Theories, models, simulations: a computational challenge

In this talk I would like to illustrate with examples taken from Quantum Field Theory and Biophysics how an intelligent exploitation of the unprecedented power of today's computers could led not only to the solution of pivotal problems in the theory of Strong Interactions, but also to the emergence of new lines of interdisciplinary research, while at the same time pushing the limits of modeling to the realm of living systems.Comment: 19 pages, 1 figure, conference pape

Isospin Mixing of Narrow Pentaquark States

Interpreting the recently discovered narrow exotic baryons as pentaquark states, we discuss, along an old argument of ours, the isospin mixing occurring within the two doublets of $Q = -1$ and Q=0 states lying inside the $S=-2$ ($\Xi$-cascade) sector. We argue that, at least within the Jaffe-Wilczek assignment, presently available data already indicate that mixing should occur at an observable level in both charge sectors, with mixing angles that can be predicted in terms of ratios of observable mass splittings.Comment: 11 pages, 2 figures, to be submitted to PL

Note on lattice regularization and equal-time correlators for parton distribution functions

We show that a recent interesting idea to circumvent the difficulties with the continuation of parton distribution functions to the Euclidean region, that consists in looking at equal time correlators between proton states of infinite momentum, encounters some problems related to the power divergent mixing pattern of DIS operators, when implemented within the lattice regularization.Comment: 15 pages, no figures, Physical Review D (2017

A non-perturbative mechanism for elementary particle mass generation

Taking inspiration from lattice QCD data, we argue that a finite non-perturbative contribution to the quark mass is generated as a consequence of the dynamical phenomenon of spontaneous chiral symmetry breaking, in turn triggered by the explicitly breaking of chiral symmetry induced by the critical Wilson term in the action. In pure lattice QCD this mass term cannot be separated from the unavoidably associated linearly divergent contribution. However, if QCD is enlarged to a theory where also a scalar field is present, coupled to an SU(2) doublet of fermions via a Yukawa and a Wilson-like term, then in the phase where the scalar field takes a non-vanishing expectation value, a dynamically generated and "naturally" light fermion mass (numerically unrelated to the expectation value of the scalar field) is conjectured to emerge at a critical value of the Yukawa coupling where the symmetry of the model is maximally enhanced. Masses dynamically generated in this way display a natural hierarchy according to which the stronger is the strongest of the interactions the fermion is subjected to the larger is its mass.Comment: Added more information in Fig 1. Added Fig. 10. Added an extra Appendix. Restructured a few sentences according to referee suggestions. Corrected a few misprints. All results unchanged. Now 50 pages and 10 Figure

Chirally improving Wilson fermions II. Four-quark operators

In this paper we discuss how the peculiar properties of twisted lattice QCD at maximal twist can be employed to set up a consistent computational scheme in which, despite the explicit breaking of chiral symmetry induced by the presence of the Wilson and mass terms in the action, it is possible to completely bypass the problem of wrong chirality and parity mixings in the computation of the CP-conserving matrix elements of the $\Delta S=1,2$ effective weak Hamiltonian and at the same time have a positive determinant for non-degenerate quarks as well as full O($a$) improvement in on-shell quantities with no need of improving the lattice action and the operators.Comment: Replaced with published version in JHEP style: 43 pages, no figures. Added few references and discussion on "critical mass and O(a) improvement" as well as on "tests and numerical issues" in the Conclusions (sect. 6

Quantum Cloning by Cellular Automata

We introduce a quantum cellular automaton that achieves approximate phase-covariant cloning of qubits. The automaton is optimized for 1-to-2N economical cloning. The use of the automaton for cloning allows us to exploit different foliations for improving the performance with given resources.Comment: 4 pages, 6 figures, 1 table, published versio