Majorana force

WIGNER FORCE. Short-range nuclear force of noncxchangc type postulated phenomenologically as pait of the interaction between nucleons. Postulated exchange forces are Bartlett, Heisenberg, and Majorana forces. 

The effect of neutron-proton symmetry breaking on the distribution of M1 strength in the SU(3) limit of the Interacting Boson Model (IBA-2) is studied. A possible alternative choice for the Majorana force is investigated, with a structure that resembles more closely that which is calculated in microscopic theories. It is found that the specific choice for the Majorana interaction has important consequences for the magnetic strength distribution function. In addition it allows for an alternative interpretation of the second excited K7T=0+ band in rare earth nuclei, as a mixed-symmetry state. 

In the IBA-2 model [Ari83] the structure of the collective states in even-even nuclei is calculated by considering a system of interacting neutron and proton s and d bosons. We will focus attention on the Majorana force,... 

Fig. 1 A comparison between calculated bandhead energies and those observed in 156Gd. In the calculation presented on the left-hand side (calculation I) the Majorana force is parameterized (see text) by a=0.15 MeV while in the calculation on the right-hand side (II) b=0.3 MeV is used. Above an excitation energy of 2.5 MeV, the symmetry assignment may not be accurate due to the F-spin nonscalar nature of the hamiltonian.

In this contribution we have investigated the effect, on calculated observables in the IBA-2 model, of an alternative choice for the Majorana force, as suggested by microscopic calculations [Dru85]. This choice has the peculiar feature of producing in the SU(3) limit a spectrum in which there appears a mixed-symmetry band at approximately the same energy... 

Despite all these impressive progress, we are still too far from the ultimate theory of everything. I listed some obvious avenues for future research in particle physics and cosmology. If I am allowed to say my personal prejudice, I would say that the flavor problem is beyond our reach for years to come, but our understanding of the law of force may further be advanced by a new discovery of violation of empirical conservation laws. The Majorana nature of neutrino masses and proton decay are just manifestation of violation of lepton and baryon numbers, and in my view there is no fundamental obstacle against these being discovered in future, however remote it might be. 

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