Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 4D GUT (and SM) Model Building from Intersecting D-Branes   We provide a general overview of the current state of the art in three
generation model building proposals - using intersecting D-brane toroidal
compactifications of IIA string theories - which have, only, the SM at low
energy. In this context, we focus on these model building directions, where
natural non-supersymmetric constructions based on
  $SU(4)_C \times SU(2)_L \times SU(2)_R$, SU(5) and flipped SU(5) GUT groups,
have at low energy only the Standard Model. In the flipped SU(5) GUTS, the
special build up structure of the models accommodates naturally a see-saw
mechanism and a new solution to the doublet-triplet splitting problem.

22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
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The categories of this paper are: eess
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th