188 research outputs found
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
reveals that tribimaximal mixing can be derived not only from the well known
tetrahedral flavor symmetry , but also by using the binary
tetrahedral symmetry which does not contain the
tetrahedral group as a subgroup. 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
- …