10,231 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
Spokes cluster: The search for the quiescent gas
Context. Understanding the role of fragmentation is one of the most important
current questions of star formation. To better understand the process of star
and cluster formation, we need to study in detail the physical structure and
properties of the parental molecular cloud. The Spokes cluster, or NGC 2264 D,
is a rich protostellar cluster where previous N2H+(1-0) observations of its
dense cores presented linewidths consistent with supersonic turbulence.
However, the fragmentation of the most massive of these cores appears to have a
scale length consistent with that of the thermal Jeans length, suggesting that
turbulence was not dominant. Aims. These two results probe different density
regimes. Our aim is to determine if there is subsonic or less-turbulent gas
(than previously reported) in the Spokes cluster at higher densities. Methods.
We present APEX N2H+(3-2) and N2D+(3-2) observations of the NGC2264-D region to
measure the linewidths and the deuteration fraction of the higher density gas.
The critical densities of the selected transitions are more than an order of
magnitude higher than that of N2H+(1-0). Results. We find that the N2H+(3-2)
and N2D+(3-2) emission present significantly narrower linewidths than the
emission from N2H+(1-0) for most cores. In two of the spectra, the nonthermal
component is close (within 1-sigma) to the sound speed. In addition, we find
that the three spatially segregated cores, for which no protostar had been
confirmed show the highest levels of deuteration. Conclusions. These results
show that the higher density gas, probed with N2H+ and N2D+(3-2), reveals more
quiescent gas in the Spokes cluster than previously reported. More high-angular
resolution interferometric observations using high-density tracers are needed
to truly assess the kinematics and substructure within NGC2264-D. (Abridged)Comment: 8 pages, 4 figures. Accepted in A&
Model-independent determination of the gluon condensate in four-dimensional SU(3) gauge theory
We determine the non-perturbative gluon condensate of four-dimensional SU(3)
gauge theory in a model independent way. This is achieved by carefully
subtracting high order perturbation theory results from non-perturbative
lattice QCD determinations of the average plaquette. No indications of
dimension two condensates are found. The value of the gluon condensate turns
out to be of a similar size as the intrinsic ambiguity inherent to its
definition.Comment: 5 pages, 5 figures, v2: references added, conclusions improved,
contrast of figures improved, 1 typo correcte
Soft, collinear and non-relativistic modes in radiative decays of very heavy quarkonium
We analyze the end-point region of the photon spectrum in semi-inclusive
radiative decays of very heavy quarkonium (m alpha_s^2 >> Lambda_QCD). We
discuss the interplay of the scales arising in the Soft-Collinear Effective
Theory, m, m(1-z)^{1/2} and m(1-z) for z close to 1, with the scales of heavy
quarkonium systems in the weak coupling regime, m, m alpha_s and m alpha_s^2.
For 1-z \sim alpha_s^2 only collinear and (ultra)soft modes are seen to be
relevant, but the recently discovered soft-collinear modes show up for 1-z <<
alpha_s^2. The S- and P-wave octet shape functions are calculated. When they
are included in the analysis of the photon spectrum of the Upsilon (1S) system,
the agreement with data in the end-point region becomes excellent. The NRQCD
matrix elements and
are also obtained.Comment: Revtex, 11 pages, 6 figures. Minor improvements and references added.
Journal 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
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Biological Motion induced mu suppression is reduced in Early Psychosis (EP) patients with active negative symptoms and Autism Spectrum Disorders (ASD).
There is evidence of genetic and neural system overlap in Autism Spectrum Disorder (ASD) and Early Psychosis (EP). Five datasets were pooled to compare mu suppression index (MSI), a proxy of mirror neuron activity, in EP, high functioning ASD, and healthy subjects (HS). ASDs and EPs with "active" negative symptoms showed significant differences in mu suppression, in response to Biological Motion/point-light display animation, compared to HS. Preliminary findings suggest that similar neural network deficits in ASD and EP could be driven by the expression of negative symptoms in the latter group of patients. These findings may aid future studies on EP and ASD and facilitate the formulation of new hypotheses regarding their pathophysiology
Renormalization group improvement of the NRQCD Lagrangian and heavy quarkonium spectrum
We complete the leading-log renormalization group scaling of the NRQCD
Lagrangian at . 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 . 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 , this is equivalent to obtain the whole set of
terms in the heavy quarkonium spectrum.
The implications of our results in the non-perturbative situation are also mentioned.Comment: 16 pages, LaTeX. Minor changes. Final versio
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