(Eisenstein et al., ApJ, 2005)Surveys of large

scale structure will probe Dark Energy by measuring the BAO scale vs. redshift.

Planned:

DESI, Euclid, WFIRST, ...

2

Hydrogen Intensity Mapping

To measure BAO scale there is no need to resolve individual galaxies. Map intensity of HI gas using redshifted 21 cm emission along the line of sight.

For 15 Mpc spatial resolution at z~1-2, need ~15-25’ angular resolution. This requires observations with a ~100 m aperture and a fast mapping speed in the 400-800 MHz band.

The Canadian Hydrogen Intensity Mapping Expt. (CHIME)

Frequency: 400-800 MHz (21 cm radiation, z = 0.8-2.5)

Coverage: 20,000 sq. deg. sky; drift scanning (no moving parts); 5% of the co-moving volume of the observable universe

Resolution: 1 MHz bandwidth; 13-26 FWHM beam

Receivers: 1024 dual polarization feeds, cosmic variance limited in ~2 years

Four 20 m x 100 m N-S cylindrical reflectors with receivers along each 100 m focal line. Drift scan telescope with ~2° x 90° FOV.

4

CHIME Site: DRAO near Penticton BC

Site of Full CHIME CHIME Pathfinder

Construction of Full CHIME well underway...

CHIME Pathfinder is in operation...

CHIME Pathfinder Data Sample

8 x 8 correlation matrix from Tau-A transit in one 1 MHz frequency band.

“No mode left behind”

• Towards a program to measure all fluctuation modes within the last-scattering surface.

• CMB-oriented approach to experiment and analysis.

• Observational challenges:• Calibration (phase, pass-band, angular

response,...)• Foreground filtering (!)• Dark energy sensitivity comparable to Euclid/BAO,

with a complementary observable.• Cross correlation with other probes: galaxy

surveys, CMB lensing, Sunyaev-Zeldovich effect, etc.

An Incomplete Selection of Yesterday’s Quotes Pertaining to the Future for CMB, Paraphrased

Devlin, Pryke, Dunkley: Lots of new CMB detectors will be on the sky in 2 yrs.

Bersanelli: will need to control systematics and foregrounds at the nK level

Dunkley: You need 3N+2 bands to remove N foregrounds

Richards: Ground-based r-instruments are in their infancy; we will learn a lot from them before the next space mission.

Dunkley: What’s left to do with TT? Fully exploit the kSZ effect.

Gorski: (Make up for the) under-measured low frequency side of foregrounds.

Papitashvili: Plan on years of site testing (for any new site).

Partridge: Theorists will find new ways to use observations (if we make them).

kSZ (momentum field)

ClustersLensing B-modes

Inflationary B-modes

Reionization (first stars)

Fainter (higher z) clustersMore lensing modes

Lensing Field

30’1’

SCIENCE REACH

# frequency bands needed

ACT

SPT

See Snowmass: CF5 Neutrinos Document arxiv:1309.5383Figure by Clem Pryke

Today

A Moore’s Law of CMB sensitivity

futureSatellite?

Increasing sensitivity

ACTPolBICEP/KECK Spider

PolarbearSPTpol

Stage-2 Now

O(1000) detectors

Stage-4~2020 -

O(500,000) detectors

Stage-32016 - 2020

O(10,000) detectors

CMB-S4: A coordinated community wide program to put O(500,000) detectors spanning 30 - 300 GHz on multiple telescopes and map over 70%≳ of sky at 1 μk arcm.

Maintaining Moore’s Law for ground based CMB:focal planes are saturated so move to parallel processing and multiple telescopes.

ACTPol, BICEP/KECK,Polarbear, Spider, SPTpol

Increasing detector count

Multiple telescopes exploiting superb, established sites at Chile and South Poleand possibly northern site(s) in Greenland, Tibet…

Slide from Jeff McMahon

Tibet, Greenland

• Inflationary B-Modes: conservative goal σ(r) < 0.001 using only recombination bump with foreground cleaning and de-lensing.

• Neutrinos: σ(Neff) = 0.020, σ(Σmν) = 16 meV

• SZ clusters: Nclust ~ 100,000 with < 1% CMB lensing mass scaling

• Tests of gravity: e.g., pairwise kinematic SZ measurements

• Reionization: kinematic SZ

• CMB lensing cross correlation studies

• …

“Science Book” is focus of next CMB-S4 workshopUniversity of Michigan, tentative dates Aug 31-Sep 1

examples of CMB-S4 science

CHALLENGES • BEAMS: in situ measurement of

beams, esp. sidelobes ( n & polzn dependence, stability)

• BANDPASSES: in situ characterization, matching, polzn dependence, avoiding CO etc

• GROUND PICKUP: shielding, sufficient suppression of scan synchronous pickup, stability

• I Q/U LEAKAGE: n dependence, polarization dependence, stability, spatial dependence

• SENSITIVITY: low loading, high optical throughput

• CALIBRATION: stability, dynamic range, n dependence, pointing jitter

• POLARIZATION ANGLES: in situ measurement, n dependence

• STRIPING: minimize 1/f with fast modulation

FOREGROUNDS

SYS

TE

MATIC

S SE

NS

ITIV

ITY

- Spectral coverage

- Duration of stable conditions (HFI @+-.1mK over 900 days

- Sky coverage [Xcorr, fnl…] (value of northern hemisphere modes?)

litebirdInflation probe pixie Core+ …

Should space aim at r/μ or be definitive?

Complementarity of probes

Data challenges

• Extract the most from this expensive data flow– Moore’ s law on cpus unlikely to be enough– Simulations will become more challenging (and so will

be the size of the analysis groups?), but needed for precision science (and also for accurate science).

• Sharing the data efficiently? – at TOI level? (e.g. to surround pixelization issues) – X-correlation needs a lot of detailed knowledge in both

sides• …

Questions for all of us• When shall we be done (with the CMB) in T, E, B? • Is there a Moore’s law on residual CMB systematics?

• Can ground-based instruments measure the low-l reionization peak? • Can ground-based instruments measure large scale lensing potential? • Can big telescopes get r?• Do you need ground, balloons AND space for future CMB?• Is a space mission without an FTS/spectral measurement worth it? Or

would two smaller missions be better? • Is a space mission with only ~1 degree resolution worth it?• Will ground-based instruments have enough frequency channels to detect

r if 0.01 <r < 0.1? if 0.001 <r < 0.01? What about for other science goals?• How best to combine space, balloon, ground efforts? Does each have a

clear niche for the ultimate final measurements?

• How to address the nature of the anomalies?• How to get to the guaranteed fnl<~ 1 level?• And all other lottery tickets…