It is shown that the light scalar meson propagators in the one-loop approximation satisfy the Källen – Lehmann representation in the wide domain of coupling constants of the light scalar mesons with the two-particle states. It is proposed to use these propagators in routine fitting data about light scalar mesons.

where β = 1 2g and g is the continuum gauge coupling. We will keep b = β N fixed as N goes to infinity, and this amounts to setting gN = 1 2b . The reduced model on the lattice has a [U(1)] symmetry. The Eguchi-Kawai argument for reduction holds only if the [U(1)] symmetry remains unbroken [3]. This is not the case as b → ∞ [4]. This problem is resolved by defining the quenched reduced model [4...

All members of a recently proposed new set of (non-supersymmetric) grand unified theories with at the one-loop level vanishing beta functions for the gauge, Yukawa, and scalar-boson self-interaction coupling constants are shown to involve, already at the one-loop level, quadratically divergent contributions to both the vector-boson and scalar-boson masses.

I review the arguments in favor of/against the traditional hypothesis that the Planck, string and compactification scales are all within a couple of orders of magnitude from each other. I explain how the extreme brane-world scenario, with TeV type I scale and two large (near millimetric) transverse dimensions, creates conditions analogous to those of the energy desert and is thus naturally sing...

We consider the breaking of the grand unification group SO(10) to the standard model gauge group through several chains containing two intermediate stages. Using the values of the gauge coupling constants at scale M Z derived from recent LEP data, we determine the range of their intermediate and unification scales. In particular, we identify those chains that permit new gauge structure at relat...

Target space symmetries are studied for orbifold compactified string theories containing Wilson line background fields. The symmetries determined are for those moduli which contribute to the string loop threshold corrections of the gauge coupling constants. The groups found are subgroups of the modular group P SL(2, Z) and depend on the choice of discrete Wilson lines and the shape of the under...

We calculate the π∆∆ coupling gπ0∆++∆++ using light cone QCD sum rule. Our result is gπ0∆++∆++ = (11.8 ± 2.0). PACS numbers: 12.39.Fe, 14.20.Gk The π∆∆ coupling constant g1, like the nucleon axial charge gA, is a basic parameter which enters the loop calculation in all processes involved with delta resonance [1] in chiral perturbation theory. Unfortunately it is not directly accessible experime...

We derive the effective chiral Lagrangian for low-energy η–nucleon and η′– nucleon interactions and show that gluonic degrees of freedom, via the axial UA(1) anomaly, induce a contact term in the pp → ppη and pp → ppη′ reactions. We then discuss the consequences for the extraction of gη′NN from experimental data. ∗Work supported in part by BMBF.