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61.
62.
We briefly sketch a proof concerning the structure of the all-order ɛ expansions of generalized hypergeometric functions with special sets of parameters. 相似文献
63.
A recently proposed normalization condition for the imaginary part of the self-energy of an unstable particle is shown to lead to closed, exact expressions for the renormalized self-energy and propagator, which are consequently free of ultraviolet divergences to all orders in perturbation theory. In turn, the corresponding closed expressions for the mass and field renormalization counterterms are necessary in some important cases to avoid power-like infrared divergences in high orders of perturbation theory. In the same examples, the width plays the rôle of an infrared cutoff, and, consequently, the field renormalization counterterm is not an analytic function of the coupling constant. 相似文献
64.
Bernd A. Kniehl Gustav Kramer 《The European Physical Journal C - Particles and Fields》1999,6(3):493-501
Approximately taking into account the higher-order effects due to multiple-gluon initial-state radiation, we extract from
the latest Tevatron data of prompt hadroproduction the leading colour-octet matrix elements within the nonrelativistic-QCD (NRQCD) factorization formalism proposed
by Bodwin, Braaten, and Lepage. We find that the matrix elements which describe the formation of mesons from colour-octet pairs in the angular-momentum states and , with , which are responsible for the excess of the predicted cross section of inelastic photoproduction over the existing HERA data at high values of the inelasticity variable , are significantly reduced. We conclude that it is premature to proclaim a discrepancy between the Tevatron and HERA measurements
of inclusive production in the NRQCD framework. We also consider mesons originating from the radiative feed down of promptly produced mesons.
Received: 10 March 1998 / Revised version: 22 April 1998 / Published online: 30 July 1998 相似文献
65.
We study the inclusive hadroproduction of D0, D+, D*+, and D(s)+ mesons at next-to-leading order in the parton model of quantum chromodynamics endowed with universal nonperturbative fragmentation functions fitted to e+e- annihilation data from CERN LEP1. Working in the general-mass variable-flavor-number scheme, we resum the large logarithms through the evolution of the fragmentation functions and, at the same time, retain the full dependence on the charm-quark mass without additional theoretical assumptions. In this way, the cross section distributions in transverse momentum recently measured by the CDF Collaboration in run II at the Fermilab Tevatron are described within errors. 相似文献
66.
Bernd A. Kniehl Igor Kondrashuk Eduardo A. Notte-Cuello Ivan Parra-Ferrada Marko Rojas-Medar 《Nuclear Physics B》2013
In our previous paper (Allendes et al., 2013 [10]), we showed that multi-fold Mellin–Barnes (MB) transforms of Usyukina–Davydychev (UD) functions may be reduced to two-fold MB transforms. The MB transforms were written there as polynomials of logarithms of ratios of squares of the external momenta with certain coefficients. We also showed that these coefficients have a combinatoric origin. In this paper, we present an explicit formula for these coefficients. The procedure of recovering the coefficients is based on taking the double-uniform limit in certain series of smooth functions of two variables which is constructed according to a pre-determined iterative way. The result is obtained by using basic methods of mathematical analysis. We observe that the finiteness of the limit of this iterative chain of smooth functions should reflect itself in other mathematical constructions, too, since it is not related in any way to the explicit form of the MB transforms. This finite double-uniform limit is represented in terms of a differential operator with respect to an auxiliary parameter which acts on the integrand of a certain two-fold MB integral. To demonstrate that our result is compatible with original representations of UD functions, we reproduce the integrands of these original integral representations by applying this differential operator to the integrand of the simple integral representation of the scalar triangle four-dimensional integral J(1,1,1−ε). 相似文献
68.
We present an on-shell scheme to renormalize the Cabibbo-Kobayashi-Maskawa (CKM) matrix. It is based on a novel procedure to separate the external-leg mixing corrections into gauge-independent self-mass and gauge-dependent wave function renormalization contributions, and to implement the on-shell renormalization of the former with nondiagonal mass counterterm matrices. Diagonalization of the complete mass matrix leads to an explicit CKM counterterm matrix, which automatically satisfies all the following important properties: it is gauge independent, preserves unitarity, and leads to renormalized amplitudes that are nonsingular in the limit in which any two fermions become mass degenerate. 相似文献
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70.
The logarithmically enhanced alpha(7)ln(1/alpha) contribution to the hyperfine splitting of the positronium ground-state energy levels is calculated in the framework of dimensionally regularized nonrelativistic quantum electrodynamics. The correction is negative and amounts to about 1/3 of the leading logarithmic alpha(7)ln (2)(1/alpha) one. The discrepancy between the experimental measurements and the theoretical prediction is reduced. 相似文献