Modern Physics Letters A

We present a summary of perturbative results obtained in the framework of collective string field theory. We discuss computations of tree-level scattering amplitudes, loop corrections to tachyon self-energy, ground state energy and finite temperature free energy. A comparison with results obtained in different approaches is given. We also discuss the physical implications of our results.

We obtain a more accurate rho-meson-nucleon coupling constant g_ρ for studying nuclei in relativistic mean field theory of nucleons and mesons than used before. With this g_ρ we get a better description of finite nuclei. We have studied a number of isotopic chains of neutron-rich nuclei using the new g_ρ parameter, with important consequences for very neutron-rich exotic nuclei and the neutron-drip line. The binding energies are sensitive to the coupling constant g_ρ, but the rms radii and deformation parameters of nuclei are not at all sensitive to g_ρ.

It is shown that in quantum electrodynamics with wrong sign of the photon mass square the fermion number is spontaneously broken and the fermion number violating condensate is different from zero.

The top quark mass prediction in supersymmetric top condensate models is found to be insensitive to the inclusion of the effects of higher dimensional operators. For associated coefficients of characteristically moderate strength, the supersymmetric renormalization group trajectories are strongly focused to the infrared quasi-fixed point of the top Yukawa coupling constant.

Using Jordan algebraic techniques we define and study a family of exotic superspaces in two dimensions with two bosonic and two fermionic coordinates. They are defined by the one-parameter family of Jordan superalgebras JD(2/2)_α. For two special values of α the JD(2/2)_α can be realized in terms of a single fermionic or a single bosonic oscillator, respectively. For other values of α it can be interpreted as defining an exotic oscillator algebra. The derivation, reduced structure and Möbius superalgebras of JD(2/2)_α are identified with the rotation, Lorentz and finite-dimensional conformal superalgebras of the corresponding superspaces. The conformal superalgebras turn out to be the superalgebras D(2,1;α) with the even subgroup SO(2,2)×SU(2). We give an explicit differential operator realization of the actions of D(2,1;α) on these superspaces.

All scale-invariant differential calculi on quantum plane are found. Their operator realization is constructed and problem of defining derivatives is analyzed in some detail.

By using canonical phase space variables different from those associated with individual particles, we couple the Chern–Simons–Witten gravity to point-like sources. The resulting theory provides an alternative to the usual test particle approximation and yields 't Hooft's scattering amplitude in the limit of two very massive slowly moving particles.

We study the dynamical generation of parity-odd fermion mass in (2+1)-dimensional topologically massive gauge theory. To one-loop order, the temperature dependence of the induced fermion mass is calculated. The implications of our study pertinent to some recent results concerning the Chern–Simons terms are discussed.

Exceptional modular invariants for Kac–Moody algebras are obtained systematically by exploiting the relation with the fixed point conformal field theory.

We study the couplings of discrete states that appear in the string theory embedded in two dimensions, and show that they are given by the structure constants of the group of area preserving diffeomorphisms. We propose an effective action for these states, which is itself invariant under this infinite-dimensional group.