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Strong Interactions: From QCD to LHC

Final Activity Report Summary - STRONG INTERACTIONS (Strong Interactions: From QCD to LHC)

The main objective of this project was the study of strong interactions. In particular, we focussed on strongly coupled theories, either quantum chromodynamics (QCD) or theories beyond the Standard Model, and on the interplay between theory and astrophysics or cosmology.

One of our objectives was the study of technicolor theories that could emerge at the long anticipated large hadronic collider (LHC) experiment at the ‘Conseil Europeen pour la Recherche Nucleaire’ (CERN). The study of this type of theories was a notoriously hard problem because calculations based on perturbative techniques failed. We attacked this problem by using a quite recently developed technique which could be applied at the strong coupling regime, namely the holographic principle. This way, we managed to study realistic technicolor models that might emerge at the LHC energy scale and we made very concrete predictions about the masses and several other features of new particles predicted by technicolor theories. Our results could be confronted by the experimental data, once available, and this way we could verify or rule out a set of theories that were likely to appear at the TeV energy scale.

One of our objectives was to study QCD at extreme conditions, especially with respect to the implications in neutron star physics. In this context we studied a neutron star with a quark matter core under extremely strong magnetic fields. We demonstrated, unlike what was previously falsely assumed in literature, that such neutron stars could not cool by the usual direct or modified Urca processes once we took into account the finiteness of the quark mass. In addition, we proposed a new mechanism that was related to the emission of zero sound modes as a possible way of cooling such neutron stars. Our proposed mechanism was the only one available in the market for the time being.

We also studied the effect of weakly interactive massive particle (WIMP) annihilation on the cooling curves of typical neutron stars. We demonstrated that the effect, contrary to what was expected, might not be negligible. We showed that it was possible to impose constraints or even to exclude dark matter candidates by just observing the temperature of old neutron stars.

Furthermore, we studied the cosmological implications of strongly coupled theories at the TeV scale. We studied several possibilities of dark matter mechanisms based on realistic technicolor models. We confronted the dark matter candidates we proposed against all possible experimental and theoretical constraints. One of the achievements of this project was that we clearly demonstrated that technicolor candidates could naturally solve the dark matter problem, and therefore they could be attractive alternative scenarios to supersymmetry.