Lattice QCD in a Nutshell

• Any system can be described in terms of its degrees of freedom.
• The irreducible degrees of freedom are called elementary particles and they are classified in terms of their properties. An elementary particle does not necesassrily occupies a position in space and time and it is more similar to an "object" in a Computer Science sense than to an "object" in the common physical sense. In this CS analogy a particle is an "object" because it has "attributes" and "an internal state", Quarks and Leptons are different "classes" of which the "particles" are instances of.
• The law of dynsmics of any system can be described by one single expression expression written in the language defined by these "objects". This expression is called Lagrangian and identified by the letter L
• Any measurement on the system can be described by an expression O called Operator
• The Feynman Path Integral provides an apgorithmic technique for computing the distribution of all possible results of any measurement O on any system L:
• Our universe is a system made of elementary particles and it can be descrbed by a Lagrangian. If we ignore gravity which is very weak at small length scales, it can be described by the Standard Model Lagrangian: The blue terms in this expression are known as Quantum Chromo Dynamics (QCD in short) and they are responsible for bounding quarks together and creating composite particles such as Proton and Neutrons.

FermiQCD is a library of algorithms for performing Lattice Gauge Theory computations, i.e. numerical computations of the Feynman Path Integral for a Lagrangian L that includes QCD and QCD-like terms (for example any SU(n) gauge group).