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Stage-IV CMB Experimental Considerations and Trade-offs

Stage-IV CMB experiments led by Assistant Professor Chao-Lin Kuo from Stanford University's SLAC National Accelerator Laboratory aim to deliver groundbreaking insights into inflationary tensor modes and CMB lensing, among other key areas in cosmology and astrophysics. The experiments involve trade-offs between exploring tensor modes and lensing effects, offering significant potential for advancing our understanding of fundamental physics. Key considerations include sensitivity to tensor modes, resolution, and sky coverage, with implications for unveiling the mysteries of the early Universe and dark energy.

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Stage-IV CMB Experimental Considerations and Trade-offs

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  1. Experimental considerations for Stage-IV CMB experiments Chao-Lin Kuo Assistant Professor Department of Physics, Stanford University SLAC National Accelerator Laboratory

  2. What can a Stage-IV CMB exp. Deliver? – Inflationary tensor-modes (gravitational waves) • Comprehensive, conclusive search for degree-scale B-modes from the ground • Increase the significance and minimize sample variance, in the event of a detection with stage-III experiments – CMB Lensing • Sum of neutrino masses • Unique constraints on early dark energy • Mass calibration for weak lensing surveys – Ancillary science • Number of relativistic species Neff • Improvements on Ωk, ns, dns/dlnk, and other inflationary parameters • Dark energy/GR test/non-Gaussianity with SZ clusters • Test of CPT conservation through cosmic birefringence, stringy B-modes, cosmic axions, signatures of bubble collision • Astrophysics: reionization, cluster dynamics, cross-correlation astrophysics

  3. What can a Stage-IV CMB exp. Deliver? – Inflationary tensor-modes (gravitational waves) • Comprehensive, conclusive search for degree-scale B-modes from the ground • Increase the significance and minimize sample variance, in the event of a detection with stage-III experiments – CMB Lensing • Sum of neutrino masses • Unique constraints on early dark energy • Mass calibration for weak lensing surveys – Ancillary science • Number of relativistic species Neff • Improvements on Ωk, ns, dns/dlnk, and other inflationary parameters • Dark energy/GR test/non-Gaussianity with SZ clusters • Test of CPT conservation through cosmic birefringence, stringy B-modes, cosmic axions, signatures of bubble collision • Astrophysics: reionization, cluster dynamics, cross-correlation astrophysics

  4. Experimental trade-off: Tensor vs. Lensing • Tensor-modes (if detected): • Direct experimental evidence that gravity is quantized • Direct measurement of inflationary energy scale • Illuminate aspects of physics at the Planck scale • Consistency relations with ns , fNL, etc.. • Favors deep observations with wide frequency-coverage • CMB Lensing: • Neutrino mass, early dark energy • High S/N reconstruction of projected matter distribution • Great synergy with other precision cosmology programs • Full implication still to be explored • Favors mid-latitude sites, for large sky coverage and overlap with other surveys

  5. Experimental trade-offs for Tensor • Resolution vs. baffling/instr. rotation • Resolution vs. sensitivity • Statistical removal of lensing vs. delensing • Sky coverage vs. frequency coverage • Re-combination (l~90) vs. Re-ionization (l~5) features

  6. Experimental trade-offs for Tensor • Resolution vs. baffling/instr. rotation • Resolution vs. sensitivity • Statistical removal of lensing vs. delensing • Sky coverage vs. frequency coverage • Re-combination (l~90) vs. Re-ionization (l~5) features

  7. Sensitivity to tensor modes No delensing 100

  8. Sensitivity to tensor modes Iterative delensing Foreground ignored. using a formula given in Smith et al arXiv:1010.0048 100

  9. Experimental trade-offs for Tensor • Resolution vs. baffling/instr. rotation • Resolution vs. sensitivity • Statistical removal of lensing vs. delensing • Sky coverage vs. frequency coverage • Re-combination (l~90) vs. Re-ionization (l~5) features

  10. Beam size vs. baffling/instr. rotation • Good resolution (<5’) alleviates systematics associated with main beam effects – it requires larger optics, however • Compact optics enable complete ground shields against far sidelobes and full instrument rotation – the main beam must be understood very well, however 2 Ongoing “Stage-II” experiments 10m 1m

  11. Experimental trade-offs for Lensing • Ref: KISS Workshop, Caltech, summer 2012 • Very rich physics, a convenient figure of merit is ∑mν, assuming flatness + cosmological const. • In addition, the signature applications are – Early dark energy – Mass calibration for galaxy surveys (e.g., shear bias) – Cross correlation with other tracers • Resolution vs. sensitivity – Well studied and documented in Smith et al CMBPol whitepaper – Comes down to reconstruction noise in deflection field (Hu&Okamoto) • Sensitivity vs. frequency coverage – Foreground for CMB lensing will be less of an issue (filter out l < 500) • South Pole vs. Mid-latitude sites – DES/DESpec overlaps well with South Pole fields (4,000 sq deg); BigBOSS & PFS won’t – For stage-IV CMB, ideally we want to target Euclid and LSST for cross- correlation study w/ CMBLens

  12. Neutrino mass (mostly from lensing) uncertainty in neutrino mass; Flat, w/ H0prior Planck only s(Mn)=0.17 eV W. L. K. Wu • From CMBLensing alone, the natural threshold is around 0.05 eV. This can lead to a detection of non-zero neutrino mass, or can rule out inverted hierarchy (although only marginally) •Cross correlation with other tracers (Ly-α, galaxy surveys, lensing) will reduce the uncertainty • Partly due to degeneracy with other cosmological parameters, to be explored.

  13. Breaking the degeneracy With improved H0prior With improved Ωmprior km/s/Mpc Planck σ(H0)~ 2.0 Planck σ(ωc)~0.002

  14. Wk, Neff, ns Planck ΔΩk~ 0.003 ΔNeff~ 0.06 Δns~ 0.003 0.008 0.0053 0.23 favor large sky coverage in general

  15. Trade-offs for ancillary sience ~1’ • Cluster physics beyond SPTpol/ACTpol • kSZ from reionization • High S/N reconstruction of lensing potential • Bubble collisions • Stringy B-modes • Cosmic birefringence/cosmic axions requiring higher resolution ~10’

  16. Large-scale instrumentation Stage-IV CMB Duplicate (>10x) Focal planes (physical size limited by IR loading, size of vacuum window, lenses)

  17. Large-scale instrumentation at National Labs Stage-IV CMB Duplicate (>10x) Focal planes (physical size limited by IR loading, size of vacuum window, lenses) Fermi-LAT Super CDMS LCLS Detectors • R&D with Cornell Univ. • SLAC made 10 million pixels in total so far via robotic assembly • 80 square meters of silicon sensors • Silicon LAT assembled at SLAC • Scaling up of Germanium sensors and fab throughput

  18. Summary • A stage-IV CMB experiment will deliver exciting science results in physics of particles and fields (HEP) – Inflation: tensor modes, primordial spectra, curvature, etc.. – Neutrinos: absolute mass, number of species – Dark energy, test of gravity/spacetime – Exotic models • The configuration involves complicated trade-offs, which require more theoretical calculations and community input over the next few months • Convergence on a roadmap: large focal plane arrays (~10k elements for each receiver) (“camera”) on multiple platforms (with mixed apertures/sites)?

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