22,397 research outputs found
Renormalization of the one-body off-diagonal Coulomb field in nuclei
Isospin violation effects in nuclei are investigated within a microscopic
approach which takes into account the influence of the residual strong
interaction on the Coulomb interaction. The renormalization of the off-diagonal
Coulomb field acting within a nucleus, by the residual strong interaction is
calculated analytically in a simplified RPA. From the expression for the
suppression coefficient of the isospin violating part of the Coulomb field, the
isospin violating spreading widths of isobaric analog states are derived. The
resulting reduction of the width is in agreement with the data on the isospin
symmetry restoration and with some earlier evaluations of the isospin violating
spreading widths.Comment: 11 pages, Late
Computing Effective Hamiltonians of Doped and Frustrated Antiferromagnets By Contractor Renormalization
A review of the Contractor Renormalization (CORE) method, as a systematic
derivation of the low energy effective hamiltonian, is given, with emphasis on
its differences and advantages over traditional perturbative (weak/strong
links) real space RG. For the low energy physics of the 2D Hubbard model, we
derive the plaquette bosons (projected SO(5)) model which connects the
microscopic model to phases and phenomenology of high-Tc cuprates. For the
S=1/2 Pyrochlore and Kagome antiferromagnets, the effective hamiltonians
predict spin-disordered, lattice symmetry breaking, ground states with a large
density of low energy singlets as found by exact diagonalization of small
clusters.Comment: For the proceedings of the conference on 'Effective Models for
Low-Dimensional Strongly Correlated Systems', Peyresq, September 2005.
Peyresq Conference. 11 pages, 9 Figure
Spin Tunneling, Berry phases and Doped Antiferromagnets
Interference effects between Berry phase factors in spin tunneling systems
have been discussed in recent Letters by Loss, DiVincenzo and Grinstein and von
Delft and Henley. This Comment points out that Berry phases in spin tunneling
are important in another interesting case: the two dimensional doped
antiferromagnet. I show that the dispersion of a single hole in the t-J model
changes sign as where is the size of the spins. This provides
an interpretation of the numerical results for the s=\half model, and a
prediction for other spin sizes.Comment: 5 pages, LaTe
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