For the past two decades, string theory has been one of the most intensely investigated areas of theoretical high-energy physics. This is true chiefly because string theory offers what is currently the most successful method of unifying gravity with the other fundamental forces (strong, weak, and electromagnetic). Results from string theory have also spilled over into many other branches of physics, leading to improved understanding of gauge theories, condensed-matter physics, and heavy-ion physics. String theory has also led to powerful new insights in mathematics. In this project, the Texas high-energy theory group proposes to continue their quest for a deeper understanding of string theory, focusing, in particular, on its connection with cosmology. Making progress in this field requires a many-pronged approach, and the Texas high-energy theory group plans to probe issues ranging from the proper mathematical formulation of the theory to extracting its implications for low-energy physics. At the same they also propose to proceed by following a pragmatic phenomenological approach to questions in cosmology and physics beyond the Standard Model.
The envisioned broader impact activities of this group include the professional training of graduate students and postdocs. They also intend to continue their highly regarding outreach and education activities. For example, Professor Weinberg has recently authored a number of extremely well-received textbooks which are widely viewed as major contributions to the dissemination of knowledge in the scientific community. He also gives numerous public lectures. Likewise, Professor Distler authors a blog which discusses and elucidates many of the important research papers which appear on the daily arXiv listings, and he plans to continue his activity.
The Theory Group has during the grant period pursued research in areas ranging from particle physics phenomenology to cosmology including fundamental questions pertaining to foundations of quantum mechanics, the holographic principle and state of the art quantum field theory. Since the advent of quantum mechanics, which has been remarkably successful in describing nature, deep questions about its interpretation have been lingering since its creation. Professor Weinberg has engaged in a new approach to quantum physics in which the description of reality, in particular measurements of physical quantities, is obtained using new mathematical entities replacing the more conventional wave-functions. Equally challenging are questions that arise when quantum mechanics and gravity are put together. The various challenges are sharpened when considering black holes and the early universe. The advent of modern string theory in the mid-80’s brought new ways of thinking about these problems. In particular, it introduced the concept of holography, which in a nutshell states that the amount of information needed to describe events occurring in space is far less than what had been assumed in the past. Indeed, it had been thought that the necessary information to describe gravitational physics scaled like the volume of the space under study. However, the remarkable discovery was that the information needed scaled like the area of a suitable surface in that space. Holography did lead to substantial progress in understanding quantum field theories (QFT) when the forces involved are strong. This has come to be known as the "AdS-CFT connection". Professor Fischler, students and postdoctoral fellows used this tool to discover phenomena in QFT that otherwise could not have been studied. The new paradigm of holography is also central to Holographic Space Time, which is an attempt to formulate quantum gravity beyond string theory, an endeavor that Fischler with Professor Banks have continued to pursue through this grant. In addition to holography, string theory gave us a portal to discovering challenging and hereto unknown field theories. Professor Distler and students have pursued an active and successful program in constructing and understanding these fundamentally new theories. Professor Kaplunovsky with students discovered exciting phenomena in field theory involving new phases tantamount to discovering new crystalline structures. The group also has an active program studying the period of inflation in cosmology and its implication for measurements of the fossil light, called the microwave background. Professor Paban and students have made substantial progress in extending the predictions of inflation to a large set of initial conditions including assuming that in the early universe the various directions in space were not equivalent. Cosmology, which is a fertile ground for new physics, in particular the question of dark matter, is an active area of research that is pursued by Professor Kilic and students. Professor Kilic also investigated possible phenomena relevant to observation at the Large Hadron Collider, in particular how to improve the reach of searches for new particles whose existence is suggested by the inability of the Standard Model of particle physics to account for the particular value of the Higgs boson mass. He has also worked on improving the precision in the determination of the masses of such new particles. The Theory Group is also involved in an active outreach program, including popular lectures, interviews, and books, in addition to the development of software useful in disseminating scientific results. In conclusion, the Theory Group is engaged in active research covering a wide area of topics at the frontier of theoretical physics.
