arXiv subjects

Y. H. Ahn

Publications and source records attributed to Y. H. Ahn.

40 records · Page 3Linked to original sources

arXiv2007

Leptogenesis in a seesaw model with Fritzsch type lepton mass matrices

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.

hep-ph↗

arXiv2007

Photocurrent Imaging of p-n Junctions and Local Defects in Ambipolar Carbon Nanotube Transistors

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.

cond-mat.mtrl-sci↗

arXiv2007

$μ-τ$ Symmetry and Radiatively Generated Leptogenesis

We consider a $μ-τ$ symmetry in neutrino sectors realized at GUT scale in the context of a seesaw model. In our scenario, the exact $μ-τ$ 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 $\tanβ$, 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 $θ_{23}$ and $θ_{13}$ from $π/4$ and zero, respectively. It is shown that the right amount of the baryon asymmetry $η_B$ can be achieved via so-called resonant leptogenesis, which can be realized at rather low seesaw scale with large $\tanβ$ in our scenario so that the well-known gravitino problem is safely avoided.

hep-ph↗

arXiv2006

Phased Breaking of mu-tau symmetry and Leptogenesis

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.

hep-ph↗