arXiv subjects
Publications and source records attributed to Massimo Di Pierro.
We present here the most recent version of FermiQCD, a collection of C++ classes, functions and parallel algorithms for lattice QCD, based on Matrix Distributed Processing. FermiQCD allows fast development of parallel lattice applications and includes some SSE2 optimizations for clusters of Pentium 4 PCs.
We present a set of programming tools (classes and functions written in C++ and based on Message Passing Interface) for fast development of generic parallel (and non-parallel) lattice simulations. They are collectively called MDP 1.2. These programming tools include classes and algorithms for matrices, random number generators, distributed lattices (with arbitrary topology), fields and parallel iterations. No previous knowledge of MPI is required in order to use them. Some applications in electromagnetism, electronics, condensed matter and lattice QCD are presented.
A detailed study of orbital and radial excited states in D, Ds, B and B_s systems is performed. The chiral quark model provides the framework for the calculation of pseudoscalar meson (pi, K, ...) hadronic transitions among heavy-light excited and ground states. To calculate the excited states masses and wavefunctions, we must resort to a relativistic quark model. Our model includes the leading order corrections in 1/m_(c,b) (e.g. mixing). Numerical results for masses and light hadronic transition rates are compared to existing experimental data. The effective coupling of the chiral quark model can be determined by comparing with independent results from lattice simulations (g^8_A = 0.53 +-/- 0.11) or fitting to known widths (g^8_A = 0.82 +-/- 0.09).
Matrix Distributed Processing is a collection of classes and functions written in C++ for fast development of efficient parallel algorithms for the most general lattice/grid application. FermiQCD is an Object Oriented Lattice QCD application of MDP, under development at Fermilab.
We studied the hadronic decays of excited states of heavy mesons (D, D_s, B and B_s) to lighter states by emission of pi, eta or K. Wavefunctions and energy levels of these excited states are determined using a Dirac equation for the light quark in the potential generated by the heavy quark (including first order corrections in the heavy quark expansion). Transition amplitudes are computed in the context of the Heavy Chiral Quark Model.
This is a manual (built by examples) to explain the use of MDP_QCD. It consists of an ensemble of classes and functions (written in GNU C++) to help in writing programs for lattice QCD in a particularly Object Oriented fashion. Some tricks are implemented to optimize speed and reduce memory usage on PCs, workstations and parallel computers with sheared memory. The basic classes are: Matrix, gauge_field, fermi_field and stochastic light_propagators (the code works for any SU(N) gauge group).
We evaluate the matrix elements of the four-quark operators which contribute to the lifetimes of $B$-mesons and the $Λ_b$-baryon. We find that the spectator effects are not responsible for the discrepancy between the theoretical prediction and experimental measurement of the ratio of lifetimes $τ(Λ_b)/τ(B)$.
Several physics aspects of the Seiberg-Witten solution of N=2 supersymmetric Yang-Mills theory with SU(2) gauge group, supplemented with a small mass term for the "matter" fields which leads to an $N=1$ theory with confinement, are discussed. The light spectrum of the theory is understood on the basis of current algebra relations, and CP invariance of the massless and massive theories is studied. We find that in the massive (confining) theory the low energy physics has an exact CP symmetry, while in a generic vacuum in the massless theory CP invarince is spontaneously broken.