# Angular momentum conservation law in light-front quantum field theory

## Abstract

We prove the Lorentz invariance of the angular momentum conservation law and the helicity sum rule for relativistic composite systems in the light-front formulation. We explicitly show that j ^{3}, the z -component of the angular momentum remains unchanged under Lorentz transformations generated by the light-front kinematical boost operators. The invariance of j ^{3} under Lorentz transformations is a feature unique to the front form. Applying the Lorentz invariance of the angular quantum number in the front form, we obtain a selection rule for the orbital angular momentum which can be used to eliminate certain interaction vertices in QED and QCD. We also generalize the selection rule to any renormalizable theory and show that there exists an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory.

- Authors:

- SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Publication Date:

- Research Org.:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Sponsoring Org.:
- USDOE

- OSTI Identifier:
- 1360755

- Alternate Identifier(s):
- OSTI ID: 1349545

- Grant/Contract Number:
- AC02-76SF00515

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- Physical Review D

- Additional Journal Information:
- Journal Volume: 95; Journal Issue: 6; Journal ID: ISSN 2470-0010

- Publisher:
- American Physical Society (APS)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS

### Citation Formats

```
Chiu, Kelly Yu-Ju, and Brodsky, Stanley J.
```*Angular momentum conservation law in light-front quantum field theory*. United States: N. p., 2017.
Web. doi:10.1103/PhysRevD.95.065035.

```
Chiu, Kelly Yu-Ju, & Brodsky, Stanley J.
```*Angular momentum conservation law in light-front quantum field theory*. United States. doi:10.1103/PhysRevD.95.065035.

```
Chiu, Kelly Yu-Ju, and Brodsky, Stanley J. Fri .
"Angular momentum conservation law in light-front quantum field theory". United States.
doi:10.1103/PhysRevD.95.065035. https://www.osti.gov/servlets/purl/1360755.
```

```
@article{osti_1360755,
```

title = {Angular momentum conservation law in light-front quantum field theory},

author = {Chiu, Kelly Yu-Ju and Brodsky, Stanley J.},

abstractNote = {We prove the Lorentz invariance of the angular momentum conservation law and the helicity sum rule for relativistic composite systems in the light-front formulation. We explicitly show that j3, the z -component of the angular momentum remains unchanged under Lorentz transformations generated by the light-front kinematical boost operators. The invariance of j3 under Lorentz transformations is a feature unique to the front form. Applying the Lorentz invariance of the angular quantum number in the front form, we obtain a selection rule for the orbital angular momentum which can be used to eliminate certain interaction vertices in QED and QCD. We also generalize the selection rule to any renormalizable theory and show that there exists an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory.},

doi = {10.1103/PhysRevD.95.065035},

journal = {Physical Review D},

number = 6,

volume = 95,

place = {United States},

year = {Fri Mar 31 00:00:00 EDT 2017},

month = {Fri Mar 31 00:00:00 EDT 2017}

}

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