Self-existing objects and auto-generated information in chronology-violating space-times : a philosophical discussion

Consistency demands an harmony between local and global affairs that excludes grandfather-like paradoxes. However, self-existing objects trapped in CTCs are not seemingly avoided by the standard interpretation of this principle, usually constrained to a dynamical framework. In this paper we discuss whether we are committed to accept an ontology with self-existing objects if CTCs actually occur in the universe. In addition, the epistemological status of the Principle of SelfConsistency is analyzed and a discussion on the information flux through CTCs is presented.Fil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Torres, Diego F.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentin

On hadronic beam models for quasars and microquasars

Most of the hadronic jet models for quasars (QSOs) and microquasars (MQs) found in literature represent beams of particles (e.g. protons). These particles interact with the matter in the stellar wind of the companion star in the system or with crossing clouds, generating gamma-rays via proton-proton processes. Our aim is to derive the particle distribution in the jet as seen by the observer, so that proper computation of the $\gamma$-ray and neutrino yields can be done. We use relativistic invariants to obtain the transformed expressions in the case of a power-law and power-law with a cutoff particle distribution in the beam. We compare with previous expressions used earlier in the literature. We show that formerly used expressions for the particle distributions in the beam as seen by the observer are in error, differences being strongly dependent on the viewing angle. For example, for $\Gamma =10$ ($\Gamma$ is the Lorentz factor of the blob) and angles larger than $\sim 20^o$, the earlier-used calculation entails an over-prediction (order of magnitude or more) of the proton spectra for $E>\Gamma mc^2$, whereas it always over-predicts (two orders of magnitude) the proton spectrum at lower energies, disregarding the viewing angle. All the results for photon and neutrino fluxes in hadronic models in beams that have made use of the earlier calculation are affected. Given that correct gamma-ray fluxes will be in almost any case significantly diminished in comparison with published results, and that the time of observations in Cherenkov facilities grows with the square of the flux-reduction factor in a statistically limited result, the possibility of observing hadronic beams is undermined.Comment: Accepted for publication in A&A Letter

Chromaticity effects in microlensing by wormholes

Chromaticity effects introduced by the finite source size in microlensing events by presumed natural wormholes are studied. It is shown that these effects provide a specific signature that allow to discriminate between ordinary and negative mass lenses through the spectral analysis of the microlensing events. Both galactic and extragalactic situations are discussed.Comment: To appear in Modern Physics Letters A, 200

On the time variability of gamma-ray sources: A numerical analysis of variability indices

We present a Monte Carlo analysis of the recently introduced variability indices $\tau$ (Tompkins 1999) and $I$ (Zhang et al. 2000 & Torres et al. 2001) for $\gamma$-ray sources. We explore different variability criteria and prove that these two indices, despite the very different approaches used to compute them, are statistically correlated (5 to 7$\sigma$). This conclusion is maintained also for the subset of AGNs and high latitude ($|b|>10$ deg) sources, whereas the correlation is lowered for the low latitude ones, where the influence of the diffuse galactic emission background is strong.Comment: Small changes to match published version in Astronomische Nachrichten (2001). Paper accepted in July 200

High-energy gamma-rays from stellar associations

It is proposed that TeV gamma-rays and neutrinos can be produced by cosmic rays (CRs) through hadronic interactions in the innermost parts of the winds of massive O and B stars. Convection prevents low-energy particles from penetrating into the wind, leading to an absence of MeV-GeV counterparts. It is argued that groups of stars located close to the CR acceleration sites in OB stellar associations may be detectable by ground-based Cherenkov telescopes.Comment: 10 pages, 1 figure. Accepted for publication in Astrophysical Journal Letter

On the possibility of an astronomical detection of chromaticity effects in microlensing by wormhole-like objects

We study the colour changes induced by blending in a wormhole-like microlensing scenario with extended sources. The results are compared with those obtained for limb darkening. We assess the possibility of an actual detection of the colour curve using the difference image analysis method.Comment: Accepted for publication in Modern Physics Letters A. 13 report pages, 7 figure