Neutrino Mixing and Flavour Changing Processes

We study the implications of a large nu_mu - nu_tau mixing angle on flavour changing transitions of quarks and leptons in supersymmetric extensions of the standard model. Two patterns of supersymmetry breaking are considered, models with modular invariance and the standard scenario of universal soft breaking terms at the GUT scale. The analysis is performed for two symmetry groups G x U(1)_F, with G=SU(5) and G=SU(3)^3, where U(1)_F is a family symmetry. Models with modular invariance are in agreement with observations only for restricted scalar quark and gaugino masses, (M_squark^2)/(m_gluino^2) \simeq 7/9 and m_bino > 350 GeV. A characteristic feature of models with large tan beta and radiatively induced flavour mixing is a large branching ratio for mu -> e gamma. For both symmetry groups and for the considered range of supersymmetry breaking mass parameters we find BR(mu -> e gamma) > 10^(-14).Comment: 25 pages, 6 figure

A model for the symmetry breaking of the reverse Benard-von Karman vortex street produced by a flapping foil

The vortex streets produced by a flapping foil of span-to-chord aspect ratio of 4:1 are studied in a hydrodynamic tunnel experiment. In particular, the mechanisms giving rise to the symmetry breaking of the reverse B\'enard-von K\'arm\'an vortex street that characterizes fish-like swimming and forward flapping flight are examined. Two-dimensional particle image velocimetry measurements in the mid-plane perpendicular to the span axis of the foil are used to characterize the different flow regimes. The deflection angle of the mean jet flow with respect to the horizontal observed in the average velocity field is used as a measure of the asymmetry of the vortex street. Time series of the vorticity field are used to calculate the advection velocity of the vortices with respect to the free-stream, defined as the phase velocity $U_{phase}$, as well as the circulation $\Gamma$ of each vortex and the spacing $\xi$ between consecutive vortices in the near wake. The observation that the symmetry breaking results from the formation of a dipolar structure from each couple of counter-rotating vortices shed on each flapping period serves as starting point to build a model for the symmetry breaking threshold. A symmetry breaking criterion based on the relation between the phase velocity of the vortex street and an idealized self-advection velocity of two consecutive counter-rotating vortices in the near wake is established. The predicted threshold for symmetry breaking accounts well for the deflected wake regimes observed in the present experiments and may be useful to explain other experimental and numerical observations of similar deflected propulsive vortex streets reported in the literature.Comment: 10 page

Symmetries of Symmetry Breaking Constraints

Symmetry is an important feature of many constraint programs. We show that any symmetry acting on a set of symmetry breaking constraints can be used to break symmetry. Different symmetries pick out different solutions in each symmetry class. We use these observations in two methods for eliminating symmetry from a problem. These methods are designed to have many of the advantages of symmetry breaking methods that post static symmetry breaking constraint without some of the disadvantages. In particular, the two methods prune the search space using fast and efficient propagation of posted constraints, whilst reducing the conflict between symmetry breaking and branching heuristics. Experimental results show that the two methods perform well on some standard benchmarks.Comment: To appear in the Proceedings of the Ninth International Workshop on Symmetry and Constraint Satisfaction Problems, held alongside the 15th International Conference on Principles and Practice of Constraint Programming (CP 2009), Lisbon, Portuga