Who: Andrea Bussone (CP3-Origins)

When: Tuesday, August 29, 2017 at 11:00

Where: U143

Andrea Bussone defends his PhD thesis. His PhD advisor was Michele Della Morte.

The opponents are Professor Isabel Campos Plasencia (Instituto de Fisila de Cantabria) and Professor Francesco Knechtli (Bergische Universität Wuppertal).

I start by reviewing the basic features of QCD and how it is implemented on a lattice.

The essential quantities to be computed on the lattice are expectation values of operators.

Since the path integral is a high dimensional integral Monte Carlo methods are suitable to deal with those.

This naturally leads to the well-known HMC algorithm, a way to generate fixed background QCD vacuum configurations with the inclusion of dynamical fermions.

In the rest I present an economical strategy to optimize HMC parameters in simulation of QCD and QCD-like theories.

I specialize to the case of a mass-preconditioning, with multiple-time-step Omelyan integrators.

Starting from properties of the shadow Hamiltonian I show how the optimal set-up for the integrator can be chosen once the forces and their variances are measured, assuming that those only depend on the mass-preconditioning parameter.

The second part of the talk is dedicated to the EM corrections to the hadronic contribution to the (g-2) anomaly of the muon.

I discuss the famous zero mode problem, some issues related to it, and its solution on the lattice adopted by the lattice community nowadays.

I consider QED\({}_{\rm L}\) and QED\({}_{\rm M}\) to deal with the finite-volume zero modes.

I compare results for the Wilson loops with exact analytical determinations.

In addition I make sure that the volumes and photon masses used in QED\({}_{\rm M}\) are such that the correct dispersion relation is reproduced by the energy levels extracted from the charged pions two-point functions.

Finally I compare results for pion masses and the HVP between QED\({}_{\rm L}\) and QED\({}_{\rm M}\).

For the vacuum polarization, corrections with respect to the pure QCD case, at fixed pion masses, turn out to be at the percent level.