[en] We construct a 1+1 dimensional superstring-bit model for D=3 Type IIB superstring. This low dimension model escapes the problem encountered in higher dimension models: (1) It possesses full Galilean supersymmetry; (2) For noninteracting Polymers of bits, the exactly soluble linear superpotential describing bit interactions is in a large universality class of superpotentials which includes ones bounded at spatial infinity; (3) The latter are used to construct a superstring-bit model with the clustering properties needed to define an S-matrix for closed polymers of superstring-bits

[en] A procedure for Pauli-Villars regularization of locally and globally supersymmetric theories is described. Implications for specific theories, especially those obtained from superstrings, are discussed with emphasis on the role of field theory anomalies

[en] We study nonperturbative superpotentials with positive exponents, i.e. the form like Ae^aT with positive constant a and the modulus T.

No abstract available

[en] The pattern of duality symmetries acting on the states of compactified superstring models reinforces an earlier suggestion that the Monster sporadic group is a hidden symmetry for superstring models. This in turn points to a supersymmetric theory of self-dual and anti-self-dual K3 manifolds joined by Dirac strings and evolving in a 13 dimensional spacetime as the fundamental theory. In addition to the usual graviton and dilaton this theory contains matter-like degrees of freedom resembling the massless states of the heterotic string, thus providing a completely geometric interpretation for ordinary matter. 25 refs

[en] A couple of issues concerning the effective dynamics of D-branes in string theory are discussed. Primarily, I am concerned with linearization of the actions by introduction of non-propagating fields and a full super- and κ-symmetric description of D-branes. (orig.)

[en] The structure of tree-level open and closed superstring amplitudes is analyzed. For the open superstring amplitude we find a striking and elegant form, which allows one to disentangle its α′-expansion into several contributions accounting for different classes of multiple zeta values. This form is bolstered by the decomposition of motivic multiple zeta values, i.e. the latter encapsulate the α′-expansion of the superstring amplitude. Moreover, a morphism induced by the coproduct maps the α′-expansion onto a non-commutative Hopf algebra. This map represents a generalization of the symbol of a transcendental function. In terms of elements of this Hopf algebra the α′-expansion assumes a very simple and symmetric form, which carries all the relevant information. Equipped with these results we can also cast the closed superstring amplitude into a very elegant form. (paper)

[en] It has recently been realised that polystable, holomorphic sums of line bundles over smooth Calabi-Yau three-folds provide a fertile ground for heterotic model building. Large numbers of phenomenologically promising such models have been constructed for various classes of Calabi-Yau manifolds. In this paper we focus on a case study for the tetra-quadric — a Calabi-Yau hypersurface embedded in a product of four ℂℙ"1 spaces. We address the question of finiteness of the class of consistent and physically viable line bundle models constructed on this manifold. Further, for a specific semi-realistic example, we explore the embedding of the line bundle sum into the larger moduli space of non-Abelian bundles, both by means of constructing specific polystable non-Abelian bundles and by turning on VEVs in the associated low-energy theory. In this context, we explore the fate of the Higgs doublets as we move in bundle moduli space. The non-Abelian compactifications thus constructed lead to SU(5) GUT models with an additional global B−L symmetry. The non-Abelian compactifications inherit many of the appealing phenomenological features of the Abelian model, such as the absence of dimension four and dimension five operators triggering fast proton decay

[en] The Grand Unification Theory with the (SU₅ circle-times U₁)circle-times(SU₃ circle-times U₁)_H gauge group, in which (SU₃ circle-times U₁)_H is the horizontal symmetry of quark-lepton generations, is considered within the framework of the approach using a four-dimensional superstring with free fermions. The horizontal hypercharge Y_H is used to quantize electromagnetic charges of quarks and leptons within the framework of standard SO₁₀ 16-plets. In the authors approach, construction of the horizontal gauge symmetry leads to the appearance of a new massive SO₁₀ 16-plet, which is a singlet with respect to the horizontal group. The resulting Higgs sector may enable the hidden gauge group to be suppressed significantly and to break the flip SU₅ circle-times U₁ symmetry first to SM and then to SU^c₃ circle-times U^em₁. The Q_em construction allows the authors to avoid states with exotic charges (Q^ex_em = 1/nQ_em), whose emergence is characteristic of the approach using four-dimensional superstrings. In the authors approach, the horizontal group can be violated in the low-energy limit, which offers a possibility for the existence of a superweaklike mechanism of CP violation in the gauge sector of the SU_3H group. 19 refs., 2 tabs

[en] We investigate the NBI matrix model with the potential $X/Λ+X^-1+(2/η+1)/log X$ recently proposed to describe IIB superstrings. With the proper normalization, using Virasoro constraints, we prove the equivalence of this model and the Kontsevich matrix model for $/η/ne0$ and find the explicit transformation between the two models. (author)