Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The spectral theorem of many-body Green's function theory when there are
  zero eigenvalues of the matrix governing the equations of motion   In using the spectral theorem of many-body Green's function theory in order
to relate correlations to commutator Green's functions, it is necessary in the
standard procedure to consider the anti-commutator Green's functions as well
whenever the matrix governing the equations of motion for the commutator
Green's functions has zero eigenvalues. We show that a singular-value
decomposition of this matrix allows one to reformulate the problem in terms of
a smaller set of Green's functions with an associated matrix having no zero
eigenvalues, thus eliminating the need for the anti-commutator Green's
functions. The procedure is quite general and easy to apply. It is illustrated
for the field-induced reorientation of the magnetization of a ferromagnetic
Heisenberg monolayer and it is expected to work for more complicated cases as
well.

37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th