15990400
Minimal Seesaw Textures with Two Heavy Neutrinos
We systematically analyze the Dirac and the Majorana mass matrices in seesaw models with two heavy right-handed neutrinos. We perform thorough classification of the vanishing matrix elements which are compatible with the results from the current neutrino oscillation experiments. We include the possibility of a nondiagonal Majorana mass matrix which leads to new solutions viable with data. In a basis where the Majorana mass matrix is diagonal, these solutions imply a Dirac matrix with specific relationships amongst its elements. We find that at the level of total four zeros together in m{sub D} and M{sub R} the mass matrices are almost consistent with the data but one mixing angle is predicted to be unsuitable. At the next level, i.e. with total three zeros, only seven patterns of mass matrices describe the experimental data well. The seven solutions have testable predictions for the future neutrino experiments. In particular, each solution has definite predictions about the observation of the 1-3 leptonic mixing angle and the effective mass measured in neutrinoless double beta decay. The solutions of the mass matrices contain novel texture forms and provide new insights into the lepton-generation structure. We also discuss possible connections between these textures and the tri-bimaximal more » mixing to search for symmetry principles behind the mass matrix structure. « less
119111931
Relating large Ue3 to the ratio of neutrino mass-squared differences
Abstract The non-zero and sizable value of U e 3 puts pressure on flavor symmetry models which predict an initially vanishing value. Hence, the tradition of relating fermion mixing matrix elements with fermion mass ratios might need to be resurrected. We note that the recently observed non-vanishing value of U e 3 can be related numerically to the ratio of solar and atmospheric mass-squared differences. The most straightforward realization of this can be achieved with a combination of texture zeros and a vanishing neutrino mass. We analyze the implications of some of these possibilities and construct explicit flavor symmetry models that predict these features.
119212786
Seesaw in the Bulk
A five-dimensional seesaw framework is analyzed with the lepton-number-violating propagator of bulk right-handed neutrinos. That can bypass summing up the effects of heavy Majorana particles whose masses and wavefunctions are not exactly known. The propagator method makes it easier to evaluate the seesaw-induced neutrino mass for various boundary conditions of bulk neutrinos and in a general background geometry, including the warped extra dimension. It is also found that the higherdimensional seesaw gives a natural framework for the inverse seesaw suppression of low-energy neutrino masses.
15261294
Twisted flavors and tribimaximal neutrino mixing.
A new framework for handling flavor symmetry breaking in the neutrino sector is discussed where the source of symmetry breaking is traced to the global property of right-handed neutrinos in extra-dimensional space. Light neutrino phenomenology has rich and robust predictions such as the tribimaximal form of generation mixing, controlled mass spectrum, and no need of flavor mixing couplings in the theory.
11888215
The Role and Detectability of the Charm Contribution to Ultra High Energy Neutrino Fluxes
It is widely believed that charm meson production and decay may play an important role in high energy astrophysical sources of neutrinos, especially those that are baryon-rich, providing an environment conducive to pp interactions. Using slow-jet supernovae (SJS) as an example of such a source, we study the detectability of high-energy neutrinos, paying particular attention to those produced from charmed-mesons. We highlight important distinguishing features in the ultra-high energy neutrino flux which would act as markers for the role of charm in the source. In particular, charm leads to significant event rates at higher energies, after the conventional (π,K) neutrino fluxes fall off. We calculate event rates both for a nearby single source and for diffuse SJS fluxes for an IceCube-like detector. By comparing muon event rates for the conventional and prompt fluxes in different energy bins, we demonstrate the striking energy dependence in the rates induced by the presence of charm. We also show that it leads to an energy dependant flux ratio of shower to muon events, providing an additional important diagnostic tool for the presence of prompt neutrinos. Motivated by the infusion of high energy anti-electron neutrinos into the flux by charm decay, we also study the detectability of the Glashow resonance due to these sources.
56570203
Diffuse Ultra-High Energy Neutrino Fluxes and Physics Beyond the Standard Model
Abstract We study spectral distortions of diffuse ultra-high energy (UHE) neutrino flavour fluxes resulting due to physics beyond the Standard Model (SM). Even large spectral differences between flavours at the source are massaged into a common shape at earth by SM oscillations, thus, any significant observed spectral differences are an indicator of new physics present in the oscillation probability during propagation. Lorentz symmetry violation (LV) and neutrino decay are examples, and result in significant distortion of the fluxes and of the well-known bounds on them, which may allow UHE detectors to probe LV parameters, lifetimes and the mass hierarchy over a broad range.
119262648
Transition from soft- to hard-Pomeron in the structure functions of hadrons at small-$x$ from holography
We study the nucleon and pion structure functions at small Bjorken-$x$ region in the framework of holographic QCD with a special emphasis on the roles of AdS space wave functions. Using the BPST kernel for the Pomeron exchange and calculating its coupling to target hadrons in the AdS space, we obtain $F_2$ structure functions at the small-$x$. Results for the proton $F^p_2$ as well as the pion $F^\pi_2$ are consistent with experimental data of the deep inelastic scattering and the forward electroproduction of a neutron. Observed $Q^2$ dependence of the Pomeron intercept is well reproduced from soft non-perturbatibve $(Q^2 \sim 0)$ to hard perturbative $(Q^2 \gg 1 GeV^2)$ region. We find the interplay between soft and hard Pomerons is closely related with behavior of AdS wave functions of hadrons and the virtual photon.
119232581
Pomeron dynamics in the AdS space and structure functions of hadrons at small x
The Pomeron dynamics is investigated via deep inelastic scattering (DIS) at small x in the framework of holographic quantum chromodynamics. The small x DIS process is assumed to be described by the graviton exchange between external vector current and hadron in the AdS space. Our calculations for Fp2, Fπ2, as well as the longitudinal counterpart FpL are consistent with the experimental data. We discuss origins of a difference between F2 and FL in our approach.
119097645
Nucleon structure functions at small $x$ via the Pomeron exchange in AdS space with a soft infrared wall
We present analyses on nucleon structure functions at the small Bjorken-$x$ in the framework of holographic QCD. In this study, we improve the description of the target nucleon in the current setup of the holographic model by introducing a soft-wall AdS/QCD model, in which the AdS geometry is smoothly cut off at IR. Combining the improved Pomeron-nucleon coupling and the wave function of the 5D U(1) vector field with the BPST Pomeron exchange kernel, then we obtain the structure functions. Here we focus on the nonperturbative kinematical region, where $10^{-6} \leq x \leq 10^{-2}$ and $0.1 \leq Q^2 \leq 10$ [GeV$^2$], and show that our calculations for $F_2^p$ and $F_L^p$ are consistent with experimental data of the deep inelastic scattering at HERA. Furthermore, we find that the resulting longitudinal-to-transverse ratio of the structure functions, $F_L^p/F_T^p$, depends on both of $x$ and $Q^2$.