Have you ever wondered what is there inside a star? Obviously it is very hard to get in there and give a look... We are therefore constrained to indirect observation that we must match with some theoretical description we have in mind.

This task is extremely challenging. The properties of the nucleon-nucleon interaction (acting on the scale of a few fm) must be exploited to explain why there are no observations of compact stars with masses larger than 1.4 solar masses, or to understand the properties of the stars cooling.

What we need is

1. 1)a very accurate knowledge of the nucleon nucleon interaction;
   

2. 2)a very accurate method to compute the properties of extensive nucleon systems.
   

Our approach is based on Quantum Monte Carlo techniques, i.e. stochastic methods that allow for solving almost exalctly the many-body Schroedinger equation.

Nuclear Physics

Electrons are Fermions, and if I know how to manage nucleons, I should also know how to manage electrons... Quantum Monte Carlo techniques are very popular in the fields of chemistry and materials science.

Here we try to extend the capabilities of the method to the study of confined systems (imagine a wire just a hundred nanometers thick...), and to include effects due to the straordinarily complex environment that an electron sees in a semiconductor.

We use the so-called “electron gas” model, i.e. we consider electrons confined by some external potential, or just kept in equilibrium by a “jellium” of positive charge. Despite it looks oversimplified, this model enables to make sensible qualitative predictions on the properties of semiconductor nanostructures that are becoming a popular piece of technology.

Unfortunately Quantum Monte Carlo does not always work so well... It suffers of some heavy limitations that have a well defined mathematical origin. Can we improve the method? I have been working now for more than 10 years together with Malvin H. Kalos, one of the dads of the method, in order to overcome the so-called “sign-problem”

Nanostructures

Sign Problem in DMC