Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ricci-flat and Einstein pseudoriemannian nilmanifolds   This is partly an expository paper, where the authors' work on
pseudoriemannian Einstein metrics on nilpotent Lie groups is reviewed. A new
criterion is given for the existence of a diagonal Einstein metric on a nice
nilpotent Lie group. Classifications of special classes of Ricci-flat metrics
on nilpotent Lie groups of dimension $\leq8$ are obtained. Some related open
questions are presented.

14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th