A Simulation Model Outline for the Hungarian Forest Sector

The model presented in this paper describes the structure of the Hungarian forest sector. The planning of the sector at a national and company level as well as the mechanism of regulation concerning production, investments, and consumption are also investigated and the exports and imports linked. One of the most important objectives is to create this model in order to study the behavior of the system so as to aid the decision making both in strategic and tactical areas. Apart from forestry the model also includes the wood processing activities

On the Ultraviolet Behaviour of Newton's constant

We clarify a point concerning the ultraviolet behaviour of the Quantum Field Theory of gravity, under the assumption of the existence of an ultraviolet Fixed Point. We explain why Newton's constant should to scale like the inverse of the square of the cutoff, even though it is technically inessential. As a consequence of this behaviour, the existence of an UV Fixed Point would seem to imply that gravity has a built-in UV cutoff when described in Planck units, but not necessarily in other units.Comment: 8 pages; CQG class; minor changes and rearrangement

Generalized Dirac monopoles in non-Abelian Kaluza-Klein theories

A method is proposed for generalizing the Euclidean Taub-NUT space, regarded as the appropriate background of the Dirac magnetic monopole, to non-Abelian Kaluza-Klein theories involving potentials of generalized monopoles. Usual geometrical methods combined with a recent theory of the induced representations governing the Taub-NUT isometries lead to a general conjecture where the potentials of the generalized monopoles of any dimensions can be defined in the base manifolds of suitable principal fiber bundles. Moreover, in this way one finds that apart from the monopole models which are of a space-like type, there exists a new type of time-like models that can not be interpreted as monopoles. The space-like models are studied pointing out that the monopole fields strength are particular solutions the Yang-Mills equations with central symmetry producing the standard flux of $4\pi$ through the two-dimensional spheres surrounding the monopole. Examples are given of manifolds with Einstein metrics carrying SU(2) monopoles.Comment: 32 page

Gauge-Higgs Unification in Orbifold Models

Six-dimensional orbifold models where the Higgs field is identified with some internal component of a gauge field are considered. We classify all possible T^2/Z_N orbifold constructions based on a SU(3) electroweak gauge symmetry. Depending on the orbifold twist, models with two, one or zero Higgs doublets can be obtained. Models with one Higgs doublet are particularly interesting because they lead to a prediction for the Higgs mass, which is twice the W boson mass at leading order: m_H=2 m_W. The electroweak scale is quadratically sensitive to the cut-off, but only through very specific localized operators. We study in detail the structure of these operators at one loop, and identify a class of models where they do not destabilize the electroweak scale at the leading order. This provides a very promising framework to construct realistic and predictive models of electroweak symmetry breaking.Comment: 27 pages, uses axodraw.sty; v2: version to appear in JHE

The Accelerated expansion of the Universe as a crossover phenomenon

We show that the accelerated expansion of the Universe can be viewed as a crossover phenomenon where the Newton constant and the Cosmological constant are actually scaling operators, dynamically evolving in the attraction basin of a non-Gaussian infrared fixed point, whose existence has been recently discussed. By linearization of the renormalized flow it is possible to evaluate the critical exponents, and it turns out that the approach to the fixed point is ruled by a marginal and a relevant direction. A smooth transition between the standard Friedmann--Lemaitre--Robertson--Walker (FLRW) cosmology and the observed accelerated expansion is then obtained, so that $\Omega_M \approx \Omega_\Lambda$ at late times.Comment: 12 pages, latex, use bibtex. In the final version, the presentation has been improved, and new references have been adde

Heterogeneous Catalysis on a Disordered Surface

We introduce a simple model of heterogeneous catalysis on a disordered surface which consists of two types of randomly distributed sites with different adsorption rates. Disorder can create a reactive steady state in situations where the same model on a homogeneous surface exhibits trivial kinetics with no steady state. A rich variety of kinetic behaviors occur for the adsorbate concentrations and catalytic reaction rate as a function of model parameters.Comment: 4 pages, gzipped PostScript fil

Exact free energy distribution function of a randomly forced directed polymer

We study the elastic (1+1)-dimensional string subject to a random gaussian potential on scales smaller than the correlation radius of the disorder potential (Larkin problem). We present an exact calculation of the probability function ${\cal P} [F(u,L)]$ for the free energy $F$ of a string starting at $(0,0)$ and ending at $(u,L)$. The function ${\cal P}(F)$ is strongly asymmetric, with the left tail decaying exponentially ($\ln {\cal P}(F\to-\infty)\propto F$) and the right tail vanishing as $\ln {\cal P}(F\to +\infty)\propto -F^{3}$. Our analysis defines a strategy for future attacks on this class of problems.Comment: RevTeX, 4 pages, 1 figure inserte

On the Cosmology of Massive Vector Fields with SO(3) Global Symmetry

A relevant reference ([14]) has been added.Comment: 19 pages, plain tex, DF/IST-3/92 and DFFCUL 03-5/199

Enhancons, Fuzzy Spheres and Multi-Monopoles

We study the `enhancon', a spherical hypersurface apparently made of D-branes, which arises in string theory studies of large N SU(N) pure gauge theories with eight supercharges. When the gauge theory is 2+1 dimensional, the enhancon is an S^2. A relation to charge N BPS multi-monopoles is exploited to uncover many of its detailed properties. It is simply a spherical slice through an Atiyah-Hitchin-like submanifold of the charge $N$ BPS monopole moduli space. In the form of Nahm data, it is built from the N dimensional irreducible representation of SU(2). In this sense the enhancon is a non-commutative sphere, reminiscent of the spherical `dielectric' branes of Myers.Comment: 25 pages, latex, 3 primary figures, psfig (v2: Omission of references to important early work on multi-monopoles is fixed. Note added on possible relations to certain other recent work on large N, monopoles, and non-commutativity. A few typos fixed.) (v3: Extensive revision. Statements about role of Atiyah-Hitchin manifold and instanton corrections refined. Speculation about location of Higgs zeros removed. Discussion improved in many places.