Speakers and Participants

Erik Aurell (Stockholm University)

"What is being disorganized in a gravitational collapse to a black hole?"

The Bekenstein-Hawking entropy of a black hole is a central quantity in modern physics. In the simplest setting of a non-rotating electrically neutral black hole (Schwarzschild geometry) such an entropy turns out to be proportional to the mass squared of the black hole. Therefore, assuming that mass is proportional to volume, black-hole entropy is super extensive. This means that, for a large enough mass, the corresponding entropy will become larger than the entropy of any normal physical body that could have given rise to the black hole. Just to make an example, if a star like the sun could collapse to a black hole its entropy would increase about 20 orders of magnitude. From which degrees of freedom does this excess entropy come from? The existence of such a super-extensive entropy seems hard to be reconciled with the definition of entropy from Boltzmann's formula S=log(W) . Which is the phase space volume W that gives rise to such a large entropy? Why is it so big and which degrees of freedom does it take into account? In the present talk I will frame the black-hole entropy problem in the context of statistical mechanics, presenting some of the points of view which can be found in the current literature, drawing some conclusions but also leaving some open questions.

Nicola Bartolo (University of Padova)

"Primordial non-Gaussianity and quantum decoherence on cosmological scales"

Cosmic Inflation crucially explains the origin of structures in the Universe starting from microscopic quantum fluctuations, and with the same mechanism it also predicts the production of a stochastic background of gravitational waves out of vacuum quantum fluctuations of the metric tensor describing gravity. On the other hand, the structures we see in the Universe are classical objects, requiring a quantum-to-classical transition of the primordial perturbations that originated from inflation. This is a long-standing open question for inflation. It can be addressed for example with decoherence of open quantum systems on cosmological scales. In this talk I will focus on possible signatures that such a transition can induce on primordial quantum correlators, focusing in particular on primordial non-Gaussianity, that in the last 15 years has emerged as a one of the most powerful precision-tests of ​the inflationary mechanism.

Angelo Bassi (University of Trieste)

"Spontaneous wave function collapse models"

Quantum mechanics is grounded on the superposition principle, which is the source both of its tremendous success and technological power, as well as of the problems in understanding it. The reason why superpositions do not propagate from the microscopic to the macroscopic world are subject to debate. Spontaneous wave function collapse models have been formulated to take into account a progressive breakdown of quantum superpositions when systems are large enough; they do so by modifying the Schrödinger dynamics, and therefore they are empirically testable. Deviations are tiny, and require precision measurements. I will review collapse models, together the most recent experimental tests.

Massimo Bianchi (Tor Vergata, University of Rome)

"String foot-prints on gravitational waves signals: can we tell a fuzzball from a black hole?"

After reviewing the fuzzball proposal as a string theory solution to long-standing paradoxes in black-holes physics, we will argue that certain fuzzball observables may not average to the corresponding values for classical black holes, which are not allowed “states” at the quantum level. In particular we will consider multi-polar structures, quasinormal modes, tidal deformations and gravitational memory effects and discuss how string corrections can be used to discriminate fuzz-balls from black holes.

Lapo Casetti (University of Florence)

"Statistical physics with long-range interactions: challenges and opportunities"

Many physical systems of astrophysical and cosmological interest have a large number of degrees of freedom, so that it would be natural to approach them using the toolbox of statistical physics. However, gravity is the dominant interaction in most of these systems, and it is long-ranged. The energy of a system with long-range interactions is not additive: therefore, some of the most basic results of statistical physics and thermodynamics, taken for granted when dealing with condensed matter, no longer hold. At equilibrium, different statistical ensembles are no longer equivalent (e.g., equilibrium states at constant energy are different from states at constant temperature) and equilibrium thermodynamics no longer holds (at least, in the usual form). Out-of-equilibrium physics is even more challenging: relaxation times to thermal equilibrium (maximum entropy states) grow with the size of the system, diverging when the number of constituents becomes infinite, so that many astrophysical systems did not have the time to relax to equilibrium in the thermodynamic sense; yet, when a system starts far from equilibrium, it often relaxes to non-thermal stationary states, and this relaxation is both fast (i.e., its timescale does not depend on the system's size) and non-collisional (so that it does not necessarily lead to maximum-entropy states). No general rule is known to predict the properties of the end states of this relaxation, that are those we expect to observe in most cases. We shall review some of the general results and open problems and discuss their relevance to systems where gravity is the dominant interaction.

