
Anderson, P. R., Balbinot, R., Fabbri, A., & Parentani, R. (2014). Graybody factor and infrared divergences in 1D BEC acoustic black holes. Phys. Rev. D, 90(10), 104044–6pp.
Abstract: It is shown that the graybody factor for a onedimensional elongated BoseEinstein condensate (BEC) acoustic black hole with one horizon does not vanish in the lowfrequency (omega > 0) limit. This implies that the analog Hawking radiation is dominated by the emission of an infinite number (1/omega) of soft phonons in contrast with the case of a Schwarzschild black hole where the graybody factor vanishes as omega > 0 and the spectrum is not dominated by lowenergy particles. The infrared behaviors of certain correlation functions are also discussed.



Anderson, P. R., Balbinot, R., Fabbri, A., & Parentani, R. (2013). Hawking radiation correlations in BoseEinstein condensates using quantum field theory in curved space. Phys. Rev. D, 87(12), 124018–18pp.
Abstract: The densitydensity correlation function is computed for the Bogoliubov pseudoparticles created in a BoseEinstein 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.



Anderson, P. R., Fabbri, A., & Balbinot, R. (2015). Low frequency graybody factors and infrared divergences: Rigorous results. Phys. Rev. D, 91(6), 064061–18pp.
Abstract: Formal solutions to the mode equations for both spherically symmetric black holes and BoseEinstein condensate acoustic black holes are obtained by writing the spatial part of the mode equation as a linear Volterra integral equation of the second kind. The solutions work for a massless minimally coupled scalar field in the swave or zero angular momentum sector for a spherically symmetric black hole and in the longitudinal sector of a onedimensional BoseEinstein condensate acoustic black hole. These solutions are used to obtain in a rigorous way analytic expressions for the scattering coefficients and graybody factors in the zero frequency limit. They are also used to study the infrared behaviors of the symmetric twopoint function and two functions derived from it: the pointsplit stressenergy tensor for the massless minimally coupled scalar field in Schwarzschildde Sitter spacetime and the densitydensity correlation function for a BoseEinstein condensate acoustic black hole.



Balbinot, R., Carusotto, I., Fabbri, A., & Recati, A. (2010). Testing Hawking Particle Creation By Black Holes Through Correlation Measurements. Int. J. Mod. Phys. D, 19(14), 2371–2377.
Abstract: Hawking's prediction of thermal radiation by black holes has been shown by Unruh to be expected also in condensed matter systems. We show here that in a black holelike configuration realized in a BEC this particlecreation does indeed take place and can be unambiguously identified via a characteristic pattern in the densitydensity correlations. This opens the concrete possibility of the experimental verification of this effect.



Balbinot, R., & Fabbri, A. (2024). The Unruh Vacuum and the “InVacuum” in ReissnerNordström Spacetime. Universe, 10(1), 18–14pp.
Abstract: The Unruh vacuum is widely used as a quantum state to describe black hole evaporation since, near the horizon, it reproduces the physical state of a quantum field, the socalled “invacuum”, in the case where a black hole is formed by gravitational collapse. We examine the relation between these two quantum states in the background spacetime of a ReissnerNordstrom black hole (both extremal and not), highlighting the similarities and striking differences.



Balbinot, R., & Fabbri, A. (2023). Quantum energy momentum tensor and equal time correlations in a ReissnerNordström black hole. Phys. Rev. D, 108, 045004–9pp.
Abstract: We consider a ReissnerNordström black hole formed by the collapse of a charged null shell. The renormalized expectation values of the energymomentum tensor operator for a massless scalar field propagating in the twodimensional section of this spacetime are given. We then analyze the acrossthehorizon correlations of the related energy density operator for freefalling observers to reveal the correlations between the Hawking particles and their interior partners.



Balbinot, R., & Fabbri, A. (2023). The Hawking Effect in the ParticlesPartners Correlations. Physics, 5(4), 968–982.
Abstract: We analyze the correlations functions across the horizon in Hawking black hole radiation to reveal the correlations between Hawking particles and their partners. The effects of the underlying spacetime on this are shown in various examples ranging from acoustic black holes to regular black holes.



Balbinot, R., & Fabbri, A. (2022). Quantum correlations across the horizon in acoustic and gravitational black holes. Phys. Rev. D, 105(4), 045010–20pp.
Abstract: We investigate, within the framework of quantum field theory in curved space, the correlations across the horizon of a black hole in order to highlight the particlepartner pair creation mechanism at the origin of Hawking radiation. The analysis concerns both acoustic black holes, formed by BoseEinstein condensates, and gravitational black holes. More precisely, we have considered a typical acoustic black hole metric with two asymptotic homogeneous regions and the Schwarzschild metric as describing a gravitational black hole. By considering equaltime correlation functions, we find a striking disagreement between the two cases: the expected characteristic peak centered along the trajectories of the Hawking particles and their partners seems to appear only for the acoustic black hole and not for the gravitational Schwarzschild one. The reason for that is the existence of a quantum atmosphere displaced from the horizon as the locus of origin of Hawking radiation together, and this is the crucial aspect, with the presence of a central singularity in the gravitational case swallowing everything is trapped inside the horizon. Correlations, however, are not absent in the gravitational case; to see them, one simply has to consider correlation functions at unequal times, which indeed display the expected peak.



Balbinot, R., & Fabbri, A. (2014). Amplifying the Hawking Signal in BECs. Adv. High. Energy Phys., 2014, 713574–8pp.
Abstract: We consider simple models of BosepEinstein condensates to study analog pairpcreation effects, namely, the Hawking effect from acoustic black holes and the dynamical Casimir effect in rapidly timepdependent backgrounds. We also focus on a proposal by Cornell to amplify the Hawking signal in densitydensity correlators by reducing the atoms' interactions shortly before measurements are made.



Balbinot, R., Fabbri, A., Dudley, R. A., & Anderson, P. R. (2019). Particle production in the interiors of acoustic black holes. Phys. Rev. D, 100(10), 105021–13pp.
Abstract: Phonon creation inside the horizons of acoustic black holes is investigated using two simple toy models. It is shown that, unlike what occurs in the exterior regions, the spectrum is not thermal. This nonthermality is due to the anomalous scattering that occurs in the interior regions.

