Modern Physics Letters A

We discuss the contributions of PGBs (technipions, top-pions) to the top quark production at the high energy e⁺e^- linear collider (LC) experiments in TC2 theory. We find that the corrections to the production cross-section mainly come from top-pions. The corrections of the charged top-pions are significantly large in most of the parameter space. With reasonable value of the parameters, the correction to can reach about 8% which may be detected at LC experiments.

Electromagnetic form factors of the nucleon from relativistic quark models are analyzed: Results from null-plane projection of the Feynman triangle diagram are compared with a Bakamjian–Thomas model. The magnetic form factors of the models differ by about 15% at spacelike momentum transfer 0.5 GeV², while the charge form factors are much closer. Spurious contributions to electromagnetic form factors due to violations of rotational symmetry are eliminated for both models. One method changes magnetic form factors by about 10%, whereas the charge form factors remain nearly the same. Another one changes the charge form factor of the Bakamjian–Thomas model by more than 50%.

We consider (2+1)-dimensional classical noncommutative scalar field theory. The general ansatz for a radially symmetric solution is obtained. Some exact solutions are presented. Their possible physical meaning is discussed. The case of finite θ is discussed qualitatively and illustrated by some numerical results.

Using traversable wormholes as theoretical background, we revisit a deep question of general relativity: Does a uniformly accelerated charged particle radiate? We particularize to the recently proposed gravitational Čerenkov radiation, that happens when the spatial part of the Ricci tensor is negative. If ⁽³⁺¹⁾Rⁱ_i<0 the matter threading the gravitational field violates the weak energy condition. In this case, the effective refractive index for light is larger than 1, i.e. particles propagate faster than photons in that medium. This leads to a violation of the equivalence principle.

The scattering of a cold atomic beam by a perfectly conducting spherical mass when gravitational and quantum electrodynamical, retarded dispersion forces are simultaneously relevant allows one to naturally introduce and realistically measure the Planck mass in the laboratory.