String Phenomenology and Cosmology

Date :From 2011-09-06 To 2011-11-11
Advisory committee :
Local coordinators :Bin Chen(陈斌), Bo Feng(冯波), Miao Li(Contact Person), Tian Jun Li(李田军), Jianxin Lu(卢建新), Hong Lu(吕宏)
International coordinators :Ralph Blumenhagen, Michael Douglas (Chair), Miao Li, Hong Liu, Fernando Quevedo

With the turn-on of LHC, particle physics is entering an exciting new era in which the mechanism of electroweak symmetry breaking will be revealed and likely other clues to physics beyond the Standard Model may be found. As a leading candidate for the quantum theory of gravity, string theory unifies all fundamental interactions in nature. As such, it provides the only known framework in which one can systematically explore physics beyond the Standard Model from a fundamental description (top-down approach). During the last two decades, developments in string theory have inspired or influenced many new ideas in phenomenological model building (bottomup approach), including large extra dimensions, Randall-Sundrum models, and many others. Almost all current leading phenomenological scenarios of electroweak symmetry breaking, including  supersymmetry, can be (or have been) embedded in string theory. In the LHC era, with guidance from experimental data, we expect interactions between string phenomenology and particle physics will further be reinforced and intensify, likely leading to new breakthroughs.

Furthermore, there has been recent outstanding progress in large scale observation of our universe. The evidence for Dark Energy is already compelling and the precision level achieved on observations of the cosmic microwave background, by WMAP and previous efforts, has allowed a detailed understanding of the structure of the density perturbations. With the imminent launch of the PLANCK satellite and other planned projects, these observations will reach a new level of precision. Modifications to the standard picture, such as deviations from a Gaussian spectrum and even the potential existence of observable primordial gravitational waves, could be discovered or else subjected to much stronger bounds. Data on bispectrum and even trispectrum will help to constrain inflation models and rule out many of them. Classes of cosmological models based on a fundamental theory such as string theory could then be contrasted with observations and a closer interaction between string theorists and cosmologists is expected.

The last decade has also seen many new conceptual and technical developments in string phenomenology itself, in confronting the problem of moduli stabilization characterizing the string landscape (addressing general issues such as dark energy and supersymmetry breaking), in explicitly constructing both particle physics models (from intersecting branes, heterotic, F-theory constructions) and the first computable string models of inflation (brane and moduli inflation, etc), and in identifying possible stringy signatures in colliders and a variety of other particle physics and astrophysical experiments. Contrary to field theoretical models of particle physics, a successful string construction should satisfy a large number of consistency conditions and be consistent with all particle physics and cosmological data. Given the importance of the problem, given possible new exciting experimental data in the next couple of years, and given that much theoretical progress has been made in string phenomenology during the last decade, we believe it will be fruitful to have a KITPC program in the fall of 2011 devoted to string phenomenology and cosmology, to bring experts together to exchange ideas and collaborate, and to help educate young people interested in this exciting field.

The topics we plan to cover range from more phenomenological, such as collider physics, cosmology (including inflationary and post-inflationary cosmology and alternatives to inflation) and contact with string-inspired extensions of the Standard Model, to more formal, such as the theory of compactification, and development of related mathematical and computational methods. In the area of related mathematics, Gang Tian has offered the cooperation of his institute in Beijing.

The opportunity of bringing global expertise to China, in an area which is likely to see significant development in the next decade, is clearly very valuable. It will inspire new research, allow current international links to be strengthened, and lead to initiation of fresh collaborations. The program would involve many research talks from Chinese scientists and the wider community, as well as pedagogic lectures from world experts aimed at local students/postdocs. We believe that the acceptance of this proposal will benefit the KITPC, the research community in China, and lead to progress of this exciting field.