17,639 research outputs found
Searching for Effects of Spatial Noncommutativity via Chern-Simons' Processes
The possibility of testing spatial noncommutativity in the case of both
position-position and momentum-momentum noncommuting via a Chern-Simons'
process is explored. A Chern-Simons process can be realized by an interaction
of a charged particle in special crossed electric and magnetic fields, in which
the Chern-Simons term leads to non-trivial dynamics in the limit of vanishing
kinetic energy. Spatial noncommutativity leads to the spectrum of the orbital
angular momentum possessing fractional values. Furthermore, in both limits of
vanishing kinetic energy and subsequent vanishing magnetic field, the
Chern-Simons term leads to this system having non-trivial dynamics again, and
the dominant value of the lowest orbital angular momentum being ,
which is a clear signal of spatial noncommutativity. An experimental
verification of this prediction by a Stern-Gerlach-type experiment is
suggested.Comment: 18 page
Relating quarks and leptons without grand-unification
In combination with supersymmetry, flavor symmetry may relate quarks with
leptons, even in the absence of a grand-unification group. We propose an
SU(3)xSU(2)xU(1) model where both supersymmetry and the assumed A4 flavor
symmetries are softly broken, reproducing well the observed fermion mass
hierarchies and predicting: (i) a relation between down-type quarks and charged
lepton masses, and (ii) a correlation between the Cabibbo angle in the quark
sector, and the reactor angle characterizing CP violation in neutrino
oscillations.Comment: 4 pages, 2 figures, version published in PR
Neutrino Mass and Mixing: from Theory to Experiment
The origin of fermion mass hierarchies and mixings is one of the unresolved
and most difficult problem in high-energy physics. One possibility to address
the flavour problem is by extending the Standard Model to include a family
symmetry. In the recent years it has become very popular to use non-Abelian
discrete flavour symmetries because of their power in the prediction of the
large leptonic mixing angles relevant for neutrino oscillation experiments.
Here we give an introduction to the flavour problem and to discrete groups
which have been used to attempt a solution for it. We review the current status
of models in the light of the recent measurement of the reactor angle and we
consider different model building directions taken. The use of the flavons or
multi Higgs scalars in model building is discussed as well as the direct vs.
indirect approaches. We also focus on the possibility to distinguish
experimentally flavour symmetry models by means of mixing sum rules and mass
sum rules. In fact, we illustrate in this review the complete path from
mathematics, via model building, to experiments, so that any reader interested
to start working in the field could use this text as a starting point in order
to get a broad overview of the different subject areas.Comment: Accepted for publication in NJP, 62 pages, 9 tables, 7 figure
Peculiar mean velocity profiles within a porous bed of an open channel
Peer reviewedPublisher PD
A Relativistic Description of Gentry's New Redshift Interpretation
We obtain a new expression of the Friedmann-Robertson-Walker metric, which is
an analogue of a static chart of the de Sitter space-time. The reduced metric
contains two functions, and , which are interpreted as,
respectively, the mass function and the gravitational potential. We find that,
near the coordinate origin, the reduced metric can be approximated in a static
form and that the approximated metric function, , satisfies the
Poisson equation. Moreover, when the model parameters of the
Friedmann-Robertson-Walker metric are suitably chosen, the approximated metric
coincides with exact solutions of the Einstein equation with the perfect fluid
matter. We then solve the radial geodesics on the approximated space-time to
obtain the distance-redshift relation of geodesic sources observed by the
comoving observer at the origin. We find that the redshift is expressed in
terms of a peculiar velocity of the source and the metric function, ,
evaluated at the source position, and one may think that this is a new
interpretation of {\it Gentry's new redshift interpretation}.Comment: 11 pages. Submitted to Modern Physics Letters
Magnetic Flux Loss and Flux Transport in a Decaying Active Region
We estimate the temporal change of magnetic flux perpendicular to the solar
surface in a decaying active region by using a time series of the spatial
distribution of vector magnetic fields in the photosphere. The vector magnetic
fields are derived from full spectropolarimetric measurements with the Solar
Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux
transport rate in a decaying sunspot and its surrounding moat region. The
amount of magnetic flux that decreases in the sunspot and moat region is very
similar to magnetic flux transported to the outer boundary of the moat region.
The flux loss rates [] of magnetic elements with positive and
negative polarities are balanced each other around the outer boundary of the
moat region. These results suggest that most of the magnetic flux in the
sunspot is transported to the outer boundary of the moat region as moving
magnetic features, and then removed from the photosphere by flux cancellation
around the outer boundary of the moat region.Comment: 16 pages, 7 figures, Accepted for publication in Ap
Decreased Specific Star Formation Rates in AGN Host Galaxies
We investigate the location of an ultra-hard X-ray selected sample of AGN
from the Swift Burst Alert Telescope (BAT) catalog with respect to the main
sequence (MS) of star-forming galaxies using Herschel-based measurements of the
star formation rate (SFR) and stellar mass (\mstar) from Sloan Digital Sky
Survey (SDSS) photometry where the AGN contribution has been carefully removed.
We construct the MS with galaxies from the Herschel Reference Survey and
Herschel Stripe 82 Survey using the exact same methods to measure the SFR and
\mstar{} as the Swift/BAT AGN. We find a large fraction of the Swift/BAT AGN
lie below the MS indicating decreased specific SFR (sSFR) compared to non-AGN
galaxies. The Swift/BAT AGN are then compared to a high-mass galaxy sample
(COLD GASS), where we find a similarity between the AGN in COLD GASS and the
Swift/BAT AGN. Both samples of AGN lie firmly between star-forming galaxies on
the MS and quiescent galaxies far below the MS. However, we find no
relationship between the X-ray luminosity and distance from the MS. While the
morphological distribution of the BAT AGN is more similar to star-forming
galaxies, the sSFR of each morphology is more similar to the COLD GASS AGN. The
merger fraction in the BAT AGN is much higher than the COLD GASS AGN and
star-forming galaxies and is related to distance from the MS. These results
support a model in which bright AGN tend to be in high mass star-forming
galaxies in the process of quenching which eventually starves the supermassive
black hole itself.Comment: 23 pages, 14 figures, Accepted for publication in MNRAS 2015 June 23.
In original form 2015 January 2
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