On 2022 October 9, an extremely powerful gamma-ray burst, GRB 221009A, was detected by several instruments. Despite being obstructed by the Milky Way galaxy, its afterglow outburst outshone all other GRBs seen before. LHAASO detected several thousand very high energy photons extending up to 18 TeV. Detection of such energetic photons is unexpected due to the large opacity of the universe. It is possible that in the afterglow epoch, the intrinsic very high energy photon flux from the source might have increased manifolds, which could compensate for the attenuation by pair production with the extragalactic background light. We propose such a scenario and show that very high energy photons can be observed on the Earth from the interaction of very high energy protons with the seed synchrotron photons in the external forward shock region of the GRB jet.

We study the success to describe hyperon semileptonic decays of four models that incorporate second-order SU(3) symmetry-breaking corrections. The criteria to assess their success is by determining $V_{\mathrm{us}}$ in each of the three relevant hyperon semileptonic decays and comparing the values so obtained with one another and also with the one that comes from $K_{l3\mathrm{}}$ decays. A strong dependence on the particular symmetry-breaking model is observed. Values of $V_{\mathrm{us}}$ which do not agree with the one of $K_{l3\mathrm{}}$ are generally obtained. However, in the context of chiral perturbation theory, only the model whose corrections are $O\left(m_s\right)$ and $O\left(m_s^{\frac{3}{2}}\right)$ is successful. Using its predictions for the $f_1$ form factors one can quote a value of $V_{\mathrm{us}}$ from this model, namely, $V_{\mathrm{us}}=0.2176\mathrm{}\pm 0.0026$, which is in excellent agreement with the $K_{l3\mathrm{}}$ one.

A priori mixings of eigenstates in physical states are quantum mechanical effects well known in several realms of physics. The possibility that such effects are also present in particle physics, in the form of flavour and parity mixings, is studied. Applications to weak radiative and non-leptonic decays of hyperons are discussed.

Strong flavour and parity a priori mixing in hadrons are shown to describe well the experimental evidence on weak radiative decays of hyperons. An independent determination of the a priori mixing angles is performed. The values obtained for them are seen to have a universality-like property, when compared with their values in non-leptonic decays of hyperons.

Non-leptonic decays of hyperons can provide a detailed determination of the a priori mixing angles that appear in physical hadrons in the approach in which non-perturbative flavour and parity violations are present in tiny pieces of the hadron mass operator. The determination of such angles in these decays will provide a benchmark to test their necessary universality-like property in other types of decays. Our main result is that the magnitudes of the a priori mixing angles can be determined quite accurately.