Research

Quantum gravity epoch

Understanding the nature of the “big bang” is at the heart of cosmology and requires synthesis of a wide variety of fundamental elements such as quantum theory, gravitational physics, particle physics and/or string theory. Further, for a theory of the big bang to be confirmed or falsified, it has to be connected to experiment and observations. Theoretical members of the group are pursuing fundamental aspects of quantum theory, gravitational and particle physics, and are tying in their models with current cosmological data. Of interest are the number of dimensions and how we can detect any extra dimensions, the energy of the vacuum (“dark energy”) and why it is so small yet still not zero, dualities between gravity and quantum field theory, and the significance of life in our observable universe.

Particle physics in cosmology

Soon after the big bang, the universe is filled with a dense, hot plasma containing fundamental particles. From this primordial soup, a homogeneous universe has to emerge, most antimatter has to annihilate with matter and disappear, electroweak symmetry of the Standard Model is broken, and matter has to form protons, neutrons, and the nuclei of the light elements. The light nuclei then have to combine with electrons to form atoms. Once atoms are formed, scattering between light and matter becomes much rarer, and the universe effectively becomes transparent: we can observe light from the other side of the universe. These formation phases determine crucial aspects of cosmology such as the abundance of protons and neutrons, and other as yet unseen (but felt!) elements such as dark matter, the neutrino background, and magnetic fields. Depending on the nature of the fundamental interactions, phase transitions can lead to the presence of exotic remnants such as magnetic monopoles, cosmic strings, quark nuggets, a background of gravitational waves, and black holes. Members of the group are investigating the nature of the fundamental interactions and the consequences for terrestrial experiments and cosmological observations. They are also using observations of extreme objects such as neutron stars and supernovae as probes of neutrino properties and other aspects of fundamental physics.

Dark Ages and First Light

The cosmic Dark Ages started when the universe became transparent, and ended during the era of Cosmic Dawn, when the first stars, galaxies, and black holes emerged only 200 to 500 million years after the Big Bang.  During the Dark Ages, the Universe consisted almost entirely of neutral hydrogen gas (75% by mass).  Members of the group are building novel low-frequency radio experiments in collaboration with colleagues around the world to detect and characterize neutral hydrogen from this period for the first time, as well as observing the progenitors of galaxies from the epoch of Cosmic Dawn directly with the Hubble Space Telescope, James Webb Space Telescope, and ground-based optical/IR instruments.

Epoch of Reionization

Early galaxies caused the last major phase transition in the Universe approximately 1 billion years after the Big Bang, as the UV and X-ray emission from their constituent stars and black holes ionized the residual primordial hydrogen gas between galaxies.  ASU Cosmology Group members are leading observational programs charting the evolution of galaxies during this epoch of reionization and their influence on the intergalactic medium, and developing new techniques to enable and exploit 21 cm surveys of the intergalactic medium from the Murchison Widefield Array (MWA), Hydrogen Epoch of Reionization Array (HERA), and other radio telescopes.

Galaxy Evolution and Supermassive Black Holes

As galaxies grow, it is clear that massive black holes play a crucial role in their evolution  by acting as central engines for a variety of extremely violent cosmic processes, some of which dominated events in the early Universe.   Our members are observing unique active galactic nuclei (AGN) to understand how supermassive black holes accrete matter from their surroundings, and how feedback from these objects shape the subsequent processes of galaxy formation and evolution. We are also analyzing observations of molecular gas in galaxies and clusters, using instruments like the Atacama Large Millimeter/submillimeter Array (ALMA), to learn about star formation and other processes.

Cosmic Microwave Background

At microwave frequencies, the radiation we observe on the sky tells us about how the universe looked about 380,000 years after the big bang. The statistics of fluctuations in the intensity and polarization of this radiation tell us what the universe is made of and how it has behaved since the Big Bang, and potentially bear the imprints of new physics. A small fraction of these photons have undergone scattering in the recent universe, and the signatures of various scattering processes (called "secondary effects", such as gravitational lensing and interactions with clumps of ionized gas) can act as probes of the total distribution of matter, the sum of neutrino masses, early universe physics, and the astrophysics of galaxies, clusters, and the intergalactic medium. ASU Cosmology Group members work with data from the Atacama Cosmology Telescope (ACT), the Simons Observatory (SO), CMB-S4, and the Fred Young Submillimeter Telescope (FYST) to realize the scientific potential of the cosmic microwave background, and also design new ways to analyze current and future data.

Large-Scale Structure

The large-scale clustering patterns of galaxies and other tracers of large-scale structure can provide clues as to the nature of dark energy, dark matter, and beyond-Standard-Model physics that may be operative in the early universe. At very large distances, these clustering patterns can be cleanly predicted from theory; at very small distances, we must resort to computer simulations; and in the intermediate regime, a perturbative description can be formulated, based on ideas from effective field theories of particle physics. ASU Cosmology group members work across all of these regimes, developing new predictions for large-scale structure and connecting these predictions with observations. Clustering patterns in the distribution of neutral hydrogen gas, as observed in redshifted 21cm radiation, are a potentially powerful probe of large-scale structure, and ASU researchers work with data from telescopes custom-designed to measure this radiation, namely the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD).

Astrobiology

One of the distinctive properties of the universe is that it supports life. A major unsolved problem that we are tackling is whether the observed bio-friendliness of the universe is a coincidence, or evidence for a multiverse, or arises in some other way. The subject cannot be divorced from the question of the nature and origin of the laws of physics. An ultimate explanation of physical existence needs to include account of how the laws of physics arise and whether they are unique. A corollary of the fact that the universe is so well suited to life is the question of whether it is confined to Earth, or widespread in the galaxy and beyond. The answer hinges on the probability that life will emerge under earthlike conditions. One way we are investigating the problem is to seek evidence for multiple terrestrial origins of life, for example, by looking for a “shadow biosphere” of radically different microbial life intermingled with known life. If it can be established that there is more than one form of life on Earth then it is certain that the universe will be teeming with it, and the question of whether or not we are alone in the universe will take on a new urgency.

Instrumentation

Our group members are active in the design and development of the next generation of detectors and instruments for observational cosmology, from new CCD arrays for UV through near-IR imaging to radio, microwave, and THz receivers. We are also working on smaller-scale laboratory experiments for precision measurements and tests of fundamental physics. We are pushing the state of the art in technology to expand our understanding of the evolution of the Universe and its fundamental properties.