574 research outputs found
Complete (O_7,O_8) contribution to B -> X_s gamma at order alpha_s^2
We calculate the set of O(alpha_s^2) corrections to the branching ratio and
to the photon energy spectrum of the decay process B -> X_s gamma originating
from the interference of diagrams involving the electromagnetic dipole operator
O_7 with diagrams involving the chromomagnetic dipole operator O_8. The
corrections evaluated here are one of the elements needed to complete the
calculations of the B -> X_s gamma branching ratio at next-to-next-to-leading
order in QCD. We conclude that this set of corrections does not change the
central value of the Standard Model prediction for Br(B -> X_s gamma) by more
than 1 %.Comment: 19 pages, 8 figure
NLO QCD calculations with HELAC-NLO
Achieving a precise description of multi-parton final states is crucial for
many analyses at LHC. In this contribution we review the main features of the
HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections
for tt + 2 jet production at LHC are illustrated and discussed.Comment: 7 pages, 4 figures. Presented at 10th DESY Workshop on Elementary
Particle Theory: Loops and Legs in Quantum Field Theory, Worlitz, Germany,
April 25-30, 201
Hadronic mass and q^2 moments of charmless semileptonic B decay distributions
We report OPE predictions for hadronic mass and q^2 moments in inclusive
semileptonic B decays without charm, taking into account experimental cuts on
the charged lepton energy and on the hadronic invariant mass, and address the
related theoretical uncertainty.Comment: 16 pages, 1 figure; v3: we have corrected a mistake in the code that
produced the numerical results; tables replaced, small changes in the tex
Optimizing the Reduction of One-Loop Amplitudes
We present an optimization of the reduction algorithm of one-loop amplitudes
in terms of master integrals. It is based on the exploitation of the polynomial
structure of the integrand when evaluated at values of the loop-momentum
fulfilling multiple cut-conditions, as emerged in the OPP-method. The
reconstruction of the polynomials, needed for the complete reduction, is rended
very versatile by using a projection-technique based on the Discrete Fourier
Transform. The novel implementation is applied in the context of the NLO QCD
corrections to u d-bar --> W+ W- W+
Il Conto Economico nell'informativa di bilancio: il modello IASB.
Nell\u2019ambito dei documenti di bilancio il conto economico, come modificato dallo IASB, \ue8 quello che maggiormente si differenzia rispetto agli schemi previsti dalla normativa nazionale.
La funzione del conto economico, in passato orientata essenzialmente alla determinazione del reddito prodotto dalla gestione e all\u2019analisi delle componenti che lo hanno determinato, nel modello IASB viene ampliata con l\u2019aggiunta di componenti che prudenzialmente erano invece esposti esclusivamente come variazioni del patrimonio netto nello specifico prospetto; la finalit\ue0 di tale modifica \ue8 quella di fornire, direttamente nel conto economico, informazioni pi\uf9 complete in merito alla performance ottenuta dall'impresa nell'esercizio. In tal modo, l'informativa \ue8 orientata al raggiungimento degli obiettivi di sistematicit\ue0 e interconnessione delle informazioni per fornire anche elementi utili a comprendere e a spiegare i motivi delle variazioni dei prezzi di mercato dei titoli rappresentativi del capitale dell\u2019impresa.
Tuttavia, parallelamente al positivo effetto in termini di completezza dell\u2019informativa di bilancio, si palesa il rischio che, qualora non continuino ad essere individuabili le due macro categorie di componenti reddituali, si generi confusione tra le componenti economiche che partecipano stabilmente alla formazione del risultato di gestione e quelle che possono derivare da pura attivit\ue0 di valutazione effettuata nel breve o brevissimo termine.
