2,123 research outputs found
Instanton-Induced Correlations in Hadrons
QCD instantons generate non-perturbative spin- and flavor- dependent forces
between quarks. We review the results of a series of studies on
instanton-induced correlations in hadrons. We first present some evidence for
instanton-mediated interactions in QCD, based on lattice simulations. Then we
show that the Instanton Liquid Model can reproduce the available data on proton
and pion form factors at large momentum transfer and explain the delay of the
onset of the perturbative regime in several hard reactions. We also show that
instantons generate a deeply bound scalar color anti-triplet diquark, with a
mass of about 450 MeV and size comparable with that of the proton. The strong
attraction in the anti-triplet scalar diquark channel leads to a quantitative
description of non-leptonic weak decays of hyperons and provides a microscopic
dynamical explanation of the Delta I=1/2 rule.Comment: Summary of the results presented at the "8th Workshop on
Non-perturbative Quantum Chromodynamics", Paris 7-11 June 2003, the "26th
International School on Nuclear Physics", Erice 16-24 September 2004, and the
"X Convegno sui Problemi della Fisica Nucleare Teorica", Cortona, 6-9 October
200
Molecular Dynamics at Low Time Resolution
The internal dynamics of macro-molecular systems is characterized by widely
separated time scales, ranging from fraction of ps to ns. In ordinary molecular
dynamics simulations, the elementary time step dt used to integrate the
equation of motion needs to be chosen much smaller of the shortest time scale,
in order not to cut-off important physical effects. We show that, in systems
obeying the over-damped Langevin Eq., the fast molecular dynamics which occurs
at time scales smaller than dt can be analytically integrated out and gives
raise to a time-dependent correction to the diffusion coefficient, which we
rigorously compute. The resulting effective Langevin equation describes by
construction the same long-time dynamics, but has a lower time resolution
power, hence it can be integrated using larger time steps dt. We illustrate and
validate this method by studying the diffusion of a point-particle in a
one-dimensional toy-model and the denaturation of a protein.Comment: 12 pages, 5 figure
Rotation-invariant relations in vector meson decays into fermion pairs
The rotational properties of angular momentum eigenstates imply the existence
of a frame-independent relation among the parameters of the decay distribution
of vector mesons into fermions. This relation is a generalization of the
Lam-Tung identity, a result specific to Drell-Yan production in perturbative
QCD, here shown to be equivalent to the dynamical condition that the dilepton
always originates from a transversely polarized photon
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