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What could cosmic neutrinos tell us about gravity, if anything?

  1. Jan 13, 2004 #1


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    the cosmic photon background (CMB) evidently contains a lot of information about gravity and the structure of the universe
    and it is expected that when instruments get good enough we will
    see a cosmic neutrino background (CNB) consisting of even older particles

    what do you know about this, what links have you found
    I have only enough to whet my appetite and would like to find out more
    (about what is expected or predicted, since we have no data yet)

    Lineweaver, page 24, gives an estimate of the CNB temperature of 1.95 kelvin

    A guy at last summer's "What Comes After the Standard Model" conference gave an estimate of 100 big bang neutrinos per cubic centimeter throughout space.
    The proceedings of that conference were just posted on arxiv.

    Gianpiero Mangano "Cosmological Neutrinos"

    Is anybody here up for guessing what, if anything, might be learned from observing CNB about quantum theories of spacetime.

    this guy said that cosmology already gives a stronger bound on neutrino mass than is gotten from tritium-decay earthbound experiments. this is weird but here is the quote:

    "We are pretty confident that our Universe is presently filled with quite a large number of neutrinos, of the order of 100 cm−3 for each flavor, despite of the fact that there are no direct evidences for this claim and,more sadly, it will be also very hard to achieve this goal in the future.

    However several stages of the evolution of the Universe have been influenced by neutrinos, and their silent contribution has
    been first communicated to other species via weak interactions, and eventually through their coupling with gravity. In fact, Big Bang Nucleosynthesis (BBN), the CosmicMicrowave Background (CMB) and the spectrum of Large Scale Structure (LSS) keep traces of their presence, so that by observing the power spectrum P(k),
    the photon temperature-temperature angular correlation, and primordial abundances of light nuclei, we can obtain important pieces of information on several features of the neutrino background, aswell as on some fundamental parameters, such as their mass scale.

    It is astonishing, at least for all those of the elementary particle community who moved to ”astroparticle” physics, to see that in fact the present bound on the neutrino mass , order 1 eV, obtained by studying their effect on suppressing structure formation at small scales, is already stronger than the limit obtained in terrestrial measurement from 3H decay.

    In this short lecture I briefly review some of the cosmological observables which indeed lead to relevant information on both dynamical (number density, chemical potential) and kinematical (masses) neutrino properties, as well as on extra weakly coupled light species.

    2 Cosmological neutrinos: standard features
    For large temperatures neutrinos are kept in thermodynamical equilibrium with other species, namely e− − e+ and nucleons, which in turn share the very same temperature of photons because of electromagnetic interactions...."

    and so on. Mangano's article "cosmological neutrinos" is
    in the rather long conference PDF file
    Last edited: Jan 13, 2004
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  3. Jan 14, 2004 #2


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  4. Jan 14, 2004 #3


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    Amanda II one of the most beautiful neutrino experiments going----glass balls hung in a hole hollowed out a mile deep under Antarctic Ice---making a neutrino-map of the Northern Hemisphere sky as seen thru the earth from a point near the north pole.

    BTW I should have said "cosmological" neutrinos---Mangano used that term to mean the neutrinos from the first fraction of a second of the universe, ones we cant detect yet. What Amanda sees is not that primordial neutrino background but neutrinos from more recent (albeit still very old and distant) events.


    This paper is pure dynamite.
    "Updated Limits on TeV-Scale Gravity from Absence of Neutrino Cosmic Ray Showers Mediated by Black Holes"

    Luis A. Anchordoqui (Boston's Northeastern)
    Jonathan L. Feng (UC Irvine)
    Haim Goldberg (MIT)
    Alfred D. Shapere (Kentucky)

    11 pages, 4 figures

    Journal-ref: Phys.Rev. D68 (2003)

    "We revise existing limits on the D-dimensional Planck scale M_D from the nonobservation of microscopic black holes produced by high energy cosmic neutrinos in scenarios with D=4+n large extra dimensions. Previous studies have neglected the energy radiated in gravitational waves by the multipole moments of the incoming shock waves. We include the effects of energy loss, as well as form factors for black hole production and recent null results from cosmic ray detectors. For n>4, we obtain M_D > 1.0 - 1.4 TeV. These bounds are among the most stringent and conservative to date.

