A SUSY A4 model for fermion masses and mixings

We study a supersymmetric extension of the Standard Model based on discrete A4xZ3xZ4 flavor symmetry. We obtain quark mixing angles as well as a realistic fermion mass spectrum and we predict tribimaximal leptonic mixing by a spontaneous breaking of A4. The top quark Yukawa interaction is present at the renormalizable level in the superpotential while all the other Yukawa interactions arise only at higher orders. We study the Higgs potential and show that it can potentially solve the so called vacuum alignment problem. The leading order predictions are not spoiled by subleading corrections.Comment: version accepted in JHEP, Z3xZ2 changed in Z3xZ4, typos in table corrected, references adde

Flavor Symmetry for Quarks and Leptons

Present data on neutrino masses and mixing favor the highly symmetric tribimaximal neutrino mixing matrix which suggests an underlying flavor symmetry. A systematic study of non-abelian finite groups of order $g \leq 31$ reveals that tribimaximal mixing can be derived not only from the well known tetrahedral flavor symmetry $T \equiv A_4$, but also by using the binary tetrahedral symmetry $T^{'} \equiv SL_2(F_3)$ which does not contain the tetrahedral group as a subgroup. $T^{'}$ has the further advantage that it can also neatly accommodate the quark masses including a heavy top quark.Comment: 12 pages latex. More typos correcte

Astrophysical constraints on primordial black holes in Brans-Dicke theory

We consider cosmological evolution in Brans-Dicke theory with a population of primordial black holes. Hawking radiation from the primordial black holes impacts various astrophysical processes during the evolution of the Universe. The accretion of radiation by the black holes in the radiation dominated era may be effective in imparting them a longer lifetime. We present a detailed study of how this affects various standard astrophysical constraints coming from the evaporation of primordial black holes. We analyze constraints from the present density of the Universe, the present photon spectrum, the distortion of the cosmic microwave background spectrum and also from processes affecting light element abundances after nucleosynthesis. We find that the constraints on the initial primordial black hole mass fractions are tightened with increased accretion efficiency.Comment: 15 page

Primordial black holes in braneworld cosmologies: astrophysical constraints

In two recent papers we explored the modifications to primordial black hole physics when one moves to the simplest braneworld model, Randall--Sundrum type II. Both the evaporation law and the cosmological evolution of the population can be modified, and additionally accretion of energy from the background can be dominant over evaporation at high energies. In this paper we present a detailed study of how this impacts upon various astrophysical constraints, analyzing constraints from the present density, from the present high-energy photon background radiation, from distortion of the microwave background spectrum, and from processes affecting light element abundances both during and after nucleosynthesis. Typically, the constraints on the formation rate of primordial black holes weaken as compared to the standard cosmology if black hole accretion is unimportant at high energies, but can be strengthened in the case of efficient accretion.Comment: 17 pages RevTeX4 file with three figures incorporated; final paper in series astro-ph/0205149 and astro-ph/0208299. Minor changes to match version accepted by Physical Review

A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4

We discuss a grand unified model based on SUSY SU(5) in extra dimensions and on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing for neutrinos with the accuracy required by the data, also leads to a natural description of the observed pattern of quark masses and mixings.Comment: 19 page

How spiking neurons give rise to a temporal-feature map

A temporal-feature map is a topographic neuronal representation of temporal attributes of phenomena or objects that occur in the outside world. We explain the evolution of such maps by means of a spike-based Hebbian learning rule in conjunction with a presynaptically unspecific contribution in that, if a synapse changes, then all other synapses connected to the same axon change by a small fraction as well. The learning equation is solved for the case of an array of Poisson neurons. We discuss the evolution of a temporal-feature map and the synchronization of the single cells’ synaptic structures, in dependence upon the strength of presynaptic unspecific learning. We also give an upper bound for the magnitude of the presynaptic interaction by estimating its impact on the noise level of synaptic growth. Finally, we compare the results with those obtained from a learning equation for nonlinear neurons and show that synaptic structure formation may profit from the nonlinearity

Characterization of the GlnK protein of Escherichia coli

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75120/1/j.1365-2958.1999.01349.x.pd

Group space scan of flavor symmetries for nearly tribimaximal lepton mixing

We present a systematic group space scan of discrete Abelian flavor symmetries for lepton mass models that produce nearly tribimaximal lepton mixing. In our models, small neutrino masses are generated by the type-I seesaw mechanism. The lepton mass matrices emerge from higher-dimension operators via the Froggatt-Nielsen mechanism and are predicted as powers of a single expansion parameter \epsilon that is of the order of the Cabibbo angle \theta_C\simeq 0.2. We focus on solutions that can give close to tribimaximal lepton mixing with a very small reactor angle \theta_{13}\approx 0 and find several thousand explicit such models that provide an excellent fit to current neutrino data. The models are rather general in the sense that large leptonic mixings can come from the charged leptons and/or neutrinos. Moreover, in the neutrino sector, both left- and right-handed neutrinos can mix maximally. We also find a new relation \theta_{13}\lesssim\epsilon^3 for the reactor angle and a new sum rule \theta_{23}\approx\pi/4+\epsilon/\sqrt{2} for the atmospheric angle, allowing the models to be tested in future neutrino oscillation experiments.Comment: 18 pages, 2 tables, 2 figures, references added, final version to appear in JHE