Fermion spectra from superstrings

Some compactifications of the ten-dimensional anomaly-free E₈ × E₈ and SO(32) theories that correspond to superstrings are studied. Compactification is achieved by setting the classical gauge field equal to the spin connection. The resulting chiral fermion spectra are obtained for any six-dimensional manifold, under the condition Tr F² = 30 Tr R², plus a quantization condition for U(1) charges. For E₈ × E₈ these conditions lead to potentially realistic models for any irreducible six-dimensional manifold and any embedding of the holonomy group. Apart from a few more exotic examples, the four-dimensional models we obtain are more or less standard SU(5), SO(10), SU(4) × SU(2) × SU(2) or E₆ models.     

Solar neutrino oscillations from superstrings

A recently proposed model of neutrino mass based on the heterotic superstring is shown to lead naturally to large oscillations of the SU(2)-doublet neutrino into sterile fermions leading to the possibility of substantial depletion of the solar electron neutrino flux as suggested by Davis' results. The model also leads to a psuedo-Dirac nuetrino with m_v = 10–20 eV, without conflict with null searches for neutrinoless double beta decay.     

p-adic superstrings

Different possibilities to construct p-adic superstring amplitudes are discussed. To describe one of these possibilities we formulate a p-adic generalization of the conformal technique. p-adic conformal rules allow us to explicitly write down the amplitude for massless particles. They do not have the form of the usual kinematical factors multiplied by the p-adic modification of the usual amplitudes. The relation between open and closed p-adic superstring amplitudes is discussed.     

Rigid superstrings

A recently proposed bosonic string action containing a term proportional to the world sheet is supersymmetrized in the light-cone gauge. We compute the one-loop contribution to the β function of the new coupling constant and find that the asymptotic freedom present in the bosonic case is not destroyed by the addition of the fermionic degrees of freedom.     

Cosmic superstrings II

Modern string theory provides a rich array of objects which could potentially appear as cosmic strings in our observable four-dimensional universe. However, there are many possible decay modes which would prevent the appearance of such strings. We investigate the conditions under which metastable strings can exist, and we find that such strings are present in many models. Hence cosmic strings give a potentially large window into string physics. To cite this article: E.J. Copeland et al., C. R. Physique 5 (2004).

Résumé

La théorie moderne des supercordes fournit un choix riche d'objets qui pourraient potentiellement apparaître en tant que cordes cosmiques dans notre univers quadridimensionnel observable. Cependant, il y a beaucoup de modes possibles de désintégration qui empêcheraient l'apparition de telles cordes. Nous étudions les conditions dans lesquelles des cordes métastables peuvent exister, et nous constatons que de telles cordes sont présentes dans beaucoup de modèles. Par conséquent les cordes cosmiques ouvrent une fenêtre potentiellement grande vers la physique des supercordes. Pour citer cet article : E.J. Copeland et al., C. R. Physique 5 (2004).     

Inflation with superstrings

Cosmological solutions with three exponentially expanding space dimensions in the N=1 supersymmetric Yang-Mills supergravity system are found under the assumption of gluino and “subgravitino” condensation. The potential has a long flat region providing sufficient inflation.     

Thermodynamics of superstrings

We study the thermal properties and the thermodynamical equilibrium fluctuations of a gas of massive heterotic string excitations at Planck energy scales. The behavior of this system parallels in several ways that of massive Schwarzschild black holes. We briefly comment on its possible influence on primeval entropy generation.     

Two-loop statsum of superstrings

We discuss, whether there is a choice of odd moduli on super-Riemann surfaces of genus p≳2, which leads to the vanishing of statistical sums of superstrings before integration over the space of even moduli. The answer is shown to be positive at least for p=2, when odd moduli are localized at ramification points. The relation between various definitions of many-loop statistical sums in superstring theory is discussed.     

Scherk-Schwarz mechanism and superstrings

It is shown that a particular choice of massless classical backgrounds provides an exact solution to the equations of motion of closed superstrings while spontaneously breaking supersymmetry at an arbitrary scale.     

Compactified superstrings and torsion

String theories on a background manifold with torsion are constructed and investigated in the light-cone gauge with holonomy group H ⊆ SU(3). The appropriate non-linear sigma model is constructed on a hermitian manifold. The relationship between the Neveu-Schwarz-Ramond and the Green-Schwarz versions of the theory is discussed. Under the assumption that the β-function vanishes identically we show that the only viable compactification is on a manifold with zero torsion. This result is obtained from effective field considerations as well as directly from string considerations.     

Aspects of fractional superstrings

We investigate some issues relating to recently proposed fractional superstring theories withD _critical<10. Using the factorization approach of Gepner and Qiu, we systematically rederive the partition functions of theK=4, 8, and 16 theories and examine their spacetime supersymmetry. Generalized GSO projection operators for theK=4 model are found. Uniqueness of the twist field, _K/4 ^K/4, as source of spacetime fermions is demonstrated.Work supported in part by the U.S. Department of Energy under Contract no. DEAC-0381ER40050     

Beltrami parametrization for superstrings

We introduce a parametrization of the metric and supersymmetry structure of the superstring world sheet which permits the derivation of the superstring action for general backgrounds. Factorization is explicit at each step of the construction.     

Anomalies,ambiguities and superstrings

It is shown that anomalies only change trivially if a covariant term is added to the gauge connection. As a result, for the superstring, the anomalies can be cancelled if the anti-symmetric tensor field strength H is modified by the Chern-Simons form of any spin-connection, possibly with torsion. The low-energy effective field theory is, then, not uniquely determined by requiring anomaly cancellation and supersymmetry. Implications for string compactifications are considered.