Observers and the mystery of electrical energy loss in the quantum-critical QCD

The subject of observer-independent energy loss in the quantum-critical QCD is still a mystery and physicists are still trying to understand how and when energy is lost. We investigate the problem by using systematic techniques of quantum field theory, and we show that the observer-induced energy loss can be understood in terms of the entanglement entropy and the entanglement entropy for quantum-critical systems. We also show that the entanglement entropy in the quantum-critical QCD can be computed using the constant-energy method.