Compactification Models Research Articles

Local cosmic strings from Pseudo-anomalous U(1)

Local cosmic strings solutions are introduced in a model with a pseudo-anomalous U(1) gauge symmetry. Such a symmetry is present in many superstring compactification models. The coupling of those strings with the axion necessary in order to cancel the anomalies does not prevent them from being local, even though their energy per unit length is found to diverge logarithmically. We discuss briefly the formation of such strings and the phenomenological constraints that apply to their parameters.

Global versus local cosmic strings from pseudo-anomalous U(1)

We study the structure of cosmic strings produced at the breaking of an anomalous U(1) gauge symmetry present in many superstring compactification models. We show that their coupling with the axion necessary in order to cancel the anomalies does not prevent them from being local, even though their energy per unit length is found to diverge logarithmically. We discuss the formation of such strings and the phenomenological constraints that apply to their parameters.

Excitation of a Kaluza-Klein mode by parametric resonance

In this paper we investigate a parametric resonance phenomenon of a Kaluza-Klein mode in a $D$-dimensional generalized Kaluza-Klein theory. As the origin of the parametric resonance we consider a small oscillation of a scale of the compactification around a present-day value of it. To make our arguments definite and for simplicity we consider two classes of models of the compactification: those by ${S}_{d}$ $(d=D\ensuremath{-}4)$ and those by ${S}_{{d}_{1}}\ifmmode\times\else\texttimes\fi{}{S}_{{d}_{2}}$ ${(d}_{1}>~{d}_{2},$ ${d}_{1}{+d}_{2}=D\ensuremath{-}4).$ For these models we show that parametric resonance can occur for the Kaluza-Klein mode. After that, we give formulas of a creation rate and a number of created quanta of the Kaluza-Klein mode due to the parametric resonance, taking into account the first and the second resonance bands. By using the formulas we calculate those quantities for each model of compactification. Finally we give conditions for the parametric resonance to be efficient and discuss cosmological implications.

F-theory, geometric engineering and N = 1 dualities

We consider geometric engineering of N = 1 supersymmetric QFTs with matter in terms of a local model for compactification of F-theory on Calabi-Yau fourfold. By bringing 3-branes near 7-branes we engineer N = 1 supersymmetric SU( N c ) gauge theory with N f flavors in the fundamental. We identify the Higgs branch of this system with the instanton moduli space on the compact four-dimensional space of the 7-brane world-volume. Moreover we show that the Euclidean 3-branes wrapped around the compact part of the 7-brane world-volume can generate superpotential for N f = N c − 1 as well as lead to quantum corrections to the moduli space for N f = N c . Finally we argue that Seiberg's duality for N = 1 supersymmetric QCD may be mapped to T-duality exchanging 7-branes with 3-branes.

Back Reaction and Graceful Exit in String Inflationary Cosmology.

Classical string cosmology consists of two branches related to each other by scale-factor duality: a superinflation branch and a Friedmann-Robertson-Walker (FRW) branch. Curvature and string coupling singularity separates the two branches, hence posing ``graceful exit problem'' to superinflationary string cosmology. In an exactly soluble two-dimensional compactification model it is shown that quantum back reaction retards curvature and string coupling growth and connects the superinflation branch to the FRW branch without encountering a singularity. This may offer an attractive solution to the graceful exit problem in string inflationary cosmology.

Closed superstrings in magnetic flux tube background

We consider a 2-parameter class of solvable closed superstring models which `interpolate' between Kaluza-Klein and dilatonic Melvin magnetic flux tube backgrounds. The spectrum of string states has similarities with Landau spectrum for a charged particle in a uniform magnetic field. The presence of spin-dependent `gyromagnetic' interaction implies breaking of supersymmetry and possible existence (for certain values of magnetic parameters) of tachyonic instabilities. We study in detail the simplest example of the Kaluza-Klein Melvin model describing a superstring moving in flat but non-trivial 10-d space containing a 3-d factor which is a `twisted' product of a 2-plane and an internal circle. We also discuss the compact version of this model constructed by `twisting' the product of the two groups in SU(2) x U(1) WZNW theory without changing the local geometry (and thus the central charge). We explain how the supersymmetry is broken by continuous `magnetic' twist parameters and comment on possible implications for internal space compactification models. (Contribution to the Proceedings of the 1995 Erice School "String Gravity and Physics at the Planck Scale")

Flavor-changing neutral current constraints on standardlike orbifold models.

We examine for standard-like orbifold compactification models the constraints due to quarks and leptons generation non-universality of soft supersymmetry breaking interactions. We follow the approach initiated by Ibanez and Lust and developed by Brignole, Ibanez and Munoz. The breaking of supersymmetry is represented in terms of dilaton and moduli auxiliary field components and, consistently with a vanishing cosmological constant, is parametrized in terms of the dilaton-moduli mixing angle $\theta $ and the gravitino mass scale $m_g$. The soft breaking interactions (gaugino masses, squarks and sleptons mass matrices, scalars interactions A and B coupling constants) are calculable as a function of these parameters and of the discrete set of modular weight parameters specifying the modular transformation properties of the low-energy fields. We solve the renormalization group one-loop equations for the full set of gauge, Yukawa and supersymmetry breaking coupling constants.

