Thesis

Chiral transitions in a recently developed effective QCD Lagrangian

• Call:

  IDPASC Portugal - PHD Programme 2015

• Academic Year:

  2015 / 2016

• Domains:

• Supervisor:

  Brigitte Hiller

• Co-Supervisor:

  Alex Blin

• Institution:

  Universidade de Coimbra

• Host Institution:

  CFisUC

• Abstract:

  The adequate description of low energy phenomena in strongly interacting matter represents a long standing and present challenge for Physics. Techniques of quantum field theory will be applied in the non-perturbative regime of Quantum Chromodynamics (QCD) to address the relevant features of the QCD interacting vacuum at the scale of dynamical chiral symmetry breaking in terms of effective multi-quark interactions. The line of research will follow and develop the effective Lagrangian approach recently proposed to obtain the most general spin 0 interaction Lagrangian active at that scale [1], which includes also the complete subset of explicit symmetry breaking interactions. The latter turned out to be indispensable for the accurate description of the low lying pseudoscalar and scalar meson nonets and other related observables [1],[2]. The model parameters are fully controlled on the theoretical side by symmetry arguments and on the experimental side by well known low energy meson characteristics. First this yields a detailed picture of the hadronic vacuum, described by the effective potential of the theory, providing for a solid ground to test its response to external parameters, such as temperature, baryonic chemical potential, magnetic fields, etc., of great importance in the description of critical lines associated with chiral transitions in the phase diagram of QCD. It also furnishes a good basis to study the dynamical chiral symmetry breaking and its restoration for a uniformly accelerated observer through the mechanism of the Hawking-Unruh thermalization effect, which may be of importance in relativistic heavy ion reactions. In addition, decays and scattering phenomena will carry the signatures of the vacuum, thus allowing to better understand the microscopic (multi-quark) structures relevant for these processes. In particular, we expect that the generalized Lagrangian is apt to extract and explain the source of violation of the Okubo-Zweig-Iizuka (OZI) rule (suppression of processes with disconnected quark line diagrams) in many channels and to understand the multi-quark interactions that are at play in strong decays, as well as recombinations that can occur at a different probed scale, such as in electromagnetic and weak decays. At different stages of the research, extensions of the Lagrangian may contemplate the inclusion of the spin 1 channels, derivative interactions, and interactions which become relevant for order parameters which may compete with the chiral condensates in the excited QCD vacuum. [1]Light Quark Masses in Multi-Quark Interactions A.A. Osipov, B. Hiller, A.H. Blin, Eur.Phys.J. A49 (2013) 14, e-Print: arXiv:1206.1920 [hep-ph] [2] Effective multiquark interactions with explicit breaking of chiral symmetry A.A. Osipov, B. Hiller, A.H. Blin, Phys.Rev. D88 (2013) 5, 054032 e-Print: arXiv:1309.2497 [hep-ph]