Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Imaginary action, spinfoam asymptotics and the 'transplanckian' regime
  of loop quantum gravity   It was recently noted that the on-shell Einstein-Hilbert action with
York-Gibbons-Hawking boundary term has an imaginary part, proportional to the
area of the codimension-2 surfaces on which the boundary normal becomes null.
We discuss the extension of this result to first-order formulations of gravity.
As a side effect, we settle the issue of the Holst modification vs. the
Nieh-Yan density by demanding a variational principle with suitable boundary
conditions. We then set out to find the imaginary action in the large-spin
4-simplex limit of the Lorentzian EPRL/FK spinfoam. It turns out that the
spinfoam's effective action indeed has the correct imaginary part, but only if
the Barbero-Immirzi parameter is set to +/- i after the quantum calculation. We
point out an agreement between this effective action and a recent black hole
state-counting calculation in the same limit. Finally, we propose that the
large-spin limit of loop quantum gravity can be viewed as a high-energy
'transplanckian' regime.

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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph