Charge state of C10 and C5 energetic cluster ions in amorphous carbon targets: simulations

We present here detailed simulations of the interaction of energetic C10 and C5 clusters at the energies of 1, 2, and 4 MeV per carbon atom with an amorphous carbon target. The spatial evolution of the cluster components is simulated accounting for both scattering and Coulomb explosion. The former is calculated by means of the Monte Carlo method while the latter is computed by means of molecular dynamics. The charge state of the individual cluster components is calculated as a function of penetration depth, and is determined by the competition between electron ionization and recombination. The results of calculations of the effect of the neighbouring cluster components on the suppression of the values of the charge state are presented and compared to the experimental values of Brunelle et al. Charge state suppression calculations for the 2 MeV/C clusters for both C10 and C5 agree well with the experimental results for penetration depths of less than about 500 and 250 Å respectively, assuming the intracluster Coulomb potential is screened by four target valence electrons. At 4 MeV/C the results are similar although less screening is required; a possible explanation is the inability of the plasma to completely screen the higher velocity projectiles. The 1 MeV/C calculated results however differ in their behaviour from the 2 and 4 MeV/C cases

Simulation of the channelling of ions from MeV C60 in crystalline solids

Simulations were performed describing the motion and breakup of energetic C60 ions interacting with crystalline targets. A hybrid algorithm was used that employs a binary collision model for the scattering of the carbon ions by the atoms of the solid, and molecular dynamics for the Coulomb interactions of the 60 carbon ions with one another. For the case of yttrium iron garnet (YIG), directions such as [1 1 0], [1 0 0], [0 1 0] and [0 0 1] demonstrate channelling for a large fraction of the C ions. For directions such as [1 1 1], [2 1 1] and [7 5 3] the trajectories show no more channelling than for random directions. The effects of tilt, shielding and wake-field interactions were investigated for YIG and α-quartz

Simulation of the interaction of high-energy C60 cluster ions with amorphous targets

Detailed simulations of the interaction of energetic C-60 beams with amorphous targets are presented here. The spatial evolution of the cluster components is calculated accounting for multiple scattering and Coulomb explosion by means of Monte Carlo and molecular dynamics, respectively. The charge states of the individual cluster components (atoms, atomic ions, fragment cluster ions) as a function of penetration depth are also calculated in tandem with the above calculations by means of the Monte Carlo method. The relative importance of scattering versus Coulomb repulsion is studied as a function of the C-60 cluster energy. The effect of the neighboring cluster constituents on the average charge state of the cluster atoms is calculated as a function of the depth of penetration for a C-60 cluster of 40 MeV. The calculation accounts for the increase in ionization energy of the atom due to the other constituents. Relative track radii are calculated as a function of penetration depth and good agreement with the experimental results is obtained for the interaction of a 30 MeV carbon cluster with silicon. Track splitting observed well into the target as measured by Dunlop in yttrium iron garnet is obtained in the simulations described here for the case of amorphous carbon, provided the Coulomb repulsion is screened by the four valence electrons. Collective energy deposition enhancement is calculated for the 720 MeV cluster. Here the cluster constituents are nearly fully ionized, thereby minimizing the ambiguity related to the value of the ionic charge in the calculation

Leptogenesis without violation of B-L

We study the possibility of generating the observed baryon asymmetry via leptogenesis in the decay of heavy Standard Model singlet fermions which carry lepton number, in a framework without Majorana masses above the electroweak scale. Such scenario does not contain any source of total lepton number violation besides the Standard Model sphalerons, and the baryon asymmetry is generated by the interplay of lepton flavour effects and the sphaleron decoupling in the decay epoch.Comment: V2 (published version): 21 pages, 4 figures. Some explanations have been adde

