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The stransverse mass variable M T 2 was originally proposed for the study of hadron collider events in which N = 2 parent particles are produced and then decay semi-invisibly. Here we consider the generalization to the case of N ≥ 3 semi-invisibly decaying parent particles. We introduce the corresponding class of kinematic variables M TN and illustrate their mathematical properties. Many of the celebrated features of the M T 2 kinematic endpoint are retained in this more general case, including the ability to measure the mass of the invisible daughter particle from the stransverse mass kink. We describe and validate a numerical procedure for computing M TN in practice. We also identify the configurations of visible momenta which result in nontrivial ( M TN ≠ 0) values, and derive a pure phase-space estimate for the fraction of such events for any N. [ABSTRACT FROM AUTHOR]

We show that an instanton with high charge can provoke the creation of extra curvature on the space that holds it. Geometrically, this corresponds to a new surgery operation, which we name grafting. Curvature around a sphere increases by grafting when the charge of an instanton decays. [ABSTRACT FROM AUTHOR]

The existing discrepancy between neutron lifetime measurements in bottle and beam experiments has been interpreted as a sign of the neutron decaying to dark particles. We summarize the current status of this proposal, including a discussion of particle physics models involving such a portal between the Standard Model and a baryonic dark sector. We also review further theoretical developments around this idea and elaborate on the prospects for verifying the neutron dark decay hypothesis in current and upcoming experiments. [ABSTRACT FROM AUTHOR]