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A new scheme for Yukawa matrices is proposed for free of flavor changing neutral currents (FCNCs) at tree level in general two-Higgs-doublet model (THDM) without imposing symmetry. We find that the new type couplings of charged Higgs to fermions not only depend on the flavors, but also can be ascribed by new CP violating phases. Unlike conventional THDM, the resulted new charged Higgs effects could have the specialties: (a) the influence on $\Gamma(K^\pm_{e 2})/\Gamma(K^\pm_{\mu 2})$ cannot be eliminated, (b) the decay constant of $D_s$ could be enhanced, and (c) enhancement of branching ratio for $B^+\to \tau^+ \nu$ could be achieved., Comment: 13 pages, 5 figures, references added, typos corrected, constraints from R_\pi and B\to D \tau \bar \nu included, final version to appear in PLB

We consider an effective theory with an $SU(2)\times U(1)\times A_{4}\times Z_{2}\times Z_{4}$ symmetry and investigate the possibility of a linking TeV-leptogenesis with a reactor angle $|U_{e3}|$ through spontaneous $A_{4}$ symmetry breaking which is at a scale higher than electroweak scale under the framework of radiative seesaw. It has been shown that tri-bimaximal(TBM) can be obtained by forging vacuum expectation value (VEV) alignment of the $A_{4}$. Especially, one $A_{4}$ triplet scalar field with cut-off scale $\Lambda$ is added in neutrino Yukawa sector, which is responsible for the deviation of the exact TBM, to explain leptogenesis as well as a non-zero $|U_{e3}|$. Above the scale of $\Lambda$ the leptonic Yukawa sectors will lead to the exact TBM. We analyze possible spectrums of light neutrinos and their flavor mixing angles corresponding to heavy Majorana neutrino mass ordering, and show that non-resonance leptogenesis at TeV-scale constrained by low energy data is achievable, both analytically as well as numerically. We show that only normal hierarchical spectrum of light neutrino would be strongly favored by the current Wilkinson Microwave Anisotropy Probe (WMAP) data, and also show that a relatively large $|U_{e3}|$ corresponds to the value of baryon asymmetry $6.2\times10^{-10}$., Comment: 32 pages, 21 figures, 3 tables. Final version to appear in Phys. Rev. D

We consider an exact mu-tau reflection symmetry in neutrino sectorrealized at the GUT scale in the context of the seesaw model with and without supersymmetry. Assuming the two lighter heavy Majorana neutrinos are degenerate at the GUT scale, it is shown that the renormalization group (RG) evolution from the GUT scale to the seesaw scale gives rise to breaking of the mu-tau symmetry and a tiny splitting between two degenerate heavy Majorana neutrino masses as well as small variations of the CP phases in Y_nu, which are essential to achieve a successful leptogenesis. Such small RG effects lead to tiny deviations of theta_{23} from the maximal value and the CP phase delta_{CP} from pi/2 imposed at the GUT scale due to mu-tau reflection symmetry. In our scenario, the required amount of the baryon asymmetry eta_B can be generated via so-called resonant e-leptogenesis, in which the wash-out factor concerned with electron flavor plays a crucial role in reproducing a successful leptogenesis. We show that CP violation responsible for the generation of baryon asymmetry of our universe can be directly linked with CP violation measurable through neutrino oscillation as well as neutrino mixing angles theta_{12} and theta_{13}. We expect that, in addition to the reactor and long baseline neutrino experiments, the measurements for the supersymmetric parameter tan{beta} at future collider experiments would serve as an indirect test of our scenario of baryogenesis based on the mu-tau reflection symmetry., Comment: 32 pages, 16 figures

We study a $\mu - \tau$ reflection symmetry in neutrino sector realized at the GUT scale in the context of the seesaw model. In our scenario, the exact $\mu - \tau$ reflection symmetry realized in the basis where the charged lepton and heavy Majorana mass matrices are diagonal, leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetry extension of the seesaw model with appropriate values of $\tan\beta$, the renormalization group (RG) evolution from the GUT scale to seesaw scale can induce a successful leptogenesis. It is shown that the right amount of the baryon asymmetries $\eta_B$ can be achieved via so-called resonant leptogenesis, which can be realized at rather low seesaw scale in our scenario, so that the well-known gravitino problem is safely avoided. In this work, we consider both flavor dependent and flavor independent leptogenesis, and demonstrate how they lead to different amounts of baryon asymmetries in detail., Comment: This paper has been withdraw

