A new test of the Einstein equivalence principle

Tutte le teorie metriche di gravitazione, inclusa la relatività generale, sono basate sul principio di equivalenza di Einstein (EEP). Nonostante la sua grande importanza, l’EEP è provato direttamente solo con una precisione assai scarsa (10-4). Tuttavia è possibile provare l’EEP indirettamente, collegandolo con il principio di equivalenza di Galileo, che è provato con grande precisione (10-13). Questo collegamento funziona solo purché non ci sia rotazione del piano di polarizzazione lineare della luce su grandi distanze (la cosiddetta CPR). Quindi la ricerca sulla CPR ha assunto grande importanza ed è stata fatta usando la polarizzazione di radio galassie distanti e del fondo cosmico a micro-onde, finora con esito negativo. Recentemente abbiamo proposto un nuovo metodo per cercare la CPR, usando un particolare tipo di polarizzazione del fondo cosmico.All metric theories of gravity, including general relativity, are based on Einstein’s equivalence principle (EEP). Despite its great importance, the EEP is tested directly only with a fairly low accuracy (10-4). It is nevertheless possible to test the EEP indirectly by connecting it with Galileo’s equivalence principle, which is tested with very high precision (10-13). This connection functions only as long as there is no rotation of the plane of linear polarisation of the light traveling over great distances (the so-called Cosmic Polarization Rotation, CPR). Consequently the search for the CPR has assumed great importance, and has been carried out using the polarisation of distant radio galaxies and of the cosmic microwave background, to date with negative results. Recently we have proposed a new method for seeking the CPR, using a special type of polarisation of the cosmic background

Infrared imaging of WENSS radio sources

We have performed deep imaging in the IR J- and K-bands for three sub-samples of radio sources extracted from the Westerbork Northern Sky Survey, a large low-frequency radio survey containing Ultra Steep Spectrum (USS), Gigahertz Peaked Spectrum (GPS) and Flat Spectrum (FS) sources. We present the results of these IR observations, carried out with the ARcetri Near Infrared CAmera (ARNICA) at the Nordic Optical Telescope (NOT), providing photometric and morphologic information on high redshift radio galaxies and quasars. We find that the radio galaxies contained in our sample do not show the pronounced radio/IR alignment claimed for 3CR sources. IR photometric measurements of the gravitational lens system 1600+434 are also presented.Comment: 8 pages, 54 Postscript figures, to be published in Astronomy and Astrophysics, Supplement Serie