21 research outputs found
Strongly interacting neutrinos as the highest energy cosmic rays
We show that all features of the ultrahigh energy cosmic ray spectrum from
10^{17} eV to 10^{21} eV can be described with a simple power-like injection
spectrum of protons under the assumption that the neutrino-nucleon
cross-section is significantly enhanced at center of mass energies above
\approx 100 TeV. In our scenario, the cosmogenic neutrinos produced during the
propagation of protons through the cosmic microwave background initiate air
showers in the atmosphere, just as the protons. The total air shower spectrum
induced by protons and neutrinos shows excellent agreement with the
observations. A particular possibility for a large neutrino-nucleon
cross-section exists within the Standard Model through electroweak
instanton-induced processes.Comment: 8 pages, 4 figures, talk given at Beyond the Desert '03, Castle
Ringberg, 9-14 June, 200
Axion cosmology, lattice QCD and the dilute instanton gas
Axions are one of the most attractive dark matter candidates. The evolution
of their number density in the early universe can be determined by calculating
the topological susceptibility of QCD as a function of the
temperature. Lattice QCD provides an ab initio technique to carry out such a
calculation. A full result needs two ingredients: physical quark masses and a
controlled continuum extrapolation from non-vanishing to zero lattice spacings.
We determine in the quenched framework (infinitely large quark
masses) and extrapolate its values to the continuum limit. The results are
compared with the prediction of the dilute instanton gas approximation (DIGA).
A nice agreement is found for the temperature dependence, whereas the overall
normalization of the DIGA result still differs from the non-perturbative
continuum extrapolated lattice results by a factor of order ten. We discuss the
consequences of our findings for the prediction of the amount of axion dark
matter.Comment: 9 pages, 7 figure
Determination of absolute neutrino masses from Z-bursts
Ultrahigh energy neutrinos (UHE\nu) scatter on relic neutrinos (R\nu)
producing Z bosons, which can decay hadronically producing protons (Z-burst).
We compare the predicted proton spectrum with the observed ultrahigh energy
cosmic ray (UHECR) spectrum and determine the mass of the heaviest R\nu via a
maximum likelihood analysis. Our prediction depends on the origin of the
power-like part of the UHECR spectrum: m_\nu=2.75^{+1.28}_{-0.97} eV for
Galactic halo and 0.26^{+0.20}_{-0.14} eV for extragalactic (EG) origin. The
necessary UHE\nu flux should be detected in the near future.Comment: slight rewording, revised neutrino fluxes, conclusions unchanged,
version to appear in Phys. Rev. Let
Bounds on the cosmogenic neutrino flux
Under the assumption that some part of the observed highest energy cosmic
rays consists of protons originating from cosmological distances, we derive
bounds on the associated flux of neutrinos generated by inelastic processes
with the cosmic microwave background photons. We exploit two methods. First, a
power-like injection spectrum is assumed. Then, a model-independent technique,
based on the inversion of the observed proton flux, is presented. The inferred
lower bound is quite robust. As expected, the upper bound depends on the
unknown composition of the highest energy cosmic rays. Our results represent
benchmarks for all ultrahigh energy neutrino telescopes.Comment: 12 pages, 6 figure
Relic neutrino masses and the highest energy cosmic rays
We consider the possibility that a large fraction of the ultrahigh energy
cosmic rays are decay products of Z bosons which were produced in the
scattering of ultrahigh energy cosmic neutrinos on cosmological relic
neutrinos. We compare the observed ultrahigh energy cosmic ray spectrum with
the one predicted in the above Z-burst scenario and determine the required mass
of the heaviest relic neutrino as well as the necessary ultrahigh energy cosmic
neutrino flux via a maximum likelihood analysis. We show that the value of the
neutrino mass obtained in this way is fairly robust against variations in
presently unknown quantities, like the amount of neutrino clustering, the
universal radio background, and the extragalactic magnetic field, within their
anticipated uncertainties. Much stronger systematics arises from different
possible assumptions about the diffuse background of ordinary cosmic rays from
unresolved astrophysical sources. In the most plausible case that these
ordinary cosmic rays are protons of extragalactic origin, one is lead to a
required neutrino mass in the range 0.08 eV - 1.3 eV at the 68 % confidence
level. This range narrows down considerably if a particular universal radio
background is assumed, e.g. to 0.08 eV - 0.40 eV for a large one. The required
flux of ultrahigh energy cosmic neutrinos near the resonant energy should be
detected in the near future by AMANDA, RICE, and the Pierre Auger Observatory,
otherwise the Z-burst scenario will be ruled out.Comment: 19 pages, 22 figures, REVTeX
Upper Bounds on the Neutrino-Nucleon Inelastic Cross Section
Extraterrestrial neutrinos can initiate deeply developing air showers, and
those that traverse the atmosphere unscathed may produce cascades in the ice or
water. Up to now, no such events have been observed. This can be translated
into upper limits on the diffuse neutrino flux. On the other hand, the
observation of cosmic rays with primary energies > 10^{10} GeV suggests that
there is a guaranteed flux of cosmogenic neutrinos, arising from the decay of
charged pions (and their muon daughters) produced in proton interactions with
the cosmic microwave background. In this work, armed with these cosmogenic
neutrinos and the increased exposure of neutrino telescopes we bring up-to-date
model-independent upper bounds on the neutrino-nucleon inelastic cross section.