The complete matter sector in a three-generation compactification

We consider a Calabi-Yau compactification paradigm with three light generations and anR-symmetry. From a special form of the Tian-Yau manifold, we also construct a new three-generation model with markedly different phenomenology. Thecomplete spectrum of all light matter fields is obtained in a universal way and moreover in a physically suitable basis, allowing a straightforward analysis of all their couplings. Here we discuss all the renormalizable Yukawa couplings. This computation can equally well be repeated for all compactification models based on Calabi-Yau complete intersections in products of homogeneous spaces.

MASSLESS FERMIONS IN KALUZA-KLEIN MODELS: SU(N) GAUGE FIELDS, ZN SYMMETRY AND STABILITY OF THE METASTABLE VACUUM

Kaluza-Klein model on M4×S1 with SU (N) gauge fields and Nf fermions in fundamental representation is considered. It is noted that on one-loop level the lowest state of this theory corresponds to effective four-dimensional theory which has no massless fermions. This statement does not depend on fermion boundary conditions. The state with mass-less four-dimensional fermions is metastable. It is shown that this metastable states can be stabilized by effects of classical gravitation. The same problem of metastability of states with zero fermionic modes can appear in more realistic superstring compactification models and these effects of classical gravitation can resolve this problem of metastability.

Strings and statistics

Abstract We discuss the possibility of unusual statistics in four dimensional string theory through the use of Aharonov-Bohm like phases. Such phases are closely related to anomaly cancellation in four dimensions and thus can be exactly calculated in terms of the low energy fermion spectrum of the theory. We illustrate this connection by calculating the statistical phases exactly in sample models of heterotic string compactification. We discuss some of the difficulties in applying these ideas to fundamental strings, and mention some possible applications to cosmic string scenarios.

Neutral Z0 bosons in a superstring-relatedSU(2)L×U(1)B×U(1)C×U(1)D electroweak model

ASU(2)L×U(1)B×U(1)C×U(1)D electroweak model arising from certain orbifold compactification models of string theory is examined. The three neutral vector bosons, their masses, and mixing angles are discussed. It is shown that the model is practically the same as the standardSU(2)L×U(1)Y model in the low-energy limit.

A simplified model for orbifold compactification

The problem of vacuum stability in orbifold compactification is addressed. The spectrum of fermions and the effective potential in a simple model of compactification on the T2/Z2 orbifold with a topologically nontrivial gauge field background is calculated.

Fermionic External Field and Space Compactification in the Heterotic String Theory

An interaction of the heterotic string with a fermionic massless external field is investigated in the manifestly Lorentz-covariant lagrangian formulation. Further compactification of a part of the 10 dimensions, as in the orbifold compactification model or Calabi-Y au compactification model, is . necessary to allow such a coupling. The theory naturally contains the quark fields of Eguchi­ Higashijima. Recently the heterotic string theoryl) has received much attention. The theory provides the phenomenologically promising E8 X E8 Kac-Moody algebra. 2 ) And it has

Quantum effects in a model of cosmological compactification.

The quantum effects in a Kaluza-Klein theory with a Robertson-Walker ansatz are studied. Explicit wave functions for this model are obtained, their normalization and certain effects of the boundary conditions used are discussed.

Algebraic method of constructing and analyzing spontaneous compactification models

A method is proposed for determining the ground-state symmetry superalgebra in Kaluza-Klein models. It is used to construct and investigate solutions of 11 dimensional supergravity with the sphere S/sup 7/ as internal manifold. The possible supersymmetry numbers for an arbitrary internal manifold are found.

Kaluza-Klein cosmology: Phenomenology and exact solutions with three-component matter

We explain the general fact that Friedmann models in Kaluza-Klein cosmologies, in which ordinary space-time is supplemented by internal factor spaces, are equivalent to the motion of tensorial-mass particle in a scalar field. We find exact solutions for an important class of three-component matter in the case of one internal space of dimensiond. The three components in question are the curvature of the internal space, the Zeldovich matter, and dust of the protoradiation type. The method includes one-component solutions for all the different models of compactification discussed so far.

Stable compactification to CP(3) of Einstein-Yang-Mills SU(3) × U(1) theory

Abstract A new classically stable model of spontaneous compactification is investigated. D = 10 dimensional Einstein-Yang-Mills SU(3) × U(1) theory compactifies to CP(3) giving SU(4) × U(1) effective D = 4 theory with no tachyons. An effective SU(4) coupling constant is calculated.