Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Operator product expansion of the energy momentum tensor in 2D conformal
  field theories on manifolds with boundary   Starting from the well-known expression for the trace anomaly we derive the
$T\cdot T$ operator product expansion of the energy-momentum tensor in 2D
conformal theories defined in the upper halfplane $without$ making use of the
additional condition of no energy-momentum flux across the boundary. The OPE
turns out to be the same as in the absence of the boundary. For this result it
is crucial that the trace anomaly is proportional to the Gau\ss-Bonnet density.
Some relations to the $\sigma$ - model approach for open strings are discussed.

3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat