6,697,169 research outputs found
Large and Almost Maximal Neutrino Mixing within the Type II See-Saw Mechanism
Within the type II see-saw mechanism the light neutrino mass matrix is given
by a sum of a direct (or triplet) mass term and the conventional (type I)
see-saw term. Both versions of the see-saw mechanism explain naturally small
neutrino masses, but the type II scenario offers interesting additional
possibilities to explain large or almost maximal or vanishing mixings which are
discussed in this paper. We first introduce ``type II enhancement'' of neutrino
mixing, where moderate cancellations between the two terms can lead to large
neutrino mixing even if all individual mass matrices and terms generate small
mixing. However, nearly maximal or vanishing mixings are not naturally
explained in this way, unless there is a certain initial structure (symmetry)
which enforces certain elements of the matrices to be identical or related in a
special way. We therefore assume that the leading structure of the neutrino
mass matrix is the triplet term and corresponds to zero U_{e3} and maximal
theta_{23}. Small but necessary corrections are generated by the conventional
see-saw term. Then we assume that one of the two terms corresponds to an
extreme mixing scenario, such as bimaximal or tri-bimaximal mixing. Deviations
from this scheme are introduced by the second term. One can mimic Quark-Lepton
Complementarity in this way. Finally, we note that the neutrino mass matrix for
tri-bimaximal mixing can be -- depending on the mass hierarchy -- written as a
sum of two terms with simple structure. Their origin could be the two terms of
type II see-saw.Comment: 25 pages. Comments and references added, to appear in JHE
Reflections on Metaphysical Explanation
The nature of metaphysical explanation is a question that should be constantly on every metaphysicianâs mind, and yet it is rare to see explicit statements about the methodological approach that writers take. We tend to just enter the flow of ideas and words in a particular âdiscourseâ and see where it leads us. It is easier that way but can lead us astray. I canât claim to be a role-model in this respect. I have offered a comment here, a remark there, but plenty room for improvement. However, I have come across quite a few confusions that can be traced to failed understanding of method/approach, and one or two really interesting statements of method. Here I share one such confusion about method, and one interesting view about method
Videoconferencing via satellite. Opening Congress to the people: Technical report
The feasibility of using satellite videoconferencing as a mechanism for informed dialogue between Congressmen and constituents to strengthen the legislative process was evaluated. Satellite videoconferencing was defined as a two-way interactive television with the TV signals transmitted by satellite. With videoconferencing, one or more Congressmen in Washington, D. C. can see, hear and talk with groups of citizens at distant locations around the country. Simultaneously, the citizens can see, hear and talk with the Congressmen
From probabilities to categorical beliefs: Going beyond toy models
According to the Lockean thesis, a proposition is believed just in case it is highly probable. While this thesis enjoys strong intuitive support, it is known to conflict with seemingly plausible logical constraints on our beliefs. One way out of this conflict is to make probability 1 a requirement for belief, but most have rejected this option for entailing what they see as an untenable skepticism. Recently, two new solutions to the conflict have been proposed that are alleged to be non-skeptical. We compare these proposals with each other and with the Lockean thesis, in particular with regard to the question of how much we gain by adopting any one of them instead of the probability 1 requirement, that is, of how likely it is that one believes more than the things one is fully certain of
On the asymptotic spatial behaviour of the solutions of the nerve system
In this paper we investigate the asymptotic spatial behavior of the solutions for several models for the nerve fibers.
First, our analysis deals with the coupling of two parabolic equations. We prove that, under suitable assumptions on the coefficients
and the nonlinear function, the decay is similar to the one corresponding to the heat equation. A limit case of this system
corresponds to the coupling of a parabolic equation with an ordinary differential equation. In this situation, we see that for suitable
boundary conditions the solution ceases to exist for a finite value of the spatial variable. Next two sections correspond to
the coupling of a hyperbolic/parabolic and hyperbolic/ordinary differential problems. For the first one we obtain that the decay
is like an exponential of a second degree polynomial in the spatial variable. In the second one, we prove a similar behaviour to
the one corresponding to the wave equation. In these two sections we use in a relevant way an exponentially weighted Poincaré
inequality which has been revealed very useful in several thermal and mechanical problems. This kind of results have relevance
to understand the propagation of perturbations for nerve models.Peer ReviewedPostprint (authorâs final draft
TheĆsis: A Comparative Study of T. F. Torrance and RÄmÄnuja
This essay is an imaginative conversation as I engage two religious thinkersâthe prolific Reformed theologian Thomas F. Torrance (1913-2007) and the great VedÄntin RÄmÄnuja (traditionally, 1017â1137). I will compare Torranceâs theology1 of theĆsis2 (participation in the life of God) and theĆria (contemplation as a way of participation in the life of God) with those of RÄmÄnuja. Though the words themselves were likely unknown to RÄmÄnuja, through his works one can see a notion of theĆsis
Diffuse emission in the presence of inhomogeneous spin-orbit interaction for the purpose of spin filtration
A lateral interface connecting two regions with different strengths of the
Bychkov-Rashba spin-orbit interaction can be used as a spin polarizer of
electrons in two dimensional semiconductor heterostructures. [Khodas \emph{et
al.}, Phys. Rev. Lett. \textbf{92}, 086602 (2004)]. In this paper we consider
the case when one of the two regions is ballistic, while the other one is
diffusive. We generalize the technique developed for the solution of the
problem of the diffuse emission to the case of the spin dependent scattering at
the interface, and determine the distribution of electrons emitted from the
diffusive region. It is shown that the diffuse emission is an effective way to
get electrons propagating at small angles to the interface that are most
appropriate for the spin filtration and a subsequent spin manipulation.
Finally, a scheme is proposed of a spin filter device, see Fig. 9, that creates
two almost fully spin-polarized beams of electrons.Comment: 11 pages, 9 figure
Topology in 2D CP**(N-1) models on the lattice: a critical comparison of different cooling techniques
Two-dimensional CP**(N-1) models are used to compare the behavior of
different cooling techniques on the lattice. Cooling is one of the most
frequently used tools to study on the lattice the topological properties of the
vacuum of a field theory. We show that different cooling methods behave in an
equivalent way. To see this we apply the cooling methods on classical
instantonic configurations and on configurations of the thermal equilibrium
ensemble. We also calculate the topological susceptibility by using the cooling
technique.Comment: 24 pages, 10 figures (from 16 eps files
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