Modern Physics Letters A

We show that positronium hyperfine splitting and Delbrück scattering impose stringent bounds on the coupling of a light neutral boson to the electron-positron and the photon field. These limits are relevant for the “new-particle interpretation” of coincident electron-positron lines observed at GSI.

Accretion of collisionless particles onto cosmic strings leads to the formation of galactic halos. The halo density is determined uniquely by the string-line density µ as ρ(r)=µr⁻² where (size of string loop) <r<(Gµ)^1/2 (horizon size). The rotation velocity of galactic spirals in such halos is given by υ_rot=(4Gµ)^1/2, which requires a value of µ suggested by the unified theory as Gµ= 10^−7.2×(υ_rot/250 km sec⁻¹)².

We calculate the multiplicity distributions in fixed pseudorapidity intervals |η|≤η_c for collisions at GeV from the total multiplicity distribution. Agreement with experimental data is good where expected. This calculation may be regarded as giving a relation between the number of clusters lying inside |η|≤η_c and the partition temperature T_p(N) introduced by Chou, Yang and Yen for N produced particles.

The nonlinear sigma model describes Goldstone bosons originating from spontaneous symmetry breaking. A set of local counterterms is found to shift the anomaly of the nonlinear sigma model to that of the original model with fermions interacting with external gauge fields. The ‘t Hooft consistency conditions are matched automatically.

The appearance of vorticity 01 twists in 2-dim. current algebra associated with a compact Lie group G can lead to the absence of some of the global symmetry generators of G and one expects the symmetry to be reduced to a smaller subgroup H of G. Contrary to expectations, all gauge bosons, including those of H become massive. This is because the zero point energy of the string is uniformly shifted upward affecting the masses of all particles by the same amount.

We discuss the cosmological implications of a gas of hot heterotic superstring in the very early universe. There is a possibility of generating entropy in the non-equilibrium region T₀<T<T_c, where T₀ is the limiting temperature of the string and T_c is the critical temperature. The imperfect fluid is introduced to take account of this entropy production.

It is shown that, owing to the threshold effect of colored exotic fermions, the exotic color condensates can provide only one realistic dynamical scale of ~1 TeV which could come from the condensates of either colored 8-plet or colored 6-plet fermions.

The space-time extension of neutralization of colour and electric charges of quarks in e⁺e⁻ annihilation can be revealed by hard bremsstrahlung photons at large angles.

We compile phenomenological constraints on the minimal low-energy effective theory which can be obtained from the superstring by Calabi-Yau compactification. Mixing with the single additional neutral gauge boson in this model reduces the mass of the conventional Z⁰, Field vacuum expectation values are constrained by the experimental upper bound on this shift. Then, requiring the sneutrino mass squared to be positive constrains the scale of supersymmetry breaking more than do lower bounds on the masses of new charged particles and of sparticles. More model-dependent constraints follow from the “naturalness” requirement that observables do not depend sensitively on input parameters. We find a preference for the second neutral gauge boson to weigh ≲320 GeV, GeV and GeV. Dynamical generation of the gauge hierarchy is possible if m_t≲70 GeV, with lower values of m_t being favoured.