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

These are contained in Diagram which in turn is contained in FeynML.

Attributes

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

Attributes	tikz	pyx	feynmp	feynman	dot	mermaid	asciipdf	unicodepdf	madgraph
class	✔	✔	✔	✔	✔	✔	✔	✔	✔
label	✔	✔	✔	✔	✔	✔	✔	✔	✔
shape	✔	✔	✔	✔	✔	✔	✔	✔	✔
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 */
diagram { ... }                        /* all diagrams */
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.