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E. Dudas

Publications and source records attributed to E. Dudas.

66 records · Page 4Linked to original sources
arXiv1997

Solitons in the Horava-Witten supergravity

We study classical BPS five-brane solutions in the Horava-Witten supergravity. The presence of the eleventh dimension add a new feature, namely the dependence of the solution on this new coordinate. For gauge five-branes with an instanton size less than the eleventh radius and in the neighborhood of the center of the neutral five-brane, important corrections to the ten-dimensional solution appear for all values of the string coupling constant. We compute the mass and magnetic charge of the five-brane solitons and the result is shown to agree with the membrane and five-brane quantization conditions. Compactified to four dimensions, our solutions are interpreted as axionic strings.

hep-th↗
arXiv1997

Quark flavour conserving violations of the lepton number

We study supersymmetric models of lepton and baryon number violation based on an abelian family gauge group. Due to possible lepton-Higgs mixing, the lepton violating couplings are related to the Yukawa couplings and may be generated by them even if they were absent in the original theory. Such terms may be dominant and are not given by the naive family charge counting rules. This enhancement mechanism can provide an alignment between lepton-number violating terms and Yukawa couplings: as a result they conserve quark flavour. A natural way of suppressing baryon number violation in this class of models is also proposed.

hep-ph↗
arXiv1997

Four-dimensional M-theory and supersymmetry breaking

We investigate compactifications of M-theory from $11\to 5\to 4$ dimensions and discuss geometrical properties of 4-d moduli fields related to the structure of 5-d theory. We study supersymmetry breaking by compactification of the fifth dimension and find that an universal superpotential is generated for the axion-dilaton superfield $S$. The resulting theory has a vacuum with $ =1$, zero cosmological constant and a gravitino mass depending on the fifth radius as $m_{3/2} \sim R_5^{-2}/M_{Pl}$. We discuss phenomenological aspects of this scenario, mainly the string unification and the decompactification problem.

hep-th↗
arXiv1997

On the strongly coupled heterotic string

We analyze in detail the anomaly cancellation conditions for the strongly coupled $E_8 \times E_8$ heterotic string introduced by Horava and Witten and find new features compared to the ten-dimensional Green-Schwarz mechanism. We project onto ten dimensions the corresponding Lagrangian of the zero-mode fields. We find that it has a simple interpretation provided by the conjectured heterotic string/fivebrane duality. The part which originates from eleven-dimensions is naturally described in fivebrane language. We discuss physical couplings and scales in four dimensions.

hep-th↗
arXiv1996

Abelian Flavour Symmetries in Supersymmetric Models

We propose a theory of flavour based on abelian horizontal gauge symmetries and modular invariances. We construct explicit supergravity models where the scale of the horizontal $U(1)$ symmetry breaking is fixed by the Green-Schwarz mechanism for anomaly cancellation. The supersymmetric spectrum is obtained in terms of the $U(1)$ charges which are determined by the Yukawa matrices.

hep-ph↗
arXiv1995

Holomorphy and dynamical scales in supersymmetric gauge theories

New recent results in supersymmetric gauge theories based on holomorphy and symmetry considerations are extended to the case where the gauge coupling constant is given by the real part of a chiral superfield. We assume here that its dynamics can be described by an effective quantum field theory. Then its vacuum expectation value is a function of the other coupling constants, viewed as chiral background superfields. This functional dependence can be determined exactly and satisfies highly non-trivial consistency checks.

hep-th↗
arXiv1995

Dynamical mass matrices from effective superstring theories

We analyze the general structure of the fermion mass matrices in effective superstrings. They are generically given at low energy by non-trivial functions of the gauge singlet moduli fields. Interesting structures appear in particular if they are homogeneous functions of zero degree in the moduli. In this case we find Yukawa matrices very similar to the ones obtained by imposing a $U(1)$ family symmetry to reproduce the observed hierarchy of masses and mixing angles. The role of the $U(1)$ symmetry is played here by the modular symmetry. Explicit orbifold examples are given where realistic quark mass matrices can be obtained. Finally, a complete scenario is proposed which generates the observed hierarchies in a dynamical way.

hep-ph↗
arXiv1995

Yukawa matrices from a spontaneously broken abelian symmetry

We classify all the phenomenologically viable fermion mass matrices coming from a spontaneously broken abelian symmetry $ U(1)_X, $ with one and two additional chiral fields of opposite charges $ X=\pm 1. $ We find that the non-trivial Kähler metric can fill zeroes of the fermion mass matrices up to phenomenologically interesting values. A general anomaly analysis shows that for one additional chiral field the only way to achieve anomaly cancellation is by use of the Green-Schwarz mechanism. For two additional fields with $X=\pm 1$ and negative charge differences in the lepton sector the anomalies can however be directly put to zero. This case gives a unique prediction for the ratio of the two Higgs scalars of MSSM, ${\rm tg} β\sim { m_t \over m_b} (sin θ_c)^ 2$, where $θ_c$ is the Cabibbo angle.

hep-ph↗
arXiv1994

Fermion mass hierarchies in low energy supergravity and superstring models

We investigate the problem of the fermion mass hierarchy in supergravity models with flat directions of the scalar potential associated with some gauge singlet moduli fields. The low-energy Yukawa couplings are nontrivial homogeneous functions of the moduli and a geometric constraint between them plays, in a large class of models, a crucial role in generating hierarchies. Explicit examples are given for no-scale type supergravity models. The Yukawa couplings are dynamical variables at low energy, to be determined by a minimization process which amounts to fixing ratios of the moduli fields. The Minimal Supersymmetric Standard Model (MSSM) is studied and the constraints needed on the parameters in order to have a top quark much heavier than the other fermions are worked out. The bottom mass is explicitly computed and shown to be compatible with the experimental data for a large region of the parameter space.

hep-ph↗
arXiv1994

Nambu mass hierarchies in low energy string models

This paper explores a recent idea of Nambu to generate hierarchies among Yukawa couplings in the context of effective supergravity and superstrings models. The Yukawa couplings are homogeneous functions of the moduli and a geometrical constraint between them with a crucial role in the Nambu mechanism is found in a class of models of no-scale type. The Yukawas are dynamical variables at low energy to be determined by a minimization process. (Based on the talk given at ICHEP94, Glasgow, july 1994)

hep-th↗
arXiv1994

Nambu mass hierarchies in strings

We show that a recent proposal by Nambu to generate a hierarchy among Yukawa couplings in the standard model may be easily implemented in superstring models. In such models, two of the main ingredients of the Nambu proposal find a natural explanation: minimising with respect to the Yukawas amounts to a minimisation with respect to the underlying moduli fields and a constraint on the Yukawas of the type of the Veltman condition may be attributed to the relaxation process to a phenomenologically viable string vacuum.

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