The only known
rigorous method of general applicability to study QCD in the non-perturbative (i.e. at low-energy) regime is its
formulation on the lattice. However, the computational cost of QCD
simulations grows very fast with increasing lattice sizes, smaller
lattice spacings and smaller quark masses.
This is particularly true in the difficult observables needed in nuclear
physics. Extrapolations from numerically accessible ranges of
parameters to realistic values are then the only practical way to
connect QCD with nuclear phenomenology. Effective field theories, which
received so much attention in the last few years, are the necessary tool
used in these extrapolations. This has motivated an added interest in
the combined EFT and lattice description of nuclear interactions,
beyond and above the one stressed in the past. In the meson sector, the
combination of lattice calculations and effective theories, i.e. chiral perturbation theory and its quenched and
partially quenched generalization, is a program being pursued currently
in full force. We intend to explore in this workshop the possibility of
extending this program to the two-nucleon system and beyond. The
effort to understand many of these physical phenomena has already stimulated world-wide collaborations,
motivated the development of sophisticated and dedicated algorithms and
massively parallel computers (in the range of tens of Teraflops). The
next years, starting in 2005, will see the realization of a European
project (apeNEXT), a
Even though phenomenological models, as meson-exchange or quark models,
have provided us with an impressive improvement of the description of
the short-distance part of the baryon-baryon interaction, its physical
origin still reveals large uncertainties. Since Weinberg original idea
of applying EFT to nuclear physics a lot of work has been done using
this approach, and a remarkable success has been achieved, especially in
the two- and three-nucleons sector. One encounters indeed some
difficulties in an EFT description of nuclear forces not found in the
meson or one-baryon sectors. Since nuclear bound states are necessarily
non-perturbative, the renormalization of the EFT has to be understood at
a non-perturbative level. Additional complications arise with the
presence of a new length scale in the EFT formulation when discussing
systems with barely bound states, the scattering length. Those issues
have motivated much theoretical effort during the last decade and,
together with the extension of EFTs above the pion production threshold,
their extension to the strange sector, and the description of few-body
systems, are the current lines of research in the field.
Crucial to the description of nuclear interactions on the lattice, is
the understanding of how to perform chiral extrapolations. EFTs provide
the appropriate guideline to the extrapolation, if the values of the
relevant parameters of lattice simulations are within the range of
applicability of EFTs. Another important issue is the quantitative
understanding of systematic uncertainties which affect lattice
simulations, due to finite volume corrections and (partial) quenching.
This is particularly important since many hadrons interaction can only
be studied through finite volume effects on an Euclidean lattice, and
it is important to distinguish those from the finite volume effects in
each single hadron. All of these issues depend on the particular system
studied and have not yet been fully investigated in the baryon sector.
Other closely related topics will also be discussed at this workshop,
like the electric dipole moments of nucleons (and atoms). Ongoing
experimental programmes for the measurement of electric dipole moments
need to confront with a solid theoretical prediction in order to shed
light on the possible presence of new physics
contributions.
Since new lattice
calculations with two baryon operators should become available by the
summer of 2005, the workshop would be at the right time to explore the
potentials and limitations of the lattice approach to nuclear problems.
This workshop intends to facilitate the exchange of ideas and expertise
by bringing together researchers from different communities, as particle
physicists, nuclear physicists and lattice experts.