Effects of a general set of interactions on neutrino propagation in matter

This talk is based on the article hep-ph/9903517 written in collaboration with Sven Bergmann and Yuval Grossman. An analysis of the effective potential for neutrino propagation in matter, assuming a generic set of Lorentz invariant non-derivative interactions is presented. In addition to vector and axial vector couplings, also tensor interactions can give coherent effects if the medium is polarized, and the components of a tensor potential transverse to the direction of neutrino propagation can induce a neutrino spin-flip.Comment: 7 pages; plenary talk given at COSMO-99, Trieste, Italy, Sept 27 - Oct 2, 199

Leptogenesis, Z' bosons, and the reheating temperature of the Universe

We study the impact for leptogenesis of new U(1) gauge bosons coupled to the heavy Majorana neutrinos. They can significantly enhance the efficiency of thermal scenarios in the weak washout regime as long as the Z' masses are not much larger than the reheating temperature ($M_{Z'}<10 T_{rh}$), with the highest efficiencies obtained for Z' bosons considerably heavier than the heavy neutrinos ($M_{Z'} > 100 M_1$). We show how the allowed region of the parameter space is modified in the presence of a Z' and we also obtain the minimum reheating temperature that is required for these models to be successful.Comment: 14 pages, 6 figures; One figure added, discussion on the reheating temperature extende

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

Introducing the concept of infinite series: Preliminary analyses of curriculum content and pedagogical practice

Introducing the concept of infinite series: preliminary analyses of curriculum content and pedagogical practice

Identifying Unconventional E6_{\bf 6} Models at e+e−e^+ e^- Colliders

Recently it was shown that, in the framework of superstring inspired \E models, the presence of generation dependent discrete symmetries allows us to construct a phenomenologically viable class of models in which the three generations of fermions do not have the same embedding within the fundamental {\bf 27} dimensional representation of E$_6$. In this scenario, these different embeddings of the conventional fermions imply that the left-handed charged leptons and the right-handed $d$-type quarks are coupled in a non--universal way to the new neutral gauge bosons $(Z_\theta)$ present in these models. It was also shown that a unique signature for this scenario, would be a deviation from unity for the ratio of cross sections for the production of two different lepton species in $e^+e^-$ annihilation. However, several different scenarios are possible, depending on the particular assignment chosen for $e_L$, $\mu_L$ and $\tau_L$ and for the right-handed $d$-type quarks, as well as on the type of $Z_\theta$ boson. Such scenarios can not be disentangled from one another by means of cross section measurements alone. In this paper we examine the possibility of identifying the pattern of embeddings through measurements of polarized and unpolarized asymmetries for fermion pair-production at the 500 GeV $e^+e^-$ Next Linear Collider (NLC). We show that it will be possible to identify the different patterns of unconventional assignments for the left-handed leptons and for the $b_R$ quark, for $Z_\theta$ masses as large as $\sim 1.5$ TeV.Comment: Plain Tex, 15 pages, + 9 figure available upon request ([email protected] or [email protected]), UM-TH 93--1

On Higgs and sphaleron effects during the leptogenesis era

We discuss the effects of various processes that can be active during the leptogenesis era, and present the Boltzmann equations that take them into account appropriately. A non-vanishing Higgs number asymmetry is always present, enhancing the washout of the lepton asymmetry. This is the main new effect when leptogenesis takes place at $T>10^{12}$ GeV, reducing the final baryon asymmetry and tightening the leptogenesis bound on the neutrino masses. If leptogenesis occurs at lower temperatures, electroweak sphalerons partially transfer the lepton asymmetry to a baryonic one, while Yukawa interactions and QCD sphalerons partially transfer the asymmetries of the left-handed fields to the right-handed ones, suppressing the washout processes. Depending on the specific temperature range in which leptogenesis occurs, the final baryon asymmetry can be enhanced or suppressed by factors of order 20%--40% with respect to the case when these effects are altogether ignored.Comment: one reference 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

Horizontal U(1)HU(1)_{H} symmetry: a non-anomalous model

Spontaneously broken Abelian gauge symmetries can explain the fermion mass hierarchies of the minimal supersymmetric standard model. In most cases it is assumed that the $U(1)_H$ symmetry is anomalous. However, non-anomalous models are also viable and yield an interesting phenomenology. Cancellation of the gauge anomalies implies the following results: unification of leptons and down-type quarks Yukawa couplings is allowed at most for two generations. The $\mu$ term is necessarily somewhat below the supersymmetry breaking scale. The superpotential has accidental $B$ and $L$ symmetries, and R-parity is automatically conserved in the supersymmetric limit. Anomaly canncellation also implies that the determinant of the quark mass matrix must vanish, wich is possible only if $m_{up}=0$. This solves the strong CP problem and provides an unambiguous low energy test of the model