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We discuss the possible influence of a cosmic magnetic field on the macroscopic quantum tunneling process associated, in a cosmological context, to the decay of the "false vacuum." We find a close analogy with the effects of an external magnetic field applied to a Josephson junction in the context of low-temperature/high-temperature superconducting devices., 4 pages, 1 pdf figure. Added references and an inset in Fig. 1, results unchanged. To appear in Phys. Rev. D (Brief Report)

We study classical resonant activation (CRA) for a Josephson junction embedded in a shell circuit consisting of one capacitive and one inductive element. The low dissipation quality factor of this device is calculated analytically at the fundamental frequency for two different models of the shell circuit. From our numerical results it emerges that CRA and energy level quantization (ELQ) are distinct processes that can be distinguished in measurements on Josephson devices at low temperatures. CRA at subharmonic frequencies is a highly nonlinear process very different from the corresponding quantum multiphoton process. These results are relevant for the interpretation of a recent experiment on ELQ in high-temperature superconductors Josephson junctions.

Recent experiments on high-temperature superconductors show paramagnetic behavior localized at grain boundaries (GB). This paramagnetism can be attributed to the presence unconventional d-wave induced $\pi$-junctions. By modeling the GB as an array of $\pi$ and conventional Josephson junction we determine the conditions of the occurrence of the paramagnetic behavior., Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett