Cosmological Sign of Neutrino CP Violation

It is shown how, in a class of models, the sign of the baryon number of the universe can be related to CP violation in neutrino oscillation experiments.Comment: 3 pages LaTe

Constraints on SUSY Lepton Flavour Violation by rare processes

We study the constraints on flavour violating terms in low energy SUSY coming from several processes as li -> lj gamma, li -> lj lj lj and mu -> e in Nuclei. We show that a combined analysis of the processes allows us to extract additional information with respect to an individual analysis of all the processes. In particular, it makes possible to put bounds on sectors previously unconstrained by li -> lj gamma. We perform the analysis both in the mass eigenstate and in the mass insertion approximations clarifying the limit of applicability of these approximations.Comment: 23 pages, 15 figures. Typos corrected, several references and equations added. Results and conclusions completely unchanged. Accepted version for publication in JHE

Distinguishable RGE running effects between Dirac neutrinos and Majorana neutrinos with vanishing Majorana CP-violating phases

In a novel parametrization of neutrino mixing and in the approximation of $\tau$-lepton dominance, we show that the one-loop renormalization-group equations (RGEs) of Dirac neutrinos are different from those of Majorana neutrinos even if two Majorana CP-violating phases vanish. As the latter can keep vanishing from the electroweak scale to the typical seesaw scale, it makes sense to distinguish between the RGE running effects of neutrino mixing parameters in Dirac and Majorana cases. The differences are found to be quite large in the minimal supersymmetric standard model with sizable $\tan\beta$, provided the masses of three neutrinos are nearly degenerate or have an inverted hierarchy.Comment: 12 pages, 5 figure

Upper Bound on the Mass of the Type III Seesaw Triplet in an SU(5) Model

We investigate correlation between gauge coupling unification, fermion mass spectrum, proton decay, perturbativity and ultraviolet cutoff within an SU(5) grand unified theory with minimal scalar content and an extra adjoint representation of fermions. We find strong correlation between the upper bound on the mass of both the bosonic and fermionic SU(2) triplets and the cutoff. The upper bound on the mass of fermionic triplet responsible for Type III seesaw mechanism is 10^{2.1} GeV for the Planck scale cutoff. In that case both the idea of grand unification and nature of seesaw mechanism could be tested at future collider experiments through the production of those particles. Moreover, the prediction for the proton decay lifetime is at most an order of magnitude away from the present experimental limits. If the cutoff is lowered these predictions change significantly. In the most general scenario, if one does (not) neglect a freedom in the quark and lepton mixing angles, the upper bound on the fermionic triplet mass is at 10^{5.4} GeV (10^{10} GeV). Since the predictions of the model critically depend on the presence of the higher-dimensional operators and corresponding cutoff we address the issue of their possible origin and also propose alternative scenarios that implement the hybrid seesaw framework of the original proposal.Comment: 13 pages, 2 figures, minor changes introduced to match the JHEP versio

The importance of flavor in leptogenesis

We study leptogenesis from the out-of-equilibrium decays of the lightest heavy neutrino $N_1$ in the medium (low) temperature regime, T\lsim 10^{12} GeV ($10^{10}$ GeV), where the rates of processes mediated by the $\tau$ (and $\mu$) Yukawa coupling are non negligible, implying that the effects of lepton flavors must be taken into account. We find important quantitative and qualitative differences with respect to the case where flavor effects are ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of magnitude; (ii) The sign of the asymmetry can be opposite to what one would predict from the sign of the total lepton asymmetry $\epsilon_1$; (iii) Successful leptogenesis is possible even with $\epsilon_1=0$.Comment: 27 pages, 2 figures. Added 3 reference

Stability and leptogenesis in the left-right symmetric seesaw mechanism

We analyze the left-right symmetric type I+II seesaw mechanism, where an eight-fold degeneracy among the mass matrices of heavy right-handed neutrinos M_R is known to exist. Using the stability property of the solutions and their ability to lead to successful baryogenesis via leptogenesis as additional criteria, we discriminate among these eight solutions and partially lift their eight-fold degeneracy. In particular, we find that viable leptogenesis is generically possible for four out of the eight solutions.Comment: 25 pages, 11 figures, latex; minor changes, published versio

Hypercharge and baryon minus lepton number in E6

We study assignments of the hypercharge and baryon minus lepton number for particles in the $E_6$ grand unification model. It is shown that there are three assignments of hypercharge and three assignments of baryon minus lepton number which are consistent with the Standard Model. Their explicit expressions and detailed properties are given. In particular, we show that the $U(1)_{B-L}$ symmetry in $E_6$ cannot be orthogonal to the $SU(3)_R$ symmetry. Based on these investigations, we propose an alternative SU(5) grand unification model.Comment: 16 pages, JHEP3.cls, To appear in JHE

TeV scale resonant leptogenesis from supersymmetry breaking

We propose a model of TeV-scale resonant leptogenesis based upon recent models of the generation of light neutrino masses from supersymmetry-breaking effects with TeV-scale right-handed (rhd) neutrinos, $N_i$. The model leads to naturally large cosmological lepton asymmetries via the resonant behaviour of the one-loop self-energy contribution to $N_i$ decay. Our model addresses the primary problems of previous phenomenological studies of low-energy leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa couplings so that the out-of equilibrium condition for $N_i$ decay is satisfied; the origin of the tiny, but non-zero mass splitting required between at least two $N_i$ masses; and the necessary non-trivial breaking of flavour symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos and their superpartners, and the TeV-scale $A$-terms automatically contained within the model offer opportunities for partial direct experimental tests of this leptogenesis mechanism at future colliders.Comment: 10 Pages latex, version for JHE

Phenomenological interaction between current quarks

We construct a phenomenological model which describes the dynamical chiral symmetry breaking (DCSB) of QCD vacuum and reproduces meson spectra. Quark condensates, the pion decay constant, and meson spectra are well reproduced by phenomenological interaction which consists of a linear confining potential, a Coulombic potential, and the 't Hooft determinant interaction. In this model, the 't Hooft determinant interaction plays a important role not to only \eta,\eta' mass difference, but other meson masses through DCSB.Comment: 18 pages, LaTe

Two- and Three-Point Functions in the Extended NJL Model

The two-point functions in generalized Nambu--Jona-Lasinio models are calculated to all orders in momenta and quark masses to leading order in $1/N_c$. The use of Ward identities and the heat-kernel expansion allows for a large degree of regularization independence. We also show how this approach works to the same order for three-point functions on the example of the vector-pseudoscalar-pseudoscalar three-point function. The inclusion of the chiral anomaly effects at this level is shown by calculating the pseudoscalar-vector-vector three-point function to the same order. Finally we comment on how (vector-)meson-dominance comes out in the presence of explicit chiral symmetry breaking in both the anomalous and the non-anomalous sectors.Comment: Latex, 42 pages, 3 latex figures, 7 postscript figures included, NORDITA 94/11 N,P. Improvement in the regularization procedure for the PVV three point functio