arXiv subjects

Q. Ho-Kim

Publications and source records attributed to Q. Ho-Kim.

4 recordsLinked to original sources

arXiv1999

The decays "neutrino{heavy} -> neutrino{light} + photon" and "neutrino{heavy} -> neutrino{light} e+ e-" of massive neutrinos

If, as recently reported by the Super-Kamiokande collaboration, the neutrinos are massive, the heaviest one would not be stable and, though chargeless, could in particular decay into a lighter neutrino and a photon by quantum loop effects. The corresponding rate is computed in the standard model with massive Dirac neutrinos as a function of the neutrino masses and mixing angles. The lifetime of the decaying neutrino is estimated to be approximately 10^44 years for a mass 5 10^{-2} eV. If kinematically possible, the decay of a heavy neutrino into a lighter one plus an e+ e- pair occurs at tree level and its one-loop radiative corrections get enhanced by a large logarithm of the electron mass acting as an infrared cutoff. It then largely dominates the photonic mode by several orders of magnitude, corresponding to a lifetime approximately equal to 10^{-2} year for a mass 1.1 MeV.

hep-ph↗

arXiv1999

One-loop flavor changing electromagnetic transitions

We discuss the effect of the external fermion masses in the flavor-changing radiative transitions of a heavy fermion (quark or lepton) to a lighter fermion at the one-loop level, and point out an often overlooked crucial difference in the sign of a charge factor between transitions of the down type $s\to dγ$ and the up type $c\to uγ$. We give formulas for the $F\to fγ$ effective vertex in various approximations and the exact formula for $t\to cγ$ and $τ\to μγ$.

hep-ph↗

arXiv1994

The Rank four Heterotic Modular Invariant Partition Functions

In this paper, we develop several general techniques to investigate modular invariants of conformal field theories whose algebras of the holomorphic and anti-holomorphic sectors are different. As an application, we find all such ``heterotic'' WZNW physical invariants of (horizontal) rank four: there are exactly seven of these, two of which seem to be new. Previously, only those of rank $\le 3$ have been completely classified. We also find all physical modular invariants for $su(2)_{k_1}\times su(2)_{k_2}$, for $22>k_1>k_2$, and $k_1=28$, $k_2<22$, completing the classification of ref.{} \SUSU.

hep-th↗

arXiv1993

The Low Level Modular Invariant Partition Functions of Rank-Two Algebras

Using the self-dual lattice method, we make a systematic search for modular invariant partition functions of the affine algebras $g\*{(1)}$ of $g=A_2$, $A_1+A_1$, $G_2$, and $C_2$. Unlike previous computer searches, this method is necessarily complete. We succeed in finding all physical invariants for $A_2$ at levels $\le 32$, for $G_2$ at levels $\le 31$, for $C_2$ at levels $\le 26$, and for $A_1+A_1$ at levels $k_1=k_2\le 21$. This work thus completes a recent $A_2$ classification proof, where the levels $k=3,5,6,9,12,15,21$ had been left out. We also compute the dimension of the (Weyl-folded) commutant for these algebras and levels.

hep-th↗