Finite Volume Chiral Partition Functions and the Replica Method

In the framework of chiral perturbation theory we demonstrate the equivalence of the supersymmetric and the replica methods in the symmetry breaking classes of Dyson indices \beta=1 and \beta=4. Schwinger-Dyson equations are used to derive a universal differential equation for the finite volume partition function in sectors of fixed topological charge, \nu. All dependence on the symmetry breaking class enters through the Dyson index \beta. We utilize this differential equation to obtain Virasoro constraints in the small mass expansion for all \beta and in the large mass expansion for \beta=2 with arbitrary \nu. Using quenched chiral perturbation theory we calculate the first finite volume correction to the chiral condensate demonstrating how, for all \betathere exists a region in which the two expansion schemes of quenched finite volume chiral perturbation theory overlap.Comment: RevTeX, 18 pages. Some typos corrected and a note added in the introduction to section III. To appear in Phys. Rev.

Interaction of Wave-Driven Particles with Slit Structures

Can a classical system as walking oil droplets on a vibrating surface simulate the single and double slit Quantum Mechanics experiment? A systematic investigation reveals that the answer is no, but that the classical system exhibits rich and fascinating structures.Comment: Submitted to Phys. Rev. E, 22 pages, 26 postscript figure

Efimov trimers under strong confinement

The dimensionality of a system can fundamentally impact the behaviour of interacting quantum particles. Classic examples range from the fractional quantum Hall effect to high temperature superconductivity. As a general rule, one expects confinement to favour the binding of particles. However, attractively interacting bosons apparently defy this expectation: while three identical bosons in three dimensions can support an infinite tower of Efimov trimers, only two universal trimers exist in the two dimensional case. We reveal how these two limits are connected by investigating the problem of three identical bosons confined by a harmonic potential along one direction. We show that the confinement breaks the discrete Efimov scaling symmetry and destroys the weakest bound trimers. However, the deepest bound Efimov trimer persists under strong confinement and hybridizes with the quasi-two-dimensional trimers, yielding a superposition of trimer configurations that effectively involves tunnelling through a short-range repulsive barrier. Our results suggest a way to use strong confinement to engineer more stable Efimov-like trimers, which have so far proved elusive.Comment: 8 pages, 4 figures. Typos corrected, published versio

Microscopic description of exciton-polaritons in microcavities

We investigate the microscopic description of exciton-polaritons that involves electrons, holes and photons within a two-dimensional microcavity. We show that in order to recover the simplified exciton-photon model that is typically used to describe polaritons, one must correctly define the exciton-photon detuning and exciton-photon (Rabi) coupling in terms of the bare microscopic parameters. For the case of unscreened Coulomb interactions, we find that the exciton-photon detuning is strongly shifted from its bare value in a manner akin to renormalization in quantum electrodynamics. Within the renormalized theory, we exactly solve the problem of a single exciton-polariton for the first time and obtain the full spectral response of the microcavity. In particular, we find that the electron-hole wave function of the polariton can be significantly modified by the very strong Rabi couplings achieved in current experiments. Our microscopic approach furthermore allows us to properly determine the effective interaction between identical polaritons, which goes beyond previous theoretical work. Our findings are thus important for understanding and characterizing exciton-polariton systems across the whole range of polariton densities.Comment: 14 pages, 5 figure

Three-body problem in a two-dimensional Fermi gas

We investigate the three-body properties of two identical "up" fermions and one distinguishable "down" atom interacting in a strongly confined two-dimensional geometry. We compute exactly the atom-dimer scattering properties and the three-body recombination rate as a function of collision energy and mass ratio m_up/m_down. We find that the recombination rate for fermions is strongly energy dependent, with significant contributions from higher partial waves at low energies. For m_up < m_down, the s-wave atom-dimer scattering below threshold is completely described by the scattering length. Furthermore, we examine the "up-up-down" bound states (trimers) appearing at large m_up/m_down and find that the energy spectrum for the deepest bound trimers resembles that of a hydrogen atom confined to two dimensions.Comment: 6 pages, 6 figure