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.Wed, 20 Oct 2021 04:27:06 GMT2021-10-20T04:27:06Z10261Numerical analysis of backreaction in acoustic black holes.http://hdl.handle.net/11585/35553Titolo: Numerical analysis of backreaction in acoustic black holes.
Abstract: Using methods of Quantum Field Theory in curved spacetime, the first order in hbar quantum corrections to the motion of a fluid in an acoustic black hole configuration are numerically computed. These corrections arise from the non linear backreaction of the emitted phonons. Time dependent (isolated system) and equilibrium configurations (hole in a sonic cavity) are both analyzed.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/11585/355532006-01-01T00:00:00ZHawking 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/11585/304732005-01-01T00:00:00ZHawking radiation correlations in Bose-Einstein condensates using quantum field theory in curved spacehttp://hdl.handle.net/11585/266295Titolo: Hawking radiation correlations in Bose-Einstein condensates using quantum field theory in curved space
Abstract: The density-density correlation function is computed for the Bogoliubov pseudoparticles created in a Bose-Einstein condensate undergoing a black hole flow. On the basis of the gravitational analogy, the method used relies only on quantum field theory in curved spacetime techniques. A comparison with the results obtained by ab initio full condensed matter calculations is given, confirming the validity of the approximation used, provided the profile of the flow varies smoothly on scales compared to the condensate healing length.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11585/2662952013-01-01T00:00:00ZAmplifying the Hawking signal in BECshttp://hdl.handle.net/11585/388905.1Titolo: Amplifying the Hawking signal in BECs
Abstract: It is shown that the gray-body factor for a one-dimensional Bose-Einstein condensate (BEC) acoustic black hole with one horizon does not vanish in the low-frequency ($\omega\to 0$) limit. This implies that the analog Hawking radiation is dominated by the emission of an infinite number ($\frac{1}{\omega}$) of soft phonons in contrast with the case of a Schwarzschild black hole where the gray-body factor vanishes as $\omega\to 0$ and the spectrum is not dominated by low-energy particles. The infrared behaviors of certain correlation functions are also discussed
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/388905.12014-01-01T00:00:00ZFourth derivative gravity in the auxiliary fields representation and application to the black hole stabilityhttp://hdl.handle.net/11585/541466Titolo: Fourth derivative gravity in the auxiliary fields representation and application to the black hole stability
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11585/5414662015-01-01T00:00:00ZQUANTUM 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/11585/124612005-01-01T00:00:00ZHawking effect in BEC's acoustic white holeshttp://hdl.handle.net/11585/266294Titolo: Hawking effect in BEC's acoustic white holes
Abstract: Bogoliubov pseudoparticle creation in a BEC undergoing a WH-like flow is investigated analytically in the case of a one-dimensional geometry with stepwise homogeneous regions. Comparison of the results with those corresponding to a BH flow is performed. The implications for the analogous gravitational problem is discussed.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11585/2662942013-01-01T00:00:00ZNumerical observation of Hawking radiation from acoustic black holes in atomic BECs.http://hdl.handle.net/11585/67547.1Titolo: Numerical observation of Hawking radiation from acoustic black holes in atomic BECs.
Abstract: We report numerical evidence of Hawking emission of Bogoliubov phonons from a sonic horizon in a flowing one-dimensional atomic Bose-Einstein condensate. The presence of Hawking radiation is revealed from peculiar long-range patterns in the density-density correlation function of the gas. Quantitative agreement between our fully microscopic calculations and the prediction of analog models is obtained in the hydrodynamic limit. New features are predicted and the robustness of the Hawking signal against a finite temperature discussed.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/11585/67547.12008-01-01T00:00:00ZParticle production in the interiors of acoustic black holeshttp://hdl.handle.net/11585/723740.2Titolo: Particle production in the interiors of acoustic black holes
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11585/723740.22019-01-01T00:00:00ZGray body factor and infrared divergences in BEC acoustic black holeshttp://hdl.handle.net/11585/388899Titolo: Gray body factor and infrared divergences in BEC acoustic black holes
Abstract: It is shown that the gray-body factor for a one-dimensional Bose-Einstein condensate (BEC) acoustic black hole with one horizon does not vanish in the low-frequency ($\omega\to 0$) limit. This implies that the analog Hawking radiation is dominated by the emission of an infinite number ($\frac{1}{\omega}$) of soft phonons in contrast with the case of a Schwarzschild black hole where the gray-body factor vanishes as $\omega\to 0$ and the spectrum is not dominated by low-energy particles. The infrared behaviors of certain correlation functions are also discussed.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/3888992014-01-01T00:00:00Z