On the dynamics of correlations in Scaling limits of interacting particle systems

In this work, we analyze the properties of two-particle correlations in the weak-coupling and plasma limit of interacting particle systems motivated by Bogolyubov's formal derivation of kinetic equations. We prove that the leading order evolution in the weak-coupling scaling limit is stable on the macroscopic timescale, and yields the nonlinear Landau equation as kinetic equation. This result shows the transition from the non-Markovian dynamics of the interacting particle system to the Markovian, parabolic evolution in the kinetic limit. Since the system is non-dissipative before taking the limit, we introduce a time-averaged notion of stability to derive an a priori estimate on the solution. Moreover, we prove the global stability of the truncated correlation function in the plasma limit, for a time independent background distribution and soft potentials. In the case of systems with Coulombian interaction, we prove the onset of the Debye screening length and show that the limit evolution is driven by the interaction of particles with impact parameter much smaller than the Debye length

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements