38,082 research outputs found
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 ,
, --I and possibly 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
defining the former is ). The rest of the orbifolds are rather
hopeless and should be discarded on the assumption of a minimal 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
The Standard Model instability and the scale of new physics
We apply a general formalism for the improved effective potential with
several mass scales to compute the scale M of new physics which is needed to
stabilize the Standard Model potential in the presence of a light Higgs. We
find, by imposing perturbativity of the new physics, that M can be as large as
one order of magnitude higher than the instability scale of the Standard Model.
This implies that, with the present lower bounds on the Higgs mass, the new
physics could easily (but not necessarily) escape detection in the present and
future accelerators.Comment: latex2e, 12 pages, 3 figure
F-term inflation in Superstring Theories
A supersymmetric inflationary stage dominated by an -term has the problem
that the flatness of the potential is spoiled by supergravity corrections, that
is the slow-roll parameter gets contributions of order unity. We show
that in -term inflationary models based on strings there is natural way of
obtaining small values of . This happens in models of hybrid inflation
based on orbifold constructions, in which a modulus field is responsible
for the large value of the potential during inflation, and a second field
with appropriate modular weight is responsible for the roll-over. We
illustrate the mechanism with a model in which the inflaton potential is
provided by gaugino condensation, leading to succesful inflation.Comment: 9 pages, LaTe
Study of Minimal String Unification in Orbifold Models
We study the construction of the minimal supersymmetric standard model from
the orbifold models. We use a target-space duality anomaly cancellation
and a unification of gauge couplings as constraints. It is shown that some
models obtained through a systematical search realize the unification of SU(3)
and SU(2) coupling constants.Comment: 11 pages, KANAZAWA-93-08, LaTeX fil
Lessons from the Andean Community Integration. Jean Monnet/Robert Schuman Paper Series. Vol. 6, No. 12 June 2006
[From the Introduction]. Ever since it was born in the sixties, the Andean Regional Integration Process has attempted to become a strategy to promote a harmonious and balanced development among the Andean Countries. This paper has tree mains goals: (a) To explain and analyse the theoretical concept of the Andean New Regionalism in the framework of Latin American region in a comparative perspective with the European Model of Regional Integration; (b) To show the coexistence of two different regional integration models. Where the dominating one during the sixties was known as old regionalism, and the other that is currently being used is known as new regionalism, and (c) To analyse the way in which this coexistence appears to be an obstacle for the Andean countries to define their regional integration model and to advance toward their main goal: the balanced and harmonious development of each and every country member
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