41,047 research outputs found
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 and Q=0 states lying inside the
(-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 effective weak Hamiltonian
and at the same time have a positive determinant for non-degenerate quarks as
well as full O() 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
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