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Francis Halzen

Publications and source records attributed to Francis Halzen.

At least 109 records · Page 6Linked to original sources
arXiv2006

Cosmic Neutrinos and the Energy Budget of Galactic and Extragalactic Cosmic Rays

Although kilometer-scale neutrino detectors such as IceCube are discovery instruments, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 10^{20} eV and 10^{13} eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. We will discuss how the cosmic ray connection sets the scale of the anticipated cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube.

astro-ph↗
arXiv2006

IceHEP High Energy Physics at the South Pole

With the solar and SN87 neutrino observations as proofs of concepts, the kilometer-scale neutrino experiment IceCube will scrutinize its data for new particle physics. In this paper we review the prospects for the realization of such a program. We begin with a short overview of the detector response and discuss the reach of ``beam'' luminosity. After that we discuss the potential of IceCube to probe deviations of neutrino-nucleon cross sections from the Standard Model predictions at center-of-mass energies well beyond those accessible in man-made accelerators. Then we review the prospects for extremely long-baseline analyses and discuss the sensitivity to measure tiny deviations of the flavor mixing angle, expected to be induced by quantum gravity effects. Finally we discuss the potential to uncover annihilation of dark matter particles gravitationally trapped at the center of the Sun, as well as processes occurring in the early Universe at energies close to the Grand Unification scale.

hep-ph↗
arXiv2006

Astroparticle Physics with High Energy Neutrinos: from AMANDA to IceCube

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of $10^{20}$\,eV and $10^{13}$\,eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows: Introduction Why Kilometer-Scale Detectors? Cosmic Neutrinos Associated with the Highest Energy Cosmic Rays High Energy Neutrino Telescopes: Methodologies of Neutrino Detection High Energy Neutrino Telescopes: Status

astro-ph↗
arXiv2005

Coincident GRB neutrino flux predictions: Implications for experimental UHE neutrino physics

In the hadronic fireball phenomenology of Gamma Ray Bursts (GRBs), it is expected that the observed photons are accompanied by UHE neutrinos, which have not been observed yet. It is one of the challenges of experimental UHE neutrino astrophysics to look for a signal from GRBs. In this paper, the differences between a search for a diffuse signal and an examination of a source sample given by e.g. BATSE will be analyzed. Since redshift information is needed to determine the correct energy spectrum, long duration bursts with redshifts from different estimate methods will be used. We will start with an overview of the current understanding of GRB neutrino physics and will then use this knowledge to make predictions for a coincidence flux and a corresponding diffuse flux. It can be shown that shape and normalization of the spectrum is highly dependent on the set of bursts used and that individual bursts can determine the total spectrum.

astro-ph↗
arXiv2005

Prospects For Detecting Dark Matter With Neutrino Telescopes In Light Of Recent Results From Direct Detection Experiments

Direct detection dark matter experiments, lead by the CDMS collaboration, have placed increasingly stronger constraints on the cross sections for elastic scattering of WIMPs on nucleons. These results impact the prospects for the indirect detection of dark matter using neutrino telescopes. With this in mind, we revisit the prospects for detecting neutrinos produced by the annihilation of WIMPs in the Sun. We find that the latest bounds do not seriously limit the models most accessible to next generation kilometer-scale neutrino telescopes such as IceCube. This is largely due to the fact that models with significant spin-dependent couplings to protons are the least constrained and, at the same time, the most promising because of the efficient capture of WIMPs in the Sun. We identify models where dark matter particles are beyond the reach of any planned direct detection experiments while within reach of neutrino telescopes. In summary, we find that, even when contemplating recent direct detection results, neutrino telescopes still have the opportunity to play an important as well as complementary role in the search for particle dark matter.

hep-ph↗
arXiv2005

Probing Planck scale physics with IceCube

Neutrino oscillations can be affected by decoherence induced e.g. by Planck scale suppressed interactions with the space-time foam predicted in some approaches to quantum gravity. We study the prospects for observing such effects at IceCube, using the likely flux of TeV antineutrinos from the Cygnus spiral arm. We formulate the statistical analysis for evaluating the sensitivity to quantum decoherence in the presence of the background from atmospheric neutrinos, as well as from plausible cosmic neutrino sources. We demonstrate that IceCube will improve the sensitivity to decoherence effects of ${\cal O}(E^2/M_{\rm Pl})$ by 17 orders of magnitude over present limits and, moreover, that it can probe decoherence effects of ${\cal O}(E^3/M_{\rm Pl}^2)$ which are well beyond the reach of other experiments.

