Connecting Fundamental Physics with Observations

Date :From 2009-02-16 To 2009-04-30
Advisory committee :
Local coordinators :Rong-Gen Cai,Xue-Lei Chen,Zu-Hui Fan,Yi-Peng Jing,Shuang-Nan Zhang,Xin-Min Zhang
International coordinators :Robert Brandenberger,Richard Easther,Tan Lu, Ue-Li Pen,Elena Pierpaoli,Joe Silk

Observational cosmology has made enormous progress over the past two decades. Precision anisotropy experiments have provided us with detailed temperature maps of the cosmic microwave background (CMB). Redshift surveys are probing the universe to an increasing depth,yielding maps of the distribution of luminous matter in three dimensions.

New windows to explore the universe (such as weak gravitational lensing,Sunyaev-Zeldovich maps, 21cm surveys, CMB polarization)are opening up and will start producing results within the coming years.

The observational results of the past decade have revealed outstanding mysteries about the structure of the universe which we live in. Foremost, the universe appears to be dominated by dark energy (contributing about $70%$ of the energy), a mysterious component of energy which we know nothing about, and by dark matter ($25%$ of the energy). The dark energy problem is particularly pressing, not only because it concerns the dominant energy component of the universe, but in particular also since it connects with the question of why the cosmological constant is so small, and since understanding dark energy might also shed a better light on the basic mechanism of cosmic inflation. It is thus one of the greatest current challenges in physics to probe the properties of dark energy. Particle theorists do have candidates for dark matter, but it is also a key challenge for cosmology to try to either directly or indirectly detect the dark matter. A close connection between observational cosmologists,cosmologists with a phenomenological bent, high energy theorists,and experts working at the forefront of theoretical research is required in order to make progress on these key questions. One of the main goals of the KITPC cosmology program is to bring experts in the above diverse fields together to identify and work out new ways to probe aspects of dark energy, and to study new signatures for different dark matter models.

To date, the current standard paradigm of early universe cosmology, the inflationary universe scenario, has been very successful phenomenologically at predicting and explaining the observations. Nevertheless, inflationary cosmology is plagued with key conceptual problems. New fundamental physics is required to either provide a good realization of inflation, or an alternative to inflation. Since new fundamental physics will be key to the construction of a satisfactory early universe cosmology, the question arises as to how we can probe aspects of fundamental physics using observations. Another main goal of the cosmology program will be to develop further tests of inflationary universe scenarios and to identify more signatures of recently proposed alternatives to inflationary cosmology.

Dark energy, dark matter and theories of structure formation are thus the three key scientific focal points of the KITPC cosmology program. Given the large amount of new data in cosmology, the prospects of having initial data from the Large Hadron Collider at CERN,and the magnitude of the theoretical challenges facing cosmology, the he time is ideal to bring together high energy theorists and cosmologists
to combine their talents to develop new ways to probe fundamental physics with current and future observations. What signatures of models of dark energy should observers be looking for? What can planned observational strategies tell us about fundamental physics? Can new cosmological signatures of existing dark matter candidates be developed? How can future observations best test robust predictions of inflation? These are some of the questions which we hope to develop answers to by fostering close interplay between high energy theorists, theoretical and more phenomenological cosmologists and observers. We hope that by bringing cosmologists of a more phenomenological bent together with high energy theorists developing new paradigms for early universe cosmology, the KITPC program will be able to foster the kind of new breakthroughs in cosmology which the very successful 1984 cosmology workshop at the ITP (now KITP) in Santa Barbara provided, a workshop which played a key role in the development of both the ``Cold Dark Matter Model'' of structure formation and the ``Topological Defect'' models.

The KITPC cosmology program will have an educational component. Some of the more senior participants will give short lecture series on advanced topics in cosmology. The purpose of these lecture series is to provide the local participants with the background to be able to become involved in the research programs to be initiated at the Institute. New research programs will be initiated through three days focused mini-workshops which will bring experts in different subfields together to stimulate collaborations. The program coordinators will make an effort to establish links with researchers in cosmology groups thoughout China to make sure that the KITPC cosmology program will lead to a long-term benefit for cosmology research in China.