335 research outputs found
Asteroseismology of red giants & galactic archaeology
Red-giant stars are low- to intermediate-mass (~M)
stars that have exhausted hydrogen in the core. These extended, cool and hence
red stars are key targets for stellar evolution studies as well as galactic
studies for several reasons: a) many stars go through a red-giant phase; b) red
giants are intrinsically bright; c) large stellar internal structure changes as
well as changes in surface chemical abundances take place over relatively short
time; d) red-giant stars exhibit global intrinsic oscillations. Due to their
large number and intrinsic brightness it is possible to observe many of these
stars up to large distances. Furthermore, the global intrinsic oscillations
provide a means to discern red-giant stars in the pre-helium core burning from
the ones in the helium core burning phase and provide an estimate of stellar
ages, a key ingredient for galactic studies. In this lecture I will first
discuss some physical phenomena that play a role in red-giant stars and several
phases of red-giant evolution. Then, I will provide some details about
asteroseismology -- the study of the internal structure of stars through their
intrinsic oscillations -- of red-giant stars. I will conclude by discussing
galactic archaeology -- the study of the formation and evolution of the Milky
Way by reconstructing its past from its current constituents -- and the role
red-giant stars can play in that.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Negative impacts of invasive predators used as biological control agents against the pest snail Lissachatina fulica: the snail Euglandina ‘rosea’ and the flatworm Platydemus manokwari
Since 1955 snails of the Euglandina rosea
species complex and Platydemus manokwari flatworms were widely introduced in attempted biological
control of giant African snails (Lissachatina fulica)
but have been implicated in the mass extinction of
Pacific island snails. We review the histories of the 60
introductions and their impacts on L. fulica and native
snails. Since 1993 there have been unofficial releases
of Euglandina within island groups. Only three official
P. manokwari releases took place, but new populations
are being recorded at an increasing rate, probably
because of accidental introduction. Claims that these
predators controlled L. fulica cannot be substantiated;
in some cases pest snail declines coincided with
predator arrival but concomitant declines occurred
elsewhere in the absence of the predator and the
declines in some cases were only temporary. In the
Hawaiian Islands, although there had been some earlier declines of native snails, the Euglandina
impacts on native snails are clear with rapid decline
of many endemic Hawaiian Achatinellinae following
predator arrival. In the Society Islands, Partulidae tree
snail populations remained stable until Euglandina
introduction, when declines were extremely rapid with
an exact correspondence between predator arrival and
tree snail decline. Platydemus manokwari invasion
coincides with native snail declines on some islands,
notably the Ogasawara Islands of Japan, and its
invasion of Florida has led to mass mortality of
Liguus spp. tree snails. We conclude that Euglandina
and P. manokwari are not effective biocontrol agents,
but do have major negative effects on native snail
faunas. These predatory snails and flatworms are
generalist predators and as such are not suitable for
biological control
Neutrino masses: From fantasy to facts
Theory suggests the existence of neutrino masses, but little more. Facts are
coming close to reveal our fantasy: solar and atmospheric neutrino data
strongly indicate the need for neutrino conversions, while LSND provides an
intriguing hint. The simplest ways to reconcile these data in terms of neutrino
oscillations invoke a light sterile neutrino in addition to the three active
ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND
scale, while the others are at the solar mass scale. These schemes can be
distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments. I discuss the simplest theoretical scenarios, where the lightness
of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and
the generation of & all follow
naturally from the assumed lepton-number symmetry and its breaking. Although
the most likely interpretation of the present data is in terms of
neutrino-mass-induced oscillations, one still has room for alternative
explanations, such as flavour changing neutrino interactions, with no need for
neutrino mass or mixing. Such flavour violating transitions arise in theories
with strictly massless neutrinos, and may lead to other sizeable flavour
non-conservation effects, such as , conversion in
nuclei, unaccompanied by neutrino-less double beta decay.Comment: 33 pages, latex, 16 figures. Invited Talk at Ioannina Conference,
Symmetries in Intermediate High Energy Physics and its Applications, Oct.
1998, to be published by Springer Tracts in Modern Physics. Festschrift in
Honour of John Vergados' 60th Birthda
High Energy FCNC search through Colliders
We study the potential impacts of a new type of particle collider -- an
collider -- on the search for new physics beyond the Standard Model. As
our first attempt for exploring its physics potential, we demonstrate that the
the collision experiment can be highly efficient in searching for
lepton-number-violating Flavor Changing Neutral Current phenomena.Comment: 11 pages, including 2 e-postscript figures, title & abstract are
changed, minor modifications in the main tex
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