### Research field and interests

My
research field is Hadronic
Physics, the study of strongly-interacting matter with the aim to understand
its properties and interactions in terms of the underlying fundamental theory, i.e. Quantum Chromodynamics. I am interested in
the investigation of
the two emergent phenomena of the strong interaction: confinement –
the
fact that single quarks are not
observed in isolation – and dynamical
chiral-symmetry breaking
– the origin of most of the mass of ordinary matter in the Universe.
These phenomena dominate the observed properties of hadrons
measured in experiments at LHC, JLab, FAIR-GSI, and the BES
Collaboration, and they can be studied theoretically through
dynamical
quark models
describing
hadrons.
Figures:
credits to Joshua Rubin, Argonne

### Methods

### Covariant
spectator theory

For the phenomenological
investigation of
confinement and dynamical chiral-symmetry breaking we apply
non-perturbative, covariant methods based on quantum field theory, such
as formulations of field-theoretic amplitudes in terms of integral
equations that effectively sum an infinite set of diagrams. We use the
covariant spectator theory (CST), which works in
Minkowski space, to
develop a dynamical quark model that can describe the
structure and the mass spectrum of both, heavy and light quark
systems.

The
CST-Bethe-Salpeter
integral equation describes quark-antiquark bound states, i.e.
quark-antiquark mesons such as the
pion. The green triangle is the meson
vertex function and
the solid colored lines are dressed quark propagators. A colored
(white)
cross on a quark line indicates that the corresponding quark is on
mass shell with
positive (negative) energy.

Collaborators:

Franz Gross (JLab, USA)

Sofia Leitão (CFTP-IST, Portugal)

Teresa Peña (CFTP-IST, Portugal)

Emílio Ribeiro (CeFMA-IST, Portugal)

Alfred Stadler (U. Évora, Portugal)

### Point-form
Hamiltonian dynamics

Another covariant approach to
study relativistic quantum systems in
hadronic physics is point-form Hamiltonian dynamics. It can be applied
to both, relativistic quantum
mechanics and quantum field theory, and it has the advantage that only
the space-time
translations of the
Poincaré transformations are interaction dependent, and Lorentz boosts
and spatial rotations are free of interactions.The point form is
characterized by a space-time hyperboloid in Minkowski space that is
left invariant under the Lorentz group.

The forward hyperboloid x²=const., the quantization surface in the point form.

Collaborators:

William Klink (U. Iowa, USA)Wolfgang Schweiger (U. Graz, Austria)