632 research outputs found
Stimulated Neutrino Transformation with Sinusoidal Density Profiles
Large amplitude oscillations between the states of a quantum system can be
stimulated by sinusoidal external potentials with frequencies that are similar
to the energy level splitting of the states or a fraction thereof. Situations
when the applied frequency is equal to an integer fraction of the energy level
splittings are known as parametric resonances. We investigate this effect for
neutrinos both analytically and numerically for the case of arbitrary numbers
of neutrino flavors. We look for environments where the effect may be observed
and find that supernova are the one realistic possibility due to the necessity
of both large densities and large amplitude fluctuations. The comparison of
numerical and analytic results of neutrino propagation through a model
supernova reveals it is possible to predict the locations and strengths of the
stimulated transitions that occur.Comment: 14 pages, 6 figure
BBN For Pedestrians
The simplest, `standard' model of Big Bang Nucleosynthesis (SBBN) assumes
three light neutrinos (N_nu = 3) and no significant electron neutrino
asymmetry, leaving only one adjustable parameter: the baryon to photon ratio
eta. The primordial abundance of any one nuclide can, therefore, be used to
measure the baryon abundance and the value derived from the observationally
inferred primordial abundance of deuterium closely matches that from current,
non-BBN data, primarily from the WMAP survey. However, using this same estimate
there is a tension between the SBBN-predicted 4He and 7Li abundances and their
current, observationally inferred primordial abundances, suggesting that N_nu
may differ from the standard model value of three and/or that there may be a
non-zero neutral lepton asymmetry (or, that systematic errors in the abundance
determinations have been underestimated or overlooked). The differences are not
large and the allowed ranges of the BBN parameters permitted by the data are
quite small. Within these ranges, the BBN-predicted abundances of D, 3He, 4He,
and 7Li are very smooth, monotonic functions of eta, N_nu, and the lepton
asymmetry. It is possible to describe the dependencies of these abundances (or
powers of them) upon the three parameters by simple, linear fits which, over
their ranges of applicability, are accurate to a few percent or better. The
fits presented here have not been maximized for their accuracy but, for their
simplicity. To identify the ranges of applicability and relative accuracies,
they are compared to detailed BBN calculations; their utility is illustrated
with several examples. Given the tension within BBN, these fits should prove
useful in facilitating studies of the viability of proposals for non-standard
physics and cosmology, prior to undertaking detailed BBN calculations.Comment: Submitted to a Focus Issue on Neutrino Physics in New Journal of
Physics (www.njp.org
Neutrinos And Big Bang Nucleosynthesis
The early universe provides a unique laboratory for probing the frontiers of
particle physics in general and neutrino physics in particular. The primordial
abundances of the relic nuclei produced during the first few minutes of the
evolution of the Universe depend on the electron neutrinos through the
charged-current weak interactions among neutrons and protons (and electrons and
positrons and neutrinos), and on all flavors of neutrinos through their
contributions to the total energy density which regulates the universal
expansion rate. The latter contribution also plays a role in determining the
spectrum of the temperature fluctuations imprinted on the Cosmic Background
Radiation (CBR) some 400 thousand years later. Using deuterium as a baryometer
and helium-4 as a chronometer, the predictions of BBN and the CBR are compared
to observations. The successes of, as well as challenges to the standard models
of particle physics and cosmology are identified. While systematic
uncertainties may be the source of some of the current tensions, it could be
that the data are pointing the way to new physics. In particular, BBN and the
CBR are used to address the questions of whether or not the relic neutrinos
were fully populated in the early universe and, to limit the magnitude of any
lepton asymmetry which may be concealed in the neutrinos.Comment: Accepted for publication in the Proceedings of Nobel Symposium 129,
"Neutrino Physics"; to appear in Physics Scripta, eds., L Bergstrom, O.
Botner, P. Carlson, P. O. Hulth, and T. Ohlsso
Testing two nuclear physics approximations used in the standard leaky box model for the spallogenic production of LiBeB
The spallative production rates of Lithium, Beryllium and Boron (LiBeB) are a
necessary component in any calculation of the evolution of these nuclei in the
Galaxy. Previous calculations of these rates relied on two assumptions relating
to the nuclear physics aspects: the straight-ahead approximation that describes
the distribution of fragment energies and the assumption that the major
contributor to the production rate arises from single-step reactions between
primary cosmic ray projectiles and interstellar medium targets. We examine both
assumptions by using a semi-empirical description for the spall's energy
distribution and by including the reactions that proceed via intermediary
fragments. After relaxing the straight-ahead approximation we find the changes
in the production rates and emerging fluxes are small and do not warrant
rejection of this approximation. In contrast we discover that two-step
reactions can alter the production rate considerably leading to noticeable
increases in the efficiency of producing the LiBeB nuclei. Motivated by this
result we introduce a cascade technique to compute the production rates exactly
and find that the results differ only slightly from those of our two-step
calculations. We thus conclude that terminating the reaction network at the
two-step order is sufficiently accurate for current studies of spallation.Comment: accepted in Ap
The Cosmological Evolution of the Average Mass Per Baryon
Subsequent to the early Universe quark-hadron transition the universal baryon
number is carried by nucleons: neutrons and protons. The total number of
nucleons is preserved as the Universe expands, but as it cools lighter protons
are favored over heavier neutrons reducing the average mass per baryon. During
primordial nucleosynthesis free nucleons are transformed into bound nuclides,
primarily helium, and the nuclear binding energies are radiated away, further
reducing the average mass per baryon. In particular, the reduction in the
average mass per baryon resulting from Big Bang Nucleosynthesis (BBN) modifies
the numerical factor relating the baryon (nucleon) mass and number densities.
Here the average mass per baryon, m_B, is tracked from the early Universe to
the present. The result is used to relate the present ratio of baryons to
photons (by number) to the present baryon mass density at a level of accuracy
commensurate with that of recent cosmological data, as well as to estimate the
energy released during post-BBN stellar nucleosynthesis.Comment: 5 pages; no figures; updated references; final version published in
JCAP, 10 (2006) 01
Palynofacies classification of the depositional elements of confined turbidite systems : Examples from the Gres d'Annot, SE France
Acknowledgements We thank BG Brasil for financial support for this project and permission to publish. BG Group is a wholly owned subsidiary of Royal Dutch Shell. McArthur is grateful to the Coordenação de Aperfeiçoamento de Pessoal de NĂvel Superior (CAPES) for the scholarship 049/2012. The AgĂȘncia Nacional do PetrĂłleo (ANP) are thanked for supporting this project. Massimo Zecchin is thanked for handling this paper and Roberto Tinterri is thanked for his constructive review, in addition to an anonymous reviewer.Peer reviewedPostprin
Crustal distribution in the central Gulf of Mexico from an integrated geophysical analysis
This study addresses the question of the crustal composition in the central part of the northern Gulf of Mexico (GOM) â the region of the major disagreement between published tectonic models. The location of the Ocean-Continental Boundary (OCB) for different tectonic models varies within 140 km (87 mi) in the study area. I have developed a 2D model integrating the seismic reflection and refraction data with potential fields (gravity and magnetics) along the profile through the debated region. Two alternative OCB locations were tested. The preferred model suggests the OCB position near the Sigsbee Escarpment, which is in agreement with the result of Eddy, 2014 and with the findings of the LithoSPAN experiment (Makris et al, 2015). However, the model with an alternative OCB location (further to the north of the Sigsbee Escarpment) may also satisfy the observed gravity and magnetic fields, although the crust in the oceanic domain is thicker than normal. Since the potential fields do not offer the unique answer, the other geophysical data should be examined, such as the Vp/Vs ratio. This parameter was analyzed for the LithoSPAN (Makris et al., 2015) and allowed distinguishing between continental and oceanic domains; it was also examined for GUMBO 3 and 4 (Duncan, 2013). However, the values of Vs derived during retraction experiment for GUMBO 2 are not publically available at this time
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