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Roberto Balbinot

Publications and source records attributed to Roberto Balbinot.

At least 19 recordsLinked to original sources
arXiv2026

Sonic black holes with thick horizons in BECs

We consider simple one dimensional models of acoustic black holes formed by Bose-Einstein condensates where the flow is stepwise homogeneous. We shall concentrate on the case in which an extended sonic region is present, i.e. a region where the flow velocity equals exactly the speed of sound. These models can be thought of as acoustic black holes with a thick horizon. Particular attention will be devoted to the number of created particles and to the density-density correlation functions, these latter being at present time the experimental tool to identify Hawking like radiation in acoustic black holes.

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arXiv2025

Some considerations on BEC analogue black holes

In this paper, dedicated to the memory of A. Aurilia, we will review some basic features of Hawking's black hole radiation and compare them with the corresponding ones present in Bose-Einstein condensate analogue black holes.

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arXiv2025

Backreaction equations for 1+1 dimensional BEC sonic black holes

As in the gravitational context, one of the most challenging open question in analogue black holes formed in Bose-Einstein condensates concerns the backreaction of Hawking-like radiation on the condensate and its subsequent evolution. In this work we derive the basic equations describing this backreaction within the density-phase formalism, which avoids infrared divergences and is particularly well suited to one-dimensional configurations.

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arXiv2025

Acoustic black holes in BECs with an extended sonic region

In the context of Hawking-like radiation in sonic black holes formed by BECs we investigate the modifications of the emission spectrum caused by a finite width of the sonic transition region connecting the subsonic to supersonic flow.

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arXiv2024

Looking for traces of Hawking radiation in correlation functions of BEC acoustic black holes

Renaud Parentani was one of the leading figures in Quantum Field Theory in curved spacetime, in particular concerning its applications to Hawking-like radiation in analogue models. In this paper dedicated to him, we discuss the characteristic features appearing in the correlation functions in an acoustic black hole formed by a Bose-Einstein condensate, considered as signature of the presence of Hawking radiation in this system.

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arXiv2023

The Unruh vacuum and the in-vacuum in the Reissner-Nordstr\"om spacetime

The Unruh vacuum is widely used as quantum state to describe black hole evaporation since near the horizon it reproduces the physical state of a quantum field, the so called in-vacuum, in the case the black hole is formed by gravitational collapse. We examine the relation between these two quantum states in the background spacetime of a Reissner-Nordstr\"om black hole (both extremal and not) highlighting similarities and striking differences.

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arXiv2023

The Hawking effect in the particles-partners correlations

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 space-time on this are shown in various examples ranging from acoustic black holes to regular black holes.

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arXiv2023

Quantum energy momentum tensor and equal time correlations in a Reissner-Nordstr\"om black hole

We consider a Reissner-Nordstr\"om black hole formed by the collapse of a charged null shell. The renormalised expectation values of the energy momentum tensor operator for a massless scalar field propagating in the 2D section of this spacetime are given. We then analyse the across the horizon correlations of the related energy density operator for free falling observers to reveal the correlations between the Hawking particles and their interior partners.

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arXiv2021

Quantum correlations across the horizon in acoustic and gravitational Black Holes

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 particle-partner pair creation mechanism at the origin of Hawking radiation. The analysis concerns both acoustic black holes, formed by Bose-Einstein 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 equal time 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 has simply to consider correlation functions at unequal times which indeed display the expected peak.

gr-qc↗
arXiv2020

Correlations between a Hawking particle and its partner in a 1+1D Bose-Einstein condensate analog black hole

The Fourier transform of the density-density correlation function in a Bose-Einstein condensate (BEC) analog black hole is a useful tool to investigate correlations between the Hawking particles and their partners. It can be expressed in terms of $\langle ^{\text{out}}\hat{a}_{\text{up}}^{\text{ext}}\ ^{\text{out}}\hat{a}_{\text{up}}^{\text{int}} \rangle$, where $^{\text{out}}\hat{a}_{\text{up}}^{\text{ext}}$ is the annihilation operator for the Hawking particle and $^{\text{out}}\hat{a}_{\text{up}}^{\text{int}} $ is the corresponding one for the partner. This basic quantity is calculated for three different models for the BEC flow. It is shown that in each model the inclusion of the effective potential in the mode equations makes a significant difference. Furthermore, particle production induced by this effective potential in the interior of the black hole is studied for each model and shown to be nonthermal. An interesting peak that is related to the particle production and is present in some models is discussed.

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arXiv2020

Ramp-up of Hawking radiation in Bose-Einstein condensate analogue black holes

Inspired by a recent experiment by Steinhauer and co-workers, we present a simple model which describes the formation of an acoustic black hole in a Bose-Einstein condensate, allowing an analytical computation of the evolution in time of the corresponding density-density correlator. We show the emergence of analog Hawking radiation out of a "quantum atmosphere" region significantly displaced from the horizon. This is quantitatively studied both at $T=0$ and even in the presence of an initial temperature T, as is always the case experimentally.

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arXiv2019

Particle Production in the Interiors of Acoustic Black Holes

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 non-thermality is due to the anomalous scattering that occurs in the interior regions.

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arXiv2016

Scattering coefficients and gray-body factor for 1D BEC acoustic black holes: exact results

A complete set of exact analytic solutions to the mode equation is found in the region exterior to the acoustic horizon for a class of 1D Bose-Einstein condensate (BEC) acoustic black holes. From these, analytic expressions for the scattering coefficients and gray-body factor are obtained. The results are used to verify previous predictions regarding the behaviors of the scattering coefficients and gray-body factor in the low frequency limit.

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arXiv2015

Fourth derivative gravity in the auxiliary fields representation and application to the black hole stability

We consider an auxiliary fields formulation for the general fourth-order gravity on an arbitrary curved background. The case of a Ricci-flat background is elaborated in full details and it is shown that there is an equivalence with the standard metric formulation. At the same time, using auxiliary fields helps to make perturbations to look simpler and the results more clear. As an application we reconsider the linear perturbations for the classical Schwarzschild solution. We also briefly discuss the relation to the effect of massive unphysical ghosts in the theory.

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arXiv2015

Gray-body factor and infrared divergences in 1D BEC acoustic black holes

It is shown that the gray-body factor for a one-dimensional elongated Bose-Einstein condensate (BEC) acoustic black hole with one horizon does not vanish in the low-frequency ($ω\to 0$) limit. This implies that the analog Hawking radiation is dominated by the emission of an infinite number ($\frac{1}ω$) of soft phonons in contrast with the case of a Schwarzschild black hole where the gray-body factor vanishes as $ω\to 0$ and the spectrum is not dominated by low-energy particles. The infrared behaviors of certain correlation functions are also discussed.

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arXiv2015

Low frequency gray-body factors and infrared divergences: rigorous results

Formal solutions to the mode equations for both spherically symmetric black holes and Bose-Einstein 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 s-wave or zero angular momentum sector for a spherically symmetric black hole and in the longitudinal sector of a 1D Bose-Einstein condensate acoustic black hole. These solutions are used to obtain in a rigorous way analytic expressions for the scattering coefficients and gray-body factors in the zero frequency limit. They are also used to study the infrared behaviors of the symmetric two-point function and two functions derived from it: the point-split stress-energy tensor for the massless minimally coupled scalar field in Schwarzschild-de Sitter spacetime and the density-density correlation function for a Bose-Einstein condensate acoustic black hole.

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