614 research outputs found
Exact Supersymmetry on the Lattice
We discuss the possibility of representing supersymmetry exactly in a lattice
discretized system. In particular, we construct a perfect supersymmetric action
for the Wess-Zumino model.Comment: 9 pages, LaTex, no figure
Entanglement Entropy, Conformal Invariance and the Critical Behavior of the Anisotropic Spin-S Heisenberg Chains: A DMRG study
Using the density-matrix renormalization-group, we investigate the critical
behavior of the anisotropic Heisenberg chains with spins up to . We show
that through the relations arising from the conformal invariance and the DMRG
technique it is possible to obtain accurate finite-size estimates of the
conformal anomaly , the sound velocity , the anomalous dimension
, and the surface exponent of the anisotropic spin-
Heisenberg chains with relatively good accuracy without fitting parameters. Our
results indicate that the entanglement entrop of the spin-
Heisenberg chains satisfies the relation
for in the thermodynamic limit.Comment: 7 pages, 3 figs., 3 tables, to appear in PRB. Added new results for
s>1/
Scaling and Enhanced Symmetry at the Quantum Critical Point of the Sub-Ohmic Bose-Fermi Kondo Model
We consider the finite temperature scaling properties of a Kondo-destroying
quantum critical point in the Ising-anisotropic Bose-Fermi Kondo model (BFKM).
A cluster-updating Monte Carlo approach is used, in order to reliably access a
wide temperature range. The scaling function for the two-point spin correlator
is found to have the form dictated by a boundary conformal field theory, even
though the underlying Hamiltonian lacks conformal invariance. Similar
conclusions are reached for all multi-point correlators of the spin-isotropic
BFKM in a dynamical large-N limit. Our results suggest that the quantum
critical local properties of the sub-ohmic BFKM are those of an underlying
boundary conformal field theory.Comment: 4 pages, 3 embedded eps figures; published versio
Perfect Scalars on the Lattice
We perform renormalization group transformations to construct optimally local
perfect lattice actions for free scalar fields of any mass. Their couplings
decay exponentially. The spectrum is identical to the continuum spectrum, while
thermodynamic quantities have tiny lattice artifacts. To make such actions
applicable in simulations, we truncate the couplings to a unit hypercube and
observe that spectrum and thermodynamics are still drastically improved
compared to the standard lattice action. We show how preconditioning techniques
can be applied successfully to this type of action. We also consider a number
of variants of the perfect lattice action, such as the use of an anisotropic or
triangular lattice, and modifications of the renormalization group
transformations motivated by wavelets. Along the way we illuminate the
consistent treatment of gauge fields, and we find a new fermionic fixed point
action with attractive properties.Comment: 26 pages, 11 figure
The Fermion Doubling Problem and Noncommutative Geometry
We propose a resolution for the fermion doubling problem in discrete field
theories based on the fuzzy sphere and its Cartesian products.Comment: 12 pages Latex2e, no figures, typo
Path Integral Approach to Fermionic Vacuum Energy in Non-parallel D1-Branes
The fermionic one loop vacuum energy of the superstring theory in a system of
non-parallel D1-branes is derived by applying the path integral formalism.Comment: 7 pages, no figur
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