Binary Coalescences as Sources of Ultrahigh-Energy Cosmic Rays.

Binary coalescences are known sources of gravitational waves (GWs) and they encompass combinations of black holes (BHs) and neutron stars (NSs). Here we show that when BHs are embedded in magnetic fields (B's) larger than approximately 10^{10}  G, charged particles colliding around their event horizons can easily have center-of-mass energies in the range of ultrahigh energies (≳10^{18}  eV) and become more likely to escape. Such B-embedding and high-energy particles can take place in BH-NS binaries, or even in BH-BH binaries with one of the BHs being charged (with charge-to-mass ratios as small as 10^{-5}, which do not change GW waveforms) and having a residual accretion disk.

Satellite Test of the Equivalence Principle as a Probe of Modified Newtonian Dynamics.

The proposed satellite test of the equivalence principle (STEP) will detect possible violations of the weak equivalence principle by measuring relative accelerations between test masses of different composition with a precision of one part in 10^{18}. A serendipitous by-product of the experimental design is that the absolute or common-mode acceleration of the test masses is also measured to high precision as they oscillate along a common axis under the influence of restoring forces produced by the position sensor currents, which in drag-free mode lead to Newtonian accelerations as small as 10^{-14}  g. This is deep inside the low-acceleration regime where modified Newtonian dynamics (MOND) diverges strongly from the Newtonian limit of general relativity.