Cosmology observation and instrumentation work at the department includes supernovae, the cosmic microwave background, and large surveyes of galaxies. Theoretical work at the department includes the development of phenomenological aspects, and subsequent observational tests, of cosmological theories. Measurements that constrain fundamental physics are of particular interest to members of the cosmology group.

Katherine Freese works on a wide range of topics in theoretical cosmology and astroparticle physics. She has been working to identify the dark matter and dark energy that permeate the universe as well as to build a successful model for the early universe immediately after the Big Bang. She is author of a book The Cosmic Cocktail: Three Parts Dark Matter, published in June 2014 by Princeton University Press.

Ariel Goobar’s research focuses on transient phenomena in a cosmological context, e.g., the use of Type Ia supernovae to study the expansion history of the Universe to measure the properties of the dark universe (see snova.cosmoparticle.com).  Since the dawn of gravitational wave astronomy, the group is also working on the study of electromagnetic counterparts from the merger of compact objects, neutron stars and black holes (see great.cosmoparticle.com ).

Jón Gudmundsson contributes to a range of CMB experiments including a satellite mission called Planck and a balloon-borne experiment named SPIDER. The Planck satellite has completed observations and is expected to publish its final legacy data release in 2018. The SPIDER balloon-borne experiment completed its first flight from Antarctica in January 2016 and is now in data analysis phase. The SPIDER collaboration is also preparing for another flight, which is scheduled for the austral summer of 2017–2018.

In 2017, Katie Freese, Jón Gudmundsson, and other members of the CoPS division started contributing to a new CMB experiment designed to measure the polarization of the cosmic microwave background from the Atacama desert in Chile.

Jens Jasche is a cosmologist and Astro-statistician working at the interface between theory and observations. His research focuses on understanding the gravitational evolution of the cosmic large-scale structure and the imprints of dark matter and dark energy in large surveys of the observed galaxy distribution. A common element in all his research is the development and application of modern data science as well as artificial intelligence techniques to characterize fundamental properties of the dark sector physics, the theory of gravity as well as identifying new physical phenomena in observations. His research activities also encompass the propagation of ultra-high energy cosmic rays and the detection and measurement of large-scale cosmic magnetic fields.​

Edvard Mörtsell develops phenomenological aspects, and subsequent observational tests, of cosmological theories, specifically phenomena attributed to the gravitational effects of dark matter (additional attractive gravitational forces) and dark energy (a repulsive gravitational force). This work includes cosmological distance probes, gravitational lensing and generalized gravity theories.

Hiranya Peiris is a cosmologist working in both theory and observation. She studies the fossilized heat of the Big Bang, the cosmic microwave background (CMB), to understand the physics that governed the very early universe. She uses large surveys of galaxies to study the subsequent evolution of the universe, with a particular focus on measurements that constrain fundamental physics. She also work at the interface between cosmology and theoretical physics, to refine physical models that explain cosmological observations. The emerging field of astrostatistics, and the development of optimal numerical algorithms capable of handling very large datasets, are common threads that run through much of her work.