528 research outputs found
Next-to-Next-to-Leading Electroweak Logarithms for W-Pair Production at LHC
We derive the high energy asymptotic of one- and two-loop corrections in the
next-to-next-to-leading logarithmic approximation to the differential cross
section of -pair production at the LHC. For large invariant mass of the
W-pair the (negative) one-loop terms can reach more than 40%, which are
partially compensated by the (positive) two-loop terms of up to 10%.Comment: 23 pages, 9 figures, added explanations in section 3, corrected typos
and figures 7, 8,
Two-Loop Heavy-Flavor Contribution to Bhabha Scattering
We evaluate the two-loop QED corrections to the Bhabha scattering cross
section which involve the vacuum polarization by heavy fermions of arbitrary
mass m_f >> m_e. The results are valid for generic values of the Mandelstam
invariants s,t,u >> m_e^2.Comment: 13 pages, 6 figures. Equations in the appendix generalized to the
heavy-quark cas
Perturbative relations between annihilation and decay observables including resummation effects
By exploiting the analyticity properties of the two-point current-current
correlator we obtain numerical predictions for the moments in terms of
the decay rate. We perform a partial resummation of the pertinent
perturbative series expansion by solving the renormalization group equation for
Adler's function. Our predictions are renormalization scheme independent but
depend on the order of the perturbative -function expansion. The
analysis involves the unknown five-loop coefficient for which we give
some new estimates.Comment: 10 pages, LaTeX, 2 postscript figure
Heavy-quarkonium creation and annihilation with O(alpha_s^3 ln(alpha_s)) accuracy
We calculate the O(alpha_s^3 ln(alpha_s)) contributions to the
heavy-quarkonium production and annihilation rates. Our result sheds new light
on the structure of the high-order perturbative corrections and opens a new
perspective for a high-precision theoretical analysis. We also determine the
three-loop anomalous dimensions of the nonrelativistic vector and pseudoscalar
currents.Comment: 10 pages (Latex). Eq. (6) corrected, conclusions unchange
Plasma-Like Negative Capacitance in Nano-Colloids
A negative capacitance has been observed in a nano-colloid between 0.1 and
10^-5 Hz. The response is linear over a broad range of conditions. The
low-omega dispersions of both the resistance and capacitance are consistent
with the free-carrier plasma model, while the transient behavior demonstrates
an unusual energy storage mechanism. A collective excitation, therefore, is
suggested.Comment: 3 pages, 3 figure
Protected, rare and threatened plant species in France, assessment for the Pyrenean range
Dans le cadre de sa mission de connaissance, d’inventaire permanent et de suivi de la flore rare et menacée, le Conservatoire botanique pyrénéen s’est donné pour objectif de dresser un bilan précis sur les taxons présents ou signalés sur son territoire
d’action, concernés par des textes internationaux, cités par le Livre Rouge de la flore menacée de France, ou protégés au niveau national ou régional.
A partir de tableaux synthétiques et de cartes de répartition, nous présentons, pour le massif pyrénéen français, un premier état des lieux qui nous permet d’orienter nos travaux de terrain et de définir les urgences pour la conservation de ces taxons à statut. La liste de ces taxons est également donnée.The centre “Conservatoire botanique pyrénéen” is in charge of the permanent survey of the rare and endangered species over its area of duty, the Midi-Pyrénées area and the Pyrenean range. It gathers information about species concerned with the international, national or regional legislation and/or listed on the French Red list. The whole information collected is managed through a cartographic database.
We present here the first results for the Pyrenean range. This work makes possible to define priorities of preservation and field investigations for these species. The list of 140 species concerned with the legislation and/or the Red list is given
Two-Loop Corrections to Bhabha Scattering
The two-loop radiative photonic corrections to the Bhabha scattering are
computed in the leading order of the small electron mass expansion up to
nonlogarithmic term. After including the soft photon bremsstrahlung we obtain
the infrared finite result for the differential cross section, which can be
directly applied to precise luminosity determination of the present and future
colliders.Comment: Eq.(3) correcte
Gravity duals for defect quivers in the Veneziano limit
We construct gravity duals to supersymmetric gauge theories in the presence of unquenched flavor hypermultiplets in the fundamental representation of the gauge group living on the (1+1)-dimensional defect. This configuration is given by the intersection of two sets of D3-branes. Working in the Veneziano limit with large number of colors and flavors we are able to find a closed set of equations describing the dual geometry. We briefly discuss the corresponding solutions for massless flavors as well as in the small flavor limit of massive hypermultiplets. Interestingly, the 1/16-BPS supergravity solutions, preserving two Poincare supercharges, are generically only asymptotically anti de-Sitter and the dilaton does not vary with the holographic radial coordinate. This implies that the classical Type IIB supergravity solutions remain trustworthy descriptions for the gauge theories from the deep IR to the far UV.Peer reviewe
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
Electroweak and finite width corrections to top quark decays into transverse and longitudinal -bosons
We calculate the electroweak and finite width corrections to the decay of an
unpolarized top quark into a bottom quark and a -gauge boson where the
helicities of the are specified as longitudinal, transverse-plus and
transverse-minus. Together with the corrections these
corrections may become relevant for the determination of the mass of the top
quark through angular decay measurements.Comment: 4 pages, 7 postscript figures adde
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