2,714,759 research outputs found
Theoretical Models for Neutrino Masses
The recent measurements of the neutrino reactor angle require a
re-examination of flavour models based on discrete groups. Indeed, when these
models deal with the Tri-Bimaximal, the Bimaximal and the Golden Ratio mixing
patterns, some tensions arise in order to accommodate the reactor angle. In
particular, strong constraints come from lepton flavour violating processes,
like mu -> e gamma. We present the analysis and the main results.Comment: 8 pages, 3 figures. Contribution at "Les Rencontres de Physique de la
Vall\'ee d'Aoste". To be published as an issue of Nuovo Cimento
Theoretical Models of the Galactic Bulge
Near infrared images from the COBE satellite presented the first clear
evidence that our Milky Way galaxy contains a boxy shaped bulge. Recent years
have witnessed a gradual paradigm shift in the formation and evolution of the
Galactic bulge. Bulges were commonly believed to form in the dynamical violence
of galaxy mergers. However, it has become increasingly clear that the main body
of the Milky Way bulge is not a classical bulge made by previous major mergers,
instead it appears to be a bar seen somewhat end-on. The Milky Way bar can form
naturally from a precursor disk and thicken vertically by the internal
firehose/buckling instability, giving rise to the boxy appearance. This picture
is supported by many lines of evidence, including the asymmetric parallelogram
shape, the strong cylindrical rotation (i.e., nearly constant rotation
regardless of the height above the disk plane), the existence of an intriguing
X-shaped structure in the bulge, and perhaps the metallicity gradients. We
review the major theoretical models and techniques to understand the Milky Way
bulge. Despite the progresses in recent theoretical attempts, a complete bulge
formation model that explains the full kinematics and metallicity distribution
is still not fully understood. Upcoming large surveys are expected to shed new
light on the formation history of the Galactic bulge.Comment: Invited review to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing, 2015, in press. 27 pages, 7
figure
Theoretical models of ferromagnetic III-V semiconductors
Recent materials research has advanced the maximum ferromagnetic transition
temperature in semiconductors containing magnetic elements toward room
temperature. Reaching this goal would make information technology applications
of these materials likely. In this article we briefly review the status of work
over the past five years which has attempted to achieve a theoretical
understanding of these complex magnetic systems. The basic microscopic origins
of ferromagnetism in the (III,Mn)V compounds that have the highest transition
temperatures appear to be well understood, and efficient computation methods
have been developed which are able to model their magnetic, transport, and
optical properties. However many questions remain.Comment: 4 pages, 4 figures, review, to be published in Curr. Appl. Phy
Theoretical Models of Sunspot Structure and Dynamics
Recent progress in theoretical modeling of a sunspot is reviewed. The
observed properties of umbral dots are well reproduced by realistic simulations
of magnetoconvection in a vertical, monolithic magnetic field. To understand
the penumbra, it is useful to distinguish between the inner penumbra, dominated
by bright filaments containing slender dark cores, and the outer penumbra, made
up of dark and bright filaments of comparable width with corresponding magnetic
fields differing in inclination by some 30 degrees and strong Evershed flows in
the dark filaments along nearly horizontal or downward-plunging magnetic
fields. The role of magnetic flux pumping in submerging magnetic flux in the
outer penumbra is examined through numerical experiments, and different
geometric models of the penumbral magnetic field are discussed in the light of
high-resolution observations. Recent, realistic numerical MHD simulations of an
entire sunspot have succeeded in reproducing the salient features of the
convective pattern in the umbra and the inner penumbra. The siphon-flow
mechanism still provides the best explanation of the Evershed flow,
particularly in the outer penumbra where it often consists of cool, supersonic
downflows.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
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