Theoretical Astrophysics
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Theoretical
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Theory Group

The Theory Group of the Santa Cruz Institute for Particle Physics (SCIPP) consists of 8 senior investigators and numerous postdoctoral researchers and graduate students performing research at the confluence of particle physics, astrophysics and cosmology. The group is partially funded by the Department of Energy, NASA and the National Science Foundation. Of the 8 senior members, 5 are members of the UCSC Physics Department, and 3 are members of the UCSC Astronomy and Astrophysics Department:

Faculty:

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Anthony Aguirre is a professor of physics at the University of California, Santa Cruz, and the associate scientific director of the Foundational Questions Institute, a nonprofit organization that he co-founded and co-runs. He received his doctorate in astronomy from Harvard University in 2000 and then spent three years as a member of the Institute for Advanced Study in Princeton before accepting a professorship in the physics department of the University of California, Santa Cruz. He has worked on a wide variety of topics in theoretical cosmology (the study of the formation, nature, and evolution of the universe), including the early universe and inflation, gravity physics, first stars, the intergalactic medium, galaxy formation, and black holes...Website

The principle goal of my research through the years has been to address questions left unanswered by the Standard Model. These questions include understanding the hierarchy between the weak scale and the Planck scale, the strong CP problem, the origin of the generation structure of quarks and leptons, as well as the quark and lepton mass matrix, quantum general relativity and its puzzles, and questions of early universe cosmology, such as the origin of the asymmetry between matter and antimatter, the nature of the dark matter, and the physics which underlies inflation. I have made several important contributions to our thinking about a number of these subjects, and, needless to say, have been less successful in my attacks on others.

In attacking the hierarchy problem, in collaboration with Fischler and Srednicki, I was among the first to suggest that supersymmetry might play an important role, and developed (in collaborations) some of the first phenomenologically sensible models of low energy supersymmetry. Subsequently, Affleck, Seiberg and I were the first to exhibit models of dynamical supersymmetry breaking, and to understand this phenomenon in a general way. With Ann Nelson, Yossi Nir and my student Yuri Shirman, I developed the first realistic particle physics models with dynamical supersymmetry breaking, in which Gauge-Mediated Supersymmetry Breaking" plays a crucial role. On the question of strong CP violation, Fischler, Srednicki and I proposed the Invisible Axion," still among the most plausible solutions of this puzzle and the subject of active experimental search. Fischler and I were among those who first appreciated the cosmological constraints on the axion, and its possible role as a dark matter particle. String theory has lead to a much more sophisticated understanding of the invisible axion, both at a fundamental level and in cosmology, I have devoted much effort in recent years to this issue. I have also been interested in the question of spontaneous CP violation as the explanation of the small value of the $\theta$ parameter of QCD, and again string theory and supersymmetry have helped shape our understanding of these subjects.

From the start of the First String Revolution" in the mid 1980's, I have appreciated that string theory is a tool to investigate the full set of questions of physics beyond the Standard Model, and this has guided many of my investigations of the subject. This research deals with both fundamental issues and issues of a more phenomenological character. In the past, Rohm, Seiberg Witten and I discovered the gaugino condensation" mechanism which lifts the degeneracy among many string vacua. We elucidated the role of Fayet-Iliopoulos D-terms (with Seiberg and Witten) and of world sheet instantons (also with Wen). In more recent years, I have explored the phenomenology of the strongly coupled theory (with Banks), and other issues. I have throughout tried to formulate the problems of string phenomenology in a generic way, with the hope of obtaining robust predictions. In recent years, I have outlined and pursued possible programs to understand whether low energy supersymmetry might be a robust prediction of string theory, and how one might obtain predictions for the pattern of soft breakings. Recently, much of my research in string theory has focussed on understanding the so-called string theory landscape, and whether it predicts phenomena which might be observed at the Large Hadron Collider.

The basic themes underlying my research program involve the study of: (i) the dynamics responsible for electroweak symmetry breaking; (ii) the theory and phenomenology of Higgs bosons; (iii) TeV-scale supersymmetry as a framework for incorporating a weakly-coupled Higgs sector; (iv) the phenomenology of signals for new physics beyond the Standard Model at the Large Hadron Collider (LHC) and future colliders; and (v) connections of low-energy phenomena with fundamental scales that lie beyond the TeV scale (e.g. lepton number violation and implications for neutrino masses).

The properties of the newly discovered Higgs boson have profound implications for the dynamics of electroweak symmetry breaking and the possible structure of new physics that may lie beyond the Standard Model (SM) of particle physics. For example, most approaches to physics beyond the SM include extended Higgs sectors. Present Higgs data suggest that the properties of one of the scalars of the Higgs sector (identified with the observed Higgs boson) must have properties that closely approximate that of the SM Higgs boson. This constraint in turn imposes important constraints on any SM extension. The two-Higgs doublet model (2HDM) is a convenient theoretical laboratory for the study of extended Higgs sectors. Indeed, the two doublet extended Higgs sector is a key component of the simplest supersymmetric extension of the SM.

The theoretical structure and phenomenological profile of the 2HDM has attracted much attention in recent years. My recent work has advocated the importance of a basis-independent treatment of the 2HDM. Recently, I have focused on the relevance of the so-called decoupling and alignment limits of the 2HDM in which one of scalars closely resembles the SM Higgs boson. The basis-independent technology provides a very powerful and simple framework for studying and interpreting these limits.

If new physics beyond the SM emerges at the LHC, it will be essential to develop techniques for measuring new particle interaction strengths at high energy colliders. By detecting relations among various independent couplings, one can ascertain underlying symmetries and distinguish among different theoretical interpretations of the new physics. For example, with sufficient precision, it will be possible to provide convincing evidence for or against a supersymmetric interpretation of new fundamental physics phenomena. A precision Higgs program at the LHC and at a future collider (such as the proposed International Linear Collider) can also provide important clues as to what may lie beyond the Standard Model.

