This line involves a close examination of the theories of Gravitation. The main idea can be described as follows. In the beggining of the 60's, Feynmann showed that it is possible to describe all the properties of Einstein's General Relativity without recourse to the geometriccal representation, but using instead the usual tools of Field Theory. Several authors since then have examined this field formulation of Gravitation, and they achieved a systematical examination of its classical and quantum properties. As na example, we can cite the work of Deser in1970,and more recently, a revision of thet work by Grischuck, Petrov e Popova (1984). The importance of this formulation succeded in exhibiting some properties of the gravitational field that were hidden, so to say, inthe
geometric representation presented by Einstein. A particularly important property among these is the Equivalence Principle. In a simple way, we can say that this principle states that every form of
matter and radiation (for instance photons) intercact inthe same unique way with gravitation. It is often said that this hypothesis has been tested up to a level of one part in 10^11.
However, we dont have yet any experiment that tests the interaction of the gravitational energy with gravitation itself. In GeneralRelativity, it is assumed that the interaction of gravitation with
itself follows the same principle. The greatest achievement of Feynman and Deser's formulation was precisely to explicit this hypothesis, that extends the range of the Equivalence Principle
further away from the observational limits available. If we simply assume that gravitation does not couple to gravitational energy follwint the Equivalance Principle, we obtain an alternative theory,
competitive with Einstein's General Relativity. Several predictions of this new theory, elaborated by our group, are readically different from those of General Relativity. The main difference
betweenthe two theories is the prediction they make about the velocity of propagation of gravitational waves. If we take into account that sonn we will have at our disposal observations of
gravitational waves, it is of crucial importance to have alternative scenarios available to interpret the results of the observations. The research plan we propose in this line includes: Detailed study
of the properties and solutions of this new theoty of gravitation, mainly those related to compact and cosmological sources. Hamiltonian Formulation Canonical Quantization The problem of
gravitational energy in this theory. Detailed analysis of gravitational wavesin this theory, and specific predictions to be compared with future observations. The last model that we developed
following the abovementioned scenario is published in M.Novello, L.R.de Freitas e V.A.De Lorenci, Annals of Physics 254, 83, 1997. Since then we systematically explored the properties of this
new theory, trying to keep a close contact with observation. We showed that the PPN parameters of the theory are in agreement with those of General Relativity, and consequently the theory
agrees with solar system observations. In fact, the differences are manifest only in the strong field regime, and inthe propagation of gravitational waves. We also studied the latter item, showing that the predictions of our theory drastically differ from those of General Relativity. We are now proceeding with this avenue of research, by the study of the radiation emitted by the binary pulsar in the light of our theory (christened NDL theory), in the post-newtonian approximation,with the quadrupole formula. The detection of gravitational waves has become one of the most important quests of research in gravitation According to General Relativity (GR), the discontinuities in the gravitationalfield must propagate with the velocity of the electromagnetic waves. This is a desirable
property, in the sense that corresponds to a unified causal structure. The NDL theory has stood all the weak-field tests of gravity and is a good alternative to GR. The distinguishing feature of NDL theory is that the propagation of gravitational waves has a velocity different from the velocity of light. We must wait until LIGO and the other observatories are collecting data for this question to be
settled.