Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Polyhedra in spacetime from null vectors   We consider convex spacelike polyhedra oriented in Minkowski space. These are
the classical analogues of spinfoam intertwiners. We point out a
parametrization of these shapes using null face normals, with no constraints or
redundancies. Our construction is dimension-independent. In 3+1d, it provides
the spacetime picture behind a well-known property of the loop quantum gravity
intertwiner space in spinor form, namely that the closure constraint is always
satisfied after some SL(2,C) rotation. As a simple application of our
variables, we incorporate them in a 4-simplex action that reproduces the
large-spin behavior of the Barrett-Crane vertex amplitude.

17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org