Quantum Fermion Hair

It is shown that the Dirac operator in the background of a magnetic %Reissner-Nordstr\"om black hole and a Euclidean vortex possesses normalizable zero modes in theories containing superconducting cosmic strings. One consequence of these zero modes is the presence of a fermion condensate around magnetically charged black holes which violates global quantum numbers.Comment: 16pp (harvmac (l)) and 2 figs.(not included

Functional Bosonization of Non-Relativistic Fermions in (2+1)(2+1) Dimensions

We analyze the universality of the bosonization rules in non-relativistic fermionic systems in $(2+1)d$. We show that, in the case of linear fermionic dispersion relations, a general fermionic theory can be mapped into a gauge theory in such a way that the fermionic density maps into a magnetic flux and the fermionic current maps into a transverse electric field. These are universal rules in the sense that they remain valid whatever the interaction considered. We also show that these rules are universal in the case of non-linear dispersion relations provided we consider only density-density interactions. We apply the functional bosonization formalism to a non-relativistic and non-local massive Thirring-like model and evaluate the spectrum of collective excitations in several limits. In the large mass limit, we are able to exactly calculate this spectrum for arbitrary density-density and current-current interactions. We also analyze the massless case and show that it has no collective excitations for any density-density potential in the Gaussian approximation. Moreover, the presence of current interactions may induce a gapless mode with a linear dispersion relation.Comment: 26 Pages, LaTeX, Final version to appear in International Journal of Modern Physics

Formfactors and functional form of correlators in the XX spin chain

We present the new expressions for the formfactors of local operators for the XX - quantum spin chain as a Cauchy determinants. Using the known functional form of the correlator at large distances we propose the new expression for the constant for the asymptotics of the correlator as a Cauchy determinant. We calculate the momentum distribution for the general case of the XXZ spin chain and point out that it is completely different from the Luttinger model (the system of fermions). For the XX chain we compare numerically the value of the lowest formfactor and the expectation value of momentum- zero operators which is determined by the functional form of the correlator.Comment: LaTex, 18 page

General Solutions for Tunneling of Scalar Fields with Quartic Potentials

For the theory of a single scalar field $\varphi$ with a quartic potential $V(\varphi)$, we find semi-analytic expressions for the Euclidean action in both four and three dimensions. The action in four dimensions determines the quantum tunneling rate at zero temperature from a false vacuum state to the true vacuum state; similarly, the action in three dimensions determines the thermal tunneling rate for a finite temperature theory. We show that for all quartic potentials, the action can be obtained from a one parameter family of instanton solutions corresponding to a one parameter family of differential equations. We find the solutions numerically and use polynomial fitting formulae to obtain expressions for the Euclidean action. These results allow one to calculate tunneling rates for the entire possible range of quartic potentials, from the thin-wall (nearly degenerate) limit to the opposite limit of vanishing barrier height. We also present a similar calculation for potentials containing $\varphi^4 \ln \varphi^2$ terms, which arise in the one-loop approximation to the effective potential in electroweak theory.Comment: 17 pages, 6 figures not included but available upon request, UM AC 93-

Public engagement in local government: the voice and influence of citizens in online communicative spaces

The communications and engagement strategies of local councils play an important role in contributing to the public's understanding of local democracies, and their engagement with local issues. Based on a study of the local authority in the third largest city in the UK, Leeds, this article presents an empirically based analysis of the impact of new opportunities for public engagement afforded by digital media on the Council's communication with citizens. Drawing on over 20 face-to-face semi-structured interviews with elected politicians, Council strategists, Council communications specialists, mainstream journalists, and citizen journalists, the article explores perceptions of the Council's engagement and communication with citizens from the perspective of a range of actors involved in the engagement process. The research asks what the differing motivations behind the Council's communications and engagement strategies mean for the way that digital media are and might be used in the future to enhance the role of citizens in local governance. The research suggests that while there are no grounds for expecting digital media to displace existing channels of public engagement, digital media are beginning to play an important role in defining and reconfiguring the role of citizens within local governance

General Solutions for Tunneling of Scalar Fields with Quartic Potentials in de Sitter Space

The tunneling rates for scalar fields with quartic potentials in de Sitter space in the limit of no gravitational back reaction are calculated numerically and the results are fitted by analytic formulae.Comment: (Contours in Figure 1 corrected, two-dimensional fitting coefficient corrected, references added.), 16 pages, KUNS 124

Tail States in Disordered Superconductors with Magnetic Impurities: the Unitarity Limit

When subject to a weak magnetic impurity distribution, the order parameter and quasi-particle energy gap of a weakly disordered bulk s-wave superconductor are suppressed. In the Born scattering limit, recent investigations have shown that `optimal fluctuations' of the random impurity potential can lead to the nucleation of `domains' of localised states within the gap region predicted by the conventional Abrikosov-Gor'kov mean-field theory, rendering the superconducting system gapless at any finite impurity concentration. By implementing a field theoretic scheme tailored to the weakly disordered system, the aim of the present paper is to extend this analysis to the consideration of magnetic impurities in the unitarity scattering limit. This investigation reveals that the qualitative behaviour is maintained while the density of states exhibits a rich structure.Comment: 18 pages AMSLaTeX (with LaTeX2e), 6 eps figure

Time dependence of breakdown in a global fiber-bundle model with continuous damage

A time-dependent global fiber-bundle model of fracture with continuous damage is formulated in terms of a set of coupled non-linear differential equations. A first integral of this set is analytically obtained. The time evolution of the system is studied by applying a discrete probabilistic method. Several results are discussed emphasizing their differences with the standard time-dependent model. The results obtained show that with this simple model a variety of experimental observations can be qualitatively reproduced.Comment: APS style, two columns, 4 figures. To appear in Phys. Rev.

A low energy theory for superfluid and solid matter and its application to the neutron star crust

We formulate a low energy effective theory describing phases of matter that are both solid and superfluid. These systems simultaneously break translational symmetry and the phase symmetry associated with particle number. The symmetries restrict the combinations of terms that can appear in the effective action and the lowest order terms featuring equal number of derivatives and Goldstone fields are completely specified by the thermodynamic free energy, or equivalently by the long-wavelength limit of static correlation functions in the ground state. We show that the underlying interaction between particles that constitute the lattice and the superfluid gives rise to entrainment, and mixing between the Goldstone modes. As a concrete example we discuss the low energy theory for the inner crust of a neutron star, where a lattice of ionized nuclei coexists with a neutron superfluid.Comment: 21 pages, 1 figur

Exact calculation of the radiatively-induced Lorentz and CPT violation in QED

Radiative corrections arising from the axial coupling of charged fermions to a constant vector b_\mu can induce a Lorentz- and CPT-violating Chern-Simons term in the QED action. We calculate the exact one-loop correction to this term keeping the full b_\mu dependence, and show that in the physically interesting cases it coincides with the lowest-order result. The effect of regularization and renormalization and the implications of the result are briefly discussed.Comment: LaTex, 8 pages; minor correction