We have attempted to extend the parameter space of the elements of the texture 4 zero Hermitian quark mass matrices, to include the case of 'weak hierarchy' amongst them along with the usually considered 'strong hierarchy' case. This has been carried out by giving wide variation to the hierarchy defining parameters D U and D D , having implications for the structural features of the mass matrices. We find that not only the weakly hierarchical mass matrices are able to reproduce the strongly hierarchical mixing angles but also both the phases having their origin in the mass matrices have to be non zero to achieve compatibility of these matrices with recent quark mixing data. Further noting the difference between the exclusive and inclusive values of V ub , we have carried out separate analyses corresponding to these.

For Majorana or Dirac neutrinos, using Fritzsch-like texture 4 zero mass matrices with parallel texture structures for the charged leptons and the Dirac neutrino mass matrix (M_{\nu D}), detailed predictions for cases pertaining to normal/inverted hierarchy as well as degenerate scenarios of neutrino masses have been carried out. The inverted hierarchy as well as degenerate scenarios seem to be ruled out at 3 \sigma C.L. for both Majorana and Dirac neutrinos. For normal hierarchy, Jarlskog's rephasing invariant parameter J, the CP violating Dirac-like phase \delta and the effective neutrino mass m_{ee} have been calculated. For this case, lower limits of m_{\nu_1} and \theta_{13} would have implications for the nature of neutrinos.Comment: 15 pages, 3 figures, minor changes in figures and tex

Texture specific quark mass matrices which are hermitian and hierarchical are examined in detail . In the case of texture 6 zeros matrices, out of sixteen possibilities examined by us, none is able to fit the low energy data (LED), for example, |V us |= 0.2196 ± 0.0023, |V cb |= 0.0395 ± 0.0017, | V ub V cb |= 0.08 ± 0.02, |V td | lies in the range 0.004 -0.013 (PDG). Similarly none of the 32 texture 5 zeros mass matrices considered is able to reproduce LED. In particular, the latest data from LEP regarding | V ub V cb | (= 0.093 ± 0.016) rules out all of them. In the texture 4 zeros case, we find that there is a unique texture structure for U and D mass matrices which is able to fit the data. PACS number(s): 12.15. Ff, 14.60.Pq, 96.60.Jw The raison d'être for the existence of three well seperated families of charged fermions remains ununderstood in the context of present day high energy physics. The mystery regarding the fermion masses has further deepened with the observation of "neutrino oscillations" by the Superkamiokande Collaboration [1] implying nonzero masses for the neutrinos and thus, giving for the first time a strong signal for the physics beyond the standard model. In the absence of any deeper understanding of fermion masses, attempts have been made on the one hand to understand arbitrary standard model Yukawa couplings of the fermions from more fundamental theories such as GUTs [2] composite models [3], left right symmetric models [4], etc.. On the other hand, attempts have been made to discover phenomenological quark mass matrices, which are in tune with the low energy data(LED). In this regard, specific ansatz for the quark mass matrices have been tried with a fair degree of success [5] - [13] to explain quark mixing matrix. Similarly phenomenological neutrino mass matrices have been considered [13,14] which attempt to accomodate simultaneously the Solar Neutrino Problem (SNP), Atmospheric Neutrino Problem (ANP) and Neutrino Oscillations observed by LSND.

Considering Dirac neutrinos and Fritzsch-like texture 6 zero and 5 zero mass matrices, detailed predictions for cases pertaining to normal/inverted hierarchy as well as degenerate scenario of neutrino masses have been carried out. All the cases considered here pertaining to inverted hierarchy and degenerate scenario of neutrino masses are ruled out by the existing data. For the normal hierarchy cases, the lower limit of m ν 1 and of s 13 as well as the range of Dirac-like CP violating phase δ l would have implications for the texture specific cases considered here.

Using seesaw mechanism and Fritzsch-like texture 6 zero and 5 zero lepton Dirac mass matrices, detailed predictions for cases pertaining to normal/inverted hierarchy as well as degenerate scenario of neutrino masses have been carried out. All the cases considered here pertaining to inverted hierarchy and degenerate scenario of neutrino masses are ruled out by the existing data. For the normal hierarchy cases, the lower limit of m_{\nu 1} and of s_{13} as well as the range of Dirac-like CP violating phase \delta would have implications for the texture 6 zero and texture 5 zero cases considered here.Comment: 13 pages, 4 figures. Small changes to the previous version and a new reference adde