Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electromagnetic form factor of the pion from twisted-mass lattice QCD at
  Nf=2   We present a lattice calculation of the electromagnetic form factor of the
pion obtained using the tree-level Symanzik improved gauge action with two
flavors of dynamical twisted Wilson quarks. The simulated pion masses range
approximately from 260 to 580 MeV and the lattice box sizes are chosen in order
to guarantee that M L > 4. Accurate results for the form factor are obtained
using all-to-all quark propagators evaluated by a stochastic procedure. The
momentum dependence of the pion form factor is investigated up to values of the
squared four-momentum transfer Q**2 ~ 0.8 GeV**2 and, thanks to the use of
twisted boundary conditions, down to Q**2 ~ 0.05 GeV**2. Volume and
discretization effects on the form factor appear to be within the statistical
errors. Our results for the pion mass, decay constant and form factor are
analyzed using (continuum) Chiral Perturbation Theory at
next-to-next-to-leading order. The extrapolated value of the pion charge radius
is <r**2>{phys} = 0.456 +/- 0.030(stat.) +/- 0.024(syst.) in nice agreement
with the experimental result. The extrapolated values of the pion form factor
agree very well with the experimental data up to Q**2 ~ 0.8 GeV**2 within
uncertainties which become competitive with the experimental errors for Q**2 >
0.3 GeV**2. The relevant low-energy constants appearing in the chiral expansion
of the pion form factor are extracted from our lattice data, which come
essentially from a single lattice spacing, adding the experimental value of the
pion scalar radius in the fitting procedure. Our findings are in nice agreement
with the available results of ChPT analyses of pion-pion scattering data as
well as with other analyses of our collaboration.

6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg