13,138 research outputs found

### The static potential: lattice versus perturbation theory in a renormalon-based approach

We compare, for the static potential and at short distances, perturbation
theory with the results of lattice simulations. We show that a
renormalon-dominance picture explains why in the literature sometimes
agreement, and another disagreement, is found between lattice simulations and
perturbation theory depending on the different implementations of the latter.
We also show that, within a renormalon-based scheme, perturbation theory agrees
with lattice simulations.Comment: 18 pages, 11 figures, lattice data of Necco and Sommer introduced,
references added, some lengthier explanations given, physical results
unchange

### Model Independent Results for Heavy Quarkonium

We review a number of results for the spectrum and inclusive decays of heavy
quarkonium systems which can be derived from QCD under well controlled
approximations. They essentially follow from the hierarchy of scales in these
systems, which can be efficiently exploited using non-relativistic effective
field theories. In particular, we discuss under which conditions
non-relativistic potential models emerge as effective theories of QCD.Comment: 15 pages. Invited brief revie

### The Mode of Computing

The Turing Machine is the paradigmatic case of computing machines, but there
are others, such as Artificial Neural Networks, Table Computing,
Relational-Indeterminate Computing and diverse forms of analogical computing,
each of which based on a particular underlying intuition of the phenomenon of
computing. This variety can be captured in terms of system levels,
re-interpreting and generalizing Newell's hierarchy, which includes the
knowledge level at the top and the symbol level immediately below it. In this
re-interpretation the knowledge level consists of human knowledge and the
symbol level is generalized into a new level that here is called The Mode of
Computing. Natural computing performed by the brains of humans and non-human
animals with a developed enough neural system should be understood in terms of
a hierarchy of system levels too. By analogy from standard computing machinery
there must be a system level above the neural circuitry levels and directly
below the knowledge level that is named here The mode of Natural Computing. A
central question for Cognition is the characterization of this mode. The Mode
of Computing provides a novel perspective on the phenomena of computing,
interpreting, the representational and non-representational views of cognition,
and consciousness.Comment: 35 pages, 8 figure

### Renormalization group improvement of the NRQCD Lagrangian and heavy quarkonium spectrum

We complete the leading-log renormalization group scaling of the NRQCD
Lagrangian at $O(1/m^2)$. The next-to-next-to-leading-log renormalization group
scaling of the potential NRQCD Lagrangian (as far as the singlet is concerned)
is also obtained in the situation $m\alpha_s \gg \Lambda_{QCD}$. As a
by-product, we obtain the heavy quarkonium spectrum with the same accuracy in
the situation m\alpha_s^2 \simg \Lambda_{QCD}. When $\Lambda_{QCD} \ll
m\alpha_s^2$, this is equivalent to obtain the whole set of
$O(m\alpha_s^{(n+4)} \ln^n \alpha_s)$ terms in the heavy quarkonium spectrum.
The implications of our results in the non-perturbative situation $m\alpha_s
\sim \Lambda_{QCD}$ are also mentioned.Comment: 16 pages, LaTeX. Minor changes. Final versio

### Renormalization group improvement of the spectrum of Hydrogen-like atoms with massless fermions

We obtain the next-to-next-to-leading-log renormalization group improvement
of the spectrum of Hydrogen-like atoms with massless fermions by using
potential NRQED. These results can also be applied to the computation of the
muonic Hydrogen spectrum where we are able to reproduce some known double logs
at O(m\alpha^6). We compare with other formalisms dealing with log resummation
available in the literature.Comment: 9 pages, LaTeX. Minor changes, note added, final versio

### Effective field theories for heavy quarkonium

We review recent theoretical developments in heavy quarkonium physics from
the point of view of Effective Field Theories of QCD. We discuss
Non-Relativistic QCD and concentrate on potential Non-Relativistic QCD. Our
main goal will be to derive QCD Schr\"odinger-like equations that govern the
heavy quarkonium physics in the weak and strong coupling regime. We also
discuss a selected set of applications, which include spectroscopy, inclusive
decays and electromagnetic threshold production.Comment: 162 pages, 30 figures, revised version, references added. Accepted
for publication in Reviews of Modern Physic

### Synchronization in driven versus autonomous coupled chaotic maps

The phenomenon of synchronization occurring in a locally coupled map lattice
subject to an external drive is compared to the synchronization process in an
autonomous coupled map system with similar local couplings plus a global
interaction. It is shown that chaotic synchronized states in both systems are
equivalent, but the collective states arising after the chaotic synchronized
state becomes unstable can be different in these two systems. It is found that
the external drive induces chaotic synchronization as well as synchronization
of unstable periodic orbits of the local dynamics in the driven lattice. On the
other hand, the addition of a global interaction in the autonomous system
allows for chaotic synchronization that is not possible in a large coupled map
system possessing only local couplings.Comment: 4 pages, 3 figs, accepted in Phys. Rev.

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