On the Classification of Bulk and Boundary Conformal Field Theories

The classification of rational conformal field theories is reconsidered from the standpoint of boundary conditions. Solving Cardy's equation expressing the consistency condition on a cylinder is equivalent to finding integer valued representations of the fusion algebra. A complete solution not only yields the admissible boundary conditions but also gives valuable information on the bulk properties.Comment: 7 pages, LaTeX; minor correction

Kinks in the Kondo problem

We find the exact quasiparticle spectrum for the continuum Kondo problem of $k$ species of electrons coupled to an impurity of spin $S$. In this description, the impurity becomes an immobile quasiparticle sitting on the boundary. The particles are ``kinks'', which can be thought of as field configurations interpolating between adjacent wells of a potential with $k+1$ degenerate minima. For the overscreened case $k>2S$, the boundary has this kink structure as well, which explains the non-integer number of boundary states previously observed. Using simple arguments along with the consistency requirements of an integrable theory, we find the exact elastic $S$-matrix for the quasiparticles scattering among themselves and off of the boundary. This allows the calculation of the exact free energy, which agrees with the known Bethe ansatz solution.Comment: 9 pages +1 figur

Exact ϕ1,3\phi_{1,3} boundary flows in the tricritical Ising model

We consider the tricritical Ising model on a strip or cylinder under the integrable perturbation by the thermal $\phi_{1,3}$ boundary field. This perturbation induces five distinct renormalization group (RG) flows between Cardy type boundary conditions labelled by the Kac labels $(r,s)$. We study these boundary RG flows in detail for all excitations. Exact Thermodynamic Bethe Ansatz (TBA) equations are derived using the lattice approach by considering the continuum scaling limit of the $A_4$ lattice model with integrable boundary conditions. Fixing the bulk weights to their critical values, the integrable boundary weights admit a thermodynamic boundary field $\xi$ which induces the flow and, in the continuum scaling limit, plays the role of the perturbing boundary field $\phi_{1,3}$. The excitations are completely classified, in terms of string content, by $(m,n)$ systems and quantum numbers but the string content changes by either two or three well-defined mechanisms along the flow. We identify these mechanisms and obtain the induced maps between the relevant finitized Virasoro characters. We also solve the TBA equations numerically to determine the boundary flows for the leading excitations.Comment: 42 pages, 11 figures, Latex; v2: some typos corrected and few comments adde

Lattice Approach to Excited TBA Boundary Flows: Tricritical Ising Model

We show how a lattice approach can be used to derive Thermodynamic Bethe Ansatz (TBA) equations describing all excitations for boundary flows. The method is illustrated for a prototypical flow of the tricritical Ising model by considering the continuum scaling limit of the A4 lattice model with integrable boundaries. Fixing the bulk weights to their critical values, the integrable boundary weights admit two boundary fields $\xi$ and $\eta$ which play the role of the perturbing boundary fields $\phi_{1,3}$ and $\phi_{1,2}$ inducing the renormalization group flow between boundary fixed points. The excitations are completely classified in terms of (m,n) systems and quantum numbers but the string content changes by certain mechanisms along the flow. For our prototypical example, we identify these mechanisms and the induced map between the relevant finitized Virasoro characters. We also solve the boundary TBA equations numerically to determine the flows for the leading excitations.Comment: 11 pages, 3 figures, LaTeX; v2: some useful notations and one reference added; to appear in PL

Q-ball Dynamics

We investigate the dynamics of Q-balls in one, two and three space dimensions, using numerical simulations of the full nonlinear equations of motion. We find that the dynamics of Q-balls is extremely complex, involving processes such as charge transfer and Q-ball fission. We present results of simulations which illustrate the salient features of 2-Q-ball interactions and give qualitative arguments to explain them in terms of the evolution of the time-dependent phases.Comment: 37 pages, including figure

