102 research outputs found
Ultrahigh-Energy Photons as a Probe of Nearby Transient Ultrahigh-Energy Cosmic-Ray Sources and Possible Lorentz-Invariance Violation
Detecting neutrinos and photons is crucial to identifying the sources of
ultrahigh-energy cosmic rays (UHECRs), especially for transient sources. We
focus on ultrahigh-energy gamma-ray emission from transient sources such as
gamma-ray bursts, since >EeV gamma rays can be more direct evidence of UHECRs
than PeV neutrinos and GeV-TeV gamma rays. We demonstrate that coincident
detections of about 1-100 events can be expected by current and future UHECR
detectors such as Auger and JEM-EUSO, and the detection probability can be
higher than that of neutrinos for nearby transient sources at <50-100 Mpc. They
may be useful for constraining the uncertain cosmic radio background as well as
knowing the source properties and maximum energy of UHECRs. They can also give
us more than 10^4 times stronger limits on the Lorentz-invariance violation
than current constraints.Comment: 4 pages, 3 figures, replaced to match the published version (PRL,
103, 081102
Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts
We present recipes to diagnose the fireball of gamma-ray bursts (GRBs) by
combining observations of electron-positron pair-signatures (the
pair-annihilation line and the cutoff energy due to the pair-creation process).
Our recipes are largely model-independent and extract information even from the
non-detection of either pair-signature. We evaluate physical quantities such as
the Lorentz factor, optical depth and pair-to-baryon ratio, only from the
observable quantities. In particular, we can test whether the prompt emission
of GRBs comes from the pair/baryonic photosphere or not. The future-coming
Gamma-Ray Large Area Space Telescope (GLAST) satellite will provide us with
good chances to use our recipes by detecting or non-detecting pair-signatures.Comment: 7 pages, 4 figures, accepted for publication in ApJ, with extended
discussions. Conclusions unchange
Unstable GRB photospheres and electron-positron annihilation lines
We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can
reproduce the observed non-thermal spectra with high radiative efficiencies,
>50%. Internal dissipation below a photosphere can create a radiation-dominated
thermal fireball. If electron-positron pairs outnumber protons, radiative
acceleration of pairs drives the two-stream instabilities between pairs and
protons, leading to the ``proton sedimentation'' in the accelerating pair
frame. Pairs are continuously shock heated by proton clumps, scattering the
thermal photons into the broken power-law shape, with the non-thermal energy
that is comparable to the proton kinetic energy, consistent with observations.
Pair photospheres become unstable around the radius of the progenitor star
where strong thermalization occurs, if parameters satisfy the observed spectral
(Yonetoku) relation. Pair annihilation lines are predicted above continua,
which could be verified by GLAST.Comment: 4 pages, 2 figure
Genetic and Neural Modularity Underlie the Evolution of Schooling Behavior in Threespine Sticklebacks
SummaryAlthough descriptions of striking diversity in animal behavior are plentiful, little is known about the mechanisms by which behaviors change and evolve between groups. To fully understand behavioral evolution, it will be necessary to identify the genetic mechanisms that mediate behavioral change in a natural context [1–3]. Genetic analysis of behavior can also reveal associations between behavior and morphological or neural phenotypes, providing insight into the proximate mechanisms that control behavior. Relatively few studies to date have successfully identified genes or genomic regions that contribute to behavioral variation among natural populations or species [2], particularly in vertebrates [4–8]. Here, we apply genetic approaches to dissect a complex social behavior that has long fascinated biologists, schooling behavior [9–13]. We performed quantitative trait locus (QTL) analysis of schooling in an F2 intercross between strongly schooling marine and weakly schooling benthic sticklebacks (Gasterosteus aculeatus) and found that distinct genetic modules control different aspects of schooling behavior. Two key components of the behavior, tendency to school and body position when schooling, are uncorrelated in hybrids and map to different genomic regions. Our results further point to a genetic link between one behavioral component, schooling position, and variation in the neurosensory lateral line
High energy neutrino early afterglows from gamma-ray bursts revisited
The high energy neutrino emission from gamma-ray bursts (GRBs) has been
expected in various scenarios. In this paper, we study the neutrino emission
from early afterglows of GRBs, especially under the reverse-forward shock model
and late prompt emission model. In the former model, the early afterglow
emission occurs due to dissipation made by an external shock with the
circumburst medium (CBM). In the latter model, internal dissipation such as
internal shocks produces the shallow decay emission in early afterglows. We
also discuss implications of recent Swift observations for neutrino signals in
detail. Future neutrino detectors such as IceCube may detect neutrino signals
from early afterglows, especially under the late prompt emission model, while
the detection would be difficult under the reverse-forward shock model.