Supersymmetric Leptogenesis

We study leptogenesis in the supersymmetric standard model plus the seesaw. We identify important qualitative differences that characterize supersymmetric leptogenesis with respect to the non-supersymmetric case. The lepton number asymmetries in fermions and scalars do not equilibrate, and are related via a non-vanishing gaugino chemical potential. Due to the presence of new anomalous symmetries, electroweak sphalerons couple to winos and higgsinos, and QCD sphalerons couple to gluinos, thus modifying the corresponding chemical equilibrium conditions. A new constraint on particles chemical potentials corresponding to an exactly conserved $R$-charge, that also involves the number density asymmetry of the heavy sneutrinos, appears. These new ingredients determine the $3\times 4$ matrices that mix up the density asymmetries of the lepton flavours and of the heavy sneutrinos. We explain why in all temperature ranges the particle thermodynamic system is characterized by the same number of independent quantities. Numerical differences with respect to usual treatment remain at the ${\cal O}(1)$ level.Comment: 30 pages, 2 figures. Typos corrected, one reference added. Version published in JCA

CP violation in scatterings, three body processes and the Boltzmann equations for leptogenesis

We obtain the Boltzmann equations for leptogenesis including decay and scattering processes with two and three body initial or final states. We present an explicit computation of the CP violating scattering asymmetries. We analyze their possible impact in leptogenesis, and we discuss the validity of their approximate expressions in terms of the decay asymmetry. In scenarios in which the initial heavy neutrino density vanishes, the inclusion of CP asymmetries in scatterings can enforce a cancellation between the lepton asymmetry generated at early times and the asymmetry produced at later times. We argue that a sizeable amount of washout is crucial for spoiling this cancellation, and we show that in the regimes in which the washouts are particularly weak, the inclusion of CP violation in scatterings yields a reduction in the final value of the lepton asymmetry. In the strong washout regimes the inclusion of CP violation in scatterings still leads to a significant enhancement of the lepton asymmetry at high temperatures; however, due to the independence from the early conditions that is characteristic of these regimes, the final value of the lepton asymmetry remains approximately unchanged.Comment: 24 pages, 6 figures. One appendix added. Some numerical results and corresponding figures (mainly fig. 3) corrected. Final version to be published in JHE

Z', new fermions and flavor changing processes, constraints on E6_6 models from μ\mu --> eee

We study a new class of flavor changing interactions, which can arise in models based on extended gauge groups (rank $>$4) when new charged fermions are present together with a new neutral gauge boson. We discuss the cases in which the flavor changing couplings in the new neutral current coupled to the $Z^\prime$ are theoretically expected to be large, implying that the observed suppression of neutral flavor changing transitions must be provided by heavy $Z^\prime$ masses together with small $Z$-$Z^\prime$ mixing angles. Concentrating on E$_6$ models, we show how the tight experimental limit on $\mu \rightarrow eee$ implies serious constraints on the $Z^\prime$ mass and mixing angle. We conclude that if the value of the flavor changing parameters is assumed to lie in a theoretically natural range, in most cases the presence of a $Z^\prime$ much lighter than 1 TeV is unlikely.Comment: plain tex, 22 pages + 2 pages figures in PostScript (appended after `\bye'), UM-TH 92-1

On the full Boltzmann equations for Leptogenesis

We consider the full Boltzmann equations for standard and soft leptogenesis, instead of the usual integrated Boltzmann equations which assume kinetic equilibrium for all species. Decays and inverse decays may be inefficient for thermalising the heavy-(s)neutrino distribution function, leading to significant deviations from kinetic equilibrium. We analyse the impact of using the full kinetic equations in the case of a previously generated lepton asymmetry, and find that the washout of this initial asymmetry due to the interactions of the right-handed neutrino is larger than when calculated via the integrated equations. We also solve the full Boltzmann equations for soft leptogenesis, where the lepton asymmetry induced by the soft SUSY-breaking terms in sneutrino decays is a purely thermal effect, since at T=0 the asymmetry in leptons cancels the one in sleptons. In this case, we obtain that in the weak washout regime (K ~< 1) the final lepton asymmetry can change up to a factor four with respect to previous estimates.Comment: 34 pages, 6 figures, to be published in JCA