[en] The direct detection of supersymmetric dark matter in the light of recent experimental results is analysed. In particular, it is shown that there are regions in the parameter space of several scenarios where neutralino-nucleon cross sections of the order of 10^-6 pb, i.e., where current dark matter detectors are sensitive, can be obtained. These are supergravity scenarios with intermediate unification scale, and superstring scenarios with D-branes

[en] We analyze the constraints that a correct phenomenology and the absence of dangerous charge and colour breaking (CCB) minima or unbounded from below (UFB) directions impose on the parameter space of different superstring and M-theory scenarios. Namely, we analyze in detail the case where supersymmetry (SUSY) breaking is driven by non-vanishing dilaton and/or moduli F-terms in weakly and strongly coupled strings, and the specific case where the mechanism of SUSY breaking is gaugino condensation with or without the participation of non-perturbative contributions to the Kaehler potential. The results indicate that, only in some small windows of the parameter space all the previous tests are successfully passed. We also discuss the impact of non-universality of the soft breaking terms on CCB/UFB bounds

[en] We study different phenomenological aspects of compact, D = 4, N = 1 Type IIB orientifolds considered as models for unification of the standard model and gravity. We discuss the structure of the compactification, string and unification scales depending on the different possible D-brane configurations. It is emphasized that in the context of Type I models the M_W/M_Planck hierarchy problem is substantially alleviated and may be generated by geometrical factors. We obtain the effective low-energy supergravity Lagrangian and derive the form of soft SUSY-breaking terms under the assumption of dilaton/moduli dominance. We also discuss the role of anomalous U(1)'s and of twisted moduli in this class of theories. A novel mechanism based on the role of singularities is suggested to achieve consistency with gauge coupling unification in low string scale models

[en] A computer program written with the purpose of studying the magnetic field produced by a linear system of n coils is shown. Based on this a four coils system is designed that was used in an ion source of Resonance Electron-cyclotron type (REC) that is sought to build. In turn, structure characteristics of the magnetic field proper for such purpose are discussed. (Author)

[en] The duality-invariant gaugino condensation with or without massive matter fields is reanalysed, taking into account the dependence of the string threshold corrections on the moduli fields and recent results concerning one-loop corrected Kaehler potentials. The scalar potential of the theory for a generic superpotential is also calculated. (orig.)

[en] We propose a simple mechanism that, following from the presence of the Fayet-Iliopoulos terms expected in many four-dimensional superstring constructions, can give rise to a period of inflationary expansion. We have verified that, in phenomenologically interesting cases, the conditions for inflation to be realized in this way are easily fulfilled. (orig.)

[en] Explicit SU(3) x SU(2) x U(1)_Y x U(1) four-dimensional string models are obtained from the compactification of the heterotic string on the Z₃ orbifold by considering the breaking produced by the presence of a Fayet-Iliopoulos term associated with an 'anomalous' U(1). These models have three generations of particles containing the correct representations under SU(3) x SU(2) x U(1)_Y and a true hidden sector. All the extra colour triplets of the models, which could mediate fast proton decay, acquire high masses in the process. (orig.)

[en] We study the structure of the soft SUSY-breaking terms obtained from 4-D Strings under the assumption of dilaton/moduli dominance in the process of SUSY-breaking. We first analyze in detail the dilaton-dominated limit because of its finiteness properties and phenomenological predictivity, and second, we consider the new features appearing when several moduli fields contribute to SUSY breaking. In particular, we discuss in detail the case of symmetric Abelian orbifolds. Although some qualitative features indeed change in the multimoduli case with respect to the dilaton dominance one, the most natural mass relations at low-energy, m_lq≅M_g, are still similar. Only in some very specific limits these relations might be reversed. We also study the presence of tachyons pointing out that their possible existence may be, in some cases, an interesting advantage in order to break extra gauge symmetries. Finally, we compute explicitly the μ and B parameters in the context of the mechanism for generating a μ-term by the Kaehler potential, as naturally implemented in orbifolds. It leads to the prediction vertical stroke tgβ vertical stroke =1 at the String scale, independently of the Goldstino direction. It is worth noticing that, in this squeme, the dilaton-dominated case, where there is no free parameters, is excluded since it is not consistent with the measured value of the top-quark mass. In this connection, low-energy charge and color breaking minima are also discussed. (orig.)

[en] The anomalous dimensions of the proton decay operators of dimension six are calculated in supersymmetric SU(5) and SO(10) with superfield techniques. The corresponding enhancement factors are remarkably similar in both cases and practically identical to the non-supersymmetric case. Also results are given for the enhancement factors of the dimension-five operators for both unification groups. (orig.)

[en] The renormalization group equations for supersymmetric models are re-examined considering the normalization factor of the hypercharge as a free parameter. This possibility has recently been raised in the context of superstring theories. Very important (and simple) restrictions for the phenomenological viability of the models are obtained. Several examples (some of them with great physical relevance) are given in order to illustrate how the analysis of an important class of SU(3) x SU(2) x U(1)_Y superstring constructions can be carried out. Many models can be ruled out in this way, which is welcome for the predictive power of the theory. (orig.)