Massive relic neutrinos in the galactic halo and the knee in the cosmic ray spectrum

Despite many efforts to find a reasonable explanation, the origin of the "knee" in the cosmic ray spectrum at energy around 10**15.5 eV remains mysterious. In this letter we suggest that the "knee" may be due to a GZK-like effect of cosmic rays interacting with massive neutrinos in the galactic halo. Simple kinematics connects the location of the "knee" with the mass of the neutrinos, and, while the required interaction cross section is larger than that predicted by the Standard Model, it can be accommodated by a small neutrino magnetic dipole moment. The values for the neutrino parameters obtained from the analysis of existing experimental data are compatible with present laboratory bounds.Comment: 8 pages, 1 figure, uses RevTe

Hinting at primary composition using asymmetries in time distributions

Evidence of azimuthal asymmetries in the time structure and signal size have been found in non-vertical showers at the Pierre Auger Observatory. It has been previously shown that the asymmetry in time distributions offers a new possibility for the determination of the mass composition. New studies have demonstrated that the dependence of the asymmetry parameter in the rise-time and fall-time distributions with sec(theta) shows a clear peak. Both, the position of the peak, X_asymax, and the size of the asymmetry at X_asymax are sensitive to primary mass composition and have a small dependence on energy. In this paper a study of the discriminating power of the new observables to separate primary species is presented.Comment: To be published in the Proceedings of 29th International Cosmic Ray Conference (ICRC 2005), Pune, India, August 3-10, 200

METHODOLOGIES FOR THE SYNTHESIS OF THIAHELICENE-BASED PHOSPHORUS DERIVATIVES AND THEIR APPLICATIONS IN ASYMMETRIC CATALYSIS

Helicenes are ortho-annulated polycyclic aromatic or heteroaromatic compounds endowed with inherent chirality due to the helical shape of their \u3c0-conjugated system, whose unique structural features and physicochemical properties have stimulated countless studies in several fields, including nanosciences, chemosensing, materials science, biomolecular recognition, and asymmetric catalysis. However, whilst axial, central and planar chirality have been largely exploited to build chiral phosphorus ligands and organocatalysts, helical chirality has been rather neglected so far in this field. This Ph.D. thesis aims to provide a meaningful contribution in the development of heterohelicene phosphorus derivatives, especially thiahelicene derivatives, as innovative chiral ligands to use in asymmetric organic and organometallic catalysis. In particular, we set up new classes of tetrathiahelicene(7-TH)-based phosphorus derivatives, including phoshine-borane complexes, phosphine oxides, free phosphanes, phosphathiahelicenes and the corresponding gold (I) complexes. Some of these systems have shown high efficiency as organocatalysts, as well as Au(I) complexes based on chiral phosphathiahelicene ligands were found to be efficient and selective catalysts in some challenging cycloisomerization reactions (ee up to 96%). The promising results obtained in this work will stimulate further developments and applications of these and analogous ligands to new asymmetric processes

Simultaneous determinations of τ polarisation and vτ, helicity using the decay τ → a1vτ

A method is presented to extract tau polarisation Pτ and tau neutrino helicity γVA simultaneously using τ leptons produced at the Z⁰ which decay into a1 and vτ. It provides better sensitivity than independent fits to Pτ or γVA separately and in fact can be shown to be optimal. Estimates of sensitivity from Monte Carlo studies and comments regarding the use of the technique in experiments are also presented. We also discuss how results of tau polarisation determinations using other decay modes may be included.Facultad de Ciencias Exacta

Simultaneous determinations of τ polarisation and vτ, helicity using the decay τ → a1vτ

A method is presented to extract tau polarisation Pτ and tau neutrino helicity γVA simultaneously using τ leptons produced at the Z⁰ which decay into a1 and vτ. It provides better sensitivity than independent fits to Pτ or γVA separately and in fact can be shown to be optimal. Estimates of sensitivity from Monte Carlo studies and comments regarding the use of the technique in experiments are also presented. We also discuss how results of tau polarisation determinations using other decay modes may be included.Facultad de Ciencias Exacta

Large 2HDM(II) one-loop corrections in leptonic tau decays

The one-loop contributions to the branching ratios for leptonic tau decays are calculated in the CP conserving 2HDM(II). We found that these one-loop contributions, involving both neutral and charged Higgs bosons, dominate over the tree-level H^+ exchange, the latter one being totally negligible for the decay into electron. The analysis is focused on large tanbeta enhanced contributions to the considered branching ratios. We derive a simple analytical expression for the one-loop contribution which holds in this case. We show that the leptonic branching ratios of tau are complementary to the Higgsstrahlung processes for h(H) and have a large potential on constraining parameters of the model. In this work we provide upper limits on Yukawa couplings for both light h and light A scenarios and we derive new lower limit on mass of M_{H^+} as a function of tanbeta, which differs significantly from what was considered as standard constraint based on the tree-level H^{+} exchange only. Interestingly we obtain also an upper limit on M_{H^+}. For a SM-like h scenario, with heavy and degenerate additional Higgs bosons, one-loop corrections disappear.Comment: 25 pgs. Figures and their descriptions improved, references adde

Axially chiral benzo[1,2-b:4,3-b’]dithiophene derivatives: a new route to tetrathiahelicenes

Thiophene-containing fused aromatic compounds represent an interesting class of \u3c0-conjugated systems in functional organic materials [1]. Among them, benzo[1,2-b:4,3-b\u2019]dithiophene (BDT) and its derivatives are by far the most widely studied, especially as units in mono and polydisperse oligomers in the field of the materials science [2], and as \u3c0-spacers in push-pull organic chromophores for photovoltaic applications [3]. Moreover, BDT is a key intermediate for the synthesis of inherently chiral helical systems such as tetrathia[7]helicenes 3 [4]. For all these reasons, BDT can be identified as a key starting molecule that, through a judicious functionalization of the \u3b1-positions of the thiophene rings, can allow access to more complex and interesting systems. Exploiting the experience acquired in our laboratories on the synthesis and functionalization of BDT derivatives [5,6], we have studied a novel and simple synthetic route to prepare bis(benzo[1,2-b:4,3-b\u2019]dithiophene) systems 2, through Pd-catalyzed cross coupling reactions, starting from bromides 1 (Figure 1).This strategy provides a convenient route to an interesting class of chiral atropisomeric heterobiaryl derivatives 2 with C2-symmetry, which can be used as starting reagents for an innovative non-photochemical synthesis of tetrathiahelicenes exploiting a Suzuki-Miyaura cross coupling and a Pd-catalyzed annulation with internal alkynes as key steps.. Asymmetric versions of this synthesis is under study

Opacity of the microwave background radiation to ultrahigh energy cosmic rays

In this work we re-examine the influence of the microwave background radiation on the propagation of extremely high energy cosmic rays. We present a recalculation of the rate of fractional energy loss in the continuous energy loss approximation including the effects of resonances other than the Δ. We also discuss the distortion of the cosmic ray spectrum due to interactions with the relic photons.Facultad de Ciencias Exacta