# Form factors and QCD in spacelike and timelike region

## Abstract

The authors analyze the basic hard exclusive processes: {pi}{gamma}{sup *}{gamma}-transition, pion and nucleon electromagnetic form factors, and discuss the analytic continuation of QCD formulas from the spacelike q{sup 2} < 0 to the timelike region q{sup 2} > 0 of the relevant momentum transfers. They describe the construction of the timelike version of the coupling constant {alpha}{sub s}. They show that due to the analytic continuation of the collinear logarithms each eigenfunction of the evolution equation acquires a phase factor and investigate the resulting interference effects which are shown to be very small. They found no sources for the K-factor-type enhancements in the perturbative QCD contribution to the hadronic form factors. To study the soft part of the pion electromagnetic form factor, they use a QCD sum rule inspired model and show that there are non-canceling Sudakov double logarithms which result in a K-factor-type enhancement in the timelike region.

- Authors:

- Publication Date:

- Research Org.:
- Thomas Jefferson National Accelerator Facility, Newport News, VA (US)

- Sponsoring Org.:
- USDOE Office of Energy Research (ER) (US)

- OSTI Identifier:
- 754870

- Report Number(s):
- DOE/ER/40150-1418; JLAB-THY-00-12; RUB-TPII-06/00; hep-ph/0005085

TRN: US0100880

- DOE Contract Number:
- AC05-84ER40150

- Resource Type:
- Journal Article

- Journal Name:
- Phys.Rev.D62:113001,2000

- Additional Journal Information:
- Journal Volume: D; Journal Issue: 62; Other Information: Submitted to Phys.Rev.D62:113001,2000; PBD: 1 May 2000

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COUPLING CONSTANTS; EIGENFUNCTIONS; ELECTROMAGNETIC FORM FACTORS; FORM FACTORS; MOMENTUM TRANSFER; NUCLEONS; PIONS; POWER FACTOR; QUANTUM CHROMODYNAMICS; SUM RULES

### Citation Formats

```
Bakulev, A P, Radyushkin, A V, and Stefanis, N G.
```*Form factors and QCD in spacelike and timelike region*. United States: N. p., 2000.
Web. doi:10.1103/PhysRevD.62.113001.

```
Bakulev, A P, Radyushkin, A V, & Stefanis, N G.
```*Form factors and QCD in spacelike and timelike region*. United States. doi:10.1103/PhysRevD.62.113001.

```
Bakulev, A P, Radyushkin, A V, and Stefanis, N G. Mon .
"Form factors and QCD in spacelike and timelike region". United States. doi:10.1103/PhysRevD.62.113001. https://www.osti.gov/servlets/purl/754870.
```

```
@article{osti_754870,
```

title = {Form factors and QCD in spacelike and timelike region},

author = {Bakulev, A P and Radyushkin, A V and Stefanis, N G},

abstractNote = {The authors analyze the basic hard exclusive processes: {pi}{gamma}{sup *}{gamma}-transition, pion and nucleon electromagnetic form factors, and discuss the analytic continuation of QCD formulas from the spacelike q{sup 2} < 0 to the timelike region q{sup 2} > 0 of the relevant momentum transfers. They describe the construction of the timelike version of the coupling constant {alpha}{sub s}. They show that due to the analytic continuation of the collinear logarithms each eigenfunction of the evolution equation acquires a phase factor and investigate the resulting interference effects which are shown to be very small. They found no sources for the K-factor-type enhancements in the perturbative QCD contribution to the hadronic form factors. To study the soft part of the pion electromagnetic form factor, they use a QCD sum rule inspired model and show that there are non-canceling Sudakov double logarithms which result in a K-factor-type enhancement in the timelike region.},

doi = {10.1103/PhysRevD.62.113001},

journal = {Phys.Rev.D62:113001,2000},

number = 62,

volume = D,

place = {United States},

year = {2000},

month = {5}

}