309 research outputs found
On the Origin of High-Energy Cosmic Neutrinos
Recently, the IceCube collaboration made a big announcement of the first
discovery of high-energy cosmic neutrinos. Their origin is a new interesting
mystery in astroparticle physics. The present multimessenger data may give us
hints of connection to cosmic-ray and/or gamma-ray sources. We look over
possible scenarios for the cosmic neutrino signal, and emphasize the importance
of multimessenger approaches in identifying the PeV neutrino sources and
obtaining crucial clues to the cosmic-ray origin. We also discuss some
possibilities to study neutrino properties and probe new physics.Comment: 12 pages, 6 figures, based on an invited talk given at the "XXVI
International Conference on Neutrino Physics and Astrophysics (Neutrino
2014)", June 2-7, 2014, Boston, USA. To appear in AIP conference proceedings.
Figure 2 updated in v
New Prospects for Detecting High-Energy Neutrinos from Nearby Supernovae
Neutrinos from supernovae (SNe) are crucial probes of explosive phenomena at
the deaths of massive stars and neutrino physics. High-energy neutrinos are
produced through hadronic processes by cosmic rays, which are accelerated
during interaction between the supernova (SN) ejecta and circumstellar material
(CSM). Recent observations of extragalactic SNe have revealed that a dense CSM
is commonly expelled by the progenitor star. We provide new quantitative
predictions of time-dependent high-energy neutrino emission from diverse types
of SNe. We show that IceCube and KM3Net can detect about 1000 events from a SN
II-P (and about 300000 events from a SN IIn) at a distance of 10 kpc. The new
model also enables us to critically optimize the time window for dedicated
searches for nearby SNe. A successful detection will give us a multienergy
neutrino view of SN physics and new opportunities to study neutrino properties,
as well as clues to the cosmic-ray origin. GeV-TeV neutrinos may also be seen
by KM3Net, Hyper-Kamiokande, and PINGU.Comment: 6+1 pages, 3 figures, 2 tables, replaced to match the published
version, minor change
High-Energy Emission Induced by Ultra-High-Energy Photons as a Probe of Ultra-High-Energy Cosmic-Ray Accelerators Embedded in the Cosmic Web
The photomeson production in ultra-high-energy cosmic-ray (UHECR)
accelerators such as gamma-ray bursts and active galaxies may lead to
ultra-high-energy (UHE) gamma-ray emission. We show that generation of UHE
pairs in magnetized structured regions embedding the sources is inevitable, and
accompanied >0.1 TeV synchrotron emission provides an important probe of UHECR
acceleration. It would especially be relevant for powerful transient sources,
and synchrotron pair echoes may be detected by future CTA via coordinated
search for transients of duration ~0.1-1 yr for the structured regions with
~Mpc. Detections will be useful for knowing structured extragalactic magnetic
fields as well as properties of the sources.Comment: 5 pages, 4 figures, ApJL in press, minor change
Origin and Impacts of the First Cosmic Rays
Nonthermal phenomena are ubiquitous in the Universe, and cosmic rays (CRs)
play various roles in different environments. When, where, and how CRs are
first generated since the Big Bang? We argue that blast waves from the first
cosmic explosions at z~20 lead to Weibel mediated nonrelativistic shocks and
CRs can be generated by the diffusive shock acceleration mechanism. We show
that protons are accelerated at least up to sub-GeV energies, and the fast
velocity component of supernova ejecta is likely to allow CRs to achieve a few
GeV in energy. We discuss other possible accelerators of the first CRs,
including accretion shocks due to the cosmological structure formation. These
CRs can play various roles in the early universe, such as the ionization and
heating of gas, the generation of magnetic fields, and feedbacks on the galaxy
formation.Comment: 7 pages, accepted for publication in PR
Probing the Galactic Origin of the IceCube Excess with Gamma-Rays
The IceCube Collaboration has recently reported evidence for a high-energy
extraterrestrial neutrino flux. During two years of operation 28 events with
energies between 30 TeV and 1.2 PeV were observed while only 10.6 events were
expected from conventional atmospheric backgrounds. The hadronic interactions
responsible for this IceCube excess will also produce a flux of high-energy
gamma-rays that can serve as a probe of source direction and distance. We show
that existing TeV to PeV diffuse gamma-ray limits support the interpretation
that the IceCube excess is mostly of extragalactic origin. However, we point
out that gamma-ray surveys are biased in the Northern Hemisphere whereas the
recent IceCube data tentatively show a weak preference for the Southern Sky.
