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If there is a population of black holes distributed randomly in space, light rays passing in their vicinity will acquire random phases. In the "two-slit" model of an interferometer this can, for a high density of black holes, lead to a diffusion in the phase difference between the two arms of the interferometer and thus to a loss of coherence or "visibility" in interferometric observations. Hence the existence of "fringe contrast" or "visibility" in interferometric observations can be used to put a limit on the possible presence of black holes along the flight path. We give a formula for this effect and consider its application, particularly for observations in cosmology. Under the assumption that the dark matter consists of primordial black holes, we consider sources at high z , up to the CMB. While the strongest results are for the CMB as the most remote source, more nearby sources at high z lead to similar effects. The effect increases with the baseline, and in the limiting case of the CMB we find that with earth-size baselines a nonzero "visibility" would limit the mass of possible primordial black holes, to approximately M ∕ M ⊙ ≤ 1 0 − 1 . Although such limits would not appear to be as strong as those obtained, say from microlensing, they involve a much different methodology and are dominated by very early times (see Table 1). Longer baselines lead to more stringent limits and in principle with extreme lengths, the method could possibly find positive evidence for primordial black holes. In this case, however, all other kinds of phase averaging would have to be constrained or eliminated. [ABSTRACT FROM AUTHOR]

Advances in high angular resolution astronomy make it conceivable that black hole dark matter could be detected via angular deviation effects. Assuming the dark matter in the galaxy is made of solar mass black holes, there is a nontrivial probability that a line-of-sight through the galaxy, leads to μ arcsec 's deviations, a value that has been discussed for various astronomical projects. In cosmology, the effects are magnified by an increased density at early times and an opening of angles due to redshift. We stress the interest of the resolution in observations on the CMB and emphasize the distinction between this and the power spectrum. If the dark matter is made of primordial black holes, present at the CMB, random deflections of the CMB photons lead to a limit on the angular resolution, approximately 3 × 1 0 − 7 M / M ⊙  rad, with M the mass of the black holes. Using the resolutions of ∼ 1 0 − 3 rad demonstrated in observations of the "acoustic peaks" then implies the limit (M / M ⊙) ≲ 1 0 7 . While this large value seems uninteresting, improved resolutions would lead to significant exclusion limits or conceivably the discovery of primordial black holes. [ABSTRACT FROM AUTHOR]

The description of very high energy proton–proton cross-sections in terms of a "black disc" with an "edge" allows a simple generalization to highest energy proton–nucleus cross-sections. This results in a leading ln2W term and a ln W term whose coefficient depends linearly on the radius of the nucleus (W the c.m. energy). The necessary parameters are determined from the fits to p–p data. Since the coefficient of the ln W term is rather large, it is doubtful that the regime of ln2W dominance can be reached with available energies in accelerators or cosmic rays. However, the ln W term can be relevant for highest energy cosmic rays in the atmosphere, where a large increase for the cross-section on nitrogen is expected. Tests of the theory should be possible by studying the coefficient of ln W at p-nucleus colliders. [ABSTRACT FROM AUTHOR]

Analysis of the data for proton and antiproton scattering leads to a simple picture for very high energy hadronic cross-sections. There is, asymptotically, a simple 'black disc' with a smooth 'edge'. The radius of the 'disc' is expanding logarithmically with energy, while the 'edge' is constant. These conclusions follow from extensive fits to accelerator and cosmic ray data, combined with the observation that a certain combination of elastic and total cross-sections allows extraction of the 'edge'. An interesting feature of the results is that the 'edge' is rather large compared to the 'disc'. This explains the slow approach to 'asymptopia' where the 'disc' finally dominates. [ABSTRACT FROM AUTHOR]

We present our recent experiments on macroscopic tunneling in the quantum regime for underdamped Josephson junctions with different classical-quantum crossover temperatures. These experiments are performed towards the observation of macroscopic quantum coherence in Josephson systems. A new method to measure coherence in a two-level system based on the adiabatic inversion in an rf squid, is presented. This approach could open new perspectives in view of realization of an elementary quantum bit. [ABSTRACT FROM AUTHOR]