49 research outputs found
On the quasiparticle description of c=1 CFTs
We show that the description of Conformal Field Theory in terms of
quasiparticles satisfying fractional statistics can be obtained from the
sine-Gordon model with a chemical potential , in the limit where .
These quasiparticles are related to the excitations of the Calogero-Sutherland
(CS) model. We provide a direct calculation of their 2-particle S-matrix using
Korepin's method. We also reconsider the computation of the CS S-matrix in
terms of particles with fractional charge
Exactly solvable model for isospin S=3/2 fermionic atoms on an optical lattice
We propose an exact solution of a model describing a low energy behavior of
cold isospin S=3/2 fermionic atoms on a one-dimensional optical lattice.
Depending on the band filling the effective field theory has a form of a
deformed Gross-Neveu model with either (half filling)
or symmetry.Comment: 4 pages, no figures, replaced with the final version to appear in PR
Scaling of excitations in dimerized and frustrated spin-1/2 chains
We study the finite-size behavior of the low-lying excitations of spin-1/2
Heisenberg chains with dimerization and next-to-nearest neighbors interaction,
J_2. The numerical analysis, performed using density-matrix renormalization
group, confirms previous exact diagonalization results, and shows that, for
different values of the dimerization parameter \delta, the elementary triplet
and singlet excitations present a clear scaling behavior in a wide range of
\ell=L/\xi (where L is the length of the chain and \xi is the correlation
length). At J_2=J_2c, where no logarithmic corrections are present, we compare
the numerical results with finite-size predictions for the sine-Gordon model
obtained using Luscher's theory. For small \delta we find a very good agreement
for \ell > 4 or 7 depending on the excitation considered.Comment: 4 pages, 4 eps figures, RevTeX 4 class, same version as in PR
On the mass spectrum of the two-dimensional O(3) sigma model with theta term
Form Factor Perturbation Theory is applied to study the spectrum of the O(3)
non--linear sigma model with the topological term in the vicinity of . Its effective action near this value is given by the non--integrable
double Sine--Gordon model. Using previous results by Affleck and the explicit
expressions of the Form Factors of the exponential operators , we show that the spectrum consists of a stable triplet
of massive particles for all values of and a singlet state of higher
mass. The singlet is a stable particle only in an interval of values of
close to whereas it becomes a resonance below a critical value
.Comment: 4 pages REVTEX4, 2 figures reference added,corrected typo
Mass Generation in Perturbed Massless Integrable Models
We extend form-factor perturbation theory to non--integrable deformations of
massless integrable models, in order to address the problem of mass generation
in such systems. With respect to the standard renormalisation group analysis
this approach is more suitable for studying the particle content of the
perturbed theory. Analogously to the massive case, interesting information can
be obtained already at first order, such as the identification of the operators
which create a mass gap and those which induce the confinement of the massless
particles in the perturbed theory
Exactly Solvable Ginzburg-Landau theories of Superconducting Order Parameters coupled to Elastic Modes
We consider two families of exactly solvable models describing thermal
fluctuations in two-dimensional superconductors coupled to phonons living in an
insulating layer, and study the stability of the superconducting state with
respect to vortices. The two families are characterized by one or two
superconducting planes. The results suggest that the effective critical
temperature increases with the thickness of the insulating layer. Also the
presence of the additional superconducting layer has the same effect.Comment: Submitted to Physical Review
On the relationship between sigma models and spin chains
We consider the two-dimensional non-linear sigma model with
topological term using a lattice regularization introduced by Shankar and Read
[Nucl.Phys. B336 (1990), 457], that is suitable for studying the strong
coupling regime. When this lattice model is quantized, the coefficient
of the topological term is quantized as , with integer or
half-integer. We study in detail the relationship between the low energy
behaviour of this theory and the one-dimensional spin- Heisenberg model. We
generalize the analysis to sigma models with other symmetries.Comment: To appear in Int. J. MOd. Phys.
Dynamical density-matrix renormalization-group method
I present a density-matrix renormalization-group (DMRG) method for
calculating dynamical properties and excited states in low-dimensional lattice
quantum many-body systems. The method is based on an exact variational
principle for dynamical correlation functions and the excited states
contributing to them. This dynamical DMRG is an alternate formulation of the
correction vector DMRG but is both simpler and more accurate. The finite-size
scaling of spectral functions is discussed and a method for analyzing the
scaling of dense spectra is described. The key idea of the method is a
size-dependent broadening of the spectrum.The dynamical DMRG and the
finite-size scaling analysis are demonstrated on the optical conductivity of
the one-dimensional Peierls-Hubbard model. Comparisons with analytical results
show that the spectral functions of infinite systems can be reproduced almost
exactly with these techniques. The optical conductivity of the Mott-Peierls
insulator is investigated and it is shown that its spectrum is qualitatively
different from the simple spectra observed in Peierls (band) insulators and
one-dimensional Mott-Hubbard insulators.Comment: 16 pages (REVTEX 4.0), 10 figures (in 13 EPS files