525 research outputs found
Transverse Momentum Distributions in B-Decays
We consider transverse momentum distributions in B-decays. The O(alpha_S)
coefficients for soft and collinear logarithms are computed to next-to-leading
accuracy. Resummation of large logarithmic contributions is performed in impact
parameter space within the general formalism for transverese momentum
distributions. It is shown that the shape-function approach as used for the
threshold distribution case cannot be extended to the transverse momentum one.Comment: LaTex file, 8 pages, 1 postscript figur
Transverse Momentum Distribution in b-> s Gamma
We present the complete calculation of the transverse momentum distribution
for the decay b->s Gamma. The contributions of the leading operator O_7 are
computed: infrared logarithms are resummed with next-to-leading accuracy,
according to usual techniques of resummation. Non logarithmic terms are
evaluated to O(alpha_S) by calculating one loop diagrams.Comment: Talk given 10th International QCD Conference (QCD 03), Montpellier,
France, 2-9 Jul 2003. 4 page
Master integrals for the two-loop light fermion contributions to and
We give the analytic expressions of the eight master integrals entering our
previous computation of two-loop light fermion contributions to and
. The results are expressed in terms of generalized
harmonic polylogarithms with maximum weight four included.Comment: 9 pages, 6 figure
Threshold Resummed Spectra in B -> Xu l nu Decays in NLO (I)
We evaluate thresholds resummed spectra in B -> Xu l nu decays in
next-to-leading order. We present results for the distribution in E_X and in
m_X^2/E_X^2, for the distribution in E_X and E_l and for the distribution in
E_X, where E_X and m_X are the energy and the invariant mass of the final
hadronic state Xu respectively and E_l is the energy of the charged lepton. We
explicitly show that all these spectra (where there is no integration over the
hadronic energy) can be directly related to the photon spectrum in B -> Xs
gamma via short-distance coefficient functions.Comment: 33 pages, no figures. The section on the double distribution in the
hadron and electron energies has been largely rewritten with an improved
resummation scheme. Small stylistic changes in the remaining sections.
References adde
On Non Perturbative Corrections to the Potential for Heavy Quarks
We discuss non perturbative corrections to the Coulomb-like potential of
heavy quarks at short distances. We consider both the standard framework
provided by infrared renormalons and the assumption that confinement does not
allow weak fields to penetrate the vacuum. In the former case the leading
correction at short distances turns out to be quadratic in r for static quarks.
In the latter case we find a potential which is proportional to r as r
rightarrow 0. We point out that similar effects arise due to a new kind of non
perturbative correction proportional to 1/Q^2, which is unaccounted for by the
operator product expansion and which was recently discussed within a different
framework.
Phenomenological implications of the linear correction to the potential are
briefly reviewed.Comment: 13 pages, latex, 2 figures, uses eps
Inclusive Measure of |V_ub| with the Analytic Coupling Model
By analyzing B -> X_u l nu_l spectra with a model based on soft-gluon
resummation and an analytic time-like QCD coupling, we obtain |V_ub| = (3.76
+-0.13 +- 0.22)*10^(-3), where the first and the second error refers to
experimental and theoretical errors, respectively. The V_ub value is obtained
from the available measured semileptonic branching fractions in limited regions
of the phase-space. The distributions in the lepton energy E_l, the hadron
invariant mass m_X, the light-cone momentum P_+ = E_X - p_X, together with the
double distributions in (m_X,q^2) and (E_l,s_h^max), are used to select the
phase-space regions. The q^2 is the dilepton squared momentum and s_h^max is
the maximal m_X^2 at fixed q^2 and E_l. The V_ub value obtained is in complete
agreement with the value coming from exclusive B decays and from an over-all
fit to the Standard Model parameters. We show that the slight disagreement (up
to +2 sigma) with respect to previous inclusive measurements is not related to
different choices for the b (and c) masses but to a different modelling of the
threshold (Sudakov) region.Comment: 19 pages, 2 figures, revised version accepted in Eur.Phys.J.
Master integrals with 2 and 3 massive propagators for the 2-loop electroweak form factor - planar case
We compute the master integrals containing 2 and 3 massive propagators
entering the planar amplitudes of the 2-loop electroweak form factor. The
masses of the , and Higgs bosons are assumed to be degenerate. This work
is a continuation of our previous evaluation of master integrals containing at
most 1 massive propagator. The 1/\epsilon poles and the finite parts are
computed exactly in terms of a {\it new} class of 1-dimensional harmonic
polylogarithms of the variable x, with \epsilon=2-D/2 and D the pace-time
dimension. Since thresholds and pseudothresholds in s=\pm 4m^2 do appear in
addition to the old ones in s=0,\pm m^2, an extension of the basis function set
involving complex constants and radicals is introduced, together with a set of
recursion equations to reduce integrals with semi-integer powers. It is shown
that the basic properties of the harmonic polylogarithms are maintained by the
generalization. We derive small-momentum expansions |s| << m^2 of all the
6-denominator amplitudes. We also present large momentum expansions |s| >> m^2
of all the 6-denominator amplitudes which can be represented in terms of
ordinary harmonic polylogarithms. Comparison with previous results in the
literature is performed finding complete agreement.Comment: 68 pages, 7 figure
Approximate NNLO Threshold Resummation in Heavy Flavour Decays
We present an approximate NNLO evaluation of the QCD form factor resumming
large logarithmic perturbative contributions in semi-inclusive heavy flavour
decays.Comment: 16 pages, 3 figures, Latex; minor changes; 2 figures adde
On the Generalized Harmonic Polylogarithms of One Complex Variable
We describe how to compute numerically in the complex plain a set of
Generalized Harmonic Polylogarithms (GHPLs) with square roots in the weights,
using the C++/GiNaC numerical routines of Vollinga and Weinzierl. As an
example, we provide the numerical values of the NLO electroweak light-fermion
corrections to the Higgs boson production in gluon fusion in the case of
complex W and Z masses.Comment: 25 pages, 1 figur
A Nonrelativistic Chiral Soliton in One Dimension
I analyze the one-dimensional, cubic Schr\"odinger equation, with
nonlinearity constructed from the current density, rather than, as is usual,
from the charge density. A soliton solution is found, where the soliton moves
only in one direction. Relation to higher-dimensional Chern--Simons theory is
indicated. The theory is quantized and results for the two-body quantum problem
agree at weak coupling with those coming from a semiclassical quantization of
the soliton.Comment: 11 pages, Latex2
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