Recent research on the chemical nature of the red dyes isolated from Pterocarpus santalinus and certain West African plants, viz., Baphia nitida, Pterocarpus osun and Pterocarpus soyauxii, have been reviewed. P. santalinus contains santalins A, B and C, but no santarubin. Santalins and santarubins have been found in P. osun, P. soyauxii and B. nitida. The structural formulae of the santalins are presented and their differences from santarubins indicated. Santalins A and B have some similarities in structure with hematein. This is probably responsible for their staining properties; the possible mechanism of staining is discussed.
We study a model of neutrino within the framework of minimal extended seesaw (MES), which plays an important role in active and sterile neutrino phenomenology in (3+1) scheme. The A 4 flavor symmetry is augmented by additional Z 4 ×Z 3 symmetry to constraint the Yukawa Lagrangian of the model. We use non-trivial Dirac mass matrix, with broken µ − τ symmetry, as the origin of leptonic mixing. Interestingly, such structure of mixing naturally leads to the non-zero reactor mixing angle θ 13 . Non-degenerate mass structure for right-handed neutrino M R is considered so that we can further extend our study to Leptogenesis. We have also considered three different cases for sterile neutrino mass, M S to check the viability of this model, within the allowed 3σ bound in this MES framework.
We examine a simple extension of the standard model with a pair of fermions, one singlet and a doublet, in a common thread linking the dark matter problem with the smallness of neutrino masses associated with several exciting features. In the presence of a small bare Majorana mass term, the singlet fermion brings in a pseudo-Dirac dark matter capable of evading the strong spin-independent direct detection bound by suppressing the dark matter annihilation processes mediated by the neutral current. In consequence, the allowed range of a mixing angle between the doublet and the singlet fermions gets enhanced substantially. The presence of the same mass term in an association with singlet scalars also elevates tiny but nonzero masses radiatively for light Majorana neutrino satisfying observed oscillation data.
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