International Journal of Modern Physics A

The dependence of four-fermion neutral and charged current processes on the masses of the top and of the Higgs particles is analyzed. A parametrization of the leading top and Higgs vacuum polarization effects is given in the form of effective amplitudes, and a general procedure for generating quantities that to a large extent are independent of the unknown parameters of the standard model is described. A large set of these quantities is reviewed, and by explicit computation the residual theoretical uncertainty is shown to be negligible.

Some extensions to the standard model have been proposed, which require new fermions for the electroweak anomalies to cancel. We investigate some of these theories, and examine the possibility of cancelling the anomalies and yet preserve the charge quantization feature of the standard model.

Superstring solutions on twisted group manifolds are investigated, chiefly in the case of fermionizable Wess-Zumino-Witten models that yield space-time N=1 supersymmetry. Both outer and inner automorphisms are admitted as boundary conditions. The representations of the twisted current algebras are studied—their mass spectra match perfectly their fermionic realizations. The supersymmetric solutions are characterized and classified. A few especial ones are identified with Z₄ and Z₃ orbifolds by using the equality of the fermion equivalents.

The world-sheet dynamics of the first quantized string propagating in nonsimply connected space is considered. Presence of the vortices on the world sheet leads to Berezinsky-Kosterlitz-Thouless (BKT) phase transition. Bosonic and superstring cases are discussed. It is shown that Hagedorn transition can be described as BKT transition both in bosonic and superstring cases.

We use the Schrödinger formulation of quantum field theory to study symmetry behaviour in the static open Einstein universe.

The method proposed in the previous papers by the authors^1,2 is applied to calculation of quark distributions in a polarized nucleon. It is based on the operator expansion and is a generalization of the QCD sum rule approach applying to the given problem.

The characteristic equations which give the mass spectrum of the affine Toda field theories are analyzed. In order to determine the decoupling point of the finite renormalization due to the tadpoles we introduce the so-called mass formulae. We derive the recursive equations the mass formulae satisfy and study their properties for all Lie algebras. For the ADE series the mass formulae turn out to be sequences of integers.

We demonstrate the realization of supersymmetric quantum mechanics in the first-order Dirac oscillator equation by associating with it another Dirac equation, which may be considered as its supersymmetric partner. We show that both the particle and the antiparticle spectra, resulting from these two equations after filling the negative-energy states and redefining the physical ground state, indeed present the degeneracy pattern characteristic of unbroken supersymmetry. In addition, we analyze in detail two algebraic structures, each partially explaining the degeneracies present in the Dirac oscillator supersymmetric spectrum in the non-relativistic limit. One of them is the spectrum-generating superalgebra osp(2/2, ℝ), first proposed by Balantekin. We prove that it is closely connected with the supersymmetric structure of the first-order Dirac oscillator equation as its odd generators are the two sets of supercharges respectively associated with the equation and its supersymmetric partner. The other algebraic structure is an so(4)⊕so(3, 1) algebra, which is an extension of a similar algebra first considered by Moshinsky and Quesne. We prove that it is the symmetry algebra of the Dirac oscillator supersymmetric Hamiltonian. Some possible relations between the spectrum-generating superalgebra, the symmetry algebra, and their respective subalgebras are also suggested.

We study and place constraints on cosmic strings and on their cosmological evolution with emphasis on the results of five measurements: (i) millisecond pulsar timings, (ii) binary pulsar timings, (iii) spatial fluctuations in the intensity of the cosmic microwave background radiation (MBR). For superconducting strings (hereafter SCS), we add two other results: the spectrum of the MBR in (iv) the Rayleigh-Jean side and in (v) the Wien side. We find compatibility conditions between these five results which constrain the string evolution parameters independently of any numerical simulation result. We compare and comment about the gravitational decay rate of fundamental quantum strings in D=4, which appears closely related to that of classical cosmic strings.

The absence of distortion recently reported by COBE’s FIRAS experiment leads to the following upper limits on: (a) the comptonization parameter, y≤10⁻³; (b) the chemical potential due to SCS, μ_oscs≤0.5 10⁻³; (c) the electromagnetic radiation to gravitational radiation ratio, f≤2.3 10⁻²; (d) the string parameter: Gμ<10⁻⁶ for generic values of string evolution parameters, Gμ<10⁻⁷ for values derived from numerical simulations. The small value of f shows that the decay of SCS must be governed by gravitation. The latest PSR 1937+21 timing measurements and the preliminary COBE data converge to the same upper limits on Gμ. These limits continue to descend but the breaking point is not yet reached.

Perturbations of the SL(2)_kC WZNW model by relevant operators are studied. Nontrivial off-critical conservation laws in these perturbed systems are constructed. For the rational level k, one of the perturbations is shown to be an analogue of the (1, 2j+1) operator in the WZNW model. Linear systems (Lax pairs) are defined whose zero curvature conditions give rise to the classical versions of the perturbed equations of motion. The classical r-matrix for these linear systems is found.