On the uniqueness of the non-minimal matter coupling in massive gravity and bigravity

In de Rham-Gabadadze-Tolley (dRGT) massive gravity and bigravity, a non-minimal matter coupling involving both metrics generically re-introduces the Boulware--Deser (BD) ghost. A non-minimal matter coupling via a simple, yet specific composite metric has been proposed, which eliminates the BD ghost below the strong coupling scale. Working explicitly in the metric formulation and for arbitrary spacetime dimensions, we show that this composite metric is the unique consistent non-minimal matter coupling below the strong coupling scale, which emerges out of two diagnostics, namely, absence of Ostrogradski ghosts in the decoupling limit and absence of the BD ghost from matter quantum loop corrections.Comment: v2: references added, matches accepted version in Physics Letters B v1: 6 pages, two-colum

Throughput-Delay Trade-Off for Cognitive Radio Networks: A Convex Optimization Perspective

The throughput-delay trade-off problem for cooperative spectrum sensing (CSS) is investigated. It is proved that the maximum achievable throughput and the minimum transmission delay cannot be obtained simultaneously. An efficient algorithm is proposed to optimize the sensing bandwidth and the final decision threshold jointly such that the throughput is maximized while the delay is constrained. It is demonstrated that convex optimization plays an essential role in solving the problem in an efficient way. Simulation results show that the proposed optimal scheme can significantly improve the throughput of the secondary users (SUs) under the constraint that the delay Quality of Service (QoS) requirements of the SUs are satisfied