CMB-S4 Science Book: Working Draft CMB-S4 Collaboration March 5, 2016 Contents 1 Exhortations 7 1.1 Brief History and Current Status of CMB measurements . 8 1.2 SciencereachofCMB-S4...................................... 9 1.3 From science goals to CMB-S4 design . 11 1.3.1 Conceptual design of CMB-S4 . 11 1.3.1.1 Sensitivity and detector count . 11 1.3.1.2 Inflationary B-modes: low ` sensitivity, foregrounds and atmospheric noise mitigation . 12 1.3.1.3 Neutrinos and dark energy: high ` sensitivity . 12 1.3.2 Refining the CMB-S4 science case and key performance parameters . 13 1.4 The Road from Stage 3 to Stage 4 . 13 2 Inflation Physics from the Cosmic Microwave Background 17 2.1 Introduction............................................. 17 2.2 Implications of a detection of primordial gravitational waves with CMB-S4 . 18 2.2.1 The energy scale of inflation . 21 2.2.2 Planckian field ranges and symmetries . 22 2.2.3 Constraints on the graviton mass . 24 2.2.4 Following up on a detection . 25 2.2.4.1 Distinguishing vacuum fluctuations from other particle physics sources ofB-modes.................................. 25 2.2.4.2 Probing matter and gravitational interactions at the inflationary scale . 26 2.3 Lessonsfromupperlimits ..................................... 27 2.4 CMB data products and simulations required to achieve goals for PGW . 30 2.5 Improved constraints on primordial density perturbations . 30 2.5.1 The power spectrum of primordial density perturbations . 31 2 2.5.2 Higher order correlations . 31 2.5.3 Isocurvature........................................ 32 2.6 Constraints on spatial curvature, birefringence, cosmic strings, axions. 32 2.6.1 Spatial Curvature . 32 2.6.2 CosmicBirefringence................................... 33 2.6.3 CosmicStrings ...................................... 33 2.6.4 Anomalies . 33 2.7 Summary .............................................. 33 3 Neutrino Physics from the Cosmic Microwave Background 35 3.1 Introduction............................................. 35 3.2 NeutrinoMass ........................................... 36 3.2.1 TheoryReview ...................................... 36 3.2.2 Observational Signatures and Target . 38 3.2.3 CMBLensing....................................... 39 3.2.4 Other Cosmological Probes . 40 3.2.4.1 SZ Cluster Abundance . 40 3.2.4.2 Cross-correlations with External Datasets . 40 3.2.4.3 Relation to Other Surveys . 40 3.2.5 Forecasts ......................................... 40 3.2.6 Relation to Lab Experiments . 40 3.3 E↵ectiveNumberofNeutrinos................................... 42 3.3.1 Thermal History of the Early Universe . 42 3.3.2 Natural Target . 44 3.3.3 Observational Signatures . 46 3.3.4 Forecasts ......................................... 47 3.4 Sterile Neutrinos and Axions . 47 3.4.1 SterileNeutrinos ..................................... 47 3.4.2 Axion-like Particles . 48 3.5 Complementarity of CMB and BBN . 49 CMB-S4 Science Book 3 3.5.1 Standard Big Bang Nucleosynthesis . 49 3.5.2 Beyond the Standard Model . 50 3.5.3 ComplementaritywiththeCMB ............................ 50 4 Dark Energy and Dark Matter 53 4.1 DarkEnergyandModifiedGravity ................................ 53 4.1.1 Models and parameters . 53 4.1.2 CMB Dark Energy Observables . 55 4.1.2.1 Cluster abundance and mass . 55 4.1.2.2 Lensing . 57 4.1.2.3 Kinematic SZ . 58 4.2 DarkMatter............................................. 59 4.2.1 Dark Matter Annihilation . 59 4.2.2 Non-standard Dark Matter Interactions . 59 4.2.2.1 Dark Matter-Baryon Scattering . 60 4.2.2.2 Dark Matter-Dark Radiation Interaction . 60 4.2.3 Ultralight axions . 62 5CMBLensing 67 5.1 IntroductiontoCMBLensing ................................... 67 5.2 MeasuringCMBLensing...................................... 68 5.2.1 Constructing a Lensing Map . 68 5.2.2 LensingPowerSpectrum................................. 70 5.3 Cross Correlations with CMB Lensing . 71 5.3.1 CMB Lensing Cross Galaxy Density . 73 5.3.2 CMB Lensing Cross Galaxy Shear . 74 5.3.3 CMB Halo Lensing . 74 5.4 Delensing .............................................. 75 5.5 Systematic E↵ects and Mitigation . 77 5.5.1 Astrophysical Systematics . 78 5.5.2 InstrumentalandModelingSystematics . 78 CMB-S4 Science Book 4 5.6 Parameter Forecasts with Lensing . 79 6 Simulations and Data Analysis 81 6.1 Introduction............................................. 81 6.2 DataAnalysisOverview ...................................... 81 6.3 Time-OrderedDataProcessing .................................. 84 6.3.1 Pre-Processing and Mission Characterization . 84 6.3.2 Map-Making ....................................... 84 6.4 ComponentSeparation....................................... 87 6.4.1 Introduction........................................ 88 6.4.1.1 Motivations . 88 6.4.1.2 Definition of component separation . 88 6.4.2 Descriptionofmethods ................................. 90 6.4.3 Questionstobeaddressedduringfollow-upstudies . 91 6.5 StatisticsandParameters ..................................... 93 6.5.1 Currentpractice ..................................... 93 6.5.2 Challenges......................................... 95 6.5.2.1 Combining di↵erentdatasets........................ 95 6.5.2.2 Foreground-related uncertainty on cosmological parameters . 95 6.5.2.3 CMB lensing covariances for CMB S4 . 96 6.5.2.4 Delensing................................... 98 6.6 SimulationOverview ........................................ 99 6.7 SkyModeling ............................................ 100 6.7.1 Theskymodelingpipeline................................ 101 6.7.1.1 The multi-component sky model . 102 6.7.1.2 Sky emission observations . 102 6.7.2 TheGalacticinterstellarmedium . 102 6.7.2.1 Synchrotron . 102 6.7.2.2 Thermal dust . 102 6.7.2.3 Spinningdust ................................ 103 CMB-S4 Science Book 5 6.7.2.4 Free-free ................................... 103 6.7.2.5 Atomic and molecular lines . 103 6.7.3 CMB Secondary Anisotropies and Extragalactic Sources . 103 6.8 DataSimulation .......................................... 105 6.8.1 TimeDomain....................................... 105 6.8.2 Map Domain . 106 6.8.3 Spectral Domain . 106 6.9 The Simulation and Data Analysis Pipeline . 107 6.10 Forecasting ............................................. 108 6.10.1 Limits on the tensor-to-scalar ratio . 108 6.10.1.1 Spectrum-based domain forecasting . 108 6.10.1.2 Map-based domain forecasting . 108 6.10.2 Limits on parameters from TT/TE/EE/ ......................109 6.10.2.1 Instrument and atmospheric noise . 110 6.10.3 Limits on parameters from tSZ/kSZ . 111 6.11 Validation and Verification . 112 6.12 ImplementationIssues ....................................... 113 6.12.1 Time-Ordered Data Volume & High Performance Computing . 113 6.12.2 Application Interfaces, Data Objects and Formats . 114 CMB-S4 Science Book 6 CMB-S4 Science Book 1 Exhortations (send feedback on this chapter to [email protected]) Fourteen billion years ago, in the first fraction of a second of our universe’s existence, the most extreme high-energy physics experiment took place. Our ability to use the cosmic microwave background (CMB) to investigate this fantastic event, at energy scales a trillion times higher than can be obtained at the CERN, is at the very core of our quest to understand the fundamental nature of space and time and the physics that drive the evolution of the universe. The CMB allows direct tests of models of the quantum mechanical origin of all we see in the universe. Subtle correlations in its anisotropy imparted by the interplay of gravitational and quantum physics at high energies contain information on the unification of gravity and quantum physics. Separately, correlations induced on the background at later times encode details about the distribution of all the mass, ordinary and dark, in the universe, as well as the properties of the neutrinos, including the number of neutrino species and types, and their still unknown masses. Here we describe the scientific case for the next generation ground-based cosmic microwave background experiment, CMB-S4, consisting of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras that will provide a dramatic leap forward in cosmological studies, crossing critical thresholds in testing inflation, the number and masses of the neutrinos or the existence of other ‘dark radiation’, providing precise constraints on the nature of dark energy, and testing general relativity on large scales. Through the e↵orts of the CMB experimental groups over the last decade, the technologies needed for CMB-S4 are now in place. There are, however, considerable technical challenges presented by the required scaling up of the instrumentation as well as by the scope and complexity of the data analysis and in- terpretation. CMB-S4 will require: scaled up superconducting detector arrays with well understood and robust material properties and processing techniques; high throughput mm-wave telescopes and optics with unprecedented precision and rejection of systematic contamination; full characterization of astronomical foreground emission; large cosmological simulations and theoretical modeling with accuracies yet to be achieved; and computational methods for extracting minute correlations in massive, multi-frequency data sets contaminated by noise and a host of known and unknown signals. The purpose of this document is to set the scientific goals for CMB-S4 and (eventually) the