2,639 research outputs found
Cosmology and the weak interaction
The weak interaction plays a critical role in modern Big Bang cosmology. Two of its most publicized comological connections are emphasized: big bang nucleosynthesis and dark matter. The first of these is connected to the cosmological prediction of neutrine flavors, N(sub nu) is approximately 3 which in now being confirmed. The second is interrelated to the whole problem of galacty and structure formation in the universe. The role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure is demonstrated
Nuclear physics and cosmology
Nuclear physics has provided one of two critical observational tests of all Big Bang cosmology, namely Big Bang Nucleosynthesis. Furthermore, this same nuclear physics input enables a prediction to be made about one of the most fundamental physics questions of all, the number of elementary particle families. The standard Big Bang Nucleosynthesis arguments are reviewed. The primordial He abundance is inferred from He-C and He-N and He-O correlations. The strengthened Li constraint as well as D-2 plus He-3 are used to limit the baryon density. This limit is the key argument behind the need for non-baryonic dark matter. The allowed number of neutrino families, N(nu), is delineated using the new neutron lifetime value of tau(n) = 890 + or - 4s (tau(1/2) = 10.3 min). The formal statistical result is N(nu) = 2.6 + or - 0.3 (1 sigma), providing a reasonable fit (1.3 sigma) to three families but making a fourth light (m(nu) less than or equal to 10 MeV) neutrino family exceedly unlikely (approx. greater than 4.7 sigma). It is also shown that uncertainties induced by postulating a first-order quark-baryon phase transition do not seriously affect the conclusions
Probing the Big Bang with LEP
It is shown that LEP probes the Big Bang in two significant ways: (1) nucleosynthesis, and (2) dark matter constraints. In the first case, LEP verifies the cosmological standard model prediction on the number of neutrino types, thus strengthening the conclusion that the cosmological baryon density is approximately 6 percent of the critical value. In the second case, LEP shows that the remaining non-baryonic cosmological matter must be somewhat more massive and/or more weakly interacting than the favorite non-baryonic dark matter candidates of a few years ago
Could a nearby supernova explosion have caused a mass extinction?
We examine the possibility that a nearby supernova explosion could have
caused one or more of the mass extinctions identified by palaeontologists. We
discuss the likely rate of such events in the light of the recent
identification of Geminga as a supernova remnant less than 100 pc away and the
discovery of a millisecond pulsar about 150 pc away, and observations of SN
1987A. The fluxes of radiation and charged cosmic rays on the Earth
are estimated, and their effects on the Earth's ozone layer discussed. A
supernova explosion of the order of 10 pc away could be expected every few
hundred million years, and could destroy the ozone layer for hundreds of years,
letting in potentially lethal solar ultraviolet radiation. In addition to
effects on land ecology, this could entail mass destruction of plankton and
reef communities, with disastrous consequences for marine life as well. A
supernova extinction should be distinguishable from a meteorite impact such as
the one that presumably killed the dinosaurs.Comment: 10 pages, CERN-TH.6805/9
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Tidal Disruption Of Neutron Stars By Black-Holes In Close Binaries
NSF AST 74-21216Astronom
Solar neutrinos and the MSW effect for three-neutrino mixing
Researchers considered three-neutrino Mikheyev-Smirnov-Wolfenstein (MSW) mixing, assuming m sub 3 is much greater than m sub 2 is greater than m sub 1 as expected from theoretical consideration if neutrinos have mass. They calculated the corresponding mixing parameter space allowed by the Cl-37 and Kamiokande 2 experiments. They also calculated the expected depletion for the Ga-71 experiment. They explored a range of theoretical uncertainty due to possible astrophysical effects by varying the B-8 neutrino flux and redoing the MSW mixing calculation
Photoerosion and the abundances of the light elements
The abundances of the rare light elements H-2, He-3, Li-7, and B-11 are shown to be potentially affected by photoerosion. That process, involving the interaction of high energy photons from galactic centers with atomic nuclei, will increase the abundances of H-2, He-3, and B-11 while lowering slightly those of Li-7 and He-4. In some regions of galaxies the effects may be large enough to impact their chemical evolution. In particular this process may have enhanced the H-2 and He-3 abundances near the center of our galaxy over and above those from the big bang, as well as the galactic B-11 abundance over that from cosmic-ray spallation
On relative supernova rates and nucleosynthesis roles
It is shown that the Ni-56-Fe-56 observed in SN 1987A argues that core collapse supernovae may be responsible for more that 50 percent of the iron in the galaxy. Furthermore it is argued that the time averaged rate of thermonuclear driven Type I supernovae may be at least an order of magnitude lower than the average rate of core collapse supernovae. The present low rate of Type II supernovae (below their time averaged rate of approx. 1/10 yr) is either because the past rate was much higher because many core collapse supernovae are dim like SN 1987A. However, even in this latter case they are only an order of magnitude dimmer that normal Type II's due to the contribution of Ni-56 decay to the light curve
Large Scale Baryon Isocurvature Inhomogeneities
Big bang nucleosynthesis constraints on baryon isocurvature perturbations are
determined. A simple model ignoring the effects of the scale of the
perturbations is first reviewed. This model is then extended to test the claim
that large amplitude perturbations will collapse, forming compact objects and
preventing their baryons from contributing to the observed baryon density. It
is found that baryon isocurvature perturbations are constrained to provide only
a slight increase in the density of baryons in the universe over the standard
homogeneous model. In particular it is found that models which rely on power
laws and the random phase approximation for the power spectrum are incompatible
with big bang nucleosynthesis unless an {\em ad hoc}, small scale cutoff is
included.Comment: 11pages + 8figures, LaTeX (2.09), postscript figures available via
anonymous ftp from oddjob.uchicago.edu:/ftp/ibbn/fig?.ps where ?=1-8 or via
email from [email protected], Fermilab-Pub-94/???-A and UMN-TH-1307/9
Primordial Nucleosynthesis and the Abundances of Beryllium and Boron
The ability to now make measurements of Be and B as well as put constraints
on \lisix\ abundances in metal-poor stars has led to a detailed reexamination
of Big Bang Nucleosynthesis in the A\groughly6 regime. The nuclear reaction
network has been significantly expanded with many new rates added. It is
demonstrated that although a number of reaction rates are poorly
determined, even with extreme values chosen, the standard homogeneous model is
unable to produce significant yields (Be/H and B/H when
abundances fit) above and the \liseven/\lisix\ ratio always exceeds 500.
We also preliminarily explore inhomogeneous models, such as those inspired by a
first order quark-hadron phase transition, where regions with high
neutron/proton ratios can allow some leakage up to . However models that
fit the abundances still seem to have difficulty in obtaining
significant yields.Comment: Plain TeX, 28 pages, 8 figures (not included, but available from
authors). UMN-TH-1020/9
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