The time travel paradox

We define the time travel paradox in physical terms and prove its existence by constructing an explicit example. We argue further that in theories -- such as general relativity -- where the spacetime geometry is subject to nothing but differential equations and initial data no paradoxes arise.Comment: Minor changes + an explanatory note concerning the lions with the same world line

LHC signatures for Z` models with continuously distributed mass

We discuss phenomenological consequences of renormalizable Z` models with continuously distributed mass. We point out that one of possible LHC signatures for such nodel is the existence of broad resonance in Drell-Yan reaction $pp \to Z^{`} \to l^+l^-$.Comment: 7 page

What does the Letelier-Gal'tsov metric describe?

Recently the structure of the Letelier-Gal'tsov spacetime has become a matter of some controversy. I show that the metric proposed in \cite{letgal} is defined only on a dense subset of the whole manifold. In the case when it can be defined on the remainder by continuity, the resulting spacetime corresponds to a system of parallel cosmic strings at rest w.r.t. each other.Comment: 4pages, 1 figure. v2 A few words are changed in accordance with the published versio

LHC Z‘Z^` discovery potential for models with continuously distributed mass

We study the Large Hadron Collider (LHC) discovery potential for $Z^`$ models with continuously distributed mass for $\sqrt{s} = 7, 10$ and 14 TeV centre-of-mass energies. One of possible LHC signatures for such models is the existence of broad resonance in Drell-Yan reaction $pp \to Z^` + ... \to l^+l^- + ...$.Comment: 14 pages, some references and formula adde

Higgs mechanism as a collective effect due to extra dimension

A systematic analysis of the unitary electroweak model described by the higher derivative Lagrangian depending on extra dimension [1] is presented.Comment: 11 pages, no figure

Hard exclusive production of a vector meson

The processes of a light neutral vector meson, V=\rho^0, \omega, \phi, electroproduction and a heavy quarkonium, V=J/\Psi, \Upsilon, photoproduction are studied in the framework of QCD factorization. We derive a complete set of hard-scattering amplitudes which describe these processes at next-to-leading order (NLO).Comment: 3 pages, prepared for Diffraction 2004, International Workshop on Diffraction in High-Energy Physics, Cala Gonone, Sardinia, Italy, September 18 - 23, 200

Control of charge trapping in a photorefractive polymer

Modification of the trap density of the photorefractive polymer composite poly(N-vinyl carbazole) (PVK), 2,4,7-trinitro-9-fluorenone (TNF) and N,N-diethyl-para-nitroaniline (EPNA) was achieved with the addition of 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH). Measurements of the response time, the phase shift and the amplitude of the photorefractive grating are presented

Blue superradiance from neat semiconducting alternating copolymer films

Blue superradiant emission in thin polymer films with a low energy threshold, as reported here, offers hope for the possible development of solid-state electrically pumped polymer lasers The absorbance, emission, and fluorescence spectra of the blue-light emitting copolymer poly[dimethylsilylene-p-phenylene-vinylene-(2,5-di-n-octyl-p-phenylene)-vinytene-p-phenylene] are presented and discussed. It is suggested that lasing in the superradiant regime occurs as a result of the combination of optically induced net gain and waveguiding in the thin film