Photon emission in a constant magnetic field in 2+1 dimensional space-time

We calculate by the proper-time method the amplitude of the two-photon emission by a charged fermion in a constant magnetic field in (2+1)-dimensional space-time. The relevant dynamics reduces to that of a supesymmetric quantum-mechanical system with one bosonic and one fermionic degrees of freedom.Comment: 18 pages. v2: references added, some significant changes in the introductio

On the Unitarity of D=9,10,11 Conformal Supersymmetry

We consider the unitarity of D=9,10,11 conformal supersymmetry using the recently established classification of the UIRs of the superalgebras osp(1|2n,R).Comment: 7 pages, LATEX2e{czjphys} (amsmath,amssymb); v3: important corrections, Plenary talk by VKD at the XIII Colloquium "Quantum Groups and Integrable Systems", Prague, 17-19.6.2004; to appear in Czech. J. Phys.; v4: small corrections to coincide with journal versio

Toxicological Patterns of Multicomponent Polymer Systems

Development of new polymer systems (PS) based on thermo-active resins is important not only from a chemical viewpoint but also because of the opportunity for programmable changing their properties and subsequent application in clinical practice. Some chemical features of a new composition for a multicomponent polymer system (MPS) based on hydrophilized unsaturated polyester resin (HUPR) are presented. Strength parameters of several resins of different compositions are examined. The analysis of the acute oral toxicity of these resins in white Wistar rats proves that they are low toxic. These PS do not demonstrate any harmful effects on human skin after the predicting irritation and sensitization tests using epicutaneous samples. Their main advantages include preliminary water-solubility and capacity to incorporate water, good dilution into water and resin water dispersions, porosity, low relative mass, high strength indices, improved ecological features, thin-founding capacity, good relief impressions in combination with high adhesion ability towards wet surfaces. A wide MPS usage in the manufacture of orthopedic plaster dressings, prostheses, splints, insoles, positive-sample dental imprints, and casts is recommended

Quintessence and Thermal Matter

We investigate the effects of thermal interactions on tracking models of quintessence. We show that even Planck-suppressed interactions between matter and the quintessence field can alter its evolution. The dark energy equation of state is in many cases strongly affected by matter couplings. We obtain a bound on the coupling between quintessence and relativistic relic particles such as the photon or neutrino.Comment: LaTex, 11 pages, 5 figures. Minor additions. Version to appear in Physics Letters

Semantic Support for Automated Negotiation with Alliances

Companies can form alliances on the Internet to aggregate buying or selling power and create value. More concretely, together resources are shared or new possibilities are exploited that cannot be exploited individually. Most alliances are formed as a result of a negotiation process between the companies that form an alliance. This paper proposes a software framework that enables automated negotiation between alliances. Our framework allows for the semantic description of negotiation objects and their attributes, and provides a mean for the exchange of negotiation messages unambiguously interpretable by all parties involved. The proposed framework supports ad-hoc alliances by allowing parties with a common interest to negotiate on the proposal they want to make to other market participants first

Inelastic Quantum Transport

We solve a Schrodinger equation for inelastic quantum transport that retains full quantum coherence, in contrast to previous rate or Boltzmann equation approaches. The model Hamiltonian is the zero temperature 1d Holstein model for an electron coupled to optical phonons (polaron), in a strong electric field. The Hilbert space grows exponentially with electron position, forming a non-standard Bethe lattice. We calculate nonperturbatively the transport current, electron-phonon correlations, and quantum diffusion. This system is a toy model for the constantly branching ``wavefunction of the universe''.Comment: revtex, 13 pages, 4 figure

Natural Quintessence with Gauge Coupling Unification

We show that a positive accelerating universe can be obtained simply by the dynamics of a non-abelian gauge group. It is the condensates of the chiral fields that obtain a negative power potential, below the condensation scale, and allow for a quintessence interpretation of these fields. The only free parameters in this model are $N_c$ and $N_f$ and the number of dynamically gauge singlet bilinear fields $\phi$ generated below the condensation scale. We show that it is possible to have unification of all coupling constants, including the standard and non standard model couplings, while having an acceptable phenomenology of $\phi$ as the cosmological constant. This is done without any fine tuning of the initial conditions. The problem of coincidence (why the universe has only recently started an accelerating period) is not solved but it is put at the same level as what the particle content of the standard model is.Comment: minor changes(discussion on field normalization included), reference added, accepted in Phy.Rev.Lett., 5 pages,LateX,2 Figure

Palatini approach to 1/R gravity and its implications to the late Universe

By applying the Palatini approach to the 1/R-gravity model it is possible to explain the present accelerated expansion of the Universe. Investigation of the late Universe limiting case shows that: (i) due to the curvature effects the energy-momentum tensor of the matter field is not covariantly conserved; (ii) however, it is possible to reinterpret the curvature corrections as sources of the gravitational field, by defining a modified energy-momentum tensor; (iii) with the adoption of this modified energy-momentum tensor the Einstein's field equations are recovered with two main modifications: the first one is the weakening of the gravitational effects of matter whereas the second is the emergence of an effective varying "cosmological constant"; (iv) there is a transition in the evolution of the cosmic scale factor from a power-law scaling $a\propto t^{11/18}$ to an asymptotically exponential scaling $a\propto \exp(t)$; (v) the energy density of the matter field scales as $\rho_m\propto (1/a)^{36/11}$; (vi) the present age of the Universe and the decelerated-accelerated transition redshift are smaller than the corresponding ones in the $\Lambda$CDM model.Comment: 5 pages and 2 figures. Accepted in PR

Curvature of the universe and the dark energy potential

The flatness of an accelerating universe model (characterized by a dark energy scalar field $\chi$) is mimicked from a curved model that is filled with, apart from the cold dark matter component, a quintessencelike scalar field $Q$. In this process, we characterize the original scalar potential $V(Q)$ and the mimicked scalar potential $V(\chi)$ associated to the scalar fields $Q$ and $\chi$, respectively. The parameters of the original model are fixed through the mimicked quantities that we relate to the present astronomical data, such that the equation state parameter $w_{_{\chi}}$ and the dark energy density parameter $\Omega_{\chi}$.Comment: References 7 and 8 have been corrected: (7) Riess et al. 1998, AJ, 116, 1009 and (8) Perlmutter et al. 1999, ApJ, 517, 56