Understanding Nuclei in the upper sd - shell

Nuclei in the upper-$sd$ shell usually exhibit characteristics of spherical single particle excitations. In the recent years, employment of sophisticated techniques of gamma spectroscopy has led to observation of high spin states of several nuclei near A$\simeq$ 40. In a few of them multiparticle, multihole rotational states coexist with states of single particle nature. We have studied a few nuclei in this mass region experimentally, using various campaigns of the Indian National Gamma Array setup. We have compared and combined our empirical observations with the large-scale shell model results to interpret the structure of these nuclei. Indication of population of states of large deformation has been found in our data. This gives us an opportunity to investigate the interplay of single particle and collective degrees of freedom in this mass region.Comment: 8 pages, 13 figures, submitted for publication in the Proceedings of "Frontiers in Gamma-Ray Spectroscopy 2012 (FIG12), held at New Delhi, March 5th - 7th, 2012, Organized by Inter University Accelerator Center, New Delhi, Indi

Neutrino Mass Matrices in Models with Horizontal Symmetries

We have studied the most general neutrino mass matrices in models with SU(2) and SU(3) horizontal symmetries. Without going into the details of the models it is possible to write down the effective operators, which predict the structure of the Majorana neutrino mass matrices. Unlike other extensions of the standard model, the structure is now independent of the effective Yukawa couplings and depends entirely on the Higgs which gives mass to the other fermions. In the case of SU(3) symmetries the lowest dimensional operators are forbidden requiring a low mass scale for lepton number violation.Comment: 11 pages latex file, a few references added in 2nd versio

Centroids of Gamow-Teller transitions at finite temperature in fp-shell neutron-rich nuclei

The temperature dependence of the energy centroids and strength distributions for Gamow-Teller (GT) $1^+$ excitations in several fp-shell nuclei is studied. The quasiparticle random phase approximations (QRPA) is extended to describe GT states at finite temperature. A shift to lower energies of the GT$^+$ strength is found, as compared to values obtained at zero temperature.Comment: 12 pages, contains 3 tables. E-mail: [email protected], [email protected]