Possible sub-dominant contributions from Galactic neutrino sources like
remnants of supernovae and hypernovae are marginally consistent with present
gamma-ray limits. This emphasizes the importance of future diffuse TeV to PeV
gamma-ray surveys in the Southern Hemisphere, particularly in the extended
region around the Galactic Center including the Fermi Bubbles.Comment: 15 pages, 6 figure
Constraining high-energy neutrinos from choked-jet supernovae with IceCube high-energy starting events
Different types of core-collapse supernovae (SNe) have been considered as
candidate sources of high-energy cosmic neutrinos. Stripped-envelope SNe,
including energetic events like hypernovae and super-luminous SNe, are of
particular interest. They may harbor relativistic jets, which are capable of
explaining the diversity among gamma-ray bursts (GRBs), low-luminosity GRBs,
ultra-long GRBs, and broadline Type Ib/c SNe. Using the six-year IceCube data
on high-energy starting events (HESEs), we perform an unbinned maximum
likelihood analysis to search for spatial and temporal coincidences with 222
samples of SNe Ib/c. We find that the present data are consistent with the
background only hypothesis, by which we place new upper constraints on the
isotropic-equivalent energy of cosmic rays, , in the limit that all SNe are accompanied by
on-axis jets. Our results demonstrate that not only upgoing muon neutrinos but
also HESE data enable us to constrain the potential contribution of these SNe
to the diffuse neutrino flux observed in IceCube. We also discuss implications
for the next-generation neutrino detectors such as IceCube-Gen2.Comment: 18 pages, 7 figures; v2: a few clarifications and references added,
matches the version published in JCA
IceCube PeV-EeV Neutrinos and Secret Interactions of Neutrinos
We show that the PeV neutrinos detected by IceCube put unique constraints on
"secret" interactions of neutrinos with the cosmic neutrino background
(CB). The coupling must be for the mediating boson mass MeV, GeV for MeV, and
GeV in between. We also investigate the possibility
that neutrino cascades degrade high-energy neutrinos to PeV energies by
upgrading CB where the energy flux of PeV neutrinos can coincide with the
Waxman-Bahcall bound or the cosmogenic neutrino flux for protons, thanks to
energy conservation. However a large coupling is required, which is disfavored
by laboratory decay constraints. The suppression of PeV-EeV neutrinos is a
testable prediction for the Askaryan Radio Array.Comment: 6 pages, 2 figures, final version to be published in PTE
Oscillation of high-energy neutrinos from choked jets in stellar and merger ejecta
We present a comprehensive study on oscillation of high-energy neutrinos from
two different environments: blue supergiant progenitors that may harbor
low-power gamma-ray burst (GRB) jets and neutron star merger ejecta that would
be associated with short gamma-ray bursts. We incorporate the radiation
constraint that gives a necessary condition for nonthermal neutrino production,
and account for the time evolution of the jet, which allows us to treat
neutrino oscillation in matter more accurately. For massive star progenitors,
neutrino injection inside the star can lead to nonadiabatic oscillation
patterns in the 1 TeV - 10 TeV and is also visible in the flavor ratio. For
neutron star merger ejecta, we find a similar behavior in the 100 GeV - 10 TeV
region and the oscillation may result in a excess around 1 TeV. These
features, which enable us to probe the progenitors of long and short GRBs,
could be seen by future neutrino detectors with precise flavor ratio
measurements. We also discuss potential contributions to the diffuse neutrino
flux measured by IceCube, and find parameter sets allowing choked low-power GRB
jets to account for the neutrino flux in the 10 TeV - 100 TeV range without
violating the existing constraints.Comment: 11 pages, 6 figures, accepted for publication in PR
Constraints from the Time Lag between Gravitational Waves and Gamma Rays: Implications of GW 170817 and GRB 170817A
The Laser Interferometer Gravitational-Wave Observatory (LIGO) has recently
discovered gravitational waves (GWs) from its first neutron star-neutron star
merger at a distance of ~Mpc from the Earth. The associated
electromagnetic (EM) detection of the event, including the short gamma-ray
burst within ~s after the GW arrival, can be used to test
various aspects of sources physics and GW propagation. Using GW170817 as the
first GW-EM example, we show that this event provides a stringent direct test
that GWs travel at the speed of light. The gravitational potential of the Milky
Way provides a potential source of Shapiro time delay difference between the
arrival of photons and GWs, and we demonstrate that the nearly coincident
detection of the GW and EM signals can yield strong limits on anomalous
gravitational time delay, through updating the previous limits taking into
account details of Milky Way's gravitational potential. Finally, we also obtain
an intriguing limit on the size of the prompt emission region of GRB 170817A,
and discuss implications for the emission mechanism of short gamma-ray bursts.Comment: 6 pages, 1 figure; PRD versio
Detecting Asymmetric Dark Matter in the Sun with Neutrinos
Dark Matter (DM) may have a relic density that is in part determined by a
particle/antiparticle asymmetry, much like baryons. If this is the case, it can
accumulate in stars like the Sun to sizable number densities and annihilate to
Standard Model (SM) particles including neutrinos. We show that the combination
of neutrino telescope and direct detection data can be used in conjunction to
determine or constrain the DM asymmetry from data. Depending on the DM mass,
the current neutrino data from Super-K and IceCube give powerful constraints on
asymmetric DM unless its fractional asymmetry is . Future
neutrino telescopes and detectors like Hyper-K and KM3NeT can search for the
resulting signal of high-energy neutrinos from the center of the Sun. The
observation of such a flux yields information on both the DM-nucleus cross
section but also on the relative abundances of DM and anti-DM.Comment: 8 pages, 5 figure
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