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the problem of dynamics of mesons at low energies is important .
it plays a major role in the precise determination of the elements of the cabibbo - kobayashi - maskawa matrix ( ckm ) which is a main part of the study of the standard model flavour sector  @xcite . in this talk
i will concentrate on the theory behind the measurement of @xmath0 from @xmath2 ( @xmath4 ) decays and in particular on the recent work of p.  talavera and myself on the two - loop calculation and the determination of the relevant low - energy constants  @xcite .
i review shortly chiral perturbation theory ( chpt ) and the relevant two - loop calculations done up to now , followed by a discussion of @xmath2 and the present theory situation .
i include a short discussion of the validity of the linear approximation of the form factors normally used in the data analysis .
the main relevant results from chpt  @xcite can be summarized as follows .
the curvatures are important in the analysis but can be predicted using chpt from the pion electromagnetic form - factor  @xcite and all order @xmath1 parameters needed to determine @xmath0 can be experimentally obtained via the scalar form factor , @xmath5 , in @xmath2  @xcite .
the curvature of @xmath5 can be predicted as well from knowledge about scalar form factors of the pion  @xcite , albeit only at fairly low precision at present .
chpt is an effective field theory valid as an approximation to quantum chromodynamics ( qcd ) at low energies .
its modern form has was introduced by weinberg , gasser and leutwyler  @xcite .
the global chiral symmetry , @xmath6 , of qcd in the limit of massless quarks is spontaneously broken down to the diagonal subgroup @xmath7 by a nonzero quark condensate , @xmath8 the eight broken generators lead to eight goldstone bosons .
these are massless _ and _ their interactions vanish at zero momentum .
the latter allows the construction of a well defined perturbative expansion in terms of momenta , generically referred to as an expansion in @xmath9 .
quark masses are usually counted as order @xmath9 since @xmath10 . inserting an external photon or @xmath11-bosons counts as order @xmath12 since
these are included via covariant derivatives .
recent lectures , much more detailed than what is included here are  @xcite .
chpt being an effective field theory implies that the number of parameters increases order by order . in the purely mesonic strong and semi - leptonic sector
there are two parameters at lowest order ( @xmath9 ) , ten at nlo ( @xmath13 )  @xcite , and 90 at nnlo ( @xmath1 ) @xcite .
the renormalization procedure and the divergences are worked out in general to nnlo  @xcite and provide a good check on all calculations .
one problem shared with other high order loop calculations in comparing different calculations is the use of different renormalization schemes .
the calculations that were used to determine all the needed parameters are those of the masses and decay constants @xcite , @xmath14  @xcite and the electromagnetic form factors  @xcite .
the @xmath22 chpt calculation for is rather cumbersome .
i will use our work ,  @xcite but an independent calculation exists  @xcite and agrees reasonably well , the difference is discussed in  @xcite .
we write the amplitude as f_+(t ) & = & 1 + f_+^(4)(t)/f_^2 + f_+^(6)(t)/f_^4 f_+^(4)(t ) = t l_9^r/2 + , + f_+^(6)(t ) & = & -8 ( c_12^r+c_34^r ) ( m_k^2-m_^2)^2 + t r_+1^k + t^2 ( - 4 c_88^r + 4 c_90^r ) + ( l_i^r ) .
the pion electromagnetic form factor data yield  @xcite @xmath30 and @xmath31 with this input we fit the cplear data and obtain    = -(4.70.5 )  10 ^ -5  ^2 _ + = 0.01700.0015 .
the first agrees with the vmd estimate  @xcite @xmath32 .
the latter comes from chpt as _ + = 0.0283  ( p^4 )   + 0.0011  ( p^6 )   -0.0124 ( c_i^r ) .
our main conclusion follows from rewriting the full @xmath1 result for @xmath5 as f_0(t ) & = & 1-(8/f_^4)(c_12^r+c_34^r ) ( m_k^2-m_^2)^2 + ( 8 t / f_^4 ) ( 2c_12^r+c_34^r ) ( m_k^2+m_^2 ) + & & + t/(m_k^2-m_^2)(f_k / f_-1 ) -(8 t^2/f_^4 ) c_12^r + ( t)+(0 ) .
