283 research outputs found
Exploiting the directional sensitivity of the Double Chooz near detector
In scintillator detectors, the forward displacement of the neutron in the
reaction provides neutrino directional information as
demonstrated by the CHOOZ reactor experiment with 2,500 events. The near
detector of the forthcoming Double Chooz experiment will collect
events per year, enough to determine the average neutrino
direction with a half-cone aperture of in one year. It
is more difficult to separate the two Chooz reactors that are viewed at a
separation angle . If their strengths are known and
approximately equal, the azimuthal location of each reactor is obtained with
() and the probability of confusing them with a single
source is less than 11%. Five year's data reduce this ``confusion probability''
to less than 0.3%, i.e., a separation is possible. All of these
numbers improve rapidly with increasing angular separation of the sources. For
a setup with and one year's data, the azimuthal
uncertainty for each source decreases to . Of course, for Double
Chooz the two reactor locations are known, allowing one instead to measure
their individual one-year integrated power output to (), and
their five-year integrated output to ().Comment: 7 pages, 10 figure
Ethylene signalling affects susceptibility of tomatoes to Salmonella
Fresh fruits and vegetables are increasingly recognized as important reservoirs of human pathogens, and therefore, significant attention has been directed recently to understanding mechanisms of the interactions between plants and enterics, like Salmonella. A screen of tomato cultivars for their susceptibility to Salmonella revealed significant differences in the ability of this human pathogen to multiply within fruits; expression of the Salmonella genes (cysB, agfB, fadH) involved in the interactions with tomatoes depended on the tomato genotype and maturity stage. Proliferation of Salmonella was strongly reduced in the tomato mutants with defects in ethylene synthesis, perception and signal transduction. While mutation in the ripening-related ethylene receptor Nr resulted only in a modest reduction in Salmonella numbers within tomatoes, strong inhibition of the Salmonella proliferation was observed in rin and nor tomato mutants. RIN and NOR are regulators of ethylene synthesis and ripening. A commercial tomato variety heterozygous for rin was less susceptible to Salmonella under the greenhouse conditions but not when tested in the field over three production seasons
Imaging the Earth's Interior: the Angular Distribution of Terrestrial Neutrinos
Decays of radionuclides throughout the Earth's interior produce geothermal
heat, but also are a source of antineutrinos. The (angle-integrated)
geoneutrino flux places an integral constraint on the terrestrial radionuclide
distribution. In this paper, we calculate the angular distribution of
geoneutrinos, which opens a window on the differential radionuclide
distribution. We develop the general formalism for the neutrino angular
distribution, and we present the inverse transformation which recovers the
terrestrial radioisotope distribution given a measurement of the neutrino
angular distribution. Thus, geoneutrinos not only allow a means to image the
Earth's interior, but offering a direct measure of the radioactive Earth, both
(1) revealing the Earth's inner structure as probed by radionuclides, and (2)
allowing for a complete determination of the radioactive heat generation as a
function of radius. We present the geoneutrino angular distribution for the
favored Earth model which has been used to calculate geoneutrino flux. In this
model the neutrino generation is dominated by decays in the Earth's mantle and
crust; this leads to a very ``peripheral'' angular distribution, in which 2/3
of the neutrinos come from angles > 60 degrees away from the downward vertical.
We note the possibility of that the Earth's core contains potassium; different
geophysical predictions lead to strongly varying, and hence distinguishable,
central intensities (< 30 degrees from the downward vertical). Other
uncertainties in the models, and prospects for observation of the geoneutrino
angular distribution, are briefly discussed. We conclude by urging the
development and construction of antineutrino experiments with angular
sensitivity. (Abstract abridged.)Comment: 25 pages, RevTeX, 7 figures. Comments welcom
Mimicking diffuse supernova antineutrinos with the Sun as a source
Measuring the electron antineutrino component of the cosmic diffuse supernova
neutrino background (DSNB) is the next ambitious goal for low-energy neutrino
astronomy. The largest flux is expected in the lowest accessible energy bin.
However, for E < 15 MeV a possible signal can be mimicked by a solar electron
antineutrino flux that originates from the usual 8B neutrinos by spin-flavor
oscillations. We show that such an interpretation is possible within the
allowed range of neutrino electromagnetic transition moments and solar
turbulent field strengths and distributions. Therefore, an unambiguous
detection of the DSNB requires a significant number of events at E > 15 MeV.Comment: 4 pages, 1 figur
Detection potential for the diffuse supernova neutrino background in the large liquid-scintillator detector LENA
The large-volume liquid-scintillator detector LENA (Low Energy Neutrino
Astronomy) will provide high-grade background discrimination and enable the
detection of diffuse supernova neutrinos (DSN) in an almost background-free
energy window from ~10 to 25 MeV. Within ten years of exposure, it will be
possible to derive significant constraints on both core-collapse supernova
models and the supernova rate in the near universe up to redshifts z<2.Comment: 11 pages, 8 figures. accepted for publication in Phys. Rev. D.
accepted for publication in Phys. Rev.