Kyriakos Destounis (University of Tuebingen)

"Gravitational-wave astrophysics with the Laser Interferometer Space Antenna"

The historic detection of gravitational waves paved the way for precision gravitational-wave astrophysics to blossom at unprecedented proportions. The sensitivity increment of ground-based interferometers, as well as the arrival of next generation space-borne detectors, such as the Laser Interferometer Space Antenna (LISA), will unequivocally strengthen our understanding of the gravitational interaction in extreme conditions. In this talk, I will focus on one of the prime targets of LISA, the so-called extreme-mass-ratio inspirals (EMRIs). EMRIs are binaries that consist of a primary supermassive compact object, such as the black holes lurking in galactic cores, and a stellar-mass secondary companion. I will discuss  their rich waveform phenomenology as well as potential observables of  fascinating phenomena, such as the non-Kerrness of spacetime and  chaos, which can be imprinted on the gravitational waves of EMRIs and may be detected with LISA.

Giacomo Gradenigo (Gran Sasso Science Institute)

"Symplectic quantization, a new deterministic approach to the dynamics of relativistic quantum fields: numerical results and possible applications to cosmology"

We propose here a novel approach to study the quantum fluctuations of relativistic fields. By regarding the fictitious time of Parisi-Wu stochastic quantization as a true physical parameter we propose a new deterministic dynamics of quantum fluctuations well defined even for fields living in Minkowskian space-time, at variance with the stochastic protocol, which works only for Euclidean field theory. This allows one to sample the causal structure of space-time even in numerical simulations. Assuming ergodicity for the dynamics, within symplectic quantization the Feynman path integral is then obtained simply as the Fourier transform of a pseudo-microcanonical ensemble built on the conservation of a generalised action (rather than on the conservation of energy like in standard thermal ensembles): this procedure establishes a well founded probabilistic interpretation of functional integrals in quantum field theory. In this talk I will introduce the theory and I will present the results of some numerical tests for a nonlinear Klein-Gordon field in 1+1 space-time dimensions. I will also sketch how the new ideas apply to general relativity, presenting some applications in cosmology.

Raul Jimenez (University of Barcelona)

"Quantum Fisher Cosmology"

In inflationary cosmology the quasi de Sitter graceful exit allows us to measure the quantum features of the primordial de Sitter phase, in particular, the lack of scale invariance parametrized by the spectral index ns. In this talk I will  summarize our work on how the underlying primordial scaling law is implemented in the de Sitter quantum Fisher information of the de Sitter planar ground state (dSQFI). At large scales the dSQFI unequivocally sets, without any quantum-de-Sitter input, the value of the spectral index to be ns=0.9672. This value is independent of the tensor to scalar ratio, whose value requires model dependent input. In addition the dSQFI predicts, at large scales, a small running compatible with the current experimental results. Other phenomenological consequences of the dSQFI for small scales will be discussed in this talk.

Cora Uhlemann (Newcastle University)

"Capturing the complexity of the cosmic large-scale structure in one wavefunction"

On large scales, the dark matter distribution can be treated as a perfect fluid. On small scales, gravitationally bound structures form through nonlinear clustering. Capturing the resulting cascade of multiple fluid streams in 6d phase space is challenging. We suggest approximating the time evolution of the phase-space distribution using a wavefunction in the spirit of the quantum-classical correspondence. In this framework, one can solve a nonlinear Schroedinger equation in 3d position space, where the small parameter acts as a phase-space resolution scale. This method is a tool to describe phase-space dynamics of cold dark matter with wave mechanics in position-space, and the fundamental description for wavelike dark matter such as ultralight particles. With a simple dynamical model for the evolution of the dark matter wavefunction (Psi), I will demonstrate how wave interference causes large density oscillations on small scales and manifests in vortices with a vanishing density and a localised circulation of velocity. Together with the wave interference imprint on substructures that leads to exciting and varied probing mechanisms bridging cosmology, astrophysics and ideas from wave mechanics.

Sandro Wimberger (University of Parma)

"Quantum Model for the Dynamics of Cosmological Large-Scale Structures"

We review our numerical methods to integrate time-dependent and nonlinear Schrödinger equations. These include the Gross-Ginsburg-Pitaevskii equation describing ultracold atoms in mean-field approximation and the coupled Schrödinger–Poisson equation system as a model for fuzzy cold dark matter. Despite the success of Wave-like Dark Matter in explaining cosmological processes, its major issue is the high demand in computational resources. Not only does the nonlinear and nonlocal nature of the underlying Schrödinger-Poisson equation pose a problem, but also the range of scales that have to be resolved. We construct two distinct one-dimensional (1+1) toy models that are less expensive from a numerical viewpoint, but still provide analogues to the phenomena observed in three dimensions. Our high-precision numerical technique is tested by an independent method. Some exemplary results will be shown for two different ways of treating the transverse dimensions, assuming uniform matter distribution in the first and strong confinement - effectively renormalizing the mass - in the second case. Key features of the asymptotic evolution of artificial and cosmological initial states are presented. Finally, we give an outlook on the future evolution of our numerical techniques towards treating higher spatial dimensions.

