Sidney A. Bludman

Neutrinos at the Particle Physics-Astrophysics Interface

High energy astrophysics/cosmology deals with the testing and application of nuclear and elementary particle physics under extreme conditions that obtain only in compact objects or in the very early Universe. Bludman has studied the birth, evolution, and death of stars and of the Universe. He has studied astrophysical and cosmological constraints on neutrino masses and lifetimes and the role of neutrinos in the atmosphere, the Sun, supernovae, and the early Universe.

Solar Neutrinos and Stellar Structure

The core structure of cool stars, like the Sun, follows directly from pressure equilibrium and is insensitive to radiative opacities. This has enabled Bludman and Kennedy to obtain a simple analytic fit to the mechanical and thermal structure of the present Sun, to adequately describe and interpret the energy and neutrino production in standard and non-standard solar models. In addition, they found a variational formulation for the four equations of mechanical and thermal equilibrium, that permits a new, global approach to stellar structure.

Stellar Collapse and Supernova Explosions

At the end of nuclear burning, massive stars suddenly implode, emitting 10-15% of their rest mass in neutrinos, ejected matter, and light. The general features of the type II supernova were dramatically confirmed in the supernova which exploded in a neighboring galaxy in 1987, but the underlying mechanism - involving nuclear physics, neutrino physics, radiative hydrodynamics, and general relativity- remains obscure and controversial. Bludman has focused on the role of neutrino transport in making a supernova explosion. Together with Cernohorsky and Smit, he found a simple analytic algorithm for the transport of neutrino flux and energy in a supernova explosion.
Cosmological Smooth Energy

The Universe is apparently flat, has a low matter density, but a somewhat larger static or dynamic smooth energy density, which is now static or nearly static.  The supernova bound on the quintessence equation of state requires either (1) a cosmological constant or other fine-tuned "crawling quintessence" or (2) "roll-over quintessence" that tracked until recently, but now became slow rolling, because of a sharp increase in potential curvature.  Thus, fine-tuning is required by constant equation of state and inverse power potentials, but can be avoided by the SUGRA and Skordis-Albrecht potentials and other good trackers, provided quintessence energy domination and slow roll both began only recently.  This makes the time in which we live special in two respects.                     

Extending earlier anthropic arguments of Weinberg, Bludman and Roos have  shown that the observed smoooth energy density is reasonably necessary, for the timely evolution of large scale structure and of conscious observers. Indeed, the vacuum energy observed is anthropically even more likely for quintessence (dynamic vacuum energy) than for a cosmological constant (static vacuum energy).

• Prof. Emeritus Staff Physicist, Lawrence Berkeley Laboratory and Lecturer, University of California (1952-61)
• Professor of Physics & Astronomy, University of Pennsylvania (1961-99)
• Visiting Fellow, Institute for Advanced Study (1956-57)
• Institute for Theoretical Physics, University of California, Santa Barbara (1985, 1997); Center for Particle Astrophysics, Berkeley (1990-93)
• Institute for Particle and Nuclear Astrophysics, Lawrence Berkeley Laboratory (1994-95)
• Institute for Nuclear Theory, University of Washington (1996)
• Deutsches Elektronen-Synchrotron, Hamburg (1998- )
• Visiting Professor Imperial College (1967-68)
• Tel-Aviv University (1971-72)
• Hebrew University (1976-77)
• Guggenheim Fellow (1983-84)
• Scientific Director, Les Houches Summer Institute on Supernovae (1990).
• Member of the Arts and Sciences Medal Awards Committee, Franklin Institute Visiting Professor, DESY Theory Group, Hamburg (1999- )

• Analytic Models for the Mechanical Structure of the Solar Core, (with D.C. Kennedy), Astrophys. J. 525, 1024 (1999).
• Closure in Flux Limited Neutrino Diffusion and Two Moment Transport, (with J.M. Smit, L.J. van den Horn), Astronomy and Astrophysics 356, 559 (2000).
• Smooth Energy: Cosmological Constant or Quintessence?, (with M. Roos), Astroph. J. 547, 77 (2001).
• Tracking Quintessence Would Require Two Cosmic Coincidences, Phys. Rev. D (2004).
• Nonequilibrium Thermodynamics of Radiation and Matter (with C. Essex and D.C. Kennedy), in "Variational and Extremum Principles in Macroscopic Systems" (eds. Sieniutycz and H. Farkas, Elsevier, 2004).