Fermion Masses and Mixing in Four and More Dimensions

We give an overview of recent progress in the study of fermion mass and flavor mixing phenomena. Mass matrix ansatze are considered within the SM and SUSY GUTs where some predictive frameworks based on SU(5) and SO(10) are reviewed. We describe a variety of schemes to construct quark mass matrices in extra dimensions focusing on four major classes: models with the SM residing on 3-brane, models with universal extra dimensions, models with split fermions and models with warped extra dimensions. We outline how realistic patterns of quark mass matrices could be derived from orbifold models in heterotic superstring theory. Finally, we address the fermion mass problem in intersecting D-branes scenarios, and present models with D6-branes able to give a good quantitatively description of quark masses and mixing. The role of flavor/CP violation problem as a probe of new physics is emphasized.Comment: a review based on seminars presented by S.K. in different places, 34 pages, late

From Six to Four and More: Massless and Massive Maximal Super Yang-Mills Amplitudes in 6d and 4d and their Hidden Symmetries

A self-consistent exposition of the theory of tree-level superamplitudes of the 4d N=4 and 6d N=(1,1) maximally supersymmetric Yang-Mills theories is provided. In 4d we work in non-chiral superspace and construct the superconformal and dual superconformal symmetry generators of the N=4 SYM theory using the non-chiral BCFW recursion to prove the latter. In 6d we provide a complete derivation of the standard and hidden symmetries of the tree-level superamplitudes of N=(1,1) SYM theory, again using the BCFW recursion to prove the dual conformal symmetry. Furthermore, we demonstrate that compact analytical formulae for tree-superamplitudes in N=(1,1) SYM can be obtained from a numerical implementation of the supersymmetric BCFW recursion relation. We derive compact manifestly dual conformal representations of the five- and six-point superamplitudes as well as arbitrary multiplicity formulae valid for certain classes of superamplitudes related to ultra-helicity-violating massive amplitudes in 4d. We study massive tree superamplitudes on the Coulomb branch of the N=4 SYM theory from dimensional reduction of the massless superamplitudes of the six-dimensional N=(1,1) SYM theory. We exploit this correspondence to construct the super-Poincare and enhanced dual conformal symmetries of massive tree superamplitudes in N=4 SYM theory which are shown to close into a finite dimensional algebra of Yangian type. Finally, we address the fascinating possibility of uplifting massless 4d superamplitudes to 6d massless superamplitudes proposed by Huang. We confirm the uplift for multiplicities up to eight but show that finding the uplift is highly non-trivial and in fact not of a practical use for multiplicities larger than five.Comment: 77 pages, 1 figure. v2: Reference adde

More Than Homework, a Snack, and Basketball: Afterschool Programs as an Oasis of Hope for Black Parents in Four Cities

Highlights the opinions of black families on the quality and importance of public school- and community-based afterschool programs. Explores the factors that influence black parents to enroll their children in afterschool programs

Using suites of free refurbished computers may cost over four times more than buying and using ‘state of the art’ learning technologies

The lack of adequately skilled and qualified teachers in developing nations, and the impact this has on the educational experiences of children within those nations constitutes an educational crisis comparable to the challenges global medicine faces with malaria or AIDS. The educational challenges, like many other aspects of development, are often most severe in rural areas (Mulkeen, 2005). It has been argued that such a challenge requires a new open-learning architecture for teacher professional development, situated in the context of the teachers daily practice, supported by the teachers peers, and accessing the full potential of new ICTs (Leach & Moon, 2006). There is substantial activity and expenditure to provide ‘computers’ for schools in the global south, but this tends to conform to a pattern identified here as ‘thinking as usual’ about ICT; a pattern often framed by assumptions about the costs of various forms of ICT. However, little is really known about what constitutes ‘appropriate’ ICT for education in poor rural communities (InfoDev 2005); even less about ICT as a vehicle for teacher professional development in such contexts. This paper applies a model of ‘total costs of ownership’ to a ‘freely donated’ ICT suite, and finds that the costs may well be much higher than alternative, more educationally empowering forms of ICT. Demonstrating that ‘common-sense’ assumptions about appropriate ICTs may not be correct, this paper seeks to clear the ground for establishing a framework for identifying appropriate ICTs for rural teacher and community development in the global south