Contribution to the neutrino background from the early afterglow emission may
be at most comparable to that from the prompt emission unless the outflow
making the early afterglow emission loads more nonthermal protons, and it may
be important in the very high energies. Neutrino-detections are inviting
because they could provide us with not only information on baryon acceleration
but also one of the clues to the model of early afterglows. Finally, we compare
various predictions for the neutrino background from GRBs, which are testable
by future neutrino-observations.Comment: 18 pages, 12 figures, accepted for publication in PR
MAP4K3 mediates amino acid-dependent regulation of autophagy via phosphorylation of TFEB
Autophagy is the major cellular pathway by which macromolecules are degraded, and amino acid depletion powerfully activates autophagy. MAP4K3, or germinal-center kinase-like kinase, is required for robust cell growth in response to amino acids, but the basis for MAP4K3 regulation of cellular metabolic disposition remains unknown. Here we identify MAP4K3 as an amino acid-dependent regulator of autophagy through its phosphorylation of transcription factor EB (TFEB), a transcriptional activator of autophagy, and through amino acid starvation-dependent lysosomal localization of MAP4K3. We document that MAP4K3 physically interacts with TFEB and MAP4K3 inhibition is sufficient for TFEB nuclear localization, target gene transactivation, and autophagy, even when mTORC1 is activated. Moreover, MAP4K3 serine 3 phosphorylation of TFEB is required for TFEB interaction with mTORC1-Rag GTPase-Ragulator complex and TFEB cytosolic sequestration. Our results uncover a role for MAP4K3 in the control of autophagy and reveal MAP4K3 as a central node in nutrient-sensing regulation
High Energy Neutrino Emission and Neutrino Background from Gamma-Ray Bursts in the Internal Shock Model
High energy neutrino emission from GRBs is discussed. In this paper, by using
the simulation kit GEANT4, we calculate proton cooling efficiency including
pion-multiplicity and proton-inelasticity in photomeson production. First, we
estimate the maximum energy of accelerated protons in GRBs. Using the obtained
results, neutrino flux from one burst and a diffuse neutrino background are
evaluated quantitatively. We also take account of cooling processes of pion and
muon, which are crucial for resulting neutrino spectra. We confirm the validity
of analytic approximate treatments on GRB fiducial parameter sets, but also
find that the effects of multiplicity and high-inelasticity can be important on
both proton cooling and resulting spectra in some cases. Finally, assuming that
the GRB rate traces the star formation rate, we obtain a diffuse neutrino
background spectrum from GRBs for specific parameter sets. We introduce the
nonthermal baryon-loading factor, rather than assume that GRBs are main sources
of UHECRs. We find that the obtained neutrino background can be comparable with
the prediction of Waxman & Bahcall, although our ground in estimation is
different from theirs. In this paper, we study on various parameters since
there are many parameters in the model. The detection of high energy neutrinos
from GRBs will be one of the strong evidences that protons are accelerated to
very high energy in GRBs. Furthermore, the observations of a neutrino
background has a possibility not only to test the internal shock model of GRBs
but also to give us information about parameters in the model and whether GRBs
are sources of UHECRs or not.Comment: 14 pages, 17 figures, accepted for publication in PRD, with extended
descriptions. Conclusions unchange
Chemical and Photometric Evolution of Extended Ultraviolet Disks: Optical Spectroscopy of M83 (NGC5236) and NGC4625
We present the results from the analysis of optical spectra of 31
Halpha-selected regions in the extended UV (XUV) disks of M83 (NGC5236) and
NGC4625 recently discovered by GALEX. The spectra were obtained using IMACS at
Las Campanas Observatory 6.5m Magellan I telescope and COSMIC at the Palomar
200-inch telescope, respectively for M83 and NGC4625. The line ratios measured
indicate nebular oxygen abundances (derived from the R23 parameter) of the
order of Zsun/5-Zsun/10. For most emission-line regions analyzed the line
fluxes and ratios measured are best reproduced by models of photoionization by
single stars with masses in the range 20-40 Msun and oxygen abundances
comparable to those derived from the R23 parameter. We find indications for a
relatively high N/O abundance ratio in the XUV disk of M83. Although the
metallicities derived imply that these are not the first stars formed in the
XUV disks, such a level of enrichment could be reached in young spiral disks
only 1 Gyr after these first stars would have formed. The amount of gas in the
XUV disks allow maintaining the current level of star formation for at least a
few Gyr.Comment: 52 pages, 8 tables, 7 figures, accepted for publication in Ap
Dynamics of Scalar field in a Brane World
We study the dynamics of a scalar field in the brane cosmology. We assume
that a scalar field is confined in our 4-dimensional world. As for the
potential of the scalar field, we discuss three typical models: (1) a power-law
potential, (2) an inverse-power-law potential, and (3) an exponential
potential. We show that the behavior of the scalar field is very different from
a conventional cosmology when the energy density square term is dominated.Comment: 15pages, 8figures, submitted to Physical Review
Galaxy Clusters as Reservoirs of Heavy Dark Matter and High-Energy Cosmic Rays: Constraints from Neutrino Observations
Galaxy Clusters (GCs) are the largest reservoirs of both dark matter and
cosmic rays (CRs). Dark matter self-annihilation can lead to a high luminosity
in gamma rays and neutrinos, enhanced by a strong degree of clustering in dark
matter substructures. Hadronic CR interactions can also lead to a high
luminosity in gamma rays and neutrinos, enhanced by the confinement of CRs from
cluster accretion/merger shocks and active galactic nuclei. We show that
IceCube/KM3Net observations of high-energy neutrinos can probe the nature of
GCs and the separate dark matter and CR emission processes, taking into account
how the results depend on the still-substantial uncertainties. Neutrino
observations are relevant at high energies, especially at >10 TeV. Our results
should be useful for improving experimental searches for high-energy neutrino
emission. Neutrino telescopes are sensitive to extended sources formed by dark
matter substructures and CRs distributed over large scales. Recent observations
by Fermi and imaging atmospheric Cherenkov telescopes have placed interesting
constraints on the gamma-ray emission from GCs. We also provide calculations of
the gamma-ray fluxes, taking into account electromagnetic cascades inside GCs,
which can be important for injections at sufficiently high energies. This also
allows us to extend previous gamma-ray constraints to very high dark matter
masses and significant CR injections at very high energies. Using both
neutrinos and gamma rays, which can lead to comparable constraints, will allow
more complete understandings of GCs. Neutrinos are essential for some dark
matter annihilation channels, and for hadronic instead of electronic CRs. Our
results suggest that the multi-messenger observations of GCs will be able to
give useful constraints on specific models of dark matter and CRs. [Abstract
abridged.]Comment: 31 pages, 20 figures, 1 table, accepted for publication in JCAP,
references and discussions adde
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