La distinta esposizione del risultato di gestione rispetto alle altre componenti del conto economico complessivo favorisce, invece, una corretta valutazione di tutte le scelte effettuate dal management, con conseguente maggiore facilit\ue0 d\u2019individuazione e di gestione dei rischi
MR- arthrography: anatomic variant from link between lateral meniscus and anterior and posterior cruciate ligaments. A case report and review of the literature
Menisci congenital anomalies are rare morphologic abnormalities including accessory meniscus, discoid meniscus, double-layered meniscus, hypoplastic meniscus and ring-shaped meniscus (RSM). In a 35 year-old male patient, MR arthrography showed a bridging accessory bundle connecting the anterior cruciate ligament and posterior cruciate ligament with the posterior horn of the lateral meniscus. Arthroscopic examination showed a fan-like obstacle embracing the posterior horn of the lateral meniscus. It would be important to correctly identify this anatomical variant, because the bundle connecting the external meniscus to the ligaments of the central pivot can be misinterpreted as a meniscal fragment
Polarizing the Dipoles
We extend the massless dipole formalism of Catani and Seymour, as well as its
massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, to
arbitrary helicity eigenstates of the external partons. We modify the real
radiation subtraction terms only, the primary aim being an improved efficiency
of the numerical Monte Carlo integration of this contribution as part of a
complete next-to-leading order calculation. In consequence, our extension is
only applicable to unpolarized scattering. Upon summation over the helicities
of the emitter pairs, our formulae trivially reduce to their original form. We
implement our extension within the framework of Helac-Phegas, and give some
examples of results pertinent to recent studies of backgrounds for the LHC. The
code is publicly available. Since the integrated dipole contributions do not
require any modifications, we do not discuss them, but they are implemented in
the software.Comment: 20 pages, 4 figures, Integrated dipoles implemented for massless and
massive case
Feynman rules for the rational part of the Electroweak 1-loop amplitudes
We present the complete set of Feynman rules producing the rational terms of
kind R_2 needed to perform any 1-loop calculation in the Electroweak Standard
Model. Our results are given both in the 't Hooft-Veltman and in the Four
Dimensional Helicity regularization schemes. We also verified, by using both
the 't Hooft-Feynman gauge and the Background Field Method, a huge set of Ward
identities -up to 4-points- for the complete rational part of the Electroweak
amplitudes. This provides a stringent check of our results and, as a
by-product, an explicit test of the gauge invariance of the Four Dimensional
Helicity regularization scheme in the complete Standard Model at 1-loop. The
formulae presented in this paper provide the last missing piece for completely
automatizing, in the framework of the OPP method, the 1-loop calculations in
the SU(3) X SU(2) X U(1) Standard Model.Comment: Many thanks to Huasheng Shao for having recomputed, independently of
us, all of the effective vertices. Thanks to his help and by
comparing with an independent computation we performed in a general
gauge, we could fix, in the present version, the following formulae: the
vertex in Eq. (3.6), the vertex in Eq. (3.8),
Eqs (3.16), (3.17) and (3.18
Updated NNLO QCD predictions for the weak radiative B-meson decays
Weak radiative decays of the B mesons belong to the most important flavor
changing processes that provide constraints on physics at the TeV scale. In the
derivation of such constraints, accurate standard model predictions for the
inclusive branching ratios play a crucial role. In the current Letter we
present an update of these predictions, incorporating all our results for the
O(alpha_s^2) and lower-order perturbative corrections that have been calculated
after 2006. New estimates of nonperturbative effects are taken into account,
too. For the CP- and isospin-averaged branching ratios, we find B_{s gamma} =
(3.36 +_ 0.23) * 10^-4 and B_{d gamma} = 1.73^{+0.12}_{-0.22} * 10^-5, for
E_gamma > 1.6GeV. Both results remain in agreement with the current
experimental averages. Normalizing their sum to the inclusive semileptonic
branching ratio, we obtain R_gamma = ( B_{s gamma} + B_{d gamma})/B_{c l nu} =
(3.31 +_ 0.22) * 10^-3. A new bound from B_{s gamma} on the charged Higgs boson
mass in the two-Higgs-doublet-model II reads M_{H^+} > 480 GeV at 95%C.L.Comment: journal version, 5 pages, no figure
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