Cosmic strings were postulated by Kibble in 1976 and, from a theoretical point of view, their existence finds support in modern superstring theories, both in compactification models and in theories with extended additional dimensions. Their eventual discovery would lead to significant advances in both cosmology and fundamental physics. One of the most effective ways to detect cosmic strings is through their lensing signatures which appear to be significantly different from those introduced by standard lenses (i.e. compact clumps of matter). In 2003, the discovery of the peculiar object CSL‐1 raised the interest of the physics community since its morphology and spectral features strongly argued in favour of it being the first case of gravitational lensing by a cosmic string. In this paper we provide a detailed description of the expected observational effects of a cosmic string and show, by means of simulations, the lensing signatures produced on background galaxies. While high angular resolution images obtained with Hubble Space Telescope, revealed that CSL‐1 is a pair of interacting ellipticals at redshift 0.46, it represents a useful lesson to plan future surveys.

The Capodimonte–Sternberg–Lens candidate no. 1 is an extragalactic double source detected in the Osservatorio Astronomico di Capodimonte – Deep Field. It can be interpreted either as the chance alignment of two identical galaxies at z= 0.46 or as the first case of gravitational lensing by a cosmic string. Extensive modelling shows in fact that cosmic strings are the only type of lens which (at least at low angular resolution) can produce undistorted double images of a background source. We propose an experimentum crucis to disentangle these two possible explanations. If the lensing by a cosmic string should be confirmed, it would provide the first measurements of energy scale of symmetry breaking and of the energy scale of grand unified theory.

Abstract. The endpoint of black hole evaporation is a very intriguing problem of modern physics. Based on Einstein-dilaton-Gauss-Bonnet four dimensional string gravity model we show that black holes do not disappear and should become relics at the end of the evaporation process. The possibility of experimental detection of such remnant black holes is investigated. If they really exist, these objects could be a considerable part of the non baryonic dark matter in our Universe.

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CSL-1 is a peculiar object (R.A. 2000 = 12 h 23 m 30"5; δ 2000 = −12 • 38 ′ 57"0) which, for its photometric and spectroscopic properties, is possibly the first case of gravitational lensing by a cosmic string. In this paper we present additional evidences, based on medium-high resolution VLT + FORS1 observations, that the spectra of the two components of CSL-1 are identical within a confidence level higher than 98% and the velocity difference of the two components is consistent with zero. This result adds further confidence to the interpretation of the system as a true lens.