Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonperturbative 2D Gravity, Punctured Spheres and $\Theta$-Vacua in
  String Theories   We consider a model of 2D gravity with the coefficient of the
Einstein-Hilbert action having an imaginary part $\pi/2$. This is equivalent to
introduce a $\Theta$-vacuum structure in the genus expansion whose effect is to
convert the expansion into a series of alternating signs, presumably Borel
summable. We show that the specific heat of the model has a physical behaviour.
It can be represented nonperturbatively as a series in terms of integrals over
moduli spaces of punctured spheres and the sum of the series can be rewritten
as a unique integral over a suitable moduli space of infinitely punctured
spheres. This is an explicit realization \`a la Friedan-Shenker of 2D quantum
gravity. We conjecture that the expansion in terms of punctures and the genus
expansion can be derived using the Duistermaat-Heckman theorem. We briefly
analyze expansions in terms of punctured spheres also for multicritical models.

13
The categories of this paper are: quant-ph
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The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
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The categories of this paper are: math-ph
3
The categories of this paper are: physics
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs