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Photo of Johan Bijnens

Johan Bijnens


Photo of Johan Bijnens

Soft and Hard Mesons in Chiral Perturbation Theory


  • Ilaria Jemos

Summary, in English

This thesis deals with Chiral Perturbation Theory (ChPT), an effective field

theory for the strong force used to

describe meson interactions. The work done can be split in two parts.

The first one is on ChPT in its standard formulation. This theory has been very

successful so far in describing low energetic processes. However, it is still not

entirely clear how much it can be trusted for precision determinations of

hadronic observables. Paper I and II explore this aspect.

Paper I shows the results of a search for relations between several observables

calculated with ChPT at order $p^{6}$. The relations are built up such that the couplings of the theory cancel out. These combinations can

then be used to test the convergence of the perturbative expansion in a way that is almost independent from the unknown couplings.

Paper II presents the results for a new global fit at order $p^{6}$ of the

couplings of the $p^{4}$ ChPT Lagrangian. The fit includes the most

recent phenomenological information. Furthermore, a new way to deal with

the $p^{6}$ couplings, based on a random walk algorithm, is considered. This method allows to

study correlations between the couplings.

The second part, paper III and IV, focuses on an extension of ChPT out of its usual energy range. This approach is called hard pion ChPT and it is expected to be useful for the analysis of lattice data.

Paper III provides arguments that further support the use of hard pion ChPT to calculate chiral logarithms when hard external pions arise. The hard pion ChPT approach is applied in this paper to semileptonic decays of $B$ and $D$ mesons to pions.

In Paper IV hard pion ChPT is extended to the three-flavour case, thereby describing the $B$ and

$D$ meson transitions to all the light pseudoscalar mesons ($\pi$, $K$ and

$\eta$). A comparison with data is also presented and it shows that the

corrections are sizable. Moreover, the procedure is applied to scalar and

vector formfactors of the pions and kaons and to $B\rightarrow D$ decay.


  • Theoretical Particle Physics

Publishing year




Document type



  • Subatomic Physics




  • Johan Bijnens

Defence date

20 May 2011

Defence time


Defence place

Lecture Hall F, Department of Astronomy and Theoretical Physics, Sölvegatan 14A, SE--223 62 Lund, Sweden


  • Christopher Sachrajda