992 research outputs found
Magnetic Field and Flavor Effects on the Gamma-Ray Burst Neutrino Flux
We reanalyze the prompt muon neutrino flux from gamma-ray bursts (GRBs), at
the example of the often used reference Waxman-Bahcall GRB flux, in terms of
the particle physics involved. We first reproduce this reference flux treating
synchrotron energy losses of the secondary pions explicitly. Then we include
additional neutrino production modes, the neutrinos from muon decays, the
magnetic field effects on all secondary species, and flavor mixing with the
current parameter uncertainties. We demonstrate that the combination of these
effects modifies the shape of the original Waxman-Bahcall GRB flux
significantly, and changes the normalization by a factor of three to four. As a
consequence, the gamma-ray burst search strategy of neutrino telescopes may be
based on the wrong flux shape, and the constraints derived for the GRB neutrino
flux, such as the baryonic loading, may in fact be already much stronger than
anticipated.Comment: 4 pages, 3 figures. Minor clarifications. Final version to appear in
Phys. Rev.
UHE neutrino and cosmic ray emission from GRBs: revising the models and clarifying the cosmic ray-neutrino connection
Gamma-ray bursts (GRBs) have long been held as one of the most promising
sources of ultra-high energy (UHE) neutrinos. The internal shock model of GRB
emission posits the joint production of UHE cosmic ray (UHECRs, above 10^8
GeV), photons, and neutrinos, through photohadronic interactions between source
photons and magnetically-confined energetic protons, that occur when
relativistically-expanding matter shells loaded with baryons collide with one
another. While neutrino observations by IceCube have now ruled out the simplest
version of the internal shock model, we show that a revised calculation of the
emission, together with the consideration of the full photohadronic cross
section and other particle physics effects, results in a prediction of the
prompt GRB neutrino flux that still lies one order of magnitude below the
current upper bounds, as recently exemplified by the results from ANTARES. In
addition, we show that by allowing protons to directly escape their magnetic
confinement without interacting at the source, we are able to partially
decouple the cosmic ray and prompt neutrino emission, which grants the freedom
to fit the UHECR observations while respecting the neutrino upper bounds.
Finally, we briefly present advances towards pinning down the precise relation
between UHECRs and UHE neutrinos, including the baryonic loading required to
fit UHECR observations, and we will assess the role that very large volume
neutrino telescopes play in this.Comment: 4 pages, 2 figures. To be published in Proceedings of the 6th Very
Large Volume Neutrino Telescope Workshop (VLVnT13), Stockholm, Sweden, 5-7
August, 201
Are gamma-ray bursts the sources of ultra-high energy cosmic rays?
We reconsider the possibility that gamma-ray bursts (GRBs) are the sources of
the ultra-high energy cosmic rays (UHECRs) within the internal shock model,
assuming a pure proton composition of the UHECRs. For the first time, we
combine the information from gamma-rays, cosmic rays, prompt neutrinos, and
cosmogenic neutrinos quantitatively in a joint cosmic ray production and
propagation model, and we show that the information on the cosmic energy budget
can be obtained as a consequence. In addition to the neutron model, we consider
alternative scenarios for the cosmic ray escape from the GRBs, i.e., that
cosmic rays can leak from the sources. We find that the dip model, which
describes the ankle in UHECR observations by the pair production dip, is
strongly disfavored in combination with the internal shock model because a)
unrealistically high baryonic loadings (energy in protons versus energy in
electrons/gamma-rays) are needed for the individual GRBs and b) the prompt
neutrino flux easily overshoots the corresponding neutrino bound. On the other
hand, GRBs may account for the UHECRs in the ankle transition model if cosmic
rays leak out from the source at the highest energies. In that case, we
demonstrate that future neutrino observations can efficiently test most of the
parameter space -- unless the baryonic loading is much larger than previously
anticipated.Comment: 55 pages, 23 figures, 1 table. Version accepted for publication in
Astroparticle Physics. Main analysis performed with TA data; for plots with
HiRes data, see v
On the Imaginary Simple Roots of the Borcherds Algebra
In a recent paper (hep-th/9703084) it was conjectured that the imaginary
simple roots of the Borcherds algebra at level 1 are its only
ones. We here propose an independent test of this conjecture, establishing its
validity for all roots of norm . However, the conjecture fails for
roots of norm -10 and beyond, as we show by computing the simple multiplicities
down to norm -24, which turn out to be remakably small in comparison with the
corresponding multiplicities. Our derivation is based on a modified
denominator formula combining the denominator formulas for and
, and provides an efficient method for determining the imaginary
simple roots. In addition, we compute the multiplicities of all roots
up to height 231, including levels up to and norms -42.Comment: 14 pages, LaTeX2e, packages amsmath, amsfonts, amssymb, amsthm,
xspace, pstricks, longtable; substantially extended, appendix with new
root multiplicities adde
Neutrino and cosmic-ray emission from multiple internal shocks in gamma-ray bursts
Gamma-ray bursts are short-lived, luminous explosions at cosmological
distances, thought to originate from relativistic jets launched at the deaths
of massive stars. They are among the prime candidates to produce the observed
cosmic rays at the highest energies. Recent neutrino data have, however,
started to constrain this possibility in the simplest models with only one
emission zone. In the classical theory of gamma-ray bursts, it is expected that
particles are accelerated at mildly relativistic shocks generated by the
collisions of material ejected from a central engine. We consider neutrino and
cosmic-ray emission from multiple emission regions since these internal
collisions must occur at very different radii, from below the photosphere all
the way out to the circumburst medium, as a consequence of the efficient
dissipation of kinetic energy. We demonstrate that the different messengers
originate from different collision radii, which means that multi-messenger
observations open windows for revealing the evolving GRB outflows.Comment: 12 pages, 7 figures. Matches published versio
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