arXiv subjects

Claudio Coriano'

Publications and source records attributed to Claudio Coriano'.

31 records · Page 2Linked to original sources

arXiv1995

Higher-Order Corrections to BFKL Evolution from $t$-Channel Unitarity

Using reggeon diagrams as a partial implementation of $t$-channel unitarity, $O(g^4)$ corrections to the BFKL evolution equation have been obtained. We describe the spectrum and holomorphic factorization properties of the resulting scale-invariant kernel. For a gauge theory, $t$-channel unitarity can be studied directly in the complex $j$-plane by implementing Ward identity constraints together with the group structure of reggeon interactions. We discuss how both the $O(g^2)$ BFKL kernel and the $O(g^4)$ corrections can then be derived.

hep-ph↗

arXiv1995

The Electric Charge of a Dirac Monopole at Nonzero Temperature

We study the effect of nonzero temperature on the induced electric charge around a Dirac monopole. While at zero temperature the charge is known to be proportional to a CP violating $θ$ parameter, we find that at high temperature the charge is proportional to sin $θ$. Other features of the charge at nonzero temperature are discussed. We also compute the induced charge at nonzero temperature around an Aharonov-Bohm flux string in $2+1$ dimensions and compare the result with an index theorem, and also with the electron-monopole problem in $3+1$ dimensions.

hep-th↗

arXiv1995

Conformally Symmetric Contributions to BFKL Evolution at Next to Leading Order

Unitarity corrections to the BFKL evolution at next to leading order determine a new component of the evolution kernel which is shown to possess conformal invariance properties. Expressions for the complete spectrum of the new component and the correction to the intercept of the pomeron trajectory are presented.

hep-ph↗

arXiv1995

Properties of the Scale Invariant $O(g^4)$ Lipatov Kernel

We study the scale-invariant $O(g^4)$ kernel which appears as an infra-red contribution in the BFKL evolution equation and is constructed via multiparticle $t$-channel unitarity. We detail the variety of Ward identity constraints and infra-red cancellations that characterize its infrared behaviour. We give an analytic form for the full non-forward kernel. For the forward kernel controlling parton evolution at small-x, we give an impact parameter representation, derive the eigenvalue spectrum, and demonstrate a holomorphic factorisation property related to conformal invariance. The results show that, at next-to-leading-order, the transverse momentum infra-red region may produce a strong reduction of the BFKL small-x behavior.

hep-ph↗

arXiv1994

The Spectrum of the O(g^4) scale-invariant Lipatov Kernel

The scale-invariant $O(g^4)$ Lipatov kernel has been determined by t-channel unitarity. The forward kernel responsible for parton evolution is evaluated and its eigenvalue spectrum determined. In addition to a logarithmic modification of the $O(g^2)$ kernel a distinct new kinematic component appears. This component is infra-red finite without regularization and has the holomorphic factorization property necessary for conformal invariance. It gives a reduction (of ~$\sim 65α_s^2/π^2\sim 0.15$) in the power growth of parton distributions at small-x.

hep-ph↗

arXiv1994

Dispersive Methods and QCD Sum Rules for γγCollisions

It has been shown, in the case of meson photoproduction, that the power-law falloff of these reactions can be described by lowest order (real) sum rules, at moderate momentum transfer. The phases of these processes, in this regime, are usually thought to be non-perturbative. In a sum rule framework, however, they can possibly be described by radiative corrections to the hadronic spectral densities of the corresponding helicities, which become complex functions to order $α_s$, and the effects of interference can be strongly enhanced by the presence of the vacuum condensates in the dispersion relation. It is shown that the imaginary parts of these complex corrections have a factorized form and can be evaluated in a systematic fashion, while their real parts, at the same perturbative order, are down by at least 2 powers of momentum transfer. The analysis is done at two loop level, combining dimensional regularization and light-cone methods. The calculations are performed for all the independent set of scalar diagrams generated by the OPE. The analytical bounds are identified and discussed.

