ACT Collaboration

ACT Collaboration
Name	ACT Collaboration
Type	International scientific collaboration
Founded	1990s
Headquarters	Princeton University
Fields	Cosmology, Astrophysics
Instruments	Atacama Cosmology Telescope

Contents

ACT Collaboration The ACT Collaboration is an international consortium of researchers operating the Atacama Cosmology Telescope to map the Cosmic Microwave Background with arcminute resolution, linking institutions such as Princeton University, Johns Hopkins University, University of Pennsylvania, Yale University, and University of Chicago in pursuit of precision measurements that inform models like ΛCDM model and probe phenomena including inflationary cosmology and dark matter through interactions with datasets from missions such as Planck (spacecraft), Herschel Space Observatory, South Pole Telescope, BICEP2, and WMAP.

History

The project traces origins to design studies influenced by experiments such as BOOMERanG, MAXIMA (balloon experiment), DASI, and theoretical motivations from papers by Alan Guth, Andrei Linde, and Viatcheslav Mukhanov on inflation (cosmology). Early instrument proposals involved collaborations among groups at Cornell University, Carnegie Mellon University, University of California, Berkeley, and University of Toronto. Construction in the Atacama Desert region leveraged infrastructure near Cerro Toco and coordination with facilities like the ALMA Observatory and logistical support from National Science Foundation-funded programs. Subsequent expansions and upgrades paralleled developments at NRAO and bilateral links with CONICYT partners in Chile.

The primary facility, the Atacama Cosmology Telescope, uses receivers employing technologies advanced by teams from NASA Jet Propulsion Laboratory, MIT, University of California, Santa Barbara, Cardiff University, and Imperial College London. Detector arrays include transition-edge sensors influenced by work at NIST and multiplexing readout systems developed with expertise from California Institute of Technology and Stanford University. Optical design and cryogenic systems drew on engineering from Ball Aerospace and collaborations with University of Illinois Urbana-Champaign and Kyoto University. Survey strategies were optimized alongside contemporaneous programs like Sloan Digital Sky Survey and Dark Energy Survey to produce wide-field maps overlapping with surveys from BOSS and follow-up spectroscopy from Keck Observatory and Very Large Telescope.

Pipeline development incorporated algorithms related to methods used in Planck (spacecraft) analysis and map-making techniques similar to those of HEALPix implementations and Bayesian frameworks influenced by work at Max Planck Institute for Astrophysics and Princeton Plasma Physics Laboratory. Foreground separation engaged cross-correlation with catalogs from Herschel Space Observatory, Spitzer Space Telescope, and radio surveys like NVSS and SUMSS, while cosmological parameter estimation utilized tools from teams at University of Cambridge, University of Oxford, and Flatiron Institute. Statistical analyses referenced likelihood frameworks akin to those applied by WMAP and model comparison approaches used by groups at Berkeley and Rutgers University.

ACT produced high-resolution measurements of the Cosmic Microwave Background temperature and polarization power spectra contributing to constraints on parameters of the ΛCDM model, neutrino physics linked to results from Super-Kamiokande and IceCube, and joint analyses with Planck (spacecraft) that refined estimates of the Hubble constant in the context of tensions with SH0ES measurements. ACT data advanced detection of gravitational lensing of the CMB, informing mass maps compared to results from CFHTLenS and DES (Dark Energy Survey), and enabled measurements of the Sunyaev–Zel'dovich effect in galaxy clusters characterized in catalogs from ROSAT and follow-up with Chandra X-ray Observatory and XMM-Newton. Polarization studies intersected with searches for primordial B-modes pursued by BICEP/Keck and theoretical implications discussed in works by Paul Steinhardt and Joao Magueijo.

The collaboration maintained formal and informal partnerships with major observatories and consortia including Planck (spacecraft), Herschel Space Observatory, South Pole Telescope, BICEP2, Simons Observatory, and institutions such as Princeton University, Yale University, University of Pennsylvania, Johns Hopkins University, Flatiron Institute, MIT, Caltech, NRAO, ALMA Observatory, Keck Observatory, and funding agencies including National Science Foundation and international research councils like STFC and NSF-partner programs. Cross-project science alliances included joint analyses with teams from DES (Dark Energy Survey), ACTPol, AdvACT, and planning dialogues with future missions such as CMB-S4 and LiteBIRD.

Public data releases followed precedents set by Planck (spacecraft) and WMAP, providing maps, power spectra, catalogs of Sunyaev–Zel'dovich effect clusters, and lensing products integrated with archives used by NASA/IPAC and community tools like HEALPix and astrophysical software from Astropy and GetDist. Data products were archived in repositories accessible to researchers from institutions such as Princeton University, Flatiron Institute, Harvard–Smithsonian Center for Astrophysics, European Southern Observatory, and through community platforms interoperable with datasets from Sloan Digital Sky Survey and Dark Energy Survey.