100,000 clusters we would expect a ~0.5% mass calibration at a 1 uK-arcmin depth (Hu et al. 2006). How does this vary with beam size? What are systematics from TT based estimates (e.g., from tSZ leakage, cluster kSZ, etc.)? EB is likely a more promising estimator for this reason.

3) **Early Dark Energy** - Precise measurements of E-mode polarization damping tail provides a unique high-redshift window (but is there a definite goal?)

4) **Pairwise Kinetic SZ maps late-time momentum and can also constrain expansion and growth.**

Left: Expected constraints on the neutrino mass from kSZ pairwise statistic as function of the prior on a potential systematic offset in the mass-averaged optical depth, assuming 1.3 arcmin resolution (See also Mueller et al., http://arxiv.org/pdf/1412.0592.pdf - http://arxiv.org/pdf/1408.6248v1.pdf )
Need detailed study of constraints relative to Redshift Space Distortions including relevant systematics. Signal is spectrally degenerate with CMB. High resolution is required to extract this signal.

How do these Dark Energy Probes compliment other probes of Dark Energy? What are drivers for resolution and frequency coverage.

**Dark Matter annihilation Signatures**

Wimp dark matter annihilation is most constrained by relatively low ell polarization measurements. Other non-standard models predict different signatures. No strong driver for a particular experimental configuration is absence of a particular model.

**Reioinization from kSZ**

Constraint on the duration of reionization from AdvACT. Need updated projections for S4 depths, to study potential number of bands and angular resolution drivers for S4. See also Calabrese et al., http://arxiv.org/pdf/1406.4794v2.pdf.

**Action Items**

**Probes of Expansion and Growth of Structure**

1) Think about how to express improvements in Dark Energy and growth constraints as a function of redshift in model independent ways.

2) Refer to Euclid document (Amendola et al) that surveyed dark energy and modified gravity models and identified the observational constraints on each model.

**Pairwise kSZ as probe of momentum field**

1) Realizing the potential of pairwise kSZ will require spectroscope redshifts for O(N=10,000) clusters. Need to understand limitations of upcoming optical surveys(Euclid, LSST) and produce detailed plans for combination of optical and millimeter data. How far can we get with photometric redshifts?

2) Understand impact of systematic errors for pairwise kSZ, optical redshift space distortions, and cross correlations between the two methods.

3) Quantify the uncertainty in cluster tau and the impact of it on cosmological parameters.

**Cluster Counts as probe of growth and expansion**

1) Formulate plan for optical follow up. Need redshifts for O(N=1,000) clusters at z>1. Will LSST be sufficient? How much will SphereX help?

2) Mass calibration is critical to realizing the potential of this observable. Quantify the CMB cluster lensing mass calibration uncertainty as a function of beam size, sensitivity, and bands. Also, quantify the weak lensing calibration expected from an optical survey, like LSST, and the expected improvement on cosmological constraints.

3) Predict performance of CMB cluster lensing mass calibration using iterative lensing estimator (may outperform current estimates based on quadratic estimator).

**Diffuse tSZ and kSZ**

1) Quantify the impact of beam size, and frequency bands, and sensitivity on separation and recovery of these signals. This will require realistic simulations including expected radio and dust emission in clusters.

2) Quantify the impact of theoretical uncertainties on cosmological constraints from tSZ (growth) and patchy kSZ (reionization).

3) Cross-correlations with lensing maps: Quantify improvement on tSZ cosmological constraints from joint analysis with tSZ x lensing analysis, which is expected to significantly improve gastrophysics uncertainty in clusters.

**Dark Matter**

1) How do forecasts on Dark Matter annihilation change when including foregrounds?

2) What are the degeneracies of different dark matter models with other non-standard cosmological parameters (i.e., Neff)?

3) What are projected constraints on axions?