Free field representation of Toda field theories

We study the following problem: can a classical $sl_n$ Toda field theory be represented by means of free bosonic oscillators through a Drinfeld--Sokolov construction? We answer affirmatively in the case of a cylindrical space--time and for real hyperbolic solutions of the Toda field equations. We establish in fact a one--to--one correspondence between such solutions and the space of free left and right bosonic oscillators with coincident zero modes. We discuss the same problem for real singular solutions with non hyperbolic monodromy.Comment: 29 pages, Latex, SISSA-ISAS 210/92/E

From de Sitter to de Sitter: A non-singular inflationary universe driven by vacuum

A semi-classical analysis of vacuum energy in the expanding spacetime suggests that the cosmological term decays with time, with a concomitant matter production. For early times we find, in Planck units, $\Lambda \approx H^4$, where H is the Hubble parameter. The corresponding cosmological solution has no initial singularity, existing since an infinite past. During an infinitely long period we have a quasi-de Sitter, inflationary universe, with $H \approx 1$. However, at a given time, the expansion undertakes a phase transition, with H and $\Lambda$ decreasing to nearly zero in a few Planck times, producing a huge amount of radiation. On the other hand, the late-time scenario is similar to the standard model, with the radiation phase followed by a dust era, which tends asymptotically to a de Sitter universe, with vacuum dominating again.Comment: This essay received an "honorable mention" in the 2006 Essay Competition of the Gravity Research Foundatio

Gravitomagnetic Moments of the Fundamental Fields

The quadratic form of the Dirac equation in a Riemann spacetime yields a gravitational gyromagnetic ratio \kappa_S = 2 for the interaction of a Dirac spinor with curvature. A gravitational gyromagnetic ratio \kappa_S = 1 is also found for the interaction of a vector field with curvature. It is shown that the Dirac equation in a curved background can be obtained as the square--root of the corresponding vector field equation only if the gravitational gyromagnetic ratios are properly taken into account.Comment: 8 pages, RevTeX Style, no figures, changed presentation -- now restricted to fields of spin 0, 1/2 and 1 -- some references adde

Mass Generation from Lie Algebra Extensions

Applied to the electroweak interactions, the theory of Lie algebra extensions suggests a mechanism by which the boson masses are generated without resource to spontaneous symmetry breaking. It starts from a gauge theory without any additional scalar field. All the couplings predicted by the Weinberg-Salam theory are present, and a few others which are nevertheless consistent within the model.Comment: 11 pages; revtex; title and PACS have been changed; comments included in the manuscrip

de Sitter special relativity

A special relativity based on the de Sitter group is introduced, which is the theory that might hold up in the presence of a non-vanishing cosmological constant. Like ordinary special relativity, it retains the quotient character of spacetime, and a notion of homogeneity. As a consequence, the underlying spacetime will be a de Sitter spacetime, whose associated kinematics will differ from that of ordinary special relativity. The corresponding modified notions of energy and momentum are obtained, and the exact relationship between them, which is invariant under a re-scaling of the involved quantities, explicitly exhibited. Since the de Sitter group can be considered a particular deformation of the Poincar\'e group, this theory turns out to be a specific kind of deformed (or doubly) special relativity. Some experimental consequences, as well as the causal structure of spacetime--modified by the presence of the de Sitter horizon--are briefly discussed.Comment: V2: Some presentation changes; a new section introduced, with a discussion about possible phenomenological consequences; new references added; version to be published in Classical and Quantum Gravit

Gravitation: Global Formulation and Quantum Effects

A nonintegrable phase-factor global approach to gravitation is developed by using the similarity of teleparallel gravity with electromagnetism. The phase shifts of both the COW and the gravitational Aharonov-Bohm effects are obtained. It is then shown, by considering a simple slit experiment, that in the classical limit the global approach yields the same result as the gravitational Lorentz force equation of teleparallel gravity. It represents, therefore, the quantum mechanical version of the classical description provided by the gravitational Lorentz force equation. As teleparallel gravity can be formulated independently of the equivalence principle, it will consequently require no generalization of this principle at the quantum level.Comment: Latex (IOP style), 14 pages, 3 figures. To appear in Classical and Quantum Gravit

Abundances and Physical Conditions in the Interstellar Gas toward HD 192 639

We present a study of the abundances and physical conditions in the interstellar gas toward the heavily reddened star HD 192639 [E_(B-V) = 0.64], based on analysis of FUSE and HST/STIS spectra covering the range from 912 to 1361 A. This work constitutes a survey of the analyses that can be performed to study the interstellar gas when combining data from different instruments. Low-velocity (-18 to -8 km/s) components are seen primarily for various neutral and singly ionized species such as C I, O I, S I, Mg II, Cl I, Cl II, Mn II, Fe II and Cu II. Numerous lines of H2 are present in the FUSE spectra, with a kinetic temperature for the lowest rotational levels T_(01) = (90 +/- 10) K. Analysis of the C I fine-structure excitation implies an average local density of hydrogen n_H = (16 +/- 3) cm^-3. The average electron density, derived from five neutral/first ion pairs under the assumption of photoionization equilibrium, is n_e = (0.11 +/- 0.02) cm^-3. The relatively complex component structure seen in high-resolution spectra of K I and Na I, the relatively low average density, and the measured depletions all suggest that the line of sight contains a number of diffuse clouds, rather than a single dense, translucent cloud. Comparisons of the fractions of Cl in Cl I and of hydrogen in molecular form suggest a higher molecular fraction, in the region(s) where H2 is present, than that derived considering the average line of sight. In general, such comparisons may allow the identification and characterization of translucent portions of such complex lines of sight. The combined data also show high-velocity components near -80 km/s for various species which appear to be predominantly ionized, and may be due to a radiative shock. A brief overview of the conditions in this gas will be given.Comment: 37 pages, accepted for publication in Ap

Toda Fields on Riemann Surfaces: remarks on the Miura transformation

We point out that the Miura transformation is related to a holomorphic foliation in a relative flag manifold over a Riemann Surface. Certain differential operators corresponding to a free field description of $W$--algebras are thus interpreted as partial connections associated to the foliation.Comment: AmsLatex 1.1, 10 page

Evolution of density perturbations in decaying vacuum cosmology: The case of non-zero perturbations in the cosmological term

We extend the results of a previous paper where a model of interacting dark energy, with a cosmological term decaying linearly with the Hubble parameter, is tested against the observed mass power spectrum. In spite of the agreement with observations of type Ia supernovas, baryonic acoustic oscillations and the cosmic microwave background, we had shown previously that no good concordance is achieved if we include the mass power spectrum. However, our analysis was based on the ad hoc assumption that the interacting cosmological term is strictly homogeneous. Now we perform a more complete analysis, by perturbing such a term. Although our conclusions are still based on a particular, scale invariant choice of the primordial spectrum of dark energy perturbations, we show that a cosmological term decaying linearly with the Hubble parameter is indeed disfavored as compared to the standard model.Comment: Version accepted for publication in Physical Review