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We study the energy-momentum pseudotensor of gravitational waves, and examine the one introduced by Landau-Lifshitz for a general gravitational field and the effective one recently used in literature. In the short-wavelength limit after the Brill-Hartle average, both lead to the same gauge-invariant stress tensor of gravitational waves. For relic gravitational waves in the expanding universe, we examine two forms of pressure, pgw and Pgw, and trace the origin of their difference to a coupling between gravitational waves and the background matter. The difference is shown to be negligibly small for most cosmic expansion stages starting from inflation. We demonstrate that the wave equation is equivalent to the energyconservation equation using the pressure Pgw that includes the mentioned coupling. [ABSTRACT FROM AUTHOR]

We study the radiation produced by an accelerated time delay acting on the left moving modes. Through analysis via the Schrödinger picture, we find that the final state is a two-mode squeezed state of the left moving Unruh modes, implying particle production. We analyze the system from an operational point of view via the use of self-homodyne detection with broadband inertial detectors. We obtain semianalytical solutions that show that the radiation appears decohered when such an inertial observer analyzes the information of the radiation from the accelerated time-delay source. We make a connection with the case of the accelerated mirror. We investigate the operational conditions under which the signal observed by the inertial observer can be purified. [ABSTRACT FROM AUTHOR]

We show that the gravitational quasinormal modes (QNMs) of a Schwarzschild black hole play the role of a multimode squeezer that can generate particles. For a minimally coupled scalar field, the QNMs "squeeze" the initial state of the scalar field (even for the vacuum) and produce scalar particles. The maximal squeezing amplitude is inversely proportional to the cube of the imaginary part of the QNM frequency, implying that the particle generation efficiency is higher for lower decaying QNMs. Our results show that the gravitational perturbations can amplify Hawking radiation. [ABSTRACT FROM AUTHOR]

We propose that the vacuum state of a scalar field around a black hole is a modified Unruh vacuum. In (1+1) dimensions, we show that a free-faller close to such an horizon can be modeled as an inertial observer in a modified Minkowski vacuum. The modification allows for information-leaking correlations at high frequencies. Using a Gaussian detector centered at k0, we find that the expectation value of the number operator for a detector crossing the horizon is proportional to 1/|k0|, implying that the free-faller will observe unbounded numbers of high-energy photons, i.e. a firewall. [ABSTRACT FROM AUTHOR]