hep-ph↗
arXiv2005

Neutrinos as a diagnostic of cosmic ray Galactic/extra-galactic transition

Motivated by a recent change in viewing the onset of the extra-galactic component in the cosmic ray spectrum, we have fitted the observed data down to $10^{8.6}$ GeV and have obtained the corresponding power emissivity. This transition energy is well below the threshold for resonant $pγ$ absorption on the cosmic microwave background, and thus source evolution is an essential ingredient in the fitting procedure. Two-parameter fits in the spectral and redshift evolution indices show that a standard Fermi $E_i^{-2}$ source spectrum is excluded at larger than 95% confidence level (CL). Armed with the primordial emissivity, we follow Waxman and Bahcall to derive the associated neutrino flux on the basis of optically thin sources. For $pp$ interactions as the generating mechanism, the neutrino flux exceeds the AMANDA-B10 90%CL upper limits. In the case of $pγ$ dominance, the flux is marginally consistent with AMANDA-B10 data. In the new scenario the source neutrino flux dominates over the cosmogenic flux at all energies. Thus, should data from AMANDA-II prove consistent with the model, we show that IceCube can measure the characteristic power law of the neutrino spectrum, and thus provide a window on the source dynamics.

astro-ph↗
arXiv2005

Neutrinos as a Diagnostic of High Energy Astrophysical Processes

A leading candidate for the extragalactic source of high energy cosmic rays is the Fermi engine mechanism, in which protons confined by magnetic fields are accelerated to very high energy through repeated scattering by plasma shock fronts. In the process of acceleration, collisions of trapped protons with the ambient plasma produce pions which decay to electromagnetic energy and neutrinos. For optically thin sources, a strong connection between the emerging cosmic rays and secondary neutrinos can be established. In this context, we show the feasibility of using the Glashow resonance as a discriminator between the $pp$ and $pγ$ interactions in Fermi engines as sources of neutrinos. In particular, we demonstrate how three years of observation at the km$^3$ IceCube facility can serve as a filter for the dominance of the $pp$ interaction at the source.

hep-ph↗
arXiv2005

TeV photons and Neutrinos from giant soft-gamma repeaters flares

During the last 35 years three giant flares were observed from so-called Soft Gamma Repeaters (SGR's). They are assumed to be associated with star-quakes of pulsars accelerating electrons and, possibly, protons to high energy in the huge magnetic fields as inferred from the observations. Because of this and the observation of non-thermal emission it has been speculated that they may be cosmic ray accelerators producing gamma-rays up to TeV energies. Neutrino telescopes, such as AMANDA and the ANTARES now under construction, could be used as TeV-gamma detectors for very short emissions by measuring underground muons produced in $γ$ showers. We estimate signal and background rates for TeV photons from SGR giant flares in AMANDA, and we provide an estimate of the gamma shower events that Milagro could detect. Moreover, we consider that, if hadrons are accelerated in these sources, high energy neutrinos would be produced together with photons. These may be detected in neutrino telescopes using neutrino-induced cascades and upgoing muons. We argue that the Antarctic Muon and Neutrino Detector Array AMANDA may have observed the December 27, 2004 giant flare from the soft gamma-ray repeater SGR 1806-20 if the non-thermal component of the spectrum extends to TeV energies (at present the actual data is subject to blind analysis). Rates should be scaled by about two orders of magnitude in km3 detectors, such as IceCube, making SGR flares sources of primary interest.

astro-ph↗
arXiv2005

High Energy Neutrinos from the TeV Blazar 1ES 1959+650

The AMANDA neutrino telescope has recently reported the detection of high-energy neutrinos spatially and temporally coincident with the flaring of the TeV blazar 1ES 1959+650. At present, the statistical significance of this observation cannot be reliably assessed, however. In this letter, we investigate whether circumstances exist where the source can produce the flux implied by the coincident events. We show that if the TeV gamma-ray emission observed from 1ES 1959+650 or other nearby TeV blazars is the result of accelerated protons interacting with nucleons, it is reasonable that AMANDA could detect several events during a flaring period. Such rates require that the spectral index of the source be rather high (for instance $\sim2.8$ for 1ES 1959+650) and that the Lorentz factor of the jet be fairly small ($Γ\sim 1$).

astro-ph↗
arXiv2004

Galactic Point Sources of TeV Antineutrinos

High energy cosmic ray experiments have identified an excess from the region of the Galactic Plane in a limited energy range around $10^{18}$ eV (EeV). This is very suggestive of neutrons as candidate primaries, because the directional signal requires relatively-stable neutral primaries, and time-dilated neutrons can reach Earth from typical Galactic distances when the neutron energy exceeds an EeV. We here point out that if the Galactic messengers are neutrons, then those with energies below an EeV will decay in flight, providing a flux of cosmic antineutrinos above a TeV which is {\it observable} at a kilometer-scale neutrino observatory. The expected event rate per year above 1 TeV in a detector such as IceCube, for example, is 20 antineutrino showers (all flavors) and a $1^\circ$ directional signal of 4 $\bar ν_μ$ events. A measurement of this flux can serve to identify the first extraterrestrial point source of TeV antineutrinos.

