L. A. Ostrovsky1 and Y. A. Stepanyants2
1University of Colorado Boulder, Boulder, Colorado, USA;
2School of Sciences, University of Southern Queensland, Toowoomba, Australia.
The concept of “negative energy waves” (NEW) is discussed in application mostly to the waves in fluids. Historically, the existence of oscillators with negative energy was apparently first noted by H. Lamb in his work of 1907. A process involving a NEW was described by W. Heisenberg in his Ph.D. Thesis of 1923. L. Chu was the first who introduced the term NEW in 1951 in electronics. Later, this concept was introduced in hydrodynamics (B. Benjamin, 1963) and plasma physics (B. Kadomtsev et al., 1964). It is also used in quantum field theory (after the discovery of positrons by P. Dirac in 1928) and general relativity (after the possibility of radiation from black holes was shown by S. Hawking in 1974). In essence, NEW can exist in non-equilibrium media capable of transferring energy to the waves. In hydrodynamics and acoustics, the most common source of such waves is a fluid flow that can potentially be unstable.
In this presentation, we briefly outline the concept of NEW and explain how NEW can lead to instabilities due to dissipation or the coupling with waves of positive energy. Specific problems to be mentioned include wave generation in shear flows radiative instability when internal waves are radiated from a shear flow supporting NEW. We also consider nonlinear phenomena with the participation of NEW, including the explosive instability in a resonant wave triplet and amplification of solitons. In conclusion, we briefly describe hydrodynamic experiments involving a NEW and make some estimates in application to oceanic waves.