Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extra Spacetime Dimensions and Unification   We study the effects of extra spacetime dimensions at intermediate mass
scales, as expected in string theories with large-radius compactifications, and
focus on the gauge and Yukawa couplings within the Minimal Supersymmetric
Standard Model. We find that extra spacetime dimensions naturally lead to the
appearance of grand unified theories at scales substantially below the usual
GUT scale. Furthermore, we show that extra spacetime dimensions provide a
natural mechanism for explaining the fermion mass hierarchy by permitting the
Yukawa couplings to receive power-law corrections. We also discuss how
proton-decay constraints may be addressed in this scenario, and suggest that
proton-decay amplitudes may be exactly cancelled to all orders in perturbation
theory as a result of new Kaluza-Klein selection rules corresponding to the
extra spacetime dimensions.

5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: cond-mat
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs