Abstract: We study the five-body decays u(-) -> e(-)e(+)e(-)nu u (nu) over bar (e) and tau(-) -> l(-)l'+l'-nu(tau)(nu) over bar (l) for l, l' = e, u within the Standard Model (SM) and in a general effective field theory description of the weak interactions at low energies. We compute the branching ratios and compare our results with two previous – mutually discrepan – SM calculations. By assuming a general structure for the weak currents we derive the expressions for the energy and angular distributions of the three charged leptons when the decaying lepton is polarized, which will be useful in precise tests of the weak charged current at Belle II. In these decays, leptonic T-odd correlations in triple products of spin and momenta – which may signal time reversal violation in the leptonic sector – are suppressed by the tiny neutrino masses. Therefore, a measurement of such T-violating observables would be associated to neutrinoless lepton flavor violating (LFV) decays, where this effect is not extremely suppressed. We also study the backgrounds that the SM five-lepton lepton decays constitute to searches of LFV L- -> ? l(-)l'+l'(-) decays. Searches at high values of the invariant mass of the l'(+)l'(-) pair look the most convenient way to overcome the background.

Abstract: We study the effect of a hot and dense medium on the binding energy of hadronic molecules with open-charm mesons. We focus on a recent chiral quark-model-based prediction of a molecular state in the N (D) over bar system. We analyze how the two-body thresholds and the hadron-hadron interactions are modified when quark and meson masses and quark-meson couplings change in a function of the temperature and baryon density according to predictions of the Nambu-Jona-Lasinio model. We find that in some cases the molecular binding is enhanced in medium as compared to their free-space binding. We discuss the consequences of our findings for the search for exotic hadrons in high-energy heavy-ion collisions as well as in the forthcoming facilities FAIR or J-PARC.

Abstract: We study the decay mode of the a(1)(1260) into a pi(+) in p wave and the f(0)(980) that decays into pi(+)pi(-) in s wave. The mechanism proceeds via a triangular mechanism where the a(1)(1260) decays into K*K-, the K* decays to an external pi(+) and an internal K that fuses with the (K) over bar producing the f(0)(980) resonance. The mechanism develops a singularity at a mass of the a(1)(1260) around 1420 MeV, producing a peak in the cross section of the pp reaction, used to generate the mesonic final state, which provides a natural explanation of all the features observed in the COMPASS experiment, where a peak observed at this energy is tentatively associated to a new resonance called a(1)(1420). On the other hand, the triangular singularity studied here gives rise to a remarkable feature, where a peak is seen for a certain decay channel of a resonance at an energy about 200 MeV higher than its nominal mass.

Abstract: We study the chi(c1) -> eta pi(+)pi(-) decay, paying attention to the production of f(0)(500), f(0)(980), and a(0)(980) from the final state interaction of pairs of mesons that can lead to these three mesons in the final state, which is implemented using the chiral unitary approach. Very clean and strong signals are obtained for the a(0)(980) excitation in the eta pi invariant mass distribution and for the f(0)(500) in the pi(+)pi(-) mass distribution. A smaller, but also clear signal for the f(0)(980) excitation is obtained. The results are contrasted with experimental data and the agreement found is good, providing yet one more test in support of the picture where these resonances are dynamically generated from the meson-meson interaction.

Abstract: We study SO(10). SU(5) and flipped SU(5) GUT models with non-universal soft supersynrimetry-breaking scalar masses, exploring how they are constrained by LIIC super-synrimetry searches and cold dark matter experiments, and how they can be probed and distinguished in future experiments. We find characteristic differences between the-various GUT scenarios, particularly in the coannihilation region, which is very sensitive to changes of parameters. For example, the flipped SU(5) GUT predicts the possibility of (t) over tilde (1-chi) coannihilation, which is absent in the regions of the SO(10) and SU(5) GUT parameter spaces that we study. We use the relic density predictions in different models to determine upper bounds for the neutralino masses, and we find large differences between different GUT models in the sparticle spectra for the same LSP mass, leading to direct connections of distinctive possible experimental measurements with the structure of the GUT group. We find that future LHC searches for generic missing E-T, charginos and stops will be able to constrain the different GUT models in complementary ways, as will the Xenon 1 ton and Darwin dark matter scattering experiments and future FERMI or CIA gamma-ray searches.