Research at CosKASI
Research Overview
The recent progress in understanding the universe, and the massive astronomical data sets from planned surveys, provide unique opportunities to test fundamental laws of physics on cosmic scales. These lead us to new frontiers exploring the origin and fate of the Universe, the detection of invisible dark matter, and the nature of dark energy or gravity beyond Einstein. The next generation of deep wide-field surveys provide a fertile ground for expanding our knowledge and addressing cosmological questions. The Cosmology group at KASI is engaged in several of these major cosmological endeavors, such as the premier spectroscopy wide field survey of the Dark Energy Spectroscopy Instrument, the premier imaging wide field survey of Large Synoptic Survey Telescope, and the unprecedently deep and high resolution Giant Magellan Telescope. Their astronomical data will not only lead to a deeper understanding of our Universe, but deliver new, unexpected discoveries that expand our science framework. We will become central investigators of critical questions about the Universe beyond present knowledge: 1) Initial Seeds - beyond the simplest model of early universe inflation, 2) Dark Matter - beyond the invisibility of dark matter, and 3) Dark Energy - beyond Einstein's gravity and vanishing vacuum energy.
Research on Dark Universe Using Large Scale Structure of the Universe
Cosmology is at its golden ages and it would be a growing field of science in the next couple of decades considering variety of surveys functioning at the moment and the long list of surveys funded and planned to observe the Universe at different wavelengths, scales and depth in the near and far future. Two Nobel prizes in physics (in 2006 and 2011) awarded to cosmology in less than a decade probably reflects the importance of the cosmology at the current span of time.
While there have been many developments in cosmology, there are still many puzzles left to be solved. Dark energy and dark matter that together constitute more than 95% of the energy budget of the universe are still unknown and we have no clue about their nature. Initial conditions of the universe are also unknown and we are not yet confident on the mechanisms and theories that explain how the universe has began. To study the universe and getting closer to these mysterious components of the nature, there have been extensive efforts to build bigger and more advanced telescopes functioning in different wavelengths to probe the universe. Soon we will have the forth generation of astrophysical surveys performing from different corners of the earth (DESI, GMT, TMT, LSST) and from the space (Euclid, WFIRST, JWST) to probe deeper in the cosmos and shed light on these mysterious unknowns.
Korea Astronomy and Space Science Institute (hereafter KASI), considering its vibrant environment having strong infrastructure, rich human resource as well as its modern and up to date technical, instrumentation and observational facilities would certainly allow us to take part as a frontier in this international effort to understand the universe. KASI clearly has the potential to be a part of or involved in most of major international collaborations (as it is already, for example KASI is very much involved with GMT and DESI) and also being active in all fronts from instrumentation design and fabrication to observation and also in data analysis and high level theoretical works. Korea is certainly moving in this direction but still there is a way to go to catch up with frontier countries since no one stands still and to do excellence in science and reach to great achievements it requires huge effort and appropriate planning. Our strategic goal is to be a part of this ambition to get more share for Korea from global science production and major discoveries in astronomy and astrophysics. In this movement KASI is playing a crucial role and we hope we can help it to do its heavy and important duties. In our proposal we aim to become a leading center in cosmology in an international level and grow in different directions and make the environment ready for Korea to become one of the frontier countries in the world in the field of cosmology.
Cosmology group at KASI (hereafter CosKASI) joins Dark Energy Spectroscopic Instrument (DESI). Primary science goal of the DESI experiment is to clarify the nature of dark energy and/or gravity through the BAO and RSD effects, and starting in 2018, it will obtain optical spectra for tens of millions of galaxies and quasars, constructing a 3-dimensional map spanning the nearby universe to 10 billion light years. DESI will be conducted on the Mayall 4-meter telescope at Kitt Peak National Observatory. It is supported by the Department of Energy Office of Science to perform this Stage IV dark energy measurement. Two members of CosKASI participate in DESI from 2014, and collaborate on galaxy clustering and time streaming physics. CosKASI plans to sign up MoA with the Large Synoptic Survey Telescope (LSST) in 2015. LSST is a wide-field survey reflecting telescope that will photograph the entire available sky every few nights. The LSST is currently in its design and mirror development phases. Site construction began in 2014 with engineering first light in 2019, science first light in 2021, and full operations for a ten-year survey commencing in January 2022. CosKASI members join in dark energy working group. DESI is the premier spectroscopic galaxy survey and LSST is the premier imaging galaxy survey. The cross-correlation of both maps will resolve systematics in each survey to enhance cosmological constraints, and provide an unique window to test Einstein's gravity at cosmological scale. In addition, both guide the follow up observations by GMT as pathfinders to righteous targets.
With the facilities available at CosKASI, we are going to investigate key issues of standard model of the Universe, and to test fundamental physics at cosmological scales;
- Initial condition of the universe - beyond the slow roll single field inflation: Although the assumed, scale invariant initial power spectra may be a generic prediction of the simplest scenarios of generation of perturbations during inflation, initial spectra with radical deviations are known to arise from very reasonable extensions, or, refinements to the simplest scenarios. Consequently, cosmological parameter estimation from the CMB anisotropy and the matter power spectrum obtained from redshift surveys, weak gravitational lensing and Ly-alpha absorption, depends sensitively on the dimensionality, nature and freedom in the parameter space of initial conditions. Understanding the initial conditions of the universe and the form of the primordial spectrum is one of the key issues in modern cosmology that can pave the way to understand how our universe began. Measuring non-Gaussianity in the CMB fluctuations can add another dimention to the studies of the early universe since we can break the degenracies between single field inflationary models and scenarios cosnidering more than a single field.
- Dark matter - beyond the invisibility of darkness: Since Zwicky speculated that the Coma cluster may contain a large amount of dark matter (DM) in 1930's, the puzzle of its nature has become one of the foremost unresolved questions of particle physics and cosmology. Simply the existence of dark matter can explain various phenomena in the different scales of astrophysical and cosmological problems. Now more dark matter properties have been discovered and they are not dark any more. The CMB experiments gives precise relic density of dark matter, and the bullet cluster constrains the size of the their self interaction, the warmness of dark matter are more examined by the small scale structure formation such as Lyman alpha forest. The complementary experiments between direct, indirect detection of dark matter and collider experiments also used to find the visibility of dark matter.
- Dark energy versus modified gravity - beyond Einstein’s gravity: The discovery of the cosmic acceleration decades ago~\cite{cosmic_acceleration} has forced cosmologists to modify their simple picture of the Universe, i.e. a universe dominated only by matter and described solely by General Relativity (GR). Over the last ten years, physicists have suggested two main avenues for explaining the late--time acceleration of the Universe. The first is the introduction of Dark Energy (DE), with an effective negative pressure, which dominates the late--time energy density of the Universe thus causing the acceleration. An alternative explanation is to modify the law of gravity on large scales thus altering the predicted expansion history of the Universe to be in line with the observations. With the level of precision available in future surveys, we can use the high resolution maps expected to be gained from next generation surveys to test the foundations of gravity and particle physics. The premier spectroscopic survey DESI will provide us with accessing dynamic potential, and the premier imaging survey LSST will give us to know lensing potential. CosKASI has an advantaged position to test the fundamental knowledge of gravity using both precise maps in near future