404 research outputs found
Comment on Resummation of Mass Distribution for Jets Initiated by Massive Quarks
We compute in the heavy quark effective theory the soft coefficient D_2
entering the resummation of next-to-next-to-leading threshold logarithms for
jets initiated by a quark with a small mass compared to the hard scale of the
process. We find complete agreement with a previous computation in full QCD.
Contrary to our previous guess, this coefficient turns out to be different from
that one entering heavy flavor decay or heavy flavor fragmentation.Comment: 5 pages, no figures; minor changes, references added, version
accepted in Phys.Lett.
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
Leading Logarithms in Field Theory
We consider the Sudakov form factor in effective theories and we show that
one can derive correctly the double logarithms of the original, high-energy,
theory. We show that in effective theories it is possible to separate
explicitely soft and hard dynamics being these two regimes related to velocity
conserving and to velocity changing operators respectively. A new effective
theory is sketched which extracts the leading collinear singularities of the
full theory amplitudes. Finally, we show how all leading logarithmic effects in
field theory can be obtained by means of simple effective theories, where they
correspond to a renormalization effect.Comment: Latex file, 20 pages, no figures, corrected some typo
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
Model independent determination of the light-cone wave functions for exclusive processes
We present a method to compute, by numerical simulations of lattice QCD, the
light-cone wave functions which enter exclusive processes at large momentum
transfer, such as electromagnetic elastic scatterings, or exclusive
semi-leptonic decays as B -> pi (B -> rho) and radiative decays as B -> K*
gamma. The method is based on first principles and does not require any model
assumption.Comment: 7 pages, LaTeX fil
Model independent determination of the shape function for inclusive B decays and of the structure functions in DIS
We present a method to compute, by numerical simulations of lattice QCD, the
inclusive semileptonic differential decay rates of heavy hadrons and the
structure functions which occur in deep inelastic scattering. The method is
based on first principles and does not require any model assumption. It allows
the prediction of the differential rate in B semileptonic decays for values of
the recoiling hadronic mass W ~ sqrt(M_B Lambda_QCD), which is in the relevant
region to extract |V_ub| from the end-point of the lepton spectrum in inclusive
decays.Comment: 16 pages, LaTeX fil
Application of the Ergun's Equation in Porous Ceramic Based on CaO-Stabilized ZrO2
AbstractThe study of the permeability in porous ceramics with potential application as filters is essential because this parameter includes a number of processing variables such as porosity and pore size of great importance in the development of porous media. The knowledge of the relationship between permeability and these variables, provide a better criterion to determine the process variables that result in an optimization of the permeability. The optimization of this parameter is a basic requirement for an adequate operation of the ceramic as a filter material. In this study, the permeability of porous ceramic prepared from different compositions of the mixture of ZrO2 and a high alumina cement with 30 wt% CaO and sintered at 1400 ¡ C was experimental and theoretically evaluated. Theoretical evaluation of permeablity was performed using the Ergun«s equation, which describes the permeability constant as a funtion of the porosity and mean pore size of the porous materia
Renormalization of the Lattice HQET Isgur-Wise Function
We compute the perturbative renormalization factors required to match to the
continuum Isgur-Wise function, calculated using lattice Heavy Quark Effective
Theory. The velocity, mass, wavefunction and current renormalizations are
calculated for both the forward difference and backward difference actions for
a variety of velocities. Subtleties are clarified regarding tadpole
improvement, regulating divergences, and variations of techniques used in these
renormalizations.Comment: 28 pages, 0 figures, LaTeX. Final version accepted for publication in
Phys. Rev. D. (Minor changes.
Resummed Mass Distribution for Jets Initiated by Massive Quarks
We resum to all orders of perturbation theory the invariant mass distribution of jets initiated by massive quarks. We find that the inclusion of mass terms, in the N-moment space, results in the universal factor delta_N(Q^2;m^2), taking into account dead-cone effects in gluon emission, which multiplies the massless jet distribution function J_N(Q^2). The variable N is rescaled by the mass correction parameter r = m^2/Q^2 c l nu decay spectra or the inclusion of beauty mass effects in t --> b W decays, are briefly sketched
The Two Loop Crossed Ladder Vertex Diagram with Two Massive Exchanges
We compute the (three) master integrals for the crossed ladder diagram with
two exchanged quanta of equal mass. The differential equations obeyed by the
master integrals are used to generate power series expansions centered around
all the singular (plus some regular) points, which are then matched numerically
with high accuracy. The expansions allow a fast and precise numerical
calculation of the three master integrals (better than 15 digits with less than
30 terms in the whole real axis). A conspicuous relation with the equal-mass
sunrise in two dimensions is found. Comparison with a previous large momentum
expansion is made finding complete agreement.Comment: 42 pages, 1 figur
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