7,709 research outputs found
Density Matrix Renormalization Group Applied to the Ground State of the XY-Spin-Peierls System
We use the density matrix renormalization group (DMRG) to map out the ground
state of a XY-spin chain coupled to dispersionless phonons of frequency . We confirm the existence of a critical spin-phonon coupling for the onset of the spin gap bearing the signature of
a Kosterlitz-Thouless transition. We also observe a classical-quantum crossover
when the spin-Peierls gap is of order . In the classical
regime, , the mean-field parameters are strongly renormalized
by non-adiabatic corrections. This is the first application of the DMRG to
phonons.Comment: 10 pages, 5 figures. To be published in PR
Preliminary results of the analysis and of the optimization dedicated to the final focus stabilization
Phase diagram of the one-dimensional Holstein model of spinless fermions
The one-dimensional Holstein model of spinless fermions interacting with
dispersionless phonons is studied using a new variant of the density matrix
renormalisation group. By examining various low-energy excitations of finite
chains, the metal-insulator phase boundary is determined precisely and agrees
with the predictions of strong coupling theory in the anti-adiabatic regime and
is consistent with renormalisation group arguments in the adiabatic regime. The
Luttinger liquid parameters, determined by finite-size scaling, are consistent
with a Kosterlitz-Thouless transition.Comment: Minor changes. 4 pages, 4 figures. To appear in Physical Review
Letters 80 (1998) 560
Head-on infall of two compact objects: Third post-Newtonian Energy Flux
Head-on infall of two compact objects with arbitrary mass ratio is
investigated using the multipolar post-Minkowskian approximation method. At the
third post-Newtonian order the energy flux, in addition to the instantaneous
contributions, also includes hereditary contributions consisting of the
gravitational-wave tails, tails-of-tails and the tail-squared terms. The
results are given both for infall from infinity and also for infall from a
finite distance. These analytical expressions should be useful for the
comparison with the high accuracy numerical relativity results within the limit
in which post-Newtonian approximations are valid.Comment: 25 pages, 2 figures, This version includes the changes appearing in
the Erratum published in Phys. Rev.
Ground-state properties of the One-dimensional Kondo Lattice at partial Band-filling
We compute the magnetic structure factor, the singlet correlation function
and the momentum distribution of the one-dimensional Kondo lattice model at the
density . The density matrix-renormalization group method is used.
We show that in the weak-coupling regime, the ground state is paramagnetic. We
argue that a Luttinger liquid description of the model in this region is
consistent with our calculations . In the strong-coupling regime, the ground
state becomes ferromagnetic. The conduction electrons show a spinless-fermion
like behavior.Comment: 8 pages, Latex, 5 figures included, to be published in PRB (Rapid
Communications
Vibration control of the beam of the future linear collider
This paper proposes a new approach for beam stabilization of the future Compact LInear Collider (CLIC). The method attempts to increase the efficiency of traditional methods. It is composed of a hybrid adaptive filtering algorithm that uses both feedback and adaptive control. The scheme uses an estimate of the prediction error to update the adaptive filter's parameters. The strategy of this method is described considering the process environment. The method efficiency is evaluated, and it is demonstrated that it provides high damping, fast vibration suppression, good robustness and easy realization thanks to the simplicity of the computations
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