Fitting the Quark and Lepton Masses in String Theories

The capability of string theories to reproduce at low energy the observed pattern of quark and lepton masses and mixing angles is examined, focusing the attention on orbifold constructions, where the magnitude of Yukawa couplings depends on the values of the deformation parameters which describe the size and shape of the compactified space. A systematic exploration shows that for $Z_3$, $Z_4$, $Z_6$--I and possibly $Z_7$ orbifolds a correct fit of the physical fermion masses is feasible. In this way the experimental masses, which are low--energy quantities, select a particular size and shape of the compactified space, which turns out to be very reasonable (in particular the modulus $T$ defining the former is $T=O(1)$). The rest of the $Z_N$ orbifolds are rather hopeless and should be discarded on the assumption of a minimal $SU(3)\times SU(2)\times U(1)_Y$ scenario. On the other hand, due to stringy selection rules, there is no possibility of fitting the Kobayashi--Maskawa parameters at the renormalizable level, although it is remarked that this job might well be done by non--renormalizable couplings.Comment: 19 page

Complete structure of Z_n Yukawa couplings

We give the complete twisted Yukawa couplings for all the Z_n orbifold constructions in the most general case, i.e. when orbifold deformations are considered. This includes a certain number of tasks. Namely, determination of the allowed couplings, calculation of the explicit dependence of the Yukawa couplings values on the moduli expectation values (i.e. the parameters determining the size and shape of the compactified space), etc. The final expressions are completely explicit, which allows a counting of the DIFFERENT Yukawa couplings for each orbifold (with and without deformations). This knowledge is crucial to determine the phenomenological viability of the different schemes, since it is directly related to the fermion mass hierarchy. Other facts concerning the phenomenological profile of Z_n orbifolds are also discussed, e.g. the existence of non--diagonal entries in the fermion mass matrices, which is related to a non--trivial structure of the Kobayashi--Maskawa matrix. Finally some theoretical results are given, e.g. the no--participation of (1,2) moduli in twisted Yukawa couplings. Likewise, (1,1) moduli associated with fixed tori which are involved in the Yukawa coupling, do not affect the value of the coupling.Comment: 60 page

La configuration des échanges dans un modèle à biens multiples : quelques paradoxes

In the framework of a two-good, two-factor model it is evident that the pattern of trade can be inferred from the change in commodity prices resulting from the opening of trade. Thus, if trade increases the relative price of a commodity, we expect that commodity to be exported, while the good whose relative price decreases will be imported.Under certain circumstances however, it may be possible to observe a country importing a commodity even though its free trade relative price is higher than under autarky.The purpose of this paper is to point out that a similar paradox can be established even if we rule out distributional effects of changes in commodity prices on the demand for goods attributable to different tastes. In particular, we focus our attention on a simple three-good, two-factor model with fixed production coefficients. It is well known that when the number of goods exceeds the numbers of factors, a basic indeterminacy exists in the relationship between output levels and relative commodity prices. Our interest lies in establishing that one application of this indeterminacy is that technological characteristics—in particular, the factor intensity ranking of commodities and a country's factor endowment—may result in the reversal of the expected pattern of trade

Stabilité des marchés de change au comptant et à terme : une approche d’équilibre simultané

L’article analyse la relation entre les marchés de change à terme et au comptant. On obtient les conditions de stabilité statique et dynamique de l’équilibre simultané à court terme des deux marchés à partir de l’étude de l’effet des variations des taux de change au comptant et à terme sur les décisions des participants dans les deux marchés, directement et à travers l’impact de telles variations sur les anticipations. Ces conditions sont requises pour l’évaluation des effets de perturbations d’origine domestique ou étrangère et de ceux des politiques fiscales et monétaires.The paper derives the static and dynamic stability conditions of the simultaneous short run equilibrium of the spot and forward exchange markets by analyzing the direct impact of changes in the two exchange rates on the behavior of the various market participants as well as the indirect impact of such changes through their effects on expectations. These stability conditions and the underlying behavioral analysis are crucial in determining the domestic repercussions of internal and external disturbances and the effectiveness of domestic policies. The paper also discusses the properties of the long run equilibrium of the foreign exchange market

Examining the Impact of Parental Involvement in a Dual Language Program: Implications for Children and Schools - OLLAS Report No. 2

This study focuses on a dual language (Spanish-English) program in the Omaha Public Schools. Dual language programs are programs in which children develop proficiency in two languages simultaneously. These programs are currently seen as the gold standard second language education because of the large amount of empirical support they have received with respect to children’s academic gains. All of the dual language classrooms are comprised of half native English speakers and half Spanish speakers. Parental involvement has received much empirical attention with respect to traditional school programs; however, little is known about the role of parental involvement in dual language programs (Lindholm-Leary, 2001). Systematically studying dual language programs is an especially important area of investigation because of the latest census trends and because barriers to parental involvement for language minority children are likely to differ from those of language majority children. For a list of additional publications produced from this project, please visit the Faculty Publications page on the OLLAS website

Higgs Inflation as a Mirage

We discuss a simple unitarization of Higgs inflation that is genuinely weakly coupled up to Planckian energies. A large non-minimal coupling between the Higgs and the Ricci curvature is induced dynamically at intermediate energies, as a simple ratio of mass scales. Despite not being dominated by the Higgs field, inflationary dynamics simulates the `Higgs inflation' one would get by blind extrapolation of the low-energy effective Lagrangian, at least qualitatively. Hence, Higgs inflation arises as an approximate `mirage' picture of the true dynamics. We further speculate on the generality of this phenomenon and show that, if Higgs-inflation arises as an effective description, the details of the UV completion are necessary to extract robust quantitative predictions.Comment: 21 pages, 2 figure

La configuration des échanges dans un modèle à biens multiples : quelques paradoxes

In the framework of a two-good, two-factor model it is evident that the pattern of trade can be inferred from the change in commodity prices resulting from the opening of trade. Thus, if trade increases the relative price of a commodity, we expect that commodity to be exported, while the good whose relative price decreases will be imported.

Bayesian approach and Naturalness in MSSM analyses for the LHC

The start of LHC has motivated an effort to determine the relative probability of the different regions of the MSSM parameter space, taking into account the present, theoretical and experimental, wisdom about the model. Since the present experimental data are not powerful enough to select a small region of the MSSM parameter space, the choice of a judicious prior probability for the parameters becomes most relevant. Previous studies have proposed theoretical priors that incorporate some (conventional) measure of the fine-tuning, to penalize unnatural possibilities. However, we show that such penalization arises from the Bayesian analysis itself (with no ad hoc assumptions), upon the marginalization of the mu-parameter. Furthermore the resulting effective prior contains precisely the Barbieri-Giudice measure, which is very satisfactory. On the other hand we carry on a rigorous treatment of the Yukawa couplings, showing in particular that the usual practice of taking the Yukawas "as required", approximately corresponds to taking logarithmically flat priors in the Yukawa couplings. Finally, we use an efficient set of variables to scan the MSSM parameter space, trading in particular B by tan beta, giving the effective prior in the new parameters. Beside the numerical results, we give accurate analytic expressions for the effective priors in all cases. Whatever experimental information one may use in the future, it is to be weighted by the Bayesian factors worked out here.Comment: LaTeX, 19 pages, 3 figure