FeynML

FeynML is a project to develop an XML dialect for describing Feynman diagrams as used in quantum field theory calculations. The primary aim is to unambiguously describe the structure of a diagram in XML, giving a de facto representation for diagram structure which can be easily translated into another representation.

Why XML?

Okay, XML is a bit of a buzzword. Not everything is best-represented as XML. However, it does have several benefits:

• it is simple to read and write, both for humans and computers;

• there are a variety of technologies available for parsing, styling and transforming XML (see e.g. SAX, DOM, CSS, XSLT)

• its heirarchical structure maps fairly well into describing graphs.

The variety of technologies aspect is probably the most important.

Elements

A Feynman diagram is constructed of these the minimal building blocks of a diagram:

• Leg
  • ID
  • Target
  • Sense
  • PDGID
  • Name
  • Momentum
• Vertex
  • ID
• Propagator
  • ID
  • Source
  • Target
  • PDGID
  • Name
  • Momentum

Attributes

Above buildings blocks come with different attributes, which are described in the following sections

Attributes	pyx	feynmp	tikz	dot	feynman	mpl	ascii	unicode
class	✔	✔	✔	✔	✔	✔	✔	✔
label	✔	✔	✔	✔	✔	✖	✔	✔
style	✔	✖	✔	✖	✖	✖	✖	✖
type	✔	✔	✔	✔	✔	✔	✔	✔
x	✔	✖	✔	✔	✔	✔	✔	✔
y	✔	✖	✔	✔	✔	✔	✔	✔

The attributes provide additional information and metadata about the elements.

CSS

To style the diagram, the following CSS classes are available:

/* General */
* { ... }                              /* all elements */
#`id` { ... }                          /* the element with id */

/* diagram */
vertex { ... }                         /* all vertices */
propagator { ... }                     /* all propagators */
leg { ... }                            /* all legs */

/* attributes */
[type=`type`] { ... }                  /* everything of given type */
[pdgid="`pdgid`"] { ... }              /* all pdg particles of given id*/

Variables in single quotes are replaced by the actual value. The available css declarations are listed in the style. For a list of types see type.

With the class attribute, the user can add custom classes to the elements. These or above classes can also be applied to a subset of the diagram e.g.

propagator:not([pdgid="-24"]) { ... }  /* all propagators except W- bosons */

The groupings of CSS are often more practical than looping through the elements in the diagram adjusting their style. For more advanced CSS selectors see https://www.w3schools.com/cssref/css_selectors.php.

Examples

• Write FeynmanDiagram
• Write FeynML
• Read FeynML

More examples can be found in the Gallery and the different renderers are listed in Renderers.