Supercompositeness from superstrings

String Unified Models based on the k = 1 level of the Kac-Moody Algebra, predict the existence of “exotic” new states which carry fractional electric charges. We analyse the possibility of considering these “exotics” as preonic matter which can be used to form the families and the gauge group breaking higgs scalars. It is proposed that such a formation may occur provided that these states transform non-trivially under a non-Abelian gauge group with a relatively large rank in order to confine them at a sufficiently large scale. Such a situation is natural in string derived unified models, since the role of the confining group can be played by (part of) the Hidden symmetry. As an example, we present a string derived toy model based on the SU(4) × SU(2) _L × SU(2) _R Pati-Salam gauge group.     

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.     

Closed-string tachyon condensation and the worldsheet super-higgs effect

Alternative gauge choices for worldsheet supersymmetry can elucidate dynamical phenomena obscured in the usual superconformal gauge. In the particular example of the tachyonic E8 heterotic string, we use a judicious gauge choice to show that the process of closed-string tachyon condensation can be understood in terms of a worldsheet super-Higgs effect. The worldsheet gravitino assimilates the goldstino and becomes a dynamical propagating field. Conformal, but not superconformal, invariance is maintained throughout.     

Comments on worldsheet description of the Omega background

Nekrasov?s partition function is defined on a flat bundle of R⁴ over S¹ called the Omega background. When the fibration is self-dual, the partition function is known to be equal to the topological string partition function, which computes scattering amplitudes of self-dual gravitons and graviphotons in type II superstring compactified on a Calabi-Yau manifold. We propose a generalization of this correspondence when the fibration is not necessarily self-dual.     

p-adic string theories provide lattice Discretization to the ordinary string worldsheet

A class of models called p-adic strings is useful in understanding the tachyonic instability of string theory. These are found to be empirically related to the ordinary strings in the p-->1 limit. We propose that these models provide discretization for the string worldsheet and argue that the limit is naturally thought of as a continuum limit in the sense of the renormalization group.     

Primordial superstrings and the origin of the universe

We discuss some of the cosmological implications of superstring theories. We pay particular attention to the issue of the initial state and its relationship withR-duality.     

Closed twisted superstrings in the Green-Schwarz formalism

The consistency condition for the quantization of the superstring with twisted boundary conditions in the Green-Schwarz formalism is obtained. Some models satisfying this condition are constructed in 4, 6, 8 and 10 dimensions. These models can also be described by the spinning string formalism.     

Jet signatures of scalar diquarks from superstrings at CERN and Fermilab

We calculate the contribution to the four-jet yield in p̄p collisions of two scalar, colour triplet, hypercharge $\text{±}\text{1}\text{3}$ pure diquarks resulting from E₆ compactification in superstring theories. Measured cross sections at the CERN Collider are sensitive to this contribution for masses up to ∼40 GeV. Fermilab-Tevatron data with similar cuts will push this bound up to ∼70 GeV.     

Type IIB Green-Schwarz superstrings in AdS 5 × S 5 from the supercoset approach

We consider superstrings moving in the AdS ₅ × S ⁵ space-time and find their Green-Schwarz action using the supercoset approach based on the supergroup PSU(2, 2|4). We describe several parametrizations of the relevant supercoset and present the action in different κ-symmetry gauges. In particular, we discuss a gauge where all the fermionic coordinates corresponding to the conformal (S) supercharges are gauged away and also a light-cone type gauge where half of the Q and S supercoordinates are gauged away. The resulting action contains terms that are quadratic and quartic in fermions. In the flat-space limit, it reduces to the standard light-cone Green-Schwarz action. We comment on the possibility of fixing the bosonic light-cone gauge and of reformulating the action in terms of two-dimensional Dirac spinors.     

Comment on the non-renormalization theorem in the four-dimensional superstrings

We discuss the non-renormalization theorem in the context of the four-dimensional superstrings. We explicitly demonstrate that the graviton three-point one-loop amplitude does not vanish in contrast to the ten-dimensional superstring theories.     

The limiting temperature of the universe and superstrings

Some cosmological implications of superstring theories are discussed. In particular, the possible role of the limiting temperature in the early universe is examined.     

Superspace geometry from D = 4, N = 1 heterotic superstrings

The presence of classical κ-supersymmetry invariance is shown to be consistent with an off-shell D = 4, N = 1 conformal supergravity background in the presence of a tensor multiplet. We derive a suitable set of constraints, via super Weyl rescaling, for a heterotic superstring in such a background. Starting from the geometry of 16-16 supergravity and gauging the R-symmetry with a composite connection, we derive a geometrical structure similar to that of new minimal supergravity.     

Vanishing of the cosmological constant for heterotic-type lower-dimensional superstrings

We consider the recently constructed heterotic-type lower-dimensional superstrings. Using a theorem of Arbarello and Cornalba about the family of line bundles on the compactified moduli space, we prove that these models have vanishing cosmological constant.     

inflation from scale invariant supergravity and anomaly free superstrings with fluxes

The scale invariant gravity theory coupled to conformally invariant matter is investigated. We show that in the non‐supersymmetric case the conformally coupled scalars belong to an manifold, while in the supersymmetric case the scalar manifold becomes isomorphic to the Kählerian space =. In both cases when the underlying scale symmetry is preserved the vacuum corresponds to de Sitter space. Once the scale symmetry is broken by quantum effects, a transition to flat space becomes possible. We argue that the scale violating terms are induced by anomalies related to a symmetry. The anomaly is resolved via the gauging of a Peccei‐Quinn axion shift symmetry. The theory describes an inflationary transition from de Sitter to flat Minkowski space, very similar to the Starobinsky inflationary model. The extension to metastable de Sitter superstring vacua is also investigated. The scalar manifold is extended to a much richer manifold, but it contains always as a sub‐manifold. In superstrings the metastability is induced by axions that cure the anomalies in chiral (or even ) supersymmetric vacua via a Green‐Schwarz/Peccei‐Quinn mechanism generalized to four dimensions. We present some typical superstring models and discuss the possible stabilization of the no‐scale modulus.     

Quantum computing: A view from the enemy camp

Quantum computing relies on processing of information within a quantum system with many continuous degrees of freedom. The practical implementation of this idea requires complete control over all of the 2ⁿ independent amplitudes of a many-particle wave function, where n>1000. The principles of quantum computing are discussed from the practical point of view, with the conclusion that a working device cannot be built in the foreseeable future.