Modern Physics Letters A

We investigate collisions of ¹⁶O with ²⁰⁸Pb at a bombarding energy of 200 GeV/N in the lab frame. Our basis is an ideal, one-fluid 3-D hydrodynamics model. Several equations of state are used to study the qualitative relation between final baryon rapidity distributions and the stiffness of the EOS. We find that 75% of the baryonic matter lies within one unit of the initial target rapidity, in qualitative agreement with recent experimental data. In addition, our calculation is able to reproduce the integrated value of the dE_T/dy distribution that is observed experimentally.

A new analytical expression for the HI total reaction cross-section which exhibits the macroscopic features of the transparency factor is derived. Comparison with optical model calculation are made for the ¹²C+²⁰⁸Pb and ¹⁶O+²⁰⁸Pb at several energies.

For theories with noncanonical commutation relations, the generating functional (S-matrix) is constructed at a formal level, as a Hamiltonian path integral.

It is pointed out that in the Kac-Moody algebras fulfilling the fermionization criterion of Goddard, Nahm and Olive and having a non-minimal value of the central charge k, only a proper subset of the allowed unitary highest weight representations can actually be encoded in a free fermion theory. These truly fermionizable representations are selected by a very specific non-regular embedding of the fermionizable Kac-Moody algebra into the lowest level SO(N_F) Kac-Moody algebra, N_F being both the number of fermions and the dimension of the GNO symmetric space. This embedding is a particular case of the embeddings considered by Bais and Bouwknegt and by Schellekens and Warner, for which the Virasoro central charge of the subgroup is equal to that of the group. Furthermore, these fermionizable representations span an orbit of the modular group always leading to a non trivial modular invariant partition function.

It is proposed to classify multiple production processes according to the Renyi dimensions of the (pseudo) rapidity distribution of secondary particles in individual events. The method is illustrated by some examples.

We discuss the space-time interpretation of bosonic string theories, which involve d scalar fields coupled to gravity in two dimensions, with a proper quantization of the world-sheet metric. We show that for d>25, the theory cannot describe string modes consistently coupled to each other. For d=25 this is possible; however, in this case the Liouville mode acts as an extra timelike variable and one really has a string moving in 26-dimensional space-time with a Lorentzian signature. By analyzing such a string theory in background fields, we show that the d=25 theory possesses the full 26-dimensional general covariance.

Based on the dynamical model having a large anomalous dimension γ_m≃2, we propose that the t quark condensate is responsible for the mass of W and Z bosons within the framework of the SU(3)_C×SU(2)_L×U(1)_Y gauge theory (without Higgs) plus four-fermion interactions among quarks and leptons. This accounts for the largeness of the t quark mass m_t without violating the weak-isospin relation . Quark/lepton mass matrices are obtained through the four-fermion interactions, which yields no serious flavor-changing neutral currents. The model predicts a composite scalar meson with a mass ≃2m_t. A possibility for an unusual resolution of the strong CP problem is also suggested.

We point out a generalized Frenkel-Kac point for the c=N conformal field theories in fermion language. The critical value, , of the modular parameter for the c=1 case is generalized to for c=N, where R is a parameter in the moduli space which can be used to continuously deform a conformal field theory with SO(2N)_L× SO(2N)_R Kac-Moody symmetry to one with SU(N+1)_L×SU(N+1)_R symmetry. Similar deformation from to SO(N+1)_L×SO(N+1)_R is also shown to occur at .

We discuss the role of XY-like vortices on the world-sheet for the free energy of strings at high temperatures. There is a Kosterlitz-Thouless phase transition at the Hagedorn temperature, above which the vortices contribute to the free energy in genus zero and generate a mass gap. We speculate that high-temperature “string” theory could be essentially discrete.

We construct covariant field theories of both type-II and heterotic strings. Toroidal compactification is also considered. The interaction vertices are based on Witten’s vertex representing three strings interacting at the mid-point. For closed strings, we thus obtain a bilocal interaction.

As an improvement on the geometrical description of multiparticle emission in hadron-hadron collisions, a concept of intrinsic multiplicity n₀ at fixed impact parameter is introduced. The observed large fluctuation in multiplicity distribution is attributed to (i) the large spread in the intrinsic multiplicity n₀, and (ii) the Poissonian fluctuation about n₀ for each b. The dependence of the intrinsic multiplicity on the impact-parameter is estimated for collisions at 540 GeV.