Dr. Joel R. Primack specializes in the formation and evolution of galaxies and the nature of the dark matter that makes up most of the matter in the universe. After helping to create what is now called the "Standard Model" of particle physics, Primack began working in cosmology in the late 1970s, and he became a leader in the new field of particle astrophysics.  His 1982 paper with Heinz Pagels was the first to propose that a natural candidate for the dark matter is the lightest supersymmetric particle.  He is one of the principal originators and developers of the theory of Cold Dark Matter, which has become the basis for the standard modern picture of structure formation in the universe.  With support from the National Science Foundation, NASA, and the Department of Energy, he has been using supercomputers to simulate and visualize the evolution of the universe and the formation of galaxies under various assumptions, and comparing the predictions of these theories to the latest observational data. He organized and led the University of California systemwide Center for High-Performance AstroComputing (UC-HiPACC) 2010-2015.

Primack shared the APS Forum on Physics and Society Award in 1977 with Frank von Hippel of Princeton for their book Advice and Dissent: Scientists in the Political Arena (Basic Books, 1974; New American Library, 1976).  Primack was made a Fellow of the APS in 1988 "for pioneering contributions to gauge theory and cosmology."  He was elected to the Executive Committee of the APS Division of Astrophysics 2001-2002.  He was a member of the APS Panel on Public Affairs 2002-2004, and chaired the APS Forum on Physics and Society in 2005. In 2004 he chaired the APS committee on NASA funding for astronomy. He has served on numerous advisory panels to DOE, NASA, and NSF. In 2006-07 he served on the Beyond Einstein study of the National Academy of Sciences.

In 1995 Primack was made a Fellow of the AAAS "for pioneering efforts in the establishment of the AAAS Congressional Science Fellows Program and for dedication to expanding the use of science in policymaking throughout government".  He has served on the board of the Federation of American Scientists and was a founder of the Union of Concerned Scientists.  His popular articles on efforts to protect the near-Earth space environment have appeared in Bulletin of the Atomic Scientists, Science, Scientific American, and Technology Review. He was a member of the AAAS Committee on Scientific Freedom and Responsibility, and helped to establish the AAAS Science and Human Rights program.  He also served as an adviser to and participant in the Science and the Spiritual Quest project, and as chairman of the advisory committee for the AAAS Program of Dialogue on Science, Ethics, and Religion 2000-2002.

Primack was one of the main advisors for the Smithsonian Air and Space Museum's 1996 IMAX film Cosmic Voyage, and he has worked with leading planetariums to help make the invisible universe visible.  In addition to more than 200 refereed technical articles in professional journals, Primack has written a number of articles aimed at a more popular audience.  These include articles in the World Book Encyclopedia and in publications such as Astronomy, Beam Line, California Wild, IEEE Spectrum, Science, Scientific American, Sky and Telescope, and in the McGraw-Hill Encyclopedia of Science and the Encyclopedia of Astronomy and Astrophysics. With Nancy Abrams, he is the co-author of The View from the Center of the Universe: Discovering Our Extraordinary Place in the Cosmos (Riverhead/Penguin, 2006) and The New Universe and the Human Future: How a Shared Cosmology Could Transform the World (Yale University Press, 2011), both of which are also available in foreign editions.

Research Interests

• Astro-particle Physics
• Particle Dark Matter Searches and Model Building
• High Energy Astrophysics
• Theoretical High Energy
• Physics Particle Physics Beyond the Standard Model
• Models for the Generation of the Matter-Antimatter Asymmetry in the Universe
• Phenomenology of Supersymmetric and Extra-Dimensional Models

My research focuses on theoretical astrophysics and cosmology. Specific topics within these broad areas are: the physics of the intergalactic medium, first light and the dawn of galaxies, high-energy radiation backgrounds, the formation and evolution of massive black holes, the cosmic history of star formation. Other recent interests include the "Via Lactea Project", a suite of extremely high-resolution simulations of the assembly of the dark matter halo of the Milky Way.

My research focuses on the violent universe with an emphasis on stellar explosions, gamma-ray bursts and accretion phenomena. I am particularly interested in understanding the physical processes that govern accretion onto relativistic objects such as black holes and neutron stars.

Post-doctoral Researchers:

• Quantum Information
• Foundations of Quantum Mechanics
• Quantum Metrology
• Quantum Thermodynamics

The research interests of the SCIPP Theory Group fall into two broad topical categories:

• Theory and phenomenology of high-energy particles, with an emphasis on physics beyond the Standard Model of particle physics (Dine, Haber and Profumo)
• Theoretical astrophysics and cosmology (Aguirre, Madau, Primack, Ramirez-Ruiz)

There is a large overlap between the work of the two groups: for example, Dine and Profumo devote much of their studies to theoretical cosmology as well as to models and observational strategies for particle dark matter. The Theory Group hosts a vibrant community of postdoctoral associates and graduate students.

The research focus of the SCIPP Theory Group includes several aspects that have experimental or observational counterparts in other groups within SCIPP. High-energy particle physics is an outstanding example where the expertise of the Theory Group nicely complements the SCIPP experimental efforts, especially in connection with the Large Hadron Collider and the International Linear Collider. Madau, Ramirez-Ruiz, Primack and Profumo are all very active affiliated scientists of the Fermi Large Area Telescope collaboration, and have contributed to many of the key early Fermi studies and publications. The theoretical cosmology studies of Aguirre on Dark energy, and of Madau and Primack on structure formation and evolution, are key to the SCIPP involvement in the Dark Energy Survey and future large surveys.

Symposia & Meetings:

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