Enhanced release of IgE-dependent early phase mediators from nasal polyp tissue

Background: The mast cell is a crucial effector cell in allergic rhinitis and other inflammatory diseases. During the acute allergic reaction preformed mediators such as histamine, but also de novo produced mediators such as leukotrienes (LTC4/D-4/E-4) and prostaglandins (PGD(2)) are released. Mast cells represent targets for therapeutic intervention, and thus a human ex-vivo model to stimulate mast cells taken from mucosal sites would be instrumental for drug intervention studies. We have aimed to activate mast cells within ex-vivo human nasal tissue by IgE/anti-IgE specific (epsilon chain specific) stimulations and in this respect to test the usability of nasal polyps versus inferior turbinates Methods: Biopsy samples were collected from patients with nasal polyps and inferior turbinates from patients who underwent sinus or septal surgery. Tissue fragments were primed with IgE 1 mu g/ml for 60 minutes and then stimulated for 30 minutes with tissue culture medium (negative control), anti-IgE 10 mu g/ml, anti-IgE 30 mu g/ml and ionomycin 10 mu M (positive control). Histamine, leukotrienes and PGD2 were measured in supernatants. To help provide an understanding of the extent of the response, the number of tryptase and Fc epsilon RI alpha positive cells was evaluated by means of immunohistochemistry and the Fc epsilon RI alpha-chain was measured by means of quantitative PCR in the nasal polyp and inferior turbinate tissues. Finally, the correlation between IgE concentrations in the nasal tissue and the release of mediators was analysed. Results: Stimulations with anti-IgE on IgE-primed nasal tissue fragments lead to a concentration-dependent release of histamine, leukotrienes and PGD(2). The release of these early phase mediators was significantly higher in nasal polyps compared to inferior turbinates, although tryptase, Fc epsilon RI alpha positive cells and Fc epsilon RI alpha-chain transcripts were equally present in both groups. No correlation was found between baseline concentrations of IgE, and the release of histamine, LTC4/LTD4/LTE4 and PGD2 after stimulation. Conclusion: This human nasal challenge model mimics the allergic early phase reaction. The release of histamine, cys-leukotrienes and PGD(2) was significantly higher in nasal polyps versus inferior turbinates, however, this observation could not be explained by differences in mast cell or Fc epsilon RI+ cell numbers

On the soliton width in the incommensurate phase of spin-Peierls systems

We study using bosonization techniques the effects of frustration due to competing interactions and of the interchain elastic couplings on the soliton width and soliton structure in spin-Peierls systems. We compare the predictions of this study with numerical results obtained by exact diagonalization of finite chains. We conclude that frustration produces in general a reduction of the soliton width while the interchain elastic coupling increases it. We discuss these results in connection with recent measurements of the soliton width in the incommensurate phase of CuGeO_3.Comment: 4 pages, latex, 2 figures embedded in the tex

Exact N=2 Landau-Ginzburg Flows

We find exactly solvable N=2-supersymmetric flows whose infrared fixed points are the N=2 minimal models. The exact S-matrices and the Casimir energy (a c-function) are determined along the entire renormalization group trajectory. The c-function runs from c=3 (asymptotically) in the UV to the N=2 minimal model values of the central charge in the IR, leading us to interpret these theories as the Landau-Ginzburg models with superpotential $X^{k+2}$. Consideration of the elliptic genus gives further support for this interpretation. We also find an integrable model in this hierarchy which has spontaneously-broken supersymmetry and superpotential $X$, and a series of integrable models with (0,2) supersymmetry. The flows exhibit interesting behavior in the UV, including a relation to the N=2 super sine-Gordon model. We speculate about the relation between the kinetic term and the cigar target-space metric.Comment: 24 pages, BUHEP-93-17, RU-93-2

Haldane-Gapped Spin Chains as Luttinger Liquids: Correlation Functions at Finite Field

We study the behavior of Heisenberg, antiferromagnetic, integer-spin chains in the presence of a magnetic field exceeding the attendant spin gap. For temperatures much smaller than the gap, the spin chains exhibit Luttinger liquid behavior. We compute exactly both the corresponding Luttinger parameter and the Fermi velocity as a function of magnetic field. This enables the computation of a number of correlators from which we derive the spin conductance, the expected form of the dynamic structure factor relevant to inelastic neutron scattering experiments, and NMR relaxation rates. We also comment upon the robustness of the magnetically induced gapless phase both to finite temperature and finite couplings between neighbouring chains.Comment: 32 pages, 8 figures; published version includes additions discussing the robustness of the magnetically induced gapless phase to ordering between chains as well as the relationship between the spin-1 chains and spin-1/2 ladders in the presence of a magnetic fiel

Hiding relativistic degrees of freedom in the early universe

We quantify the extent to which extra relativistic energy density can be concealed by a neutrino asymmetry without conflicting with the baryon asymmetry measured by the Wilkinson Microwave Anisotropy Probe (WMAP). In the presence of a large electron neutrino asymmetry, slightly more than seven effective neutrinos are allowed by Big Bang Nucleosynthesis (BBN) and WMAP at 2\sigma. The same electron neutrino degeneracy that reconciles the BBN prediction for the primordial helium abundance with the observationally inferred value also reconciles the LSND neutrino with BBN by suppressing its thermalization prior to BBN.Comment: 5 pages, 5 figure