IRIS Università degli Studi di Bolognahttps://cris.unibo.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Tue, 19 Oct 2021 00:48:55 GMT2021-10-19T00:48:55Z1041Hawking radiation from acoustic black holes, short distance and backreaction effects.http://hdl.handle.net/11585/30473Titolo: Hawking radiation from acoustic black holes, short distance and backreaction effects.
Abstract: Using the action principle we first review how linear density perturbations (sound waves) in an Eulerian fluid obey a relativistic equation: the d'Alembert equation. This analogy between propagation of sound and that of a massless scalar field in a Lorentzian metric also applies to non-homogeneous flows. In these cases, sound waves effectively propagate in a curved four-dimensional ''acoustic'' metric whose properties are determined by the flow. Using this analogy, we consider regular flows which become supersonic, and show that the acoustic metric behaves like that of a black hole. The analogy is so good that, when considering quantum mechanics, acoustic black holes should produce a thermal flux of Hawking phonons.
We then focus on two interesting questions related to Hawking radiation which are not fully understood in the context of gravitational black holes due to the lack of a theory of quantum gravity. The first concerns the calculation of the modifications of Hawking radiation which are induced by dispersive effects at short distances, i.e., approaching the atomic scale when considering sound. We generalize existing treatments and calculate the modifications caused by the propagation near the black hole horizon. The second question concerns backreaction effects. We return to the Eulerian action, compute second order effects, and show that the backreaction of sound waves on the fluid's flow can be expressed in terms of their stress-energy tensor. Using this result in the context of Hawking radiation, we compute the secular effect on the background flow.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11585/304732005-01-01T00:00:00ZQUANTUM EFFECTS IN ACOUSTIC BLACK HOLES: THE BACKREACTION.http://hdl.handle.net/11585/12461Titolo: QUANTUM EFFECTS IN ACOUSTIC BLACK HOLES: THE BACKREACTION.
Abstract: We investigate the backreaction equations for an acoustic black hole formed in a Laval nozzle under the assumption that the motion of the fluid is one-dimensional. The solution in the near-horizon region shows that as phonons are (thermally) radiated the sonic horizon shrinks and the temperature decreases. This contrasts with the behaviour of Schwarzschild black holes, and is similar to what happens in the evaporation of (near-extremal) Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by appropriate boundary conditions the solution is extended in both the asymptotic regions of the nozzle.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11585/124612005-01-01T00:00:00ZBACKREACTION IN ACOUSTIC BLACK HOLES.http://hdl.handle.net/11585/12491Titolo: BACKREACTION IN ACOUSTIC BLACK HOLES.
Abstract: The backreaction equations for the linearized quantum fluctuations in an acoustic black hole are given. The solution near the horizon, obtained within a dimensional reduction, indicates that acoustic black holes, unlike Schwarzschild ones, get cooler as they radiate phonons. They show remarkable analogies with near-extremal Reissner-Nordstrom black holes.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11585/124912004-01-01T00:00:00ZQuantum stress tensor for extreme 2D Reissner-Nordström black holeshttp://hdl.handle.net/11585/12433Titolo: Quantum stress tensor for extreme 2D Reissner-Nordström black holes
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11585/124332004-01-01T00:00:00Z