Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The doubly virtual $(\pi^0,\eta,\eta')\to\gamma^*\gamma^*$ transition
  form factors in the light-front quark model   We report our investigation on the doubly virtual TFFs $F_{{\rm
P}\gamma^*}(Q^2_1,Q^2_2)$ for the ${\rm P}\to\gamma^*(q_1)\gamma^*(q_2) \;({\rm
P}=\pi^0,\eta,\eta')$ transitions using the light-front quark model (LFQM).
Performing a LF calculation in the exactly solvable manifestly covariant
Bethe-Salpeter (BS) model as the first illustration, we used $q^+_1=0$ frame
and found that both LF and manifestly covariant calculations produce exactly
the same results for $F_{{\rm P}\gamma^*}(Q^2_1,Q^2_2)$. This confirms the
absence of the LF zero mode in the doubly virtual TFFs. We then mapped this
covariant BS model to the standard LFQM using the more phenomenologically
accessible Gaussian wave function provided by the LFQM analysis of meson mass
spectra. For the numerical analyses of $F_{{\rm P}\gamma^*}(Q^2_1,Q^2_2)$, we
compared our LFQM results with the available experimental data and the
perturbative QCD (pQCD) and the vector meson dominance (VMD) model predictions.
As $(Q^2_1, Q^2_2)\to\infty$, our LFQM result for doubly virtual TFF is
consistent with the pQCD prediction, i.e. $F_{{\rm P}\gamma^*}(Q^2_1,
Q^2_2)\sim 1/(Q^2_1 + Q^2_2)$, while it differs far from the result of VMD
model which behaves $F^{\rm VMD}_{{\rm P}\gamma^*}(Q^2_1, Q^2_2)\sim 1/(Q^2_1
Q^2_2)$. Our LFQM prediction for $F_{\eta'\gamma^*}(Q^2_1,Q^2_2)$ shows an
agreement with the very recent experimental data obtained from the BaBar
collaboration for the ranges of $2< Q^2_1, Q^2_1 <60$ GeV$^2$.

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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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The categories of this paper are: math
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: astro-ph
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc