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RE: Big Bang Neutrinos
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Huddersfield physicist join global partners for an investigation of the Big Bang particle

Scientists at the University of Huddersfield are collaborating with experts at some of the world's leading research institutes in an attempt to unravel the mysteries of a particle that played a role in the creation of the universe.
The existence of neutrinos and anti-neutrinos - particles that are almost massless and which travel at light speed from one side of the earth to the other - was confirmed more than 50 years ago. Scientists believe that they were created at the Big Bang and might hold the key to the nature of the universe.

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Neutrino Decay
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Title: Neutrino Decays over Cosmological Distances and the Implications for Neutrino Telescopes
Authors: Philipp Baerwald, Mauricio Bustamante, Walter Winter

We discuss decays of ultra-relativistic neutrinos over cosmological distances by solving the decay equation in terms of its redshift dependence. We demonstrate that there are significant conceptual differences compared to more simplified treatments of neutrino decay. For instance, the maximum distance the neutrinos have travelled is limited by the Hubble length, which means that the common belief that longer neutrino lifetimes can be probed by longer distances does not apply. As a consequence, the neutrino lifetime limit from supernova 1987A cannot be exceeded by high-energy astrophysical neutrinos. We discuss the implications for neutrino spectra and flavour ratios from gamma-ray bursts as one example of extragalactic sources, using up-to-date neutrino flux predictions. If the observation of SN 1987A implies that \nu_1 is stable and the other mass eigenstates decay with rates much smaller than their current bounds, the muon track rate can be substantially suppressed compared to the cascade rate in the region IceCube is most sensitive to. In this scenario, no gamma-ray burst neutrinos may be found using muon tracks even with the full scale experiment, whereas reliable information on high-energy astrophysical sources can only be obtained from cascade measurements. As another consequence, the recently observed two cascade event candidates at PeV energies will not be accompanied by corresponding muon tracks.

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Neutrinos from Hell - Giorgio Gratta (SETI Talks)



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We are all submerged in a sea of undetectable particles left over from the first few seconds of the big bang, according to the latest observations from a NASA satellite. The Wilkinson Microwave Anisotropy Probe (WMAP) has confirmed the theory that the universe is filled with a fluid of cold neutrinos that remain almost entirely aloof from ordinary matter.
Cosmologists think that in the hot, dense, young universe, neutrinos should have been created in high-energy particle collisions. About two seconds after the big bang, the cauldron of colliding particles would have cooled down so much that most would not have had enough energy to interact strongly with neutrinos. The neutrinos would then have "de-coupled" from other matter and radiation.
In theory, they should still be buzzing around, a soup of slippery particles that by today has been chilled to a temperature of only 1.9 degrees Celsius above absolute zero.
Now WMAP has found evidence of this cosmic soup.

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Title: Capturing Relic Neutrinos with beta-decaying nuclei
Authors: Alfredo G. Cocco, Gianpiero Mangano, Marcello Messina

We summarise a novel approach which has been recently proposed for direct detection of low energy neutrino backgrounds such as the cosmological relic neutrinos, exploiting neutrino/antineutrino capture on nuclei that spontaneously undergo beta decay.

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Ancient Neutrinos
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British scientists are finalising plans for an ambitious experiment to discover ancient, high-speed particles from the far side of the universe by listening to them plop into the ocean.
Trials are due to take place early next month in a 200-metre-deep trench between the west coast of the Scottish mainland and the Isle of Rona, where researchers will use sensitive hydrophones to hear the almost weightless particles as they slam into the sea with the energy of a tennis ball served by a professional player.
The particles, called ultra high energy neutrinos, have never been detected before, but physicists theorise that they must exist. They are thought to be created when powerful cosmic rays collide with particles of light left over from the big bang 14bn years ago. By detecting the neutrinos, scientists hope to shed light on the origins of cosmic rays and learn more about the structure of the universe soon after its violent birth.

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Title: Neutrino mass from future high redshift galaxy surveys: sensitivity and detection threshold
Authors: Steen Hannestad, Yvonne Y. Y. Wong

We calculate the sensitivity of future cosmic microwave background probes and large scale structure measurements from galaxy redshift surveys to the neutrino mass. We find that, for minimal models with few parameters, a measurement of the matter power spectrum over a large range of redshifts has more constraining power than a single measurement at low redshifts. However, this improvement in sensitivity does not extend to larger models. We also quantify how the non-Gaussian nature of the posterior distribution function with respect to the individual cosmological parameter influences such quantities as the sensitivity and the detection threshold. For realistic assumptions about future large scale structure data, the minimum detectable neutrino mass at 95 % C.L. is about 0.05 eV in the context of a minimal 8-parameter cosmological model. In a more general model framework, however, the detection threshold can increase by as much as a factor of three.

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Title: Present bounds on the relativistic energy density in the Universe from cosmological observables
Authors: Gianpiero Mangano, Alessandro Melchiorri, Olga Mena, Gennaro Miele, Anze Slosar

We discuss the present bounds on the relativistic energy density in the Universe parameterised in terms of the effective number of neutrinos N using the most recent cosmological data on Cosmic Microwave Background (CMB) temperature anisotropies and polarisation, Large Scale galaxy clustering from the Sloan Digital Sky Survey (SDSS) and 2dF, luminosity distances of type Ia Supernovae, Lyman-alpha absorption clouds (Ly-alpha), the Baryonic Acoustic Oscillations (BAO) detected in the Luminous Red Galaxies of the SDSS and finally, Big Bang Nucleosynthesis (BBN) predictions for 4He and Deuterium abundances. We find N= 5.2+2.7-2.2 from CMB and Large Scale Structure data, while adding Ly-alpha and BAO we obtain N= 4.6+1.6-1.5 at 95 % c.l.. These results show some tension with the standard value N=3.046 as well as with the BBN range N= 3.1+1.4-1.2 at 95 % c.l., though the discrepancy is slightly below the 2-sigma level. We emphasise the impact of an improved upper limit (or measurement) of the primordial value of 3He abundance in clarifying the issue of whether the value of N at early (BBN) and more recent epochs coincide.

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Title: Constraint on the Effective Number of Neutrino Species from the WMAP and SDSS LRG Power Spectra
Authors: Kazuhide Ichikawa, Masahiro Kawasaki, Fuminobu Takahashi

We derive constraint on the effective number of neutrino species N_nu from the cosmic microwave background power spectrum of the WMAP and galaxy clustering power spectrum of the SDSS luminous red galaxies (LRGs). Using these two latest data sets of CMB and galaxy clustering alone, we obtain the limit 0.8 < N_nu < 7.6 (95% C.L.) for the power-law LambdaCDM flat universe, with no external prior. The lower limit corresponds to the lower bound on the reheating temperature of the universe T_R > 2 MeV.

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Relic Neutrinos
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Massive optical telescopes on mountain tops have been the main tools for exploring dark energy - the mysterious stuff that is accelerating the expansion of the universe. Soon the quest could move underground. Neutrinos born in stellar cataclysms and detected in gigantic water tanks buried in mines may become the new probes for dark energy.

Dark energy was discovered in the late 1990s by astronomers studying the light from stellar explosions known as type 1a supernovae. Since then telescopes around the world, such as the Very Large Telescope on Cerro Paranal in Chile, have been used to study the light from more and more supernovae. Now Lawrence Hall of the University of California at Berkeley and colleagues think that neutrinos spewed out in another type of stellar explosion, a core-collapse supernova, could be just the tool for studying dark energy.
When the core of a massive star grows too large, it collapses under its own gravity, releasing a flood of neutrinos - a theory confirmed in 1987 when a supernova went off in a nearby dwarf galaxy, the Large Magellanic Cloud, and a sudden wave of the particles hit neutrino detectors on Earth. Two of them, Kamiokande-II in Japan and the IMB detector in the US, were underground water tanks. Photomultiplier tubes lining these tanks detected the distinctive and rare blue flashes of light emitted when a neutrino hits an electron.
The millions of core-collapse supernovae that have gone off throughout the history of the universe must have created a background of supernova relic neutrinos. But the diffuse nature of these neutrinos makes them very difficult to detect. However, the next generation of neutrino detectors, such as the planned Underground Nucleon decay and Neutrino Observatory, which will be about 20 times larger than Super-Kamiokande in Japan (see right), will have tanks that can hold a million tonnes of water and so should be up to the job.

"If I have to bet on it, the next neutrinos of astrophysical origin we see will be supernova relic neutrinos" - physicist Chang Kee Jung of the State University of New York at Stony Brook, who is involved with the UNO proposal.

Hall's team has worked out that the spectrum of these relic neutrinos could hold cosmological treasure. That's because the flux of neutrinos measured today is affected by how the universe expanded in the past. So measuring the flux of supernova relic neutrinos of different energies could reveal how the universe is expanding.
This is similar to the way dark energy was first discovered, when astronomers found that type 1a supernovae were dimmer than expected. The accelerating expansion of space had diluted their light, and this was put down to some kind of invisible repulsive force whose nature is still unknown.
Relic neutrinos might merely confirm the acceleration, leaving the exact nature of dark energy a mystery - or they could reveal new physics. Neutrinos might bounce off dark energy, in which case their spectrum will be distorted in such a way as to tell us something more about this mysterious force.
Or it may be that light from distant supernovae is being distorted in some strange way - perhaps by being gradually converted into particles called axions. Finally, the spectrum of supernova relic neutrinos could reveal whether anything is awry with optical supernova studies.

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-- Edited by Blobrana at 13:05, 2006-11-28

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