Device-independent witnesses of genuine multipartite entanglement and nonlocality for GHZ states and Bell-pair tree

arXiv:2611.15283v1 Announce Type: new Abstract: We derive and compare device-independent witnesses of genuine multipartite entanglement (GME) and genuine multipartite nonlocality (GMNL) for GHZ states and trees of Bell pairs. A binary-outcome family using four global measurement contexts has the tight biseparable bound independent of the number of parties. We distinguish these GME bounds from Svetlichny-hybrid bounds, which permit arbitrary communication within either side of a bipartition. For GHZ states, we also give a $2N$-context GMNL witness and compare it with MABK and Svetlichny tests. For Bell-pair trees, sums of CHSH and chained inequalities certify GME and GMNL, respectively, with explicitly specified input protocols and multi-bit local outputs.