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Physics of the strong interaction, theory and experiment (WG Leader: Isaac Vidaña)

Compact stars, and the observed astrophysical processes related to them, give stringent constraints on the properties of dense and hot hadronic matter, such as equation of state, superfluidity, transport coefficients and elasticity parameters. Probing strongly interacting matter under extreme conditions requires bringing together experts in low-energy QCD and in many-body theories. Indeed, one of the main theoretical issues is that the theory describing the interaction and dynamics of quarks and gluons, i.e., QCD, is non-perturbative in the regimes of interest for compact stars. Additionally, many-body effects such as pairing or collective behavior make the phase diagram of hadronic matter very rich and at the same time, subtle to describe.

Several important issues will be explored in detail by this Action using the information coming from the observations and modelling of compact stars, thus in close interaction with WG1 and WG3. The first one is the structure of the phase diagram of strongly-interacting matter, with a possible deconfinement of quarks in compact stars and core-collapse supernovae or a transition to hyperonic matter. A second one concerns the properties of purely nucleonic matter. The nature of the bare nuclear interaction, in fact, is still largely debated and the recent developments of effective field-theory approaches or renormalisation-group methods illustrate its liveliness. The short-range nature of the bare nuclear interaction determines, to a large extent, the in-medium correlations, as well as the importance of many-body interactions. Additional long-range correlations, such as pairing among Cooper pairs or collective behavior, have also important consequences on the microscopic properties of dense matter, and thence on observable processes such as cooling, pulsar glitches and oscillations of compact stars. A third issue concerns the statistical description of nuclei at finite temperature and in dilute matter, which is important for the modelling of the equation of state, but also for the reaction-rates of electron-capture, photo-dissociation, and neutrino scattering in core-collapse supernovae. This Action will calculate these reaction-rates and the transport properties as applications of the best nuclear reaction models and build the background microphysical knowledge needed by WG1 and WG3.

Although at much smaller densities, nuclear experiments also represent a different way to probe the nuclear interaction and the in-medium correlations in the best-controlled systems, providing constraints on the properties of finite nuclei in their ground and excited states, and in the out-of-equilibrium plasma produced in heavy-ion collisions. The relation between nuclear experiments and the physics of compact stars is not straightforward, but the novel synergy between nuclear experiments and astronomical observations of compact stars will impact on all of the theoretical modelling relevant to this Action.

Topic Leaders in this working group are:

  • Gergely Barnaföldi
  • Nicolas Chamel
  • Laura Tolos
  • Adriana Raduta

The annual WG reports can be found here: