Transition from a relativistic constituent-quark model to the quantum-chromodynamical asymptotics: a quantitative description of the pion electromagnetic form factor at intermediate values of the momentum transfer

We adopt a non-perturbative relativistic constituent-quark model for the pi-meson electromagnetic form factor, which have successfully predicted experimental results, and supplement it with the effective momentum-dependent quark mass to study quantitatively the transition to the perturbative QCD asymptotics. The required asymptotical behaviour (including both the Q^{-2} fall-off and the correct coefficient) settles down automatically when the quark mass is switched off; however, the present experimental data on the form factor suggest that this cannot happen at the values of the momentum transfer below ~10 GeV^2. The effective constituent-quark mass below this scale acquires substantial non-perturbative contributions.Comment: 7 pages, RevTex 4.1, 5 figures. V2: a reference added, minor textual changes, version accepted by Phys. Rev.

Three fermionic generations on a topological defect in extra dimensions

We suggest a mechanism explaining the origin of three generations of the Standard Model fermions from one generation in a higher-dimensional theory. Four-dimensional fermions appear as zero modes trapped in the core of a topological defect with topological number three. We discuss hierarchical pattern of masses and mixings which arises in these models.Comment: 19 pages, no figures; v.2: references added, main text unchange

O(4) symmetric singular solutions and multiparticle cross sections in ϕ4\phi^4 theory at tree level

We solve the classical euclidean boundary value problem for tree-level multiparticle production in $\phi^4$ theory at arbitrary energies in the case of $O(4)$ symmetric field configurations. We reproduce known low-energy results and obtain a lower bound on the tree cross sections at arbitrary energies.Comment: LaTeX, 9pp + 2 Postscript figures, tar-compressed and uuencoded using uufiles; minor Postscript bug fixe

Neutrino masses with a single generation in the bulk

In a class of multidimensional models, topology of the thick brane provides three chiral fermionic families with hierarchical masses and mixings in the effective four-dimensional theory, while the full model contains a single vector-like generation. We discuss how to incorporate three non-degenerate neutrino masses in these models with the help of only one singlet bulk fermion.Comment: 16 pages, 1 EPS figur