München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 11: Theorie

HK 11.2: Vortrag

Montag, 20. März 2006, 16:45–17:00, B

How To Classify Three-Body Forces – And Why — •Harald W. Grießhammer — Institut für Theoretische Physik (T39), TU München — Centre for Nuclear Studies, The George Washington University, Washington DC, USA

To add 3-body forces whenever theory and data disagree is untenable when predictions are required. Effective Field Theories can provide a model-independent way to estimate the typical strength of 3-body forces. For the “pion-less” Effective Field Theory, valid for processes with momenta below the pion-mass, I systematise the power-counting of 3-body forces in all partial waves and orders, including external currents [1]. The underlying tenet is that low-energy observables must be insensitive to details of short-distance dynamics. Using renormalisation-group arguments, the typical strength of a 3-body force is thus determined from the superficial degree of divergence of the 3-body diagrams which contain only two-body forces. This naïve dimensional analysis must be amended as the asymptotic solution to the leading-order Faddeev equation depends for large off-shell momenta crucially on the partial wave and spin-combination of the system. 3-body forces turn out to be weaker than expected in most channels with angular momentum smaller than 3. This demotes many 3-nucleon forces to high orders. I outline the underlying principle and some consequences for Nuclear Physics. For example, the ⁴S_3/2-scattering length of the neutron-deuteron-system is less sensitive to 3-nucleon forces than guessed.

[1] H.W. Grießhammer: Nucl. Phys. A760 (2005) 110