Topological invariants for phase transition points of one-dimensional Z2\mathbb{Z}_2 topological systems

We study topological properties of phase transition points of two topologically non-trivial $\mathbb{Z}_2$ classes (D and DIII) in one dimension by assigning a Berry phase defined on closed circles around the gap closing points in the parameter space of momentum and a transition driving parameter. While the topological property of the $\mathbb{Z}_2$ system is generally characterized by a $\mathbb{Z}_2$ topological invariant, we identify that it has a correspondence to the quantized Berry phase protected by the particle-hole symmetry, and then give a proper definition of Berry phase to the phase transition point. By applying our scheme to some specific models of class D and DIII, we demonstrate that the topological phase transition can be well characterized by the Berry phase of the transition point, which reflects the change of Berry phases of topologically different phases across the phase transition point.Comment: 6 pages, 5 figure

Winding numbers of phase transition points for one-dimensional topological systems

We study topological properties of phase transition points of one-dimensional topological quantum phase transitions by assigning winding numbers defined on closed circles around the gap closing points in the parameter space of momentum and a transition driving parameter, which overcomes the problem of ill definition of winding numbers on the transition points. By applying our scheme to the extended Kitaev model and extended Su-Schrieffer-Heeger model, we demonstrate that the topological phase transition can be well characterized by winding numbers of transition points, which reflect the change of the winding number of topologically different phases across the phase transition points.Comment: 5 pages, 5 figure

Limit on Br(b→sg)Br(b\to s g) in Two Higgs Doublet Models

Using the recent CLEO measurement of $Br(b\to s \gamma)$, we find that the branching ratio of $b\to s g$ cannot be larger than $10\%$ in two Higgs doublet models. The small experimental value of $Br(b\to e\bar{\nu}X)$ can no longer be explained by charged Higgs boson effects.Comment: 11 pages + 3 Figures (not included), ReVTeX, NTUTH-94-16 and NHCU-HEP-94-1

Same-sign single dilepton productions at the LHC

We examine the same-sign single dilepton productions of $\ell_i^{\pm}\ell_j^{\pm} (\ell_{i,j}=e,\mu)$ in high-energy proton-proton collisions at the Large Hadron Collider (LHC) in models with doubly charged Higgs scalars as well as heavy Majorana neutrinos. We demonstrate that these spectacular productions can be detected at the LHC for a class model in which the doubly charged Higgs scalars couple only to the right-handed charged leptons. The ranges of the possible doubly charged Higgs masses and mixings to observe the processes at the LHC are discussed.Comment: 10 pages, 5 figure