Exact Momentum Distribution of a Fermi Gas in One Dimension

We introduce an exactly solvable model of a fermi gas in one dimension and compute the momentum distribution exactly. This is based on a generalisation of the ideas of bosonization in one dimension. It is shown that in the RPA limit(the ultra-high density limit) the answers we get are the exact answers for a homogeneous fermi gas interacting via a two-body repulsive coulomb interaction. Furthermore, the solution may be obtained exactly for arbitrary functional forms of the interaction, so long as it is purely repulsive. No linearization of the bare fermion dispersion is required. We find that for the interaction considered, the fermi surface is intact for weak repulsion and is destroyed only for sufficiently strong repulsion. Comparison with other models like the supersymmetric t-J model with inverse square interactions is made.Comment: RevTex, 5 pages, no figures., modified following ref. comments, more detailed explanations, resutls same, one new ref. adde

Exact Dynamical Structure Factor of a Bose Liquid

Based on ideas introduced in a previous preprint cond-mat/9701206 we propose an exactly solvable model of bosons interacting amongst themselves via a Van-der Waal-like repulsive interaction, and compute both the filling fraction and the dynamical structure factor exactly. The novelty of this approach involves introducing, analogous to Fermi sea (or surface) displacements, Bose fields that in this case, correspond to fluctuations of the Bose condensate. The exact dynamical structure factor has a coherent part that corresponds to the Bogoliubov spectrum and an incoherent part that is a result of correlations.Comment: RevTex, 6 pages, no figures, replaced previously empty fil

A.C. Conductivity of a Disordered Metal

The degenerate free Fermi gas coupled to a random potential is used to compute a.c. conductivity in various dimensions. We first formally diagonalise the hamiltonian using an appropriate basis that is a functional of the disorder potential. Then we compute the a.c. conductivity at zero temperature using the Kubo formula. This a.c. conductivity is a functional of the disordered potential. The wavefunction of extended states is written as exponential of the logarithm. We use the cumulant expansion to compute the disordered averaged a.c. conductivity for Gaussian disorder. The formula is valid if a certain linearization approximation is valid in the long-wavelength limit.Comment: 22 pages, no figs., Plain LaTe

Myopic Bosonization

As the title suggests, this is an attempt at bosonizing fermions in any number of dimensions without paying attention to the fact that the Fermi surface is an extended object. One is tempted to introduce the density fluctuation and its conjugate and recast the interacting problem in terms of these canonical Bose fields. However, we find that the attempt is short-sighted figuratively as well for the same reason. But surprisingly, this flaw, which manifests itself as an inconsistency between Menikoff-Sharp's construction of the kinetic energy operator in terms of currents and densities, and our ansatz for this operator, is nevertheless able to reproduce(although reluctantly) many salient features of the free theory. Buoyed by this success, we solve the interacting problem and compute the full propagator.Comment: 3 pages RevTe

Microscopic Origin of Spatial Coherence and Wolf Shifts

We show that the vacuum of electromagnetic field has intrinsic partial spatial coherence in frequency domain which effectively extends over regions of the order of wavelength $\lambda$. This spatial coherence leads to a dynamical coupling between atoms and is the cause of source correlations and Wolf shifts. We show how the source spatial correlations can lead to tailor made coherent emissions. We discuss the universality of source correlation effects and presents several application.Comment: 7 pages, 8 figure

Momentum Distribution of the Hubbard Model

Using the recently perfected sea-boson method, we compute the momentum distribution of the one-band Hubbard model in one and two spatial dimensions. We compute the asymptotic features of the momentum distribution explicitly away from half filling for weak coupling in one and two dimensions. While the results are not exact by any means, they provide the exact asymptotics, namely they are able to reproduce the exponents obtained by Shulz in one dimension obtained using Bethe ansatz. The corresponding results in more than one dimension are therefore as believeable.Comment: 12 pages, LaTex, 2d case revised, new formula for field operato

Xray-Edge Spectra From Sea-Bosons-I

The well-studied phenomenon of X-ray edge singularities is revisited using the sea-boson approach that has recently been placed on a rigorous footing. We are able to reproduce the well-known result namely, Mahan's power law divergences. Unlike the work of Schotte and Schotte, no linearization of the bare fermion dispersion is needed, which, by their own admission, is a source of some difficulty. Our approach also brings out some differences between the different dimensions which is not present in their work. Finally, our work also allows for easy generalization to potentials more realistic than the simple delta-function used commonly in the literature.Comment: 8 pages, regular LaTeX, one inbuilt fi

Quenched Disorder From Sea-Bosons

The degenerate Fermi gas coupled to a random potential is used to study metal-insulator transitions in various dimensions. We first recast the problem in the sea-boson language that allows for an easy evaluation of important physical attributes. We evaluate the dynamical number-number correlation function and from this compute the a.c. conductivity. We find that the d.c. conductivity vanishes in one and two dimensions. For a hamiltonian that forbids scattering of an electron from within the Fermi surface to another state within the Fermi surface we find that there is no metal-insulator transition in three dimensions either.Comment: 8 pages, Plain LaTe

Hydrodynamic Formulation of the Hubbard Model

In this article, we show how to recast the Hubbard model in one dimension in a hydrodynamic language and use the path integral approach to compute the one-particle Green function. We compare with the Bethe ansatz results of Schulz and find exact agreement with the formulas for spin and charge velocities and anomalous exponent in weak coupling regime. These methods may be naturally generalized to more than one dimension by simply promoting wavenumbers to wavevectors.Comment: 7 pages, no fig

Bosonization and Quantum Hydrodynamics

It is shown that it is possible to bosonize fermions in any number of dimensions using the hydrodynamic variables, namely the velocity potential and density. The slow part of the Fermi field is defined irrespective of dimensionality and the commutators of this field with currents and densities are exponentiated using the velocity potential as conjugate to the density. An action in terms of these canonical bosonic variables is proposed that reproduces the correct current and density correlations. This formalism in one dimension is shown to be equivalent to the Tomonaga-Luttinger approach as it leads to the same propagator and exponents. We compute the one-particle properties of a spinless homogeneous Fermi system in two spatial dimensions with long-range gauge interactions and highlight the metal-insulator transition in the system. A general formula for the generating function of density correlations is derived that is valid beyond the random phase approximation. Finally, we write down a formula for the annihilation operator in momentum space directly in terms of number conserving products of Fermi fields.Comment: Published version plus never before seen action footage of a new proo