Neutrino Masses and Leptogenesis with Heavy Higgs Triplets

A simple and economical extension of the minimal standard electroweak gauge model (without right-handed neutrinos) by the addition of two heavy Higgs scalar triplets would have two significant advantages. \underline {Naturally} small Majorana neutrino masses would become possible, as well as leptogenesis in the early universe which gets converted at the electroweak phase transition into the present observed baryon asymmetry.Comment: 12 pages including one figur

Leptogenesis with Heavy Majorana Neutrinos Reexamined

The mass term for Majorana neutrinos explicitly violates lepton number. Several authors have used this fact to create a lepton asymmetry in the universe by considering CP violating effects in the one loop self-energy correction for the decaying heavy Majorana neutrino. We compare and comment on the different approaches used to calculate the lepton asymmetry including those using an effective Hamiltonian and resummed propagators. We also recalculate the asymmetry in the small mass difference limit.Comment: 16 pages, LaTex, 1 figure included. 2 footnotes and 1 reference adde

Unstable Heavy Majorana Neutrinos and Leptogenesis

We propose a new mechanism producing a non-vanishing lepton number asymmetry, based on decays of heavy Majorana neutrinos. If they are produced out of equilibrium, as occurs in preheating scenario, and are superpositions of mass eigenstates rapidly decaying, their decay rates contains interference terms provided the mass differences $\Delta m$ are small compared to widths $\Gamma$. The resulting lepton asymmetry, which is the analogue of the time-integrated CP asymmetry in $B^0-\bar{B}^0$ system, is found to be proportional to $\Delta m/\Gamma$.Comment: 18 pages, latex, revised version to be published in Phys. Rev.

Leptogenesis

I present the theoretical basis for Leptogenesis and its implications for the structure of the universe. It is suggested that density fluctuations grow during the transition period and remnants of this effect should be sought in the universe. The relation between theories with Majorana neutrinos and low energy phenomena, including oscillations, advanced considerably during the past two years with a consistent picture developed in several models.Comment: 9 pages, 3 figures.To appear in the proceedings of The IXth International Symposium on Particles, Strings and Cosmology at the Tata Institute of Fundamental Research, Mumbai (Bombay), India, during 3-8 January 200

Electromagnetic Leptogenesis

We present a new leptogenesis scenario, where the lepton asymmetry is generated by CP violating decays of heavy electroweak singlet neutrinos via electromagnetic dipole moment couplings to the ordinary light neutrinos. Akin to the usual scenario where the decays are mediated through Yukawa interactions, we have shown, by explicit calculations, that the desired asymmetry can be produced through the interference of the corresponding tree-level and one-loop decay amplitudes involving the effective dipole moment operators. We also find that the relationship of the leptogenesis scale to the light neutrino masses is similar to that for the standard Yukawa-mediated mechanism.Comment: 6 pages, 6 figures; v2: some references added, minor change to discussion, accepted by PR

A Survey of Hadron Therapy Accelerator Technologies.

Hadron therapy has entered a new age [1]. The number of facilities grows steadily, and 'consumer' interest is high. Some groups are working on new accelerator technology, while others optimize existing designs by reducing capital and operating costs, and improving performance. This paper surveys the current requirements and directions in accelerator technology for hadron therapy

The role of Majorana CP phases in the bi-maximal mixing scheme -hierarchical Dirac mass case-

We discuss the energy scale profile of the bi-maximal mixing which is given at the GUT energy scale in the minimal SUSY model, associated with an assumption that Y_nu^dagger Y_nu is diagonal, where Y_nu is the neutrino-Yukawa coupling matrix. In this model, the Dirac mass matrix which appears in the seesaw neutrino mass matrix is determined by three neutrino masses, two relative Majorana phases and three heavy Majorana masses. All CP phases are related by two Majorana phases. We show that the requirement that the solar mixing angle moves from the maximal mixing at GUT to the observed one as the energy scale decreases by the renormalization effect. We discuss the leptogenesis, and the lepton flavor violation process by assuming the universal soft breaking terms.Comment: 19 pages, 2 figure

Leptogenesis with virtual Majorana neutrinos

We present a mechanism of leptogenesis based on the out-of-equilibrium decay of a scalar particle into heavy virtual Majorana neutrinos. This scheme presents many conceptual advantages over the conventional scenario of Fukugita and Yanagida. In particular, the standard techniques of quantum field theory can be used to compute the lepton asymmetry, without resorting to the phenomenological approximations usually made to describe unstable particles. This simplification allows us to address in a well-defined framework some issues raised in the recent literature. We also show, in a toy model, that a successful leptogenesis scenario is possible and requires a rather light scalar particle, $10^6 GeV < m < 10^{13} GeV$. A natural embedding of this scheme in a gauged unified theory encompassing the Majorana fermions seems however difficult.Comment: 23 pages, 9 figures, using Latex and epsfi

Signatures of heavy Majorana neutrinos and HERA's isolated lepton events

The graph of neutrinoless double beta decay is applied to HERA and generalized to final states with any two charged leptons. Considered is the case in which one of the two escapes typical identification criteria and the case when a produced tau decays hadronically. Both possibilities give one isolated lepton with high transverse momentum, hadronic activity and an imbalance in transverse momentum. We examine the kinematical properties of these events and compare them with the high p_T isolated leptons reported by the H1 collaboration. Their positive charged muon events can be explained by the ``double beta'' process and we discuss possibilities for the precise determination which original final state produced the single isolated lepton. To confirm our hypothesis one should search in the data for high pseudorapidity and/or low p_T leptons or for additional separated jets.Comment: 19 pages with 14 figures, minor change