Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Is Vtb=1 ?   The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of
the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is
relaxed, current information from top production at Tevatron still leaves open
the possibility that Vtb is sizably smaller than one. In minimal extensions of
the standard model with extra heavy quarks, the unitarity constraints are much
weaker and the EW precision parameters entail the strongest bounds on Vtb. We
discuss the experimental perspectives of discovering and identifying such new
physics models at the Tevatron and the LHC, through a precise measurement of
Vtb from the single top cross sections and by the study of processes where the
extra heavy quarks are produced.

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The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: funct-an
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: physics
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The categories of this paper are: econ