# UMICH-2015: Dark Energy / Gravity / Dark Matter break-out session 2

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### Key Questions

#### Key Science Questions:

- What are the cosmological constraints on dark energy, modified gravity, and neutrinos from a CMB-S4 SZ cluster survey?
- What new cosmological probes will be enabled by overlap other multi-wavelength surveys?

#### Key Instrumental and Systematics Questions:

- How many clusters (vs mass and redshift) will CMB-S4 detect? How will this vary with beam size, frequency coverage, and depth? Are foregrounds an issue (e.g. sources in clusters)?
- How well can we calibrate cluster masses?
- Characterize other systematics: CIB, gastrophysics, kSZ from clusters, ...

### Topics

#### SZ Cluster Survey:

- Plot of N(M,z) cluster counts for different S4 configurations. (S4 assumed depth of 1 uK-arcmin at 150 GHz, 2 uK-arcmin at 90, 220 GHz). (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). For comparison, SPT-3G would find about 13,500 clusters over the same area at the stated SPT-3G survey depth (2.5 uK-arcmin at 150 GHz). (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.)?

- tSZ power spectrum projection: 1-d pdf, auto-spectrum, bispectrum

Estimate of cosmic variance-limited experiment's SNR on the tSZ auto-spectrum (from http://arxiv.org/abs/1303.4726 ) -- presumably not far off from S4, though very dependent on number of frequency channels / component separation details, which are TBD

- kSZ power spectrum: constraints on sigma8. See Calabrese et al. 2014 http://arxiv.org/pdf/1406.4794v2.pdf

#### Cross-Correlations:

- Diffuse tSZ x optical weak lensing

- Diffuse tSZ x CMB lensing forecast Planck + S3 CMB + LSST & Euclid (see Battaglia, Hill * Murray for tSZ x CMB & optical weak-lensing measurements http://arxiv.org/pdf/1412.5593v1.pdf)

- Joint SZ+Optical cluster survey

- Cluster mass constraints / calibration from optical weak lensing (e.g., overlap with LSST, Euclid, WFIRST)

#### Cosmology:

- Mass calibration required and possible from optical Stage-4. (Left) Mass calibration required to be limited by Poisson statistics at various mass thresholds for a 10,000 deg^2 survey (http://arxiv.org/abs/1201.2434). (Right) Mass accuracy from an optical stacked WL Stage-4 experiment.

- Dark Energy FOM and growth constraints from a SZ cluster survey. (Left, Right) Improvement in DE FOM and growth from a S4 cluster survey, taken from (http://arxiv.org/abs/1201.2434, contours represent improvement from a cluster survey with a 8, 4, 2, 1e14 Msun mass threshold.

- Constraints on neutrino mass. (Left) Euclid cluster survey constraints on sigma8, neutrino mass, which project a ~ 0.01 eV constraint on the sum of the neutrino masses from clusters alone (http://arxiv.org/pdf/1505.02165v1.pdf)

#### Astrophysics:

- Simulations that incorporate lensing and gastrophysics will be key to understanding the cosmology constraints; what do we need here?

- Cluster and galaxy gastro-physics (e.g., shape of tSZ spectrum, galaxy cross-correlations, follow-up of highest redshift clusters)

See Battaglia et al 2010 (http://arxiv.org/pdf/1003.4256v2.pdf) & McCarthy et al 2014 (http://arxiv.org/pdf/1312.5341v2.pdf) for gastrophysical impacts on the tSZ PS

See Battaglia, Hill & Murray 2015 (http://arxiv.org/pdf/1412.5593v1.pdf) for gastrophysical impacts on the tSZ x lensing cross spectrum)

- Projected emissive point source catalog

- Cosmic infrared background