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[en] This discussion between 2 physicists G. Chardin and L. Blanchet sheds light on a model of anti-gravitation for antimatter. According to the equivalence principle of general relativity, any body falls the same way in a gravitational field whatever its nature: matter or antimatter. This new model studies the consequences of a different behavior of antimatter when submitted to gravitation. A negative mass for antimatter could explain the acceleration of universe expansion without the need for a cosmological constant or black energy. This model gives the right age for the universe and can explain primordial nucleosynthesis on a longer time period: 40 years instead of 3 minutes for the standard model. The future experiments Gbar, Alpha-g and Aegis that will be performed at CERN, will clarify the behaviour of anti-hydrogen toward gravity, and will be a test of this new model. (A.C.)
[en] We describe a Galilean test of the weak equivalence principle, to be conducted during the free fall portion of a sounding rocket flight. The test of a single pair of substances is aimed at a measurement uncertainty of σ(η) < 10-16 after averaging the results of eight separate drops. The weak equivalence principle measurement is made with a set of four laser gauges that are expected to achieve 0.1 pm Hz-1/2. The discovery of a violation (η ≠ 0) would have profound implications for physics, astrophysics and cosmology.
[en] We consider a simple Atwood machine consisting of a massless frictionless pulley no. 0 supporting two masses m1 and m2 connected by a massless flexible string. We show that the string that supports massless pulley no. 0 ''thinks'' it is simply supporting a mass m0, with m0 = 4m1m2/(m1+m2). This result, together with Einstein's equivalence principle, allows us to solve easily those compound Atwood machines created by replacing one or both of m1 and m2 in machine no. 0 by an Atwood machine. We may then replacing the masses in these new machines by machines, etc. The complete solution can be written down immediately, without solving simultaneous equations. Finally we give the effective mass of an Atwood machine whose pulley has nonzero mass and moment of inertia
[en] We discuss the possibility of testing the principle of equivalence with solar neutrinos. If there exists a violation of the equivalence principle quarks and leptons with different flavors may not universally couple with gravity. The method we discuss employs a quantum mechanical phenomenon of neutrino oscillation to probe into the non-university of the gravitational couplings of neutrinos. We develop an appropriate formalism to deal with neutrino propagation under the weak gravitational fields of the sun in the presence of the flavor mixing. We point out that solar neutrino observation by the next generation water Cherenkov detectors can improve the existing bound on violation of the equivalence principle by 3-4 orders of magnitude if the nonadiabatic Mikheyev-Smirnov-Wolfenstein mechanism is the solution to the solar neutrino problem
[en] It is proved that two Chevalley groups with indecomposable root systems of rank over commutative rings (which contain in addition for the types , , , , and , and for the type ) are isomorphic or elementarily equivalent if and only if the corresponding root systems coincide, the weight lattices of the representation of the Lie algebra coincide, and the rings are isomorphic or elementarily equivalent, respectively. The isomorphisms of adjoint (elementary) Chevalley groups over the rings of the above types are also described. Bibliography: 25 titles. (paper)