Infrared-sensitive Physics in QCD and in Electroweak Theory

Ciafaloni, M.

doi:10.1007/978-3-540-74233-3_8

Cited by 6 publications

(1 citation statement)

References 23 publications

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“…However, such investigations were often focused on the perturbative parts of the observables, leaving the non-perturbative parts unconsidered (see e.g. the recent overview [9] and Refs. therein).…”

Section: Introductionmentioning

confidence: 99%

Factorization and infrared properties of non-perturbative contributions to DIS structure functions

2011

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In this paper we present a new derivation of the QCD factorization. We deduce the kT -and collinear factorizations for the DIS structure functions by consecutive reductions of a more general theoretical construction. We begin by studying the amplitude of the forward Compton scattering off a hadron target, representing this amplitude as a set of convolutions of two blobs connected by the simplest, two-parton intermediate states. Each blob in the convolutions can contain both the perturbative and non-perturbative contributions. We formulate conditions for separating the perturbative and non-perturbative contributions and attributing them to the different blobs. After that the convolutions correspond to the QCD factorization. Then we reduce this totally unintegrated (basic) factorization first to the kT -factorization and finally to the collinear factorization. In order to yield a finite expression for the Compton amplitude, the integration over the loop momentum in the basic factorization must be free of both ultraviolet and infrared singularities. This obvious mathematical requirement leads to theoretical restrictions on the non-perturbative contributions (parton distributions) to the Compton amplitude and the DIS structure functions related to the Compton amplitude through the Optical theorem. In particular, our analysis excludes the use of the singular factors x −a (with a > 0) in the fits for the quark and gluon distributions because such factors contradict to the integrability of the basic convolutions for the Compton amplitude. This restriction is valid for all DIS structure functions in the framework of both the kT -factorization and the collinear factorization if we attribute the perturbative contributions only to the upper blob. The restrictions on the non-perturbative contributions obtained in the present paper can easily be extended to other QCD processes where the factorization is exploited.

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Section: Introductionmentioning

confidence: 99%

Factorization and infrared properties of non-perturbative contributions to DIS structure functions

2011

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Anomalous Sudakov form factors

Ciafaloni

Comelli

2010

J. High Energ. Phys.

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While radiative corrections of infrared origin normally depress high energy amplitudes (Sudakov form factors), we find that in some cases resummation of leading effects produces exponentials with positive exponents, giving rise to amplitudes that grow indefinitely with energy. The effect happens in broken gauge theories like the electroweak sector of the Standard Model, and is related to the existence of amplitudes that do not respect the gauge symmetry, and that contrary to expectations do not vanish in the very high energy limit, but rather become dominant. As a working example we consider a model with two chiral abelian gauge groups U ′ (1) ⊗ U (1) with large mass splitting M Z ′ ≫ MZ , and we compute leading radiative corrections corrections to the decay of the heavy extra Z ′ boson into light fermions. For proper fermionic charges, the chirality breaking magnetic dipole moment, although mass suppressed, becomes the dominant contribution to the Z ′ width at very high energies. * by "asymptotic behavior" we mean the behavior of cross sections for energies much higher than all SM particles masses. Also the case of energies higher than the weak scale yet lower than a heavy Higgs mass have been studied, see [6]

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Electroweak double-logs at smallx

Ciafaloni

Comelli

2008

J. High Energy Phys.

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We investigate enhanced EW corrections to inclusive hard processes in the TeV energy region with emphasis on the small-x situation, in which the hard scale Q is significantly smaller than the available energyWe first propose and justify a general factorization formula in which the (double-log) EW form factor at scale Q 2 is factorized from EW parton distribution functions, which satisfy evolution equations of DGLAP type. We then investigate the small-x behavior of the EW parton distributions including the novel ones for non-vanishing t-channel weak isospin T and we compare it with a BFKL-type approach. In either approach we find that large small-x corrections of order αw log x log Q 2 /M 2 (M being the EW symmetry breaking scale) are present only for T=2 and not for T=1. This implies that only transverse W W interactions (coupled to T=2) are affected, while the T=1 components feel just the form factor at scale Q 2 .

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Infrared-sensitive Physics in QCD and in Electroweak Theory

Abstract: I recall the main ideas about the treatment of QCD infrared physics, as developed in the late seventies, and I outline some novel applications of those ideas to Electroweak Theory.

Cited by 6 publications

References 23 publications

Factorization and infrared properties of non-perturbative contributions to DIS structure functions

Factorization and infrared properties of non-perturbative contributions to DIS structure functions

Anomalous Sudakov form factors

Electroweak double-logs at smallx

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