    An earlier Anchordoqui/Feng/Goldberg/Shapere paper---here's a bit from
    the abstract:
    "If extra spacetime dimensions and low-scale gravity exist, black holes will be produced in observable collisions of elementary particles. For the next several years, ultra-high energy cosmic rays provide the most promising window on this phenomenon. In particular, cosmic neutrinos can produce black holes deep in the Earth's atmosphere, leading to quasi-horizontal giant air showers. We determine the sensitivity of cosmic ray detectors to black hole production and compare the results to other probes of extra dimensions..."
    They seem to be out gunning for extra dimensions. there seem to be several different experimental/observational ways that extradimensions could be shot down. This is new to me because Im not much interested in string theory related stuff.

    I see in "Citebase" that this paper, which came out in 2001, has been cited by 73 other papers. Made rather a splash in the scholarly journals.

    ah! this was something i was wondering about thanks, appreciate this. it is a July 2003 SPR post from the reliable Ted Bunn that estimates the presentday speed of cosmic background neutrinos---that is NOT the ones that our detectors can now see but the vast amount of neutrinos that appeared in the first fraction of a second and which the expansion of the universe subsequently slowed way down.

    How slow are they now? Bunn says 5 thousandths of lightspeed.
    How many are they? Mangano says 100 per cubic centimeter.

    Here is the relevant Bunn quote, courtesy Wolram:

    "It turns out, though, that for reasonable neutrino masses
    the cosmic background neutrinos are still moving fast enough
    that they don't really fall into galaxies. Say, for instance,
    that a neutrino species has a rest mass of 20 eV. At
    the current temperature of the neutrino background (2 K), the
    thermal energy is something like 0.2 meV. So the
    neutrinos are moving at 0.005c. Although that's nonrelativistic,
    it's faster than the escape speeds from galaxies. So although
    a galaxy's gravity will cause some enhancement in the density
    of cosmic background neutrinos, it doesn't do all that much."

    Meet Chung-pei Ma, a lady astrophysicist at UCBerkeley who is doing computer simulations of the motion of clumps of dark matter around our galaxy. She finds it is not a uniform cloud but a a swarming multitude of bunches of darkstuff.

    "Dark matter could lead to Supersymmetry" Right, there is 6 times more darkstuff than there is usualmatter and the long-ago-predicted-but-but-still-unseen supersymmetric partners of ordinary particles might be out there in the clouds of dark matter. Might be. If SUSYstuff exists. Or dark matter might be something else that boffins wot not of.

    Thanks for the links. The others are probably good too but I am going to stop for now and chew over the Anchordoqui/Feng/Goldberg/Shapere.
    It does not concern Loop Gravity too much because the main result is restrictive of gravity models with 9 or more dimensions:
    that is for n > 4 so that D = 4 + n is greater than 8.

    Looks to me like they have something elegant and unexpected going.
    have to say am very impressed by this paper
    Last edited: Jan 14, 2004
  5. Jan 15, 2004 #4


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  6. Jan 18, 2004 #5


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    We calculate the time delays of neutrinos emitted in gamma ray bursts due to the effects of neutrino mass and quantum gravity using a time dependent Hubble constant which can significantly change the naive results presented hitherto in the literature for large redshifts, and gives some sensitivity to the details of dark energy. We show that the effects of neutrino mass, quantum gravity and dark energy may be disentangled by using low energy neutrinos to study neutrino mass, high energy neutrinos to study quantum gravity, and large redshifts to study dark energy. From low energy neutrinos one may obtain direct limits on neutrino masses of order 10^{-3} eV, and distinguish a neutrino mass hierarchy from an inverted mass hierarchy. From ultra-high energy neutrinos the sensitivity to the scale of quantum gravity can be pushed up to E_{QG} ~ 5 times 10^{30} GeV. By studying neutrinos from GRBs at large redshifts a cosmological constant could be distinguished from
    this 2003 paper by SANDHA CHOUBEY and S F KING. may be of interest.
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