6,092 research outputs found
Why Are Neutrinos Light? -- An Alternative
We review the recent proposal that neutrinos are light because their masses
are proportional to a low scale, f, of lepton flavor symmetry breaking. This
mechanism is testable because the resulting pseudo-Goldstone bosons, of mass
m_G, couple strongly with the neutrinos, affecting the acoustic oscillations
during the eV era of the early universe that generate the peaks in the CMB
radiation. Characteristic signals result over a very wide range of (f, m_G)
because of a change in the total relativistic energy density and because the
neutrinos scatter rather than free-stream. Thermodynamics allows a precise
calculation of the signal, so that observations would not only confirm the
late-time neutrino mass mechanism, but could also determine whether the
neutrino spectrum is degenerate, inverted or hierarchical and whether the
neutrinos are Dirac or Majorana.
The flavor symmetries could also give light sterile states. If the masses of
the sterile neutrinos turn on after the MeV era, the LSND oscillations can be
explained without upsetting big bang nucleosynthesis, and, since the sterile
states decay to lighter neutrinos and pseudo-Goldstones, without giving too
much hot dark matter.Comment: Talk given by LJH at the Fujihara Seminar on Neutrino Mass and Seesaw
Mechanism held at KEK, Japan, February 2004. 11 pages, 1 figure, 3 table
Late Time Neutrino Masses, the LSND Experiment and the Cosmic Microwave Background
Models with low-scale breaking of global symmetries in the neutrino sector
provide an alternative to the seesaw mechanism for understanding why neutrinos
are light. Such models can easily incorporate light sterile neutrinos required
by the LSND experiment. Furthermore, the constraints on the sterile neutrino
properties from nucleosynthesis and large scale structure can be removed due to
the non-conventional cosmological evolution of neutrino masses and densities.
We present explicit, fully realistic supersymmetric models, and discuss the
characteristic signatures predicted in the angular distributions of the cosmic
microwave background.Comment: 4 pages, revtex
The neuropsychological assessment of age related cognitive deficits in adults with Down's syndrome
Bounded gaps between primes in number fields and function fields
The Hardy--Littlewood prime -tuples conjecture has long been thought to be
completely unapproachable with current methods. While this sadly remains true,
startling breakthroughs of Zhang, Maynard, and Tao have nevertheless made
significant progress toward this problem. In this work, we extend the
Maynard-Tao method to both number fields and the function field
Ensemble asteroseismology and hierarchical bayesian models: new inferences of astrophysics with oscillating stars
Asteroseismology – the study of stellar oscillations – is one of the key tools used to study stars in modern astronomy. This thesis focuses on asteroseismology of solar-like oscillators, which exhibit variability driven by the same mechanism as the Sun. By studying variations in the brightness of stars on their surface, asteroseismology probes the full stellar interior, giving insight into stars’ internal processes and fundamental properties.
In this thesis, I provide an introduction to asteroseismology and the state of the field. This is followed by a description of asteroseismic analysis tools I developed for the open source Python package ‘Lightkurve’, and a presentation of two studies that use asteroseismology to probe different aspects of astrophysics.
The first study uses an asteroseismic ensemble of 5576 evolved Red Clump stars to calibrate data from the Gaia mission, and quantify systematic differences in asteroseismic modelling techniques. The second focuses on 91 main sequence stars like the Sun, using asteroseismology to measure their rotation rates. Along with asteroseismic ages, these new rotation rates are used to quantitatively state that stars experience a change in how they lose angular momentum half-way through their main sequence lifetimes. A common thread throughout both these studies is the use of Bayesian statistics, which allows us to leverage large asteroseismic ensembles to make inferences about adjacent fields of astronomy
Dark Energy and Right-Handed Neutrinos
We explore the possibility that a CP violating phase of the neutrino mass
matrix is promoted to a pseudo-Goldstone-boson field and is identified as the
quintessence field for Dark Energy. By requiring that the quintessence
potential be calculable from a Lagrangian, and that the extreme flatness of the
potential be stable under radiative corrections, we are led to an essentially
unique model. Lepton number is violated only by Majorana masses of light,
right-handed neutrinos, comparable to the Dirac masses that mix right- with
left-handed neutrinos. We outline the rich and constrained neutrino
phenomenology that results from this proposal.Comment: 10 pages, 2 figure
A four year prospective study of age-related cognitive change in adults with Down's syndrome
Background. While neuropathological studies indicate a
high risk for Alzheimer's disease in adults
with Down's syndrome, neuropsychological studies suggest a lower prevalence
of dementia. In this
study, cognitive deterioration in adults with Down's syndrome was
examined prospectively over
4 years to establish rates and profiles of cognitive deterioration.Methods. Fifty-seven people with Down's syndrome aged
30 years or older were assessed using a
battery of neuropsychological tests on five occasions across 50 months.
Assessments of domains of
cognitive function known to change with the onset of Alzheimer related
dementia were employed.
These included tests of learning, memory, orientation, agnosia, apraxia
and aphasia. The individual
growth trajectory methodology was used to analyse change over time.Results. Severe cognitive deterioration, such as acquired,
apraxia and agnosia, was evident in 28·3%
of those aged over 30 and a higher prevalence of these impairments was
associated with older age.
The rate of cognitive deterioration also increased with age and degree
of pre-existing cognitive
impairment. Additionally, deterioration in memory, learning and orientation
preceded the
acquisition of aphasia, agnosia and apraxia.Conclusions. The prevalence of cognitive impairments consistent
with the presence of Alzheimer's
disease is lower than that suggested by neuropathological studies. The
pattern of the acquisition of
cognitive impairments in adults with Down's syndrome is similar to
that seen in individuals with
Alzheimer's disease who do not have Down's syndrome.</jats:p
The association between environmental events and self-injurious behavior in Cornelia de Lange syndrome
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