Bochum 2009 – wissenschaftliches Programm

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HK: Fachverband Hadronen und Kerne

HK 44: Plenary VI

HK 44.1: Plenarvortrag

Mittwoch, 18. März 2009, 11:00–11:45, Audi-Max

Symmetries and phase transitions in nuclei — •Francesco Iachello — Yale University, New Haven, CT, USA

Quantum Phase Transitions (QPT) are phase transitions that occur as a function of a coupling constant in the quantum Hamiltonian describing the system. Atomic nuclei provide examples of quantum shape phase transitions. The phases of the system are different geometric structures of nuclei characterized by different dynamic symmetries, U(5), U(3) and SO(6), corresponding to spherical, axially deformed and so-called γ-unstable shapes. The shape phase diagram of nuclei will be discussed. It will be shown that the transition from spherical, U(5), to axially deformed, U(3), is first order, between spherical and γ-unstable, SO(6), is second order, and between axially deformed and γ-unstable is a crossover. Critical exponents and scaling behavior, i.e. dependence on the number of particles, N, will also be discussed. Recently, it has been found that at the critical value of a QPT, a new symmetry emerges, called "critical symmetry", and related to scale invariance. In the second part of this talk, this (unexpected) symmetry will be discussed and experimental examples shown. Finally, the role of supersymmetry in phase transitions in mixed systems of bosons and fermions will be mentioned. QPT in nuclei provide one of the best experimentally verified examples of phase transitions in physics.