Self-Interacting Dark Matter Solves the Final Parsec Problem of Supermassive Black Hole Mergers.

Evidence for a stochastic gravitational wave (GW) background, plausibly originating from the merger of supermassive black holes (SMBHs), is accumulating with observations from pulsar timing arrays. An outstanding question is how inspiraling SMBHs get past the "final parsec" of separation, where they have a tendency to stall before GW emission alone can make the binary coalesce. We argue that dynamical friction from the dark matter (DM) spike surrounding the black holes is sufficient to resolve this puzzle, if the DM has a self-interaction cross section of order cm^{2}/g.

The first limit on invisible decays of mesons comes from LEP.

Motivated by the recent evidence for decays at Belle II, we point out that fully invisible and meson decays are strongly constrained by LEP. A reinterpretation of an old inclusive ALEPH search for -hadron decays with large missing energy allows us to place the limits and , both at CL. The limit is only a factor of 6 looser than the world-leading one provided by the BaBar collaboration, while the one is the first limit in the literature on this decay mode.

New physics searches at kaon and hyperon factories.

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements.