Aug 9 – 13, 2021
America/Los_Angeles timezone

The 13th in the series of twice-yearly CMB-S4 workshops will focus on continuing the development of the broadest possible CMB-S4 science case, including in conjunction with other experiments and observatories. It will be a fully online meeting open to CMB-S4 members and non-members alike.

Please familiarize yourself with the meeting code of conduct (linked below) and respect it in all venues.

Connect to the meeting using the zoom app (version 5.3 or later), set your name to "First Last (preferred pronouns)", and mute your microphone. To ask a question please raise your hand or post it to the chat.

The workshop will include:

  • Social time before and after each day's session in, including career/networking and EPO gatherings
  • A session on "Creating Communities of Care" followed by an open discussion with our new Equity, Diversity & Inclusion committee
  • A poster session repeated late Tuesday and early Friday
  • A closed Junior member session
  • A "Teen Jeopardy" EPO event

The core of the workshop will be the 9 science themes, each of which will include a plenary introduction, an extended parallel session, and a plenary summary report. The themes and their conveners are:

Synergies of Large Scale Structure Surveys with CMB-S4 (Andrina Nicola & Emmanuel Schaan)

We will discuss what can only be learned from joint analyses of CMB-S4 and contemporaneous LSS observations at all wavelengths. We will review the landscape of LSS spectroscopic surveys (eg, MegaMapper, Mauna Kea Spectroscopic Explorer), photometric surveys (Rubin, Euclid, Roman), intensity mapping experiments (eg, PUMA) and more. We will point out the cosmology, astrophysics and systematics which benefit most from these synergies (eg, Nx2pt, CMB lensing tomography, kSZ, galaxy lensing calibration, cluster cosmology).

Gravitational Waves (Raphael Flauger & Sarah Shandera)

Gravitational waves provide an unobstructed view of the dynamics of the universe through cosmic history.  Measurements of the CMB, including T, E, and B-modes, inform our understanding of both primordial gravitational waves and potentially sources that could be observed by direct measurements.  This session will consider observables beyond the tensor-to-scalar ratio, and will explore the complementarity of these probes as well as opportunities to make more direct contact between these communities.

The Time-Varying mm-Wave Sky (Gregg Hallinan & Anna Ho)

Recent results from ACT & SPT have demonstrated that CMB experiments can track the dynamic mm-wave sky, with detections of flaring stars and strongly varying extragalactic sources. Searches are underway for new planets in our solar system and GRBs, and there are opportunities for multi-messenger events, such as high-energy neutrinos or gravitational waves. This session will review recent transient science at millimeter wavelengths, with a focus on gamma-ray bursts and stellar flares. We will use these results to discuss what can be achieved with the CMB-S4 surveys.

Backlighting the Baryons with CMB-S4 (Simone Ferraro &  Alexie Leauthaud)

CMB-S4 will fully determine the gas thermodynamics in unexplored environments: the outskirts of low-mass, high-redshift halos. We will discuss the complementarity of CMB (kSZ, tSZ and lensing) with other probes (eg, X rays and QSO absorption lines), and what we they will tell us about galaxy formation, cosmological hydro simulations and baryonic effects in weak lensing.

Messengers from the Early Universe (Nathaniel Craig & Joel Meyers)

Little is known about the history of the universe between the end of inflation and the beginning of big bang nucleosynthesis.  It is during this period that the dark matter and the baryon asymmetry were produced, the origin of each being enormous unsolved problems in astroparticle physics. It may even be important for the origin of the Higgs mass or the strong CP problem.  Relics from this era will leave signatures in both the primary CMB and secondaries, like CMB lensing, often appearing as corrections to Neff and/or the sum of the neutrino masses.  In this session, we will explore the myriad of connections between problems in comic history, fundamental physics and astrophysics that can be addressed through precision measurements of the CMB.

The Galactic ISM in 3D (Brandon Hensley & Gina Panopoulou)

CMB-S4 will make sensitive, high-resolution measurements of the Galactic polarized dust and synchrotron emission over large areas of the sky. We will discuss how these data can probe gas, dust, and magnetic fields over a range of scales, with particular emphasis on synergies with other datasets that enable a three-dimensional view.

From the Dark Ages to Reionization with CMB-S4 (Marcelo Alvarez & Zhilei Xu)

The history of the Universe between recombination and reionization remains mostly an unexplored territory. Reionization leaves imprints on the CMB temperature and polarization (mean optical depth, kSZ, patchy tau). In this session, we will discuss methods of measuring these effects directly from CMB and using cross-correlations utilizing the synergies with galaxy surveys or line intensity mapping. We will also discuss what these measurements tell us about the physics of reionization.

Astrophysics and Cosmology with Galaxy Clusters (Srinivasan Raghunathan &  Heidi Wu)

CMB-S4 will make a giant leap in the field of cluster astrophysics and cosmology by producing a mass-limited catalogue containing 10^5 clusters with close to 1000 distant clusters out to z~>2. In this session we will discuss how these detections and the synergy of CMB-S4 with optical/X-ray surveys such as DES, LSST, eROSITA and the future Lynx/Athena missions will help us understand the physics of the intracluster medium and constrain the model of structure formation in the Universe.

Snowmass Planning and CMB-S4 (Clarence Chang & Scott Dodelson)

Snowmass is a planning exercise for the particle physics community to identify the key questions and opportunities that will inform the strategic plan for the field in the coming decades.  CMB-S4 is the definitive ground-based CMB survey that will allow for deep cosmological insights into particle physics.  This session will bring together Snowmass organizers and members of the CMB-S4 community to identify the opportunities for synergy and cross-collaboration among the communities.

Registration for this event is currently open.