Harvard University Department of Physics

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Physics Department Faculty:

Nima Arkani-Hamed

Professor of Physics

PhD 1997, UC-Berkeley

Our current description of the basic interactions in nature, based on the standard model of particle physics and general relativity, is in spectacular agreement with all known experiments. However, it is almost certainly fundamentally incomplete. In addition to difficulties associated with strong quantum gravitational effects at the Planck length, sensible quantum-mechanical theory of gravity, two striking facts about nature clues suggest that we are missing a big part of the picture. The extreme weakness of gravity relative to the other forces, as well as the huge size and flatness of our observable universe, require absurdly delicate adjustments of the parameters of the theory. We expect that new physical principles will be revealed to address these puzzles—the “hierarchy problem” and the "cosmological constant problem.” Fortunately, these mysteries are associated with length scales—the electroweak scale and the Hubble scale—which will be probed experimentally in the near future with particle accelerators and cosmological observations. Therefore theories which address these puzzles are likely to have experimental consequences that will be checked in the next few years.

Nima Arkani-Hamed’s research in theoretical physics is driven by attempting to address these mysteries. Much of his work has centered around addressing the hierarchy problem. Together with Savas Dimopoulos and Gia Dvali, he suggested that the extreme weakness of gravity can be attributed to the existence of large extra dimensions of space, perhaps as large as 100 microns in size, with the scale of quantum gravity lowered to the electroweak scale. This opens up the possibility that quantum gravitational effects can be probed at accelerators and even in table-top experiments. In a different direction, together with Andy Cohen and Howard Georgi he has constructed models where (non-gravitational) extra dimensions are generated dynamically from purely four-dimensional models. This has also led to new approaches to the hierarchy problem. He has also investigated the possibility that gravity is modified at large distances and times in an effort to address various cosmological problems. Most recently, together with Dimopoulos, he has explored the possibility that the fine-tunings for the cosmological constant and hierarchy problems find a common explanation within a huge landscape of possible low-energy worlds that may exist in string theory, leading to a novel proposal for "split" supersymmetry at the large hadron collider.

Recent Talks:

• The Future of Fundamental Physics
• Approaches to the Hierarchy Problem
• Perspectives on Nature's Greatest Puzzles