Dynamically generated masses in supersymmetric QCD and quark mass problems

We consider possible mechanical masses that could appear in supersymmetry, other than by direct Higgs coupling to fermions and we speculate that the existence of such a type of mass would allow one to have the Higgs mass of the $u$ quark zero, and the Higgs mass of the $d$ quark (at 1 \gev) of $\approx 1 \to 2 MeV$, thus solving at the same time the strong CP problem and arranging the grand unification prediction $m_{\mu}/m_{e} = m_{s, Higgs}/m_{d, Higgs}.$ One possible mechanism for this is related to, but not identical with the quark condensate. Here a mass is generated which is the same for all quarks, and which adds to the Higgs type mass. Unfortunately, the numerical value of the generated mass falls short of the desired value (some 5 MeV) by orders of magnitude. An alternate mechanism, through Higgs-induced left-right couplings in the squark sector may produce masses of the correct order of magnitude if the mixing angles are diferent in the squark and quark sectors. To get the desired result for the $u$ quark mass, we need a stop component mixing of 1/20 for the $LR$ $\tilde{u}$ squark coupling, so the strong CP problem may still be solved. For the $d$ mass, this mechanism is not really sufficient to solve the grand unification mass ratio problem.Comment: plain TeX file. Two figure

Electron-phonon interaction in Fe-based superconductors: Coupling of magnetic moments with phonons in LaFeAsO1−x_{1-x}Fx_{x}

The coupling of Fe magnetic moments in LaFeAsO$_{1-x}$F$_{x}$ with the As $A_{1g}$ phonon is calculated. We present first principles calculations of the atomic and electronic structure of LaFeAsO as a function of electron doping. We perform calculations using the virtual crystal approximation as well as supercell calculations with F substitutional impurity atoms. The results validate the virtual crystal approximation for the electronic structure near the Fermi level. Its is found that the electronic density of states at the Fermi level is maximum for x=0.125, enhancing the electron-phonon interaction. An additional increase of the electron-phonon parameter $\lambda$ is obtained if the coupling between the $A_{1g}$ phonon and the Fe magnetic moment is included. It is found that the electron-phonon interaction can be one order of magnitude larger than its value if no spin resolution is included in the calculation. The implications of these results on the superconducting transition are discusse