Modify-and-Forward for Securing Cooperative Relay Communications

We proposed a new physical layer technique that can enhance the security of cooperative relay communications. The proposed approach modifies the decoded message at the relay according to the unique channel state between the relay and the destination such that the destination can utilize the modified message to its advantage while the eavesdropper cannot. We present a practical method for securely sharing the modification rule between the legitimate partners and present the secrecy outage probability in a quasi-static fading channel. It is demonstrated that the proposed scheme can provide a significant improvement over other schemes when the relay can successfully decode the source message.Comment: IEEE International Zurich Seminar on Communications, Feb. 201

Probing the Vacuum Structure of Spacetime

We explore the question of how to probe the vacuum structure of space time by a massive scalar field through interaction with background gravitons. Using the $\Gamma$-regularization for the in-/out-state formalism, we find the effective action of a scalar field in a conformally, asymptotically flat spacetime and a four-dimensional de Sitter space, which is a gravitational analog of the Heisenberg-Euler and Schwinger effective action for a charged scalar in a constant electric field. The effective action is nonperturbative in that it sums all one-loop diagrams with arbitrary number of external lines of gravitons. The massive scalar field becomes unstable due to particle production, the effective action has an imaginary part that determines the decay rate of the vacuum, and the out-vacuum is unitarily inequivalent to the in-vacuum.Comment: LaTex 13 pages, no figure; contributed to the 2nd Galileo-Xu Guangqi Meeting, Italy, July 12-17, 201

Particle Production from Geometric Transition in Expanding Universe

The geometric transitions from the evolution in the complex plane of time provide channels for particle production for a quantum field in expanding universes. The production rate for one pair is obtained by squaring and summing the scattering matrix between the in-vacuum and the transported one over all possible independent closed paths of winding number 1.Comment: Latex 4 pages, 1 figure; Proceedings of APPC12, to be published in J. Phys. Soc. Japan, Supplemen