astro-ph↗
arXiv2004

Neutrino Bursts from Fanaroff-Riley I Radio Galaxies

On the basis of existing observations (at the 4.5 σlevel) of TeV gamma-ray outbursts from the Fanaroff-Riley I (FRI) radio galaxy Centaurus A, we estimate the accompanying neutrino flux in a scenario where both photons and neutrinos emerge from pion decay. We find a neutrino flux on Earth dF_ν/dE_ν= 4.5\times 10^{-11} (E_ν/TeV)^{-2} TeV^{-1} cm^{-2} s^{-1}, equally spread in flavor as a result of maximal mixing. Such a flux will trigger at the IceCube facility about 10 showers/burst, with negligible background from atmospheric muons, and primary neutrino energies in excess of 100 TeV. The only other FRI radio galaxy observed in the TeV photon energy range at the 4σlevel is M87. The burst nature of this activity is not established; however, we show that the intrinsic neutrino luminosity during the active period is the same as the Centaurus A burst. On the assumption that Centaurus A typifies the FRI population, we show that IceCube should collect 10 showers (all neutrino flavors) in 3 years, attaining a 95% CL sensitivity to the diffuse neutrino flux from FRI radio galaxies in one year of observation.

astro-ph↗
arXiv2003

IceCube-Plus: An Ultra-High Energy Neutrino Telescope

While the first kilometer-scale neutrino telescope, IceCube, is under construction, alternative plans exist to build even larger detectors that will, however, b e limited by a much higher neutrino energy threshold of 10 PeV or higher rather than 10 to 100 GeV. These future projects detect radio and acoustic pulses as w ell as air showers initiated by ultra-high energy neutrinos. As an alternative, we here propose an expansion of IceCube, using the same strings, placed on a gri d with a spacing of order 500 m. Unlike other proposals, the expanded detector uses methods that are understood and calibrated on atmospheric neutrinos. Atmosp heric neutrinos represent the only background at the energies under consideratio n and is totally negligible. Also, the cost of such a detector is understood. We conclude that supplementing the 81 IceCube strings with a modest number of addi tional strings spaced at large distances can almost double the effective volume of the detector. Doubling the number of strings on a 800 m grid can deliver a d etector that this a factor of 5 larger for horizontal muons at modest cost.

astro-ph↗
arXiv2003

GRB941017: A Case Study of Neutrino Production in Gamma Ray Bursts

GRB941017, a gamma-ray burst of exceptional fluence, has recently been shown to have a high-energy component which is not consistent with the standard fireball phenomenology. If this component is the result of photomeson interactions in the burst fireball, it provides new and compelling support for substantial high-energy neutrino fluxes from this and similar sources. In this letter, we consider what impact this new information has on the neutrino spectra of gamma-ray bursts and discuss how this new evidence impacts the prospects for detection of such events in next generation neutrino telescopes.

astro-ph↗
arXiv2003

Gamma Ray Astronomy With IceCube

We demonstrate that the South Pole kilometer-scale neutrino observatory IceCube can detect multi-TeV gamma rays continuously over a large fraction of the southern sky. While not as sensitive as pointing atmospheric Cerenkov telescopes, IceCube can roughly match the sensitivity of Milagro. Also, IceCube is complementary to Milagro because it will observe, without interruption, a relatively poorly studied fraction of the southern sky. The information which IceCube must record to function as a gamma ray observatory is only the directions and possibly energies of down-going muons.

astro-ph↗
arXiv2002

Possible High-energy neutrinos from the cosmic accelerator RXJ1713.7-3946

The observation of TeV-gamma rays of neutral pion origin from the supernova remnant RX J1713.7-3946 might have revealed the first specific site where protons are accelerated to energies typical of the main component of the cosmic rays. In this letter we calculate the high-energy neutrino flux associated with this source to be at least 40 muon-type neutrinos per kilometer-squared per year. We perform the same calculations for other known sources of TeV-gamma rays and show how neutrino observations can establish whether the TeV-gamma rays emitted by blazars and supernova remnants are the decay products of neutral pions and thus unequivocally establish the sources as cosmic accelerators.

astro-ph↗
arXiv2002

High-energy Neutrino Astronomy: The Cosmic Ray Connection

This is a review of neutrino astronomy anchored to the observational fact that Nature accelerates protons and photons to energies in excess of $10^{20}$ and $10^{13}$ eV, respectively. Although the discovery of cosmic rays dates back close to a century, we do not know how and where they are accelerated. Basic elementary-particle physics dictates a universal upper limit on their energy of $5\times10^{19}$ eV, the so-called Greisen-Kuzmin-Zatsepin cutoff; however, particles in excess of this energy have been observed by all experiments, adding one more puzzle to the cosmic ray mystery. Mystery is fertile ground for progress: we will review the facts as well as the speculations about the sources including gamma ray bursts, blazars and top-down scenarios. The important conclusion is that, independently of the specific blueprint of the source, it takes a kilometer-scale neutrino observatory to detect the neutrino beam associated with the highest energy cosmic rays and gamma rays. We also briefly review the ongoing efforts to commission such instrumentation.

astro-ph↗