REGISTERED PARTICIPANTS

Erik Aurell (Stockholm University)

Nicola Bartolo (DFA, Univ. Padova)

Ajay Bassi (Centre for Theoretical Physics, Delhi)

Massimo Bianchi ("Tor Vergata", Univ. Roma)

Pierpaolo Bilotto (GSSI, L'Aquila)

Fabio Briscese (Mathematic Deptartment, Univ. Padova)

Raffaella Burioni (Physics Department, Univ. Parma)

Lapo Casetti (Univ. Firenze)

Serena Cenatiempo (GSSI, L'Aquila)

S. Mahesh Chandran (Indian Institute of Technology, Bombay)

Chetna Chauhan 

Elena Codazzo (GSSI, L'Aquila)

Valentina Danieli (SISSA, Trieste)

Marco de Cesare ("Federico II", University of Napoli)

Kyriakos Destounis (University of Tuebingen)

Pierfrancesco Di Cintio (CNR-ISC, INAF-OAA, Firenze)

Ulyana Dupletsa (GSSI-INFN, L'Aquila)

Carmelo Evoli (GSSI, L'Aquila)

Gianmaria Falasco (DFA, Univ. Padova)

Cecilia Ferrari (GSSI, L'Aquila)

Alcides Garat (Univ. de la Republica, Montevideo)

Mina Ghodsi Yengejeh (Shahid Beheshti Univ.)

Martina Giachello ("Sapienza", Univ. Roma)

Alex Gough (Newcastle Univ.)

Giacomo Gradenigo (GSSI, L'Aquila)

Velimir Ilić (Math. Institute, Beograd)

Stefano Iubini (ISC-CNR, Firenze)

Raul Jimenez (ICREA & Univ. Barcelona)

Sobhan Kazempour Ishka (Univ. Tabriz)

Goverdhan Khadekar (Univ. Nagpur)

Musfar Kozhikkal (Univ. Borgogne)

Anjali Abirami Kugarajh (GSSI, L'Aquila)

Roberto Livi (Univ. Firenze)

Francescopaolo Lopez (Univ. Padova)

Parthasarathi Majumdar 

Pierangelo Marcati (GSSI, L'Aquila)

Antonino Marciano (Fudan Univ. & INFN)

Andrea Maselli (GSSI, L'Aquila)

Sabino Matarrese (DFA, Univ. Padova)

Giorgio Mentasti (Imperial College, London)

Rahul Musale (Univ. Pune)

Marco Palleschi ("Sapienza", Univ. Roma)

Paolo Pani ("Sapienza", Univ. Roma)

Alessandro Parisi (SNS, Pisa)

Sivasish Paul 

Lorenzo Piga (Univ. Parma & INFN)

Antonio Ponno (Mathematics Department, Univ. Padova)

Dognon Rachidi Boko (UNSTIM, Benin)

Rishita Ray 

Soo-Jong Rey (QUARK Institute)

Angelo Ricciardone (DFA, Univ. Padova & INFN)

Rocco Rollo (GSSI, L'Aquila)

Stefano Ruffo (SISSA, Trieste)

Luca Salasnich (DFA, Univ. Padova)

Archana Sangwan (Indian Institute of Technology, Bombay)

Sandipan Sengupta (Indian Institute of Technology, Kharagpur)

Flavio Seno (DFA, Univ. Padova)

Samuele Marco Silveravalle (Univ. Trento)

Harikrishna Sripada (Astronomy Dept., Hyderabad)

Pawan Tiwari (Astronomy Dept., Indore)

Tommaso Tonolo (GSSI, L'Aquila)

Silvia Trabucco (GSSI, L'Aquila)

S. K. Tripathy (Institute of Technology, Sarang)

Cora Uhlemann (Newcastle University)

Franco Vazza (Univ. Bologna)

Angelo Vulpiani ("Sapienza", Univ. Roma)

Sandro Wimberger (Physics Department, Univ. Parma)

Anwar Zada (Riphah Univ, Islamabad)