How to excite the internal modes of sine-Gordon solitons

We investigate the dynamics of the sine-Gordon solitons perturbed by spatiotemporal external forces. We prove the existence of internal (shape) modes of sine-Gordon solitons when they are in the presence of inhomogeneous space-dependent external forces, provided some conditions (for these forces) hold. Additional periodic time-dependent forces can sustain oscillations of the soliton width. We show that, in some cases, the internal mode even can become unstable, causing the soliton to decay in an antisoliton and two solitons. In general, in the presence of spatiotemporal forces the soliton behaves as a deformable (non-rigid) object. A soliton moving in an array of inhomogeneities can also present sustained oscillations of its width. There are very important phenomena (like the soliton-antisoliton collisions) where the existence of internal modes plays a crucial role. We show that, under some conditions, the dynamics of the soliton shape modes can be chaotic. A short report of some of our results has been published in [J. A. Gonzalez et al., Phys. Rev. E, 65 (2002) 065601(R)].Comment: 14 .eps figures.To appear in Chaos, Solitons and Fractal

N=1 Supersymmetric Yang-Mills on the lattice at strong coupling

We study N=1 supersymmetric SU(N) Yang-Mills theory on the lattice at strong coupling. Our method is based on the hopping parameter expansion in terms of random walks, resummed for any value of the Wilson parameter r in the small hopping parameter region. Results are given for the mesonic (2-gluino) and fermionic (3-gluino) propagators and spectrum.Comment: Latex file. 43 pages. Minor additional comments, references added, typos corrected. Accepted for publication in Int. J. Mod. Phys.

RVB signatures in the spin dynamics of the square-lattice Heisenberg antiferromagnet

We investigate the spin dynamics of the square-lattice spin-1/2 Heisenberg antiferromagnet by means of an improved mean field Schwinger boson calculation. By identifying both, the long range N\'eel and the RVB-like components of the ground state, we propose an educated guess for the mean field triplet excitation consisting on a linear combination of local and bond spin flips to compute the dynamical structure factor. Our main result is that when this triplet excitation is optimized in such a way that the corresponding sum rule is fulfilled, we recover the low and high energy spectral weight features of the experimental spectrum. In particular, the anomalous spectral weight depletion at $(\pi,0)$ found in recent inelastic neutron scattering experiments can be attributed to the interference of the triplet bond excitations of the RVB component of the ground state. We conclude that the Schwinger boson theory seems to be a good candidate to adequately interpret the dynamic properties of the square-lattice Heisenberg antiferromagnet.Comment: 6 pages with 3 figure

On the spectroscopy of quantum dots in microcavities

At the occasion of the OECS conference in Madrid, we give a succinct account of some recent predictions in the spectroscopy of a quantum dot in a microcavity that remain to be observed experimentally, sometimes within the reach of the current state of the art.Comment: OECS11 Conference proceedings, in editor style. 4 pages, 1 figure. Animations provided separatel