1,008 research outputs found
Nonthermal Emission Associated with Strong AGN Outbursts at the Centers of Galaxy Clusters
Recently, strong AGN outbursts at the centers of galaxy clusters have been
found. Using a simple model, we study particle acceleration around a shock
excited by an outburst and estimate nonthermal emission from the accelerated
particles. We show that emission from secondary electrons is consistent with
the radio observations of the minihalo in the Perseus cluster, if there was a
strong AGN outburst >~10^8 yrs ago with an energy of ~1.8x10^62 erg. The
validity of our model depends on the frequency of the large outbursts. We also
estimate gamma-ray emission from the accelerated particles and show that it
could be detected with GLAST.Comment: Accepted for publication in ApJ
Big Bang Nucleosynthesis with Long Lived Charged Massive Particles
We consider Big Bang Nucleosynthesis (BBN) with long lived charged massive
particles. Before decaying, the long lived charged particle recombines with a
light element to form a bound state like a hydrogen atom. This effect modifies
the nuclear reaction rates during the BBN epoch through the modifications of
the Coulomb field and the kinematics of the captured light elements, which can
change the light element abundances. It is possible that the heavier nuclei
abundances such as Li and Be decrease sizably, while the ratios ,
D/H, and He/H remain unchanged. This may solve the current discrepancy
between the BBN prediction and the observed abundance of Li. If future
collider experiments found signals of a long-lived charged particle inside the
detector, the information of its lifetime and decay properties could provide
insights to understand not only the particle physics models but also the
phenomena in the early universe in turn.Comment: 20 pages, 6 figures, published version in Physical Review
Black hole formation and slow-roll inflation
Black hole formation may occur if the spectrum of the curvature perturbation
\zeta increases strongly as the scale decreases. As no such increase is
observed on cosmological scales, black hole formation requires strongly
positive running n' of the spectral index n, though the running might only kick
in below the `cosmological scales' probed by the CMB anisotropy and galaxy
surveys. A concrete and well-motivated way of producing this running is through
the running mass model of slow roll inflation. We obtain a new observational
bound n' < 0.026 on the running provided by this model, improving an earlier
result by a factor two. We also discuss black hole production in more general
scenarios. We show that the usual conditions \epsilon << 1 and |\eta| << 1 are
enough to derive the spectrum {\cal P}_{\zeta}(k), the introduction of higher
order parameters \xi^{2} etc. being optional.Comment: 11 pages, 6 figures, version to apper in JCA
Valence and Na content dependences of superconductivity in NaxCoO2.yH2O
Various samples of sodium cobalt oxyhydrate with relatively large amounts of
Na ions were synthesized by a modified soft-chemical process in which a
NaOH aqueous solution was added in the final step of the procedure. From these
samples, a superconducting phase diagram was determined for a section of a
cobalt valence of +3.48, which was compared with a previously obtained
one of +3.40. The superconductivity was significantly affected by the
isovalent exchanger of Na and HO, rather than by variation of
Co valence, suggesting the presence of multiple kinds of Fermi surface.
Furthermore, the high-field magnetic susceptibility measurements for one sample
up to 30 T indicated an upper critical field much higher than the Pauli limit
supporting the validity of the spin-triplet pairing mechanism.Comment: 4 figures and 1 tabl
The inflating curvaton
The primordial curvature perturbation \zeta may be generated by some curvaton
field \sigma, which is negligible during inflation and has more or less
negligible interactions until it decays. In the current scenario, the curvaton
starts to oscillate while its energy density \rho_\sigma is negligible. We
explore the opposite scenario, in which \rho_\sigma drives a few e-folds of
inflation before the oscillation begins. In this scenario for generating \zeta
it is exceptionally easy to solve the \eta problem; one just has to make the
curvaton a string axion, with anomaly-mediated susy breaking which may soon be
tested at the LHC. The observed spectral index n can be obtained with a
potential V\propto \phi^p for the first inflation; p=1 or 2 is allowed by the
current uncertainty in n but the improvement in accuracy promised by Planck may
rule out p=1. The predictions include (i) running n'\simeq 0.0026 (0.0013) for
p=1 (2) that will probably be observed, (ii) non-gaussianity parameter f_NL
\sim -1 that may be observed, (iii) tensor fraction r is probably too small to
ever observed.Comment: 5 pages, 2 figures, revtex, added important results and comment
Extended supersymmetry and its reduction on a circle with point singularities
We investigate -extended supersymmetry in one-dimensional quantum
mechanics on a circle with point singularities. For any integer ,
supercharges are explicitly constructed in terms of discrete transformations,
and a class of singularities compatible with supersymmetry is clarified. In our
formulation, the supersymmetry can be reduced to -extended supersymmetry for
any integer . The degeneracy of the spectrum and spontaneous supersymmetry
breaking are also studied.Comment: 36 pages, 5 figures, 2 table
A Search for Near-Infrared Emission From the Halo of NGC 5907 at Radii of 10 kpc to 30 kpc
We present a search for near-infrared (3.5-5 micron) emission from baryonic
dark matter in the form of low-mass stars and/or brown dwarfs in the halo of
the nearby edge-on spiral galaxy NGC 5907. The observations were made using a
256 by 256 InSb array with a pixel scale of 17" at the focus of a
liquid-helium-cooled telescope carried above the Earth's atmosphere by a
sounding rocket. In contrast to previous experiments which have detected a halo
around NGC 5907 in the V, R, I, J and K bands at galactic radii 6kpc < r <
10kpc, our search finds no evidence for emission from a halo at 10kpc < r <
30kpc. Assuming a halo mass density scaling as r^(-2), which is consistent with
the flat rotation curves that are observed out to radii of 32kpc, the lower
limit of the mass-to-light ratio at 3.5-5 microns for the halo of NGC 5907 is
250 (2 sigma) in solar units. This is comparable to the lower limit we have
found previously for NGC 4565 (Uemizu et al. 1998). Based on recent models, our
non-detection implies that hydrogen- burning stars contribute < 15% of the mass
of the dark halo of NGC 5907. Our results are consistent with the previous
detection of extended emission at r < 10kpc if the latter is caused by a
stellar population that has been ejected from the disk because of tidal
interactions. We conclude that the dark halo of NGC 5907, which is evident from
rotation curves that extend far beyond 10kpc, is not comprised of hydrogen
burning stars.Comment: 12 pages, LateX, plus 6 ps figures. Accepted by ApJ. minor changes,
added references, corrected typo
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