ERC FUNDED PROJECTS

Axions are hypothetical particles whose existence would solve two major problems: the strong P, T problem (a major blemish on the standard model); and the dark matter problem. It is a most important goal to either observe or rule out the existence of a cosmic axion background. It appears that decisive observations may be possible, but only after orchestrating insight from specialities ranging from quantum field theory and astrophysical modeling to ultra-low noise quantum measurement theory. Detailed predictions for the magnitude and structure of the cosmic axion background depend on cosmological and astrophysical modeling, which can be constrained by theoretical insight and numerical simulation. In parallel, we must optimize strategies for extracting accessible signals from that very weakly interacting source. While the existence of axions as fundamental particles remains hypothetical, the equations governing how axions interact with electromagnetic fields also govern (with different parameters) how certain materials interact with electromagnetic fields. Thus those materials embody “emergent” axions. The equations have remarkable properties, which one can test in these materials, and possibly put to practical use. Closely related to axions, mathematically, are anyons. Anyons are particle-like excitations that elude the familiar classification into bosons and fermions. Theoretical and numerical studies indicate that they are common emergent features of highly entangled states of matter in two dimensions. Recent work suggests the existence of states of matter, both natural and engineered, in which anyon dynamics is both important and experimentally accessible. Since the equations for anyons and axions are remarkably similar, and both have common, deep roots in symmetry and topology, it will be fruitful to consider them together.

2 324 391 €

Start date: 2017-09-01, End date: 2022-08-31

The most energetic electromagnetic phenomena in the Universe are believed to be powered by the collision of two neutron stars, the smallest and densest stars on which surface gravity is about 2 billion times stronger than gravity on Earth. However, a definitive identification of neutron star mergers as central engines for short-gamma-ray bursts and kilonovae transients is possible only by direct gravitational-wave observations. The latter provide us with unique information on neutron stars' masses, radii, and spins, including the possibility to set the strongest observational constraints on the unknown equation-of-state of matter at supranuclear densities. Neutron stars binary mergers are among the main targets for ground-based gravitational-wave interferometers like Advanced LIGO and Virgo, which start operations this year. The astrophysical data analysis of the signals emitted by these sources requires the availability of accurate waveform models, which are missing to date. Hence, the theoretical understanding of the gravitational spectrum is a necessary and urgent step for the development of a gravitational-based astrophysics in the next years. This project aims at developing, for the first time, a precise theoretical model for the complete gravitational spectrum of neutron star binaries, including the merger and postmerger stages of the coalescence process. Building on the PI's unique expertise and track record, the proposed research exploits synergy between analytical and numerical methods in General Relativity. Results from state of the art nonlinear 3D numerical relativity simulations will be combined with the most advanced analytical framework for the relativistic two-body problem. The model developed here will be used in the first gravitational-wave observations and will dramatically impact multimessenger astrophysics.

1 432 301 €

Start date: 2017-10-01, End date: 2022-09-30

CROSS will set the grounds for large-scale experiments searching for neutrinoless double beta decay with zero background at an exposure scale of ~1 tonne x year and with very high energy resolution – about 1.5‰ – in the region of interest. These features will enable searching for lepton number violation with unprecedented sensitivity, penetrating in prospect the direct-ordering region of the neutrino masses. CROSS will be based on arrays of TeO2 and Li2MoO4 bolometers enriched in the isotopes of interest 130Te and 100Mo, respectively. There are strong arguments in favor of these choices, such as the high double beta transition energy of these candidates, the easy crystallization processes of TeO2 and Li2MoO4, and the superior bolometric performance of these compounds in terms of energy resolution and intrinsic purity. The key idea in CROSS is to reject surface events (a dominant background source) by pulse-shape discrimination, obtained by exploiting solid-state-physics phenomena in superconductors. The surfaces of the crystals will be coated by an ultrapure superconductive aluminium film, which will act as a pulse-shape modifier by delaying the pulse development in case of shallow energy depositions, exploiting the long quasi-particle life-time in aluminium. This method will allow getting rid of the light detectors used up to now to discriminate surface alpha particles, simplifying a lot the bolometric structure and achieving the additional advantage to reject also beta surface events, which unfortunately persist as an ultimate background source if only alpha particles are tagged. The intrinsic modularity and the simplicity of the read-out will make CROSS easily expandable. The CROSS program is focused on an intermediate experiment with 90 crystals, installed underground in the Canfranc laboratory, which will be not only extremely competitive in the international context but also a decisive step to demonstrate the enormous potential of CROSS in terms of background.

3 146 598 €

Start date: 2018-01-01, End date: 2022-12-31

Predicting the collective properties of strongly interacting matter at the highest densities reached within the present-day Universe is one of the most prominent challenges in modern nuclear theory. It is motivated by the desire to map out the complicated phase diagram of the theory, and perhaps even more importantly by the mystery surrounding the inner structure of neutron stars. The task is, however, severely complicated by the notorious Sign Problem of lattice QCD, due to which no nonperturbative first principles methods are available for tackling it. The proposal at hand approaches the strong interaction challenge using a first principles toolbox containing most importantly the machinery of modern resummed perturbation theory and effective field theory. Our main technical goal is to determine three new orders in the weak coupling expansion of the Equation of State (EoS) of unpaired zero-temperature quark matter. Alongside this effort, we will investigate the derivation of a new type of effective description for cold and dense QCD, allowing us to include to the EoS contributions from quark pairing more accurately than what is possible at present. The highlight result of our work will be the derivation of the most accurate neutron star matter EoS to date, which will be obtained by combining insights from our work with those originating from the Chiral Effective Theory of nuclear interactions. We anticipate being able to reduce the current uncertainty in the EoS by nearly a factor of two, which will convert into a precise prediction for the Mass-Radius relation of the stars. This will be a milestone result in nuclear astrophysics, and in combination with emerging observational data on stellar masses and radii will contribute to solving one of the most intriguing puzzles in the field – the nature of the most compact stars in the Universe.

1 342 133 €

Start date: 2017-07-01, End date: 2022-06-30