The predictions of chiral perturbation theory for the weak non-leptonic decays of hyperons are examined beyond the leading order. For the S-wave amplitudes we find that the leading corrections to lowest order chiral perturbation theory preserve the vanishing of the Σ+ → nπ+ amplitude. However, the Lee-Sugawara relation gets a large correction indicating a breakdown of chiral perturbation theory fo

A new scenario accounting for the production of monojets with large missing transverse energy is described and a specific model implementing it is constructed. The production rate for monojets is calculated.

Models are considered which have no small Yukawa couplings unrelated to symmetry. This situation is generic in higher dimensional unification where Yukawa couplings are predicted to have a strength similar to the gauge couplings. Generations have then to be differentiated by symmetry properties and the structure of fermion mass matrices is given in terms of quantum numbers alone. Possible symmetri

We investigate unified models where all small quantities in the fermion mass matrices are given in terms of one small ratio of symmetry breaking scales. We describe for a U(1) generation symmetry how the size of masses and mixings is determined, including possible contributions from heavy mirror quarks and leptons. This can be used for computerized model scanning. We search for realistic mass patt

We present a model with continuous or discrete abelian generation group G, which predicts all orders of magnitude for fermion masses ad mixings correctly as a function of only one small parameter φS M ≈ 1 10. Here φS is the scale of G symmetry breaking and M the fundamental mass scale of the theory. No small Yukawa couplings or special choices of the scalar potential are needed. We perform a syste

En sammantällning av de 40 orientaliska mynt som framkommit på anlöpsplatsen Vester Egesborg, Själland. Mynten analyseras med hänsyn till kronologi, ursprung och grad av fragmentering. Jämförelser görs med andra vikingatida handels- och centraplatser med orientaliska mynt som Kaupang, Uppåkra, Tissø, Birka och Strøby-Toftegård.

We examine patterns where ratios of the fermion masses and the W-boson mass (xi= mi mw) are proportional to powers of a small parameter λ(xi=ciλPi). For a simple estimate of the uncertainty in the coefficients ci we determine the allowed values of Pi and the corresponding range of λ. Using this information we search for realistic patterns in a large class of anomaly-free SU(3)×SU(2)×U(1)×U(1) mode

We calculate within chiral perturbation theory the cross section for γγ→π0π0 and γγ→π+π- to next-to-leading order. The first process only depends on the one-loop contributions and forms a test of chiral perturbation theory. We also calculate the pion electromagnetic form factor and compare it to recent data.

We present a discussion of the treatment of 1 Nc-corrections in chiral perturbation theory for nonleptonic weak processes. We compare the approach with an explicit cutoff and dimensional regularization in chiral perturbation theory and present evidence that they are equivalent. The quadratic dependence on the cutoff can be subtracted consistently at each level of 1 Nc. We discuss the identificatio

We study the value of the light quark masses combination mu + md in QCD using both Finite Energy Sum Rules and Laplace Sum Rules. We have performed a detailed analysis of both the perturbative QCD and the hadronic parametrization inputs needed in these Sum Rules. As main result, we obtain mu (1 GeV2 + md (1 GeV2) = (12 ± 2.5) MeV for the running MS masses.

The two-point functions in generalized Nambu-Jona-Lasinio models are calculated to all orders in momenta and quark masses to leading order in 1/Nc. The use of Ward identities and the heat-kernel expansion allows for a large degree of regularization independence. We also show how this approach works to the same order for three-point functions on the example of the vectorpseudoscalar-pseudoscalar th

The matrix elements for K → ππlν decays are described by four form factors F, G, H and R. We complete previous calculations by evaluating R at next-to-leading order in the low-energy expansion. We then estimate higher order contributions using dispersion relations and determine the low-energy constants L1, L2 and L3 from data on Ke4 decays and on elastic pion scattering. Finally, we present predic

We show how the effective action of the Extended Nambu-Jona-Lasinio model (ENJL) can be defined in the presence of anomalies in a way that reproduces the flavour anomaly. This necessarily breaks Vector Meson Dominance (VMD) in the usual sense. The same method can be used to construct other chiral effective theories involving constituent quarks and spin-1 mesons that give the correct flavour anomal

We discuss vector, axial-vector, scalar and pseudoscalar two-point functions at low and intermediate energies. We first review what is known from chiral perturbation theory, as well as from a heat kernel expansion within the context of an extended Nambu-Jona-Lasinio (ENJL) model. We derive then these two-point functions to all orders in the momenta and to leading order in 1/N c within the framewo

We evaluate the matrix elements for the radiative kaon decays K+ → l+νlγ, l+νll′+l′- and K → πlνlγ (l, l′ = e, μ) to next-to-leading order in chiral perturbation theory. We calculate total rates and rates with several kinematical cuts and confront the results with existing data. Measurements at future kaon facilities will allow for a more detailed comparison between theory and experiment.

We calculate the O(p6) corrections to the anomalous form factors appearing in π+, K+ → e+νγ, μ+νγ and K14 decays in chiral perturbation theory. The relevant dimension 6 terms of the lagrangian are evaluated assuming their saturation by the vector meson contribution.

We present a derivation of the low-energy effective action of an extended Nambu-Jona-Lasinio (ENJL) model to O(p4) in the chiral counting. Two alternative scenarios are considered on how the ENJL model could originate as a low-energy approximation to QCD. The low-energy effective lagrangian we derive includes the usual pseudoscalar Goldstone modes, as well as the lower scalar, vector and axial-vec

The BK parameter is discussed in the general context of calculating beyond the factorization approximation for hadronic matrix elements. A variant of the 1 Nc method of Bardeen et al. is used. We present calculations within a low energy approach and a calculation within the Nambu-Jona-Lasinio model. Matching with the QCD behaviour and dependence on non-zero current quark masses is studied.

Recent measurements of the transition form factors for the P* vertices, with P=0, and are compared with different models. These include vector-meson dominance, constituent-quark loops, the QCD-inspired interpolation by Brodsky-Lepage, and chiral perturbation theory. General agreement is observed and differencesdue to SU(3) breaking are stressed and discussed.

The η→π0γγ decay amplitude is discussed in the general context of chiral perturbation theory assuming that the low-energy constants (counterterms) are saturated by the known meson resonances. The suppression of the lowest order contributions is understood in physical terms. A reasonable agreement with the experimental decay width is achieved.