@xmath33\pm0.0028[l_i^r]\ , , $ ] is known and an expression for @xmath34 can be found in ref .  @xcite the errors are an estimate of higher orders and using fits of the @xmath35 using different assumptions .
the @xmath1 estimate of @xcite corresponds to @xmath36 .
i discussed the @xmath2 form factors in chpt to order @xmath1 .
the main conclusions are that the curvatures for @xmath22 and @xmath5 can be predicted from the data on pion electromagnetic  @xcite and scalar  @xcite form - factors , the curvature in @xmath22 and @xmath5 should be taken into account in new precision experiments but from the slope and the curvature we can determine experimentally the needed parameters to calculate @xmath18 . a precision of better than one percent seems feasible for @xmath17 .      99 m.  battaglia _ et al .
_ , hep - ph/0304132 .
j.  bijnens and p.  talavera , hep - ph/0303103 , to be published in nucl .
b. j.  bijnens , talk given at 38th rencontres de moriond on qcd and high - energy hadronic interactions , les arcs , savoie , france , 22 - 29 mar 2003 , hep - ph/0304284 .
j.  bijnens and p.  dhonte , hep - ph/0307044 s.  weinberg , physica a * 96 * ( 1979 ) 327 ; j.  gasser and h.  leutwyler , annals phys .
* 158 * ( 1984 ) 142 , j.  gasser and h.  leutwyler , nucl .
b * 250 * ( 1985 ) 465 .
a.  pich , a. , hep - ph/9806303 ; g.  ecker , hep - ph/0011026 ; s.  scherer , hep - ph/0210398 .
j.  bijnens , g.  colangelo and g.  ecker , jhep * 9902 * ( 1999 ) 020 [ hep - ph/9902437 ] ; j.  bijnens , g.  colangelo and g.  ecker , annals phys .   * 280 * ( 2000 ) 100 [ hep - ph/9907333 ] .
g.  amors , j.  bijnens and p.  talavera , nucl .
b * 568 * ( 2000 ) 319 [ hep - ph/9907264 ] , nucl .
b * 602 * ( 2001 ) 87 [ hep - ph/0101127 ] .
g.  amors , j.  bijnens and p.  talavera , phys .
b * 480 * ( 2000 ) 71 [ hep - ph/9912398 ] ; nucl .
b * 585 * ( 2000 ) 293 [ erratum - ibid .
b * 598 * ( 2001 ) 665 ] [ hep - ph/0003258 ] .
j.  bijnens and p.  talavera , jhep * 0203 * ( 2002 ) 046 [ hep - ph/0203049 ]
. h.  leutwyler and m.  roos , z.  phys .
c * 25 * ( 1984 ) 91 .
v.  cirigliano _ et al .
_ , eur .
j.  c * 23 * ( 2002 ) 121 [ hep - ph/0110153 ] .
a.  apostolakis _ et al .
_ [ cplear collaboration ] , phys .
b * 473 * ( 2000 ) 186 .
a.  s.  levchenko _ et al .
_ [ kek - ps e246 collaboration ] , phys .  atom .
* 65 * ( 2002 )
2232 [ yad .  fiz .
* 65 * ( 2002 ) 2294 ] [ hep - ex/0111048 ] .
i give a very short introduction to chiral perturbation theory and an overview of the next - to - next - to - leading order three - flavour calculations done . 
 i discuss those relevant for an improvement in the accuracy of the measurement of @xmath0 in more detail . 
 one major conclusion is that all needed @xmath1 low energy constants can be obtained from experiment via the scalar form - factor in @xmath2 decays .    
 lu tp 03 - 33 + hep - ph/0307082 + july 2003    * chiral dynamics in the meson sector at two loops@xmath3 *    * johan bijnens * + department of theoretical physics 2 , lund university , + slvegatan 14a , s 22362 lund , sweden    * abstract *    i give a very short introduction to chiral perturbation theory and an overview of the next - to - next - to - leading order three - flavour calculations done . 
 i discuss those relevant for an improvement in the accuracy of the measurement of @xmath0 in more detail . 
 one major conclusion is that all needed @xmath1 low energy constants can be obtained from experiment via the scalar form - factor in @xmath2 decays . 
 @xmath3 talk presented at cipanp 2003 , conference on the intersections of particle and nuclear physics , new york may 19 - 24 , 2003 .     
 address = department of theoretical physics 2 , lund university , + slvegatan 14a , s 22362 lund , sweden