3 research outputs found
Weak-Singlet Fermions: Models and Constraints
We employ data from precision electroweak tests and collider searches to
derive constraints on the possibility that weak-singlet fermions mix with the
ordinary Standard Model fermions. Our findings are presented within the context
of a theory with weak-singlet partners for all ordinary fermions and theories
in which only third-generation fermions mix with weak singlets. In addition, we
indicate how certain results can be applied more widely in theories containing
exotic fermions.Comment: 29 pages, 12 figures; added 1 reference, expanded introductio
Chain-Boundary Excitations in the Haldane Phase of 1D Systems
The chain-boundary excitations occurring in the Haldane phaseof
antiferromagnetic spin chains are investigated. The bilinear-biquadratic
hamiltonian is used to study these excitations as a function of the strength of
the biquadratic term, , between . At the AKLT point,
, we show explicitly that these excitations are localized at the
boundaries of the chain on a length scale equal to the correlation length
, and that the on-site magnetization for the first site is
. Applying the density matrixrenormalization group we show that
the chain-boundaryexcitations remain localized at the boundaries for
. As the two critical points are approached the
size of the objects diverges and their amplitude vanishes.Comment: 4 Pages, 4 eps figures. Uses RevTeX 3.0. Submitted to PR