The see-saw mechanism: neutrino mixing, leptogenesis and lepton flavor violation
The see-saw mechanism to generate small neutrino masses is reviewed. After
summarizing our current knowledge about the low energy neutrino mass matrix we
consider reconstructing the see-saw mechanism. Low energy neutrino physics is
not sufficient to reconstruct see-saw, a feature which we refer to as ``see-saw
degeneracy''. Indirect tests of see-saw are leptogenesis and lepton flavor
violation in supersymmetric scenarios, which together with neutrino mass and
mixing define the framework of see-saw phenomenology. Several examples are
given, both phenomenological and GUT-related. Variants of the see-saw mechanism
like the type II or triplet see-saw are also discussed. In particular, we
compare many general aspects regarding the dependence of LFV on low energy
neutrino parameters in the extreme cases of a dominating conventional see-saw
term or a dominating triplet term. For instance, the absence of mu -> e gamma
or tau -> e gamma in the pure triplet case means that CP is conserved in
neutrino oscillations. Scanning models, we also find that among the decays mu
-> e gamma, tau -> e gamma and tau -> mu gamma the latter one has the largest
branching ratio in (i) SO(10) type I see-saw models and in (ii) scenarios in
which the triplet term dominates in the neutrino mass matrix.Comment: 26 pages, 7 figures. Expanded version of talk given at 10th Workshop
In High Energy Physics Phenomenology (WHEPP 10), January 2008, Chennai,
India. Typos corrected, comments and references adde
A complete 3D numerical study of the effects of pseudoscalar-photon mixing on quasar polarizations
We present the results of three-dimensional simulations of quasar
polarizations in the presence of pseudoscalar-photon mixing in the
intergalactic medium. The intergalactic magnetic field is assumed to be
uncorrelated in wave vector space but correlated in real space. Such a field
may be obtained if its origin is primordial. Furthermore we assume that the
quasars, located at cosmological distances, have negligible initial
polarization. In the presence of pseudoscalar-photon mixing we show, through a
direct comparison with observations, that this may explain the observed large
scale alignments in quasar polarizations within the framework of big bang
cosmology. We find that the simulation results give a reasonably good fit to
the observed data.Comment: 15 pages, 8 figures, significant changes, to appear in EPJ
Elastic deformation of a fluid membrane upon colloid binding
When a colloidal particle adheres to a fluid membrane, it induces elastic
deformations in the membrane which oppose its own binding. The structural and
energetic aspects of this balance are theoretically studied within the
framework of a Helfrich Hamiltonian. Based on the full nonlinear shape
equations for the membrane profile, a line of continuous binding transitions
and a second line of discontinuous envelopment transitions are found, which
meet at an unusual triple point. The regime of low tension is studied
analytically using a small gradient expansion, while in the limit of large
tension scaling arguments are derived which quantify the asymptotic behavior of
phase boundary, degree of wrapping, and energy barrier. The maturation of
animal viruses by budding is discussed as a biological example of such
colloid-membrane interaction events.Comment: 14 pages, 9 figures, REVTeX style, follow-up on cond-mat/021242
Repressing Anarchy in Neutrino Mass Textures
The recent results that is relatively large, of the order of
the previous upper bound, and the indications of a sizable deviation of
from the maximal value are in agreement with the predictions of
Anarchy in the lepton sector. The quark and charged lepton hierarchies can then
be reproduced in a SU(5) GUT context by attributing non-vanishing
charges, different for each family, only to the SU(5) tenplet states. The fact
that the observed mass hierarchies are stronger for up quarks than for down
quarks and charged leptons supports this idea. As discussed in the past, in the
flexible context of , different patterns of charges can
be adopted going from Anarchy to various types of hierarchy. We revisit this
approach by also considering new models and we compare all versions to the
present data. As a result we confirm that, by relaxing the extreme ansatz of
equal charges for all SU(5) pentaplets and singlets, better
agreement with the data than for Anarchy is obtained without increasing the
model complexity. We also present the distributions obtained in the different
models for the Dirac CP-violating phase. Finally we discuss the relative merits
of these simple models.Comment: v1: 12 pages, 3 figures; v2: 13 pages, 3 figures, text improved,
matches version accepted for publication; v3: submitted to add an
acknowledgment to a networ
Assessing the potential for ice flow piracy between the Totten and Vanderford glaciers, East Antarctica
The largest regional drivers of current surface elevation increases in the Antarctic Ice Sheet are associated with ice flow reconfiguration in previously active ice streams, highlighting the important role of ice dynamics in mass balance calculations. Here, we investigate controls on the evolution of the flow configuration of the Vanderford and Totten glaciers – key outlet glaciers of the Aurora Subglacial Basin (ASB) – the most rapidly thinning region of the East Antarctic Ice Sheet (EAIS). We synthesise factors that influence the ice flow in this region and use an ice sheet model to investigate the sensitivity of the catchment divide location to changes in surface elevation due to thinning at the Vanderford Glacier (VG) associated with ongoing retreat and thickening at the Totten Glacier (TG) associated with an intensification of the east–west snowfall gradient. The present-day catchment divide between the Totten and Vanderford glaciers is not constrained by the geology or topography but is determined by the large-scale ice sheet geometry and its long-term evolution in response to climate forcing. Furthermore, the catchment divide migrates under relatively small changes in surface elevation, leading to ice flow and basal water piracy from the Totten to the Vanderford Glacier. Our findings show that ice flow reconfigurations occur not only in regions of West Antarctica like the Siple Coast but also in the east, motivating further investigations of past, and the potential for future, ice flow reconfigurations around the whole Antarctic coastline. Modelling of ice flow and basal water piracy may require coupled ice sheet thermomechanical and subglacial hydrology models constrained by field observations of subglacial conditions. Our results have implications for ice sheet mass budget studies that integrate over catchments and the validity of the zero flow assumption when selecting sites for ice core records of past climate.</p
- …