hep-ph↗

arXiv1994

The Transition to Perturbative QCD in Compton Scattering

We investigate the transition to perturbative QCD in Compton processes, by concentrating on the specific reactions $πγ\to πγ$ and pion photoproduction at moderate energy scales. New sum rules for each of the helicities involved in the scattering and the cross section are given, together with a detailed stability analysis. Our results are then compared with those derived from higher-power factorization, incorporating Sudakov suppression for quark elastic scattering. An overlap of predictions obtained by the two approaches is observed at a momentum transfer as low as 4 GeV$^2$ and at a photon scattering angle around 40$^o$. Our work shows that factorization theorems and sum rule methods complement each other in the description of Compton scattering at moderate energy scales, and give information on the transition to perturbative QCD in these processes. The sum rule formalism is further applied to the crossed reaction $γγ\to π^+ π^-$, and is in very good agreement with the experimental data."

hep-ph↗

arXiv1993

Stability Analysis of Sum Rules for Compton Scattering

We perform a stability analysis of a recently proposed sum rule for pion Compton scattering at fixed angle and moderate Mandelstam invariants. The sum rule is found to be sensitive to the parameter $λ^2$, the contour radius of a generalized Borel transform. A modified phenomenological model for the continuum contribution is proposed to remove this dependence. It is shown that the best value of the quark-hadron duality interval $s_0=0.6$ GeV$^2$ is close to that in the form factor case ($s_0=0.7$ GeV$^2$). The application of this new model to the pion form factor is examined. A comparison of our predictions with those derived from a modified perturbative calculation including Sudakov suppression is also briefly considered.

hep-ph↗

arXiv1993

Power Corrections to QCD Sum Rules for Compton Scattering

We extend previous work on sum rules for the invariant amplitudes of pion Compton scattering by deriving a complete lowest order perturbative spectral function - and its leading non perturbative power corr ections - for a specific combination of the two helicities $(H_1 + H_2)$ of this process. Using some properties of a modified version of the Borel transform, we develop a method of calculation of the gluonic corrections which can be easily extended to other similar reactions, such as proton Compton scattering. A preliminary comparison of the new sum rule with the pion form factor sum rule is made.

hep-ph↗

arXiv1993

QCD Sum Rule and Perturbative QCD Approaches to Pion Compton Scattering

We compare two approaches to the description of pion Compton scattering at moderate momentum transfer, one being based on local duality QCD sum rules for the invariant amplitudes of the process, which have been derived recently, and the other on the modified factorization formula with Sudakov effects included. We find that perturbative QCD predictions are dominant over those from QCD sum rules only for the scattering angle greater than 90$^o$.

hep-ph↗

arXiv1993

QCD Sum Rules and Compton Scattering

We extend QCD sum rule analysis to moderate energy fixed angle Compton scattering. In this kinematic region there is a strong similarity to the sum rule treatment of electromagnetic form factors, although the four-point amplitude requires a modification of the Borel transform. To illustrate our method, we derive the sum rules for helicity amplitudes in pion Compton scattering and estimate their large-$t$ behavior in the local duality approximation.

hep-ph↗

arXiv1992

Scattering in Soliton Models and the Bosonic Exchange description

We argue that the description of meson-nucleon dynamics based on the boson-exchange approach, is compatible with the description of the nucleon as a soliton in the nonrelativistic limit. Our arguments are based on an analysis of the meson-soliton form factor and the exact meson-soliton and soliton-soliton scattering amplitudes in the Sine-Gordon model.

hep-th↗

arXiv1992

Electrodynamics in the presence of an axion

The low energy limit of an axion field coupled to gauge fields is investigated through the behaviour of the gauge field propagator in a local vaccum angle background. The local (singular) part of the effective action for the axion field is calculated at one loop level. In the case of a timelike, linearly growing axion field, representing a massive axion, we give an asymptotic expansion of the causal propagator and we solve nonlocally for the first coefficient. We show that, for a generic axionic background, short distance propagation of the gauge fields is well defined.

hep-th↗