We investigate how the baryon asymmetry of our universe via leptogenesis can be achieved within the framework of the seesaw model with Fritzsch type lepton mass matrices proposed by Fukugita $et. al$. We study the cases with CP-violating phases in charged lepton Yukawa matrix, however, with and without Dirac neutrino Yukawa phases. We consider both flavor independent and flavor dependent leptogenesis, and demonstrate how they lead to different amounts of lepton asymmetries in detail. In particular, it is shown that flavor dependent leptogenesis in this model can be worked out only when the CP phases in Dirac neutrino Yukawa matrix become zero at the GUT scale. In addition to the CP phases, for successful leptogenesis in the model it is required that the degeneracy of the heavy Majorana neutrino mass spectrum should be broken and we also show that the breakdown of the degeneracy can be radiatively induced.

We use scanning photocurrent microscopy (SPCM) to investigate the properties of internal p-n junctions as well as local defects in ambipolar carbon nanotube (CNT) transistors. Our SPCM images show strong signals near metal contacts whose polarity and positions change depending on the gate bias. SPCM images analyzed in conjunction with the overall conductance also indicate the existence and gate-dependent evolution of internal p-n junctions near contacts in the n-type operation regime. To determine the p-n junction position and the depletion width with a nanometer scale resolution, a Gaussian fit was used. We also measure the electric potential profile of CNT devices at different gate biases, which shows that both local defects and induced electric fields can be imaged using the SPCM technique. Our experiment clearly demonstrates that SPCM is a valuable tool for imaging and optimizing electrical and optoelectronic properties of CNT based devices., Comment: 5 pages, 5 figures

We consider a $\mu-\tau$ symmetry in neutrino sectors realized at GUT scale in the context of a seesaw model. In our scenario, the exact $\mu-\tau$ symmetry realized in the basis where the charged lepton and heavy Majorana neutrino mass matrices are diagonal leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetric extension of the seesaw model with large $\tan\beta$, the renormalization group (RG) evolution from GUT scale to seesaw scale can induce a successful leptogenesis even without introducing any symmetry breaking terms by hand, whereas such RG effects lead to tiny deviations of $\theta_{23}$ and $\theta_{13}$ from $\pi/4$ and zero, respectively. It is shown that the right amount of the baryon asymmetry $\eta_B$ can be achieved via so-called resonant leptogenesis, which can be realized at rather low seesaw scale with large $\tan\beta$ in our scenario so that the well-known gravitino problem is safely avoided., Comment: 17 pages, 5 figures. Published in PRD

Non-vanishing U_{e3} has been theoretically related to a certain flavor symmetry breaking in the neutrino sector. We propose a scenario to break the mu-tau symmetry so as to accommodate the non-vanishing U_{e3}. Our scenario is constructed in the context of a seesaw model, and the mu-tau symmetry breaking is achieved by introducing a CP phase in the Dirac Yukawa matrix. We also show how the deviation of theta_{23} from the maximal mixing and non-vanishing U_{e3} depend on the CP phase. Neutrino mixings and the neutrino mass-squared differences are discussed, and the amplitude in neutrinoless double beta decay m_{ee} are also predicted. We found that a tiny breaking of the mu-tau symmetry due to mass splitting between two degenerate heavy Majorana neutrinos on top of the Dirac CP phase can lead to successful leptogenesis. We examine how leptogenesis can be related with low energy neutrino measurement, and show that our predictions for U_{e3} and m_{ee} can be constrained by the current observation of baryon asymmetry., Comment: 18 pages, 7 figures, published version in PRD

A new aspect of the vacuum structure of 2+1-dimensional Thirring model is presented. Using the Fierz identity, we split the current-current four-Fermi interaction in terms of a matrix valued auxiliary scalar field and compute its effective potential. Energy consideration shows that contrary to earlier expectations, parity in general is spontaneously broken at any finite order of N, where N is the number of the two component spinors. In the large N limit, there does not exist a stable vacuum of the theory thereby making the application of the large N limit to Thirring model dangerous. A detailed analysis for parity breaking solutions in N=2,3 cases is given., Comment: 6 pages, KHTP-94-05 /SNUCTP 94-31