777 research outputs found
Dissipation of Magnetohydrodynamic Waves on Energetic Particles: Impact on Interstellar Turbulence and Cosmic Ray Transport
The physical processes involved in diffusion of Galactic cosmic rays in the
interstellar medium are addressed. We study the possibility that the nonlinear
MHD cascade sets the power-law spectrum of turbulence which scatters charged
energetic particles. We find that the dissipation of waves due to the resonant
interaction with cosmic ray particles may terminate the Kraichnan-type cascade
below wavelengths 10^13 cm. The effect of this wave dissipation has been
incorporated in the GALPROP numerical propagation code in order to asses the
impact on measurable astrophysical data. The energy-dependence of the
cosmic-ray diffusion coefficient found in the resulting self-consistent model
may explain the peaks in the secondary to primary nuclei ratios observed at
about 1 GeV/nucleon.Comment: 15 pages, 20 figures, 1 table, emulateapj.cls; To be published in ApJ
10 May 2006, v.64
Explosive Nucleosynthesis in GRB Jets Accompanied by Hypernovae
Two-dimensional hydrodynamic simulations are performed to investigate
explosive nucleosynthesis in a collapsar using the model of MacFadyen and
Woosley (1999). It is shown that 56Ni is not produced in the jet of the
collapsar sufficiently to explain the observed amount of a hypernova when the
duration of the explosion is \sim 10 sec, which is considered to be the typical
timescale of explosion in the collapsar model. Even though a considerable
amount of 56Ni is synthesized if all explosion energy is deposited initially,
the opening angles of the jets become too wide to realize highly relativistic
outflows and gamma-ray bursts in such a case. From these results, it