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

New constraints on cosmic polarization rotation from the ACTPol cosmic microwave background B-Mode polarization observation and the BICEP2 constraint update

Recently ACTPol has measured the cosmic microwave background (CMB) B-mode and E-mode polarizations and obtained TE, EE, BB, TB and EB power spectra in the multipole range 225-8725. In our previous paper (Ap. J. 792 (2014) 35 [Paper I]), we have analyzed jointly the results of three experiments on the CMB B-mode polarization -- SPTpol, POLARBEAR and BICEP2 to include in the model, in addition to the gravitational lensing and the inflationary gravitational waves components, also the fluctuation effects induced by the cosmic polarization rotation (CPR), if it exists within the upper limits at the time. In this paper, we fit both the mean CPR angle and its fluctuation from the new ACTPol data, and update our fitting of CPR fluctuations using BICEP2 data taking the new Planck dust measurement results into consideration. We follow the method of Paper I. The mean CPR angle is constrained from the EB correlation power spectra to || < 14 mrad (0.8{\deg}) and the fluctuation (rms) is constrained from the BB correlation power spectra to 1/2 < 29.3 mrad (1.68{\deg}). Assuming that the polarization angle of Tau A does not change from 89.2 to 146 GHz, the ACTPol data give = 1.0 {\pm} 0.63{\deg}. These results suggest that the inclusion of the present ACTPol data is consistent with no CPR detection. With the new Planck dust measurement, we update our fits of the BICEP2 CPR fluctuation constraint to be 32.8 mrad (1.88{\deg}). The joint ACTpol-BICEP2-POLARBEAR CPR fluctuation constraint is 23.7 mrad (1.36{\deg}).Comment: 15 pages, 2 figures, 2 tables, version to match the accepted submission to ApJ. Unfortunately there is a sign error in equation (6b). This propagated to equations (7b) and (8a) and to the results for \alpha_\beta. The errors in the last raw of Table 1 had been overestimated and correcte