1,618 research outputs found
Sensitivity of Neutrino Mass Experiments to the Cosmic Neutrino Background
The KATRIN neutrino experiment is a next-generation tritium beta decay
experiment aimed at measuring the mass of the electron neutrino to better than
200 meV at 90% C.L. Due to its intense tritium source, KATRIN can also serve as
a possible target for the process of neutrino capture, {\nu}e +3H \to 3He+ +
e-. The latter process, possessing no energy threshold, is sensitive to the
Cosmic Neutrino Background (C{\nu}B). In this paper, we explore the potential
sensitivity of the KATRIN experiment to the relic neutrino density. The KATRIN
experiment is sensitive to a C{\nu}B over-density ratio of 2.0x 10^9 over
standard concordance model predictions (at 90% C.L.), addressing the validity
of certain speculative cosmological models
Relativistic Cyclotron Radiation Detection of Tritium Decay Electrons as a New Technique for Measuring the Neutrino Mass
The shape of the beta decay energy distribution is sensitive to the mass of
the electron neutrino. Attempts to measure the endpoint shape of tritium decay
have so far seen no distortion from the zero-mass form, thus placing an upper
limit of m_nu_beta < 2.3 eV. Here we show that a new type of electron energy
spectroscopy could improve future measurements of this spectrum and therefore
of the neutrino mass. We propose to detect the coherent cyclotron radiation
emitted by an energetic electron in a magnetic field. For mildly relativistic
electrons, like those in tritium decay, the relativistic shift of the cyclotron
frequency allows us to extract the electron energy from the emitted radiation.
We present calculations for the energy resolution, noise limits, high-rate
measurement capability, and systematic errors expected in such an experiment.Comment: 4 pages, 2 figure
Kondo Resonance Decoherence by an External Potential
The Kondo problem, for a quantum dot (QD), subjected to an external bias, is
analyzed in the limit of infinite Coulomb repulsion by using a consistent
equations of motion method based on a slave-boson Hamiltonian. Utilizing a
strict perturbative solution in the leads-dot coupling, T, to T^4 and T^6
orders, we calculate the QD spectral density and conductance, as well as the
decoherent rate that drive the systemm from the strong to the weak coupling
regime. Our results indicate thet the weak coupling regime is reached for
voltages larger than a few units of the Kondo temperature.Comment: 5 figure
Dressed tunneling approximation for electronic transport through molecular transistors
A theoretical approach for the non-equilibrium transport properties of
nanoscale systems coupled to metallic electrodes with strong electron-phonon
interactions is presented. It consists in a resummation of the dominant Feynman
diagrams from the perturbative expansion in the coupling to the leads. We show
that this scheme eliminates the main pathologies found in previous simple
analytical approaches for the polaronic regime. The results for the spectral
and transport properties are compared with those from several other approaches
for a wide range of parameters. The method can be formulated in a simple way to
obtain the full counting statistics. Results for the shot and thermal noise are
presented.Comment: 11 pages, 11 figures. Accepted for publication in Physical Review
HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects
ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst
galaxies. We present for the first time in a starburst galaxy a 2D study of the
spatial behavior of collisional and radiative transfer effects in He^+. The HeI
lines are analysed based on data obtained with FLAMES and GMOS. Collisional
effects are negligible for transitions in the singlet cascade while relatively
important for those in the triplet cascade. In particular, they can contribute
up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are
important over an extended and circular area of 30pc in diameter centered at
the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction
corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the
stellar absorption equivalent width as well as the most recent emissivities. We
found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the
excitation and the total helium abundance, y_tot, is consistent with no
abundance gradient. Uncertainties in the derivation of He abundances are
dominated by the adopted assumptions. We illustrated the difficulty of
detecting a putative He enrichment due to the presence of Wolf-Rayet stars in
the main GHIIR. Data are marginally consistent with an excess in the N/He ratio
in the N enriched area of the order of both, the atmospheric N/He ratios in WR
stars and the uncertainties estimated for the N/He ratios.Comment: Accepted in Astronomy and Astrophysics; the emissivities presented in
the Corrigendum, Porter et al. 2013, arXiv:1303.5115, have been include
The extinction and dust-to-gas structure of the planetary nebula NGC 7009 observed with MUSE
The large field and wavelength range of MUSE is well suited to mapping
Galactic planetary nebulae (PN). The bright PN NGC 7009 was observed with MUSE
on the VLT during the Science Verification of the instrument in seeing of 0.6".
Emission line maps in hydrogen Balmer and Paschen lines were formed from
analysis of the MUSE cubes. The measured electron temperature and density from
the MUSE cube were employed to predict the theoretical hydrogen line ratios and
map the extinction distribution across the nebula. After correction for the
interstellar extinction to NGC 7009, the internal dust-to-gas ratio (A_V/N_H)
has been mapped for the first time in a PN. The extinction map of NGC 7009 has
considerable structure, broadly corresponding to the morphological features of
the nebula. A large-scale feature in the extinction map, consisting of a crest
and trough, occurs at the rim of the inner shell. The nature of this feature
was investigated and instrumental and physical causes considered; no convincing
mechanisms were identified to produce this feature, other than mass loss
variations in the earlier asymptotic giant branch phase. The dust-to-gas ratio
A_V/N_H increases from 0.7 times the interstellar value to >5 times from the
centre towards the periphery of the ionized nebula. The integrated A_V/N_H is
about 2 times the mean ISM value. It is demonstrated that extinction mapping
with MUSE provides a powerful tool for studying the distribution of PN internal
dust and the dust-to-gas ratio. (Abridged.)Comment: 10 pages, 7 figures. Accepted by A&
(Re)Opening Closed/ness: Hauntological Engagements with Historical Markers in the Threshold of Mastery
This project explored functionalities of (ghostly) mastery within the radical context of institutionally historical designations. We first identified historical designations of our university campuses and then, using Jackson and Mazzei’s (2012) thinking with theory, entangled our hauntological perspectives with published “material” (e.g., university website articles, materials on official websites) and researcher generated photographs. As such, the purpose of this project is to loosen the grip of narrative mastery governing the designation of historical markers located throughout learning institutions. Thus, in unleashing ghosts/hauntings, we offer a theoretically informed opening towards troubling the vulnerability of history/ies, narratives, and spaces institutions seek to—and frequently successfully—master
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