Marco Bruni

University of Portsmouth, Institute of Cosmology and Gravitation, Faculty Member

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I studied physics at the University of Rome “La Sapienza” where I graduated in 1987, with a thesis on colliding gravitational waves, supervised by Valeria Ferrari. I then obtained a studentship from SISSA (Trieste, Italy) where I worked with George Ellis on covariant and gauge-invariant cosmological perturbations, completing my PhD in 1991. After postdocs in QMUL (London), ICTP and SISSA (Trieste), and Cardiff, in 1999 I joined the Relativity and Cosmology Group of the mathematics department at the University of Portsmouth as senior lecturer. In 2002 I became member of the newly formed Institute of Cosmology and Gravitation. In 2005 I was awarded a two year visiting professorship by the Italian government, which I spent at the University of Rome “Tor Vergata”. In 2006 I was promoted to reader. I have lectured undergraduates and postgraduate students in the UK, Italy, Greece and India, I have published over 50 scientific papers in international journals and given talks in four continents (Australians I need an invitation!). I am a keen photographer/traveller/mountaineer.

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Lorenzo Iorio

Ministero dell'Istruzione, dell'Università e della Ricerca (M.I.U.R.)

Emmanuel T Rodulfo

De La Salle University

Silvia De Bianchi

Università degli Studi di Milano - State University of Milan (Italy)

Armando Marques-Guedes

UNL - New University of Lisbon

Mark Hammonds

The University of Tokyo

Ivan de Martino

University of Salamanca

Mathieu Ossendrijver

Freie Universität Berlin

Maarten Kleinhans

Utrecht University

Sergey A Khaibrakhmanov

Saint-Petersburg State University

Adalbert Ding

Technische Universität Berlin

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Shan–Chen interacting vacuum cosmology

Monthly Notices of the Royal Astronomical Society, Feb 7, 2022

In this paper, we introduce a novel class of interacting vacuum models, based on recasting the eq... more In this paper, we introduce a novel class of interacting vacuum models, based on recasting the equation of state originally developed in the context of lattice kinetic theory by Shan & Chen as the coupling between the vacuum and cold dark matter (CDM). This coupling allows the vacuum to evolve and is nonlinear around a characteristic energy scale 𝜌 * , changing into a linear coupling with a typical power law evolution at scales much lower and much higher than 𝜌 * . Focusing on the simplest sub-class of models where the interaction consists only of an energy exchange and the CDM remains geodesic, we first illustrate the various possible models that can arise from the Shan-Chen coupling, with several different behaviours at both early and late times depending on the values of the model parameters selected. We then place the first observational constraints on this Shan-Chen interacting vacuum scenario, performing an MCMC analysis to find those values of the model and cosmological parameters which are favoured by observational data. We focus on models where the nonlinearity of the coupling is relevant at late times, choosing for the reference energy scale 𝜌 * , the critical energy density in ΛCDM. We show that the observational data we use are compatible with a wide range of models which result in different cosmologies. However, we also show that ΛCDM is preferred over all of the Shan-Chen interacting vacuum models that we study, and comment on the inability of these models to relax the 𝐻 0 and 𝜎 8 tensions.

Marco Bruni

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