9 research outputs found
A dynamical symmetry for supermembranes
A dynamical symmetry for supersymmetric extended objects is given.Comment: 3 page
Partial Hamiltonian reduction of relativistic extended objects in light-cone gauge
The elimination of the non-transversal field in the standard light-cone
formulation of higher-dimensional extended objects is formulated as a
Hamiltonian reduction.Comment: 11 page
Partially gapped fermions in 2D
We compute mean field phase diagrams of two closely related interacting
fermion models in two spatial dimensions (2D). The first is the so-called 2D
t-t'-V model describing spinless fermions on a square lattice with local
hopping and density-density interactions. The second is the so-called 2D
Luttinger model that provides an effective description of the 2D t-t'-V model
and in which parts of the fermion degrees of freedom are treated exactly by
bosonization. In mean field theory, both models have a charge-density-wave
(CDW) instability making them gapped at half-filling. The 2D t-t'-V model has a
significant parameter regime away from half-filling where neither the CDW nor
the normal state are thermodynamically stable. We show that the 2D Luttinger
model allows to obtain more detailed information about this mixed region. In
particular, we find in the 2D Luttinger model a partially gapped phase that, as
we argue, can be described by an exactly solvable model.Comment: v1: 36 pages, 10 figures, v2: minor corrections; equation references
to arXiv:0903.0055 updated
Exact solution of a 2D interacting fermion model
We study an exactly solvable quantum field theory (QFT) model describing
interacting fermions in 2+1 dimensions. This model is motivated by physical
arguments suggesting that it provides an effective description of spinless
fermions on a square lattice with local hopping and density-density
interactions if, close to half filling, the system develops a partial energy
gap. The necessary regularization of the QFT model is based on this proposed
relation to lattice fermions. We use bosonization methods to diagonalize the
Hamiltonian and to compute all correlation functions. We also discuss how,
after appropriate multiplicative renormalizations, all short- and long distance
cutoffs can be removed. In particular, we prove that the renormalized two-point
functions have algebraic decay with non-trivial exponents depending on the
interaction strengths, which is a hallmark of Luttinger-liquid behavior.Comment: 59 pages, 3 figures, v2: further references added; additional
subsections elaborating mathematical details; additional appendix with
details on the relation to lattice fermion
Fermions in two dimensions and exactly solvable models
This Ph.D. thesis in mathematical physics concerns systems of interacting fermions with strong correlations. For these systems the physical properties can only be described in terms of the collective behavior of the fermions. Moreover, they are often characterized by a close competition between fermion localization versus delocalization, which can result in complex and exotic physical phenomena. Strongly correlated fermion systems are usually modelled by many-body Hamiltonians for which the kinetic- and interaction energy have the same order of magnitude. This makes them challenging to study as the application of conventional computational methods, like mean field- or perturbation theory, often gives unreliable results. Of particular interest are Hubbard-type models, which provide minimal descriptions of strongly correlated fermions. The research of this thesis focuses on such models defined on two-dimensional square lattices. One motivation for this is the so-called high-Tc problem of the cuprate superconductors. A main hypothesis is that there exists an underlying Fermi surface with nearly flat parts, i.e. regions where the surface is straight. It is shown that a particular continuum limit of the lattice system leads to an effective model amenable to computations. This limit is partial in that it only involves fermion degrees of freedom near the flat parts. The result is an effective quantum field theory that is analyzed using constructive bosonization methods. Various exactly solvable models of interacting fermions in two spatial dimensions are also derived and studied.QC 2011120
Establishing analogies between the physics of extra dimensions and carbon nanotubes
We point out a conceptual analogy between the physics of extra spatial dimensions and the physics of carbon nanotubes which arises for principle reasons, although the corresponding energy scales are at least ten orders of magnitude apart. For low energies, one can apply the Kaluza-Klein description to both types of systems, leading to two completely different but consistent interpretations of the underlying physics. In particular, we discuss in detail the Kaluza-Klein description of armchair and zig-zag carbon nanotubes. Furthermore, we describe how certain experimental results for carbon nanotubes could be re-interpreted in terms of the Kaluza-Klein description. Finally, we present ideas for new measurements that could allow to probe concepts of models with extra spatial dimensions in table-top experiments, providing further links between condensed matter and particle physics.QC 20120807</p