Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Limits on the Non-commutativity Scale   A non-vanishing vacuum expectation value for an antisymmetric tensor field
leads to the violation of Lorentz invariance, controlled by the dimension (-2)
parameter, theta_{mu nu}. We assume that the zeroth order term in
theta-expansion represents the Standard Model and study the effects induced by
linear terms in theta_{mu nu}. If coupling to theta_{mu nu} is realized in
strongly interacting sector of the theory, the clock comparison experiments
place the limit on the possible size of this background at the level of
1/\sqrt{theta}>~5X10^{14} GeV. If the interaction with theta_{mu nu} is
initially present only in the QED sector, this limit can be relaxed to
10^{11}-10^{12} GeV level. The strength of these limits obviates the
inferiority of collider physics with regard to experimental checks of Lorentz
invariance. Limits of similar strength are expected to hold in the case of
mixed non-commutativity between four-dimensional and extra-dimensional
coordinates. We also show that in certain models mixed non-commutativity can be
interpreted as 4d CPT-violating background.

5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org