Uncertainties in the cosmogenic neutrino flux are discussed and taken into
account in our analysis. The prospects for improving these bounds with the
Pierre Auger Observatory are also estimated. The unprecedented statistics to be
collected by this experiment in 6 yr of operation will probe the
neutrino-nucleon inelastic cross section at the level of Standard Model
predictions.Comment: To be published in JCA
Dark Energy from Mass Varying Neutrinos
We show that mass varying neutrinos (MaVaNs) can behave as a negative
pressure fluid which could be the origin of the cosmic acceleration. We derive
a model independent relation between the neutrino mass and the equation of
state parameter of the neutrino dark energy, which is applicable for general
theories of mass varying particles. The neutrino mass depends on the local
neutrino density and the observed neutrino mass can exceed the cosmological
bound on a constant neutrino mass. We discuss microscopic realizations of the
MaVaN acceleration scenario, which involve a sterile neutrino. We consider
naturalness constraints for mass varying particles, and find that both ev
cutoffs and ev mass particles are needed to avoid fine-tuning. These
considerations give a (current) mass of order an eV for the sterile neutrino in
microscopic realizations, which could be detectable at MiniBooNE. Because the
sterile neutrino was much heavier at earlier times, constraints from big bang
nucleosynthesis on additional states are not problematic. We consider regions
of high neutrino density and find that the most likely place today to find
neutrino masses which are significantly different from the neutrino masses in
our solar system is in a supernova. The possibility of different neutrino mass
in different regions of the galaxy and the local group could be significant for
Z-burst models of ultra-high energy cosmic rays. We also consider the cosmology
of and the constraints on the ``acceleron'', the scalar field which is
responsible for the varying neutrino mass, and briefly discuss neutrino density
dependent variations in other constants, such as the fine structure constant.Comment: 26 pages, 3 figures, refs added, typos corrected, comment added about
possible matter effect
Astrophysical Origins of Ultrahigh Energy Cosmic Rays
In the first part of this review we discuss the basic observational features
at the end of the cosmic ray energy spectrum. We also present there the main
characteristics of each of the experiments involved in the detection of these
particles. We then briefly discuss the status of the chemical composition and
the distribution of arrival directions of cosmic rays. After that, we examine
the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin
(GZK) cutoff, and discuss the level of confidence with which each experiment
have detected particles beyond the GZK energy limit. In the second part of the
review, we discuss astrophysical environments able to accelerate particles up
to such high energies, including active galactic nuclei, large scale galactic
wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley
radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding
galaxies, and gamma ray burst fireballs. In the third part of the review we
provide a brief summary of scenarios which try to explain the super-GZK events
with the help of new physics beyond the standard model. In the last section, we
give an overview on neutrino telescopes and existing limits on the energy
spectrum and discuss some of the prospects for a new (multi-particle)
astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used
to probe new physics beyond the electroweak scale.Comment: Higher resolution version of Fig. 7 is available at
http://www.angelfire.com/id/dtorres/down3.html. Solicited review article
prepared for Reports on Progress in Physics, final versio