Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Negative probabilities: What they are and what they are for   An observation space $\mathcal S$ is a family of probability distributions
$\langle P_i: i\in I \rangle$ sharing a common sample space $\Omega$ in a
consistent way. A \emph{grounding} for $\mathcal S$ is a signed probability
distribution $\mathcal P$ on $\Omega$ yielding the correct marginal
distribution $P_i$ for every $i$. A wide variety of quantum scenarios can be
formalized as observation spaces. We describe all groundings for a number of
quantum observation spaces. Our main technical result is a rigorous proof that
Wigner's distribution is the unique signed probability distribution yielding
the correct marginal distributions for position and momentum and all their
linear combinations.

22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat