103,495 research outputs found
Dispersive approach in Sudakov resummation
The dispersive approach to power corrections is given a precise
implementation, valid beyond single gluon exchange, in the framework of Sudakov
resummation for deep inelastic scattering and the Drell-Yan process. It is
shown that the assumption of infrared finite Sudakov effective couplings
implies the universality of the corresponding infrared fixed points. This
property is closely tied to the universality of the virtual contributions to
space-like and time-like processes, encapsulated in the second logarithmic
derivative of the quark form factor.Comment: 3 pages, talk given at Quark Confinement and the Hadron Spectrum 7,
Ponta Delgada, Azores, Portugal, 2-7 Sep 2006, LaTeX, uses aip-6s.clo,
aipproc.cls and aipxfm.sty (included
Conformal window and Landau singularities
A physical characterization of Landau singularities is emphasized, which
should trace the lower boundary N_f^* of the conformal window in QCD and
supersymmetric QCD. A natural way to disentangle ``perturbative'' from
``non-perturbative'' contributions below N_f^* is suggested. Assuming an
infrared fixed point is present in the perturbative part of the QCD coupling
even in some range below N_f^* leads to the condition gamma(N_f^*)=1, where
gamma is the critical exponent. This result is incompatible with the existence
of an analogue of Seiberg free dual magnetic phase in QCD. Using the Banks-Zaks
expansion, one gets
4<N_f^*<6. The low value of N_f^* gives some justification to the infrared
finite coupling approach to power corrections, and suggests a way to compute
their normalization from perturbative input. If the perturbative series are
still asymptotic in the negative coupling region, the presence of a negative
ultraviolet fixed point is required both in QCD and in supersymmetric QCD to
preserve causality within the conformal window. Some evidence for such a fixed
point in QCD is provided through a modified Banks-Zaks expansion. Conformal
window amplitudes, which contain power contributions, are shown to remain
generically finite in the N_f=-\infty one-loop limit in simple models with
infrared finite perturbative coupling.Comment: 35 pages, 1 figure, JHEP style. A new section added to point out the
results give some justification to the infrared finite coupling approach to
power corrections, and suggest a way to compute their normalization from
perturbative inpu
From stars to nuclei
We recall the basic physical principles governing the evolution of stars with
some emphasis on the role played by the nuclear reactions. We argue that in
general it is not possible from observations of stars to deduce constraints on
the nuclear reaction rates. This is the reason why precise measurements of
nuclear reaction rates are a necessity in order to make progresses in stellar
physics, nucleosynthesis and chemical evolution of galaxies. There are however
some stars which provides useful constraint on nuclear processes. The
Wolf-Rayet stars of the WN type present at their surface CNO equilibrium
patterns. There is also the particular case of the abundance of Ne at
the surface of WC stars. The abundance of this element is a measure of the
initial CNO content. Very interestingly, recent determinations of its abundance
at the surface of WC stars tend to confirm that massive stars in the solar
neighborhood have initial metallicities in agreement with the Asplund et al.
(2005) solar abundances.Comment: 8 pages, 2 figures, be published in "European Physical Journal:
Special Topics
In search of foreign influences, other than French, in nineteenth-century Belgian court decisions
In many senses, nineteenth-century Belgium can be considered to be a 'legal province' of Belgium. In the tradition of the exegetical school, legislation is the one and only formal source of law for judicial decisions. This legislation is primarily composed of the Napoleonic codes. Judges seem to be afraid of referring to other sources. If a âforeignâ source is quoted, it is a French one
No Riemann-hurwitz formula for the p-ranks of relative class groups
We disprove, by means of numerical examples, the existence of a
Riemann-Hurwitz formula for the p-ranks of relative class groups in a
p-ramified p-extension K/k of number fields of CM-type containing ?\_p. In the
cyclic case of degree p, under some assumptions on the p-class group of k, we
prove some properties of the Galois structure of the p-class group of K; but we
have found, through numerical experimentation, that some theoretical group
structures do not exist in this particular situation, and we justify this fact.
Then we show, in this context, that Kida's formula on lambda invariants is
valid for the p-ranks if and only if the p-class group of K is reduced to the
group of ambiguous classes, which is of course not always the case.Comment: 6 pages + tables num\'erique
Eigenvalues of the transversal Dirac operator on Kahler foliations
In this paper, we prove Kirchberg inequalities for any kahler spin
foliations. Their limiting cases are then characterized as being transversal
minimal Einstein foliations. The key point is to introduce the transversal
kahlerian twistor operators
Polarization of B -> VV: experimental status
The experimental status of the polarization measurements in B to charmless
vector-vector decays by both the Belle and Babar experiments is reviewed. The
results obtained in related vector-tensor, axial vector-vector, and axial
vector-axial vector modes are also given.Comment: 6 pages, 5 figures, Proceedings of CKM2010, the 6th International
Workshop on the CKM Unitarity Triangle, University of Warwick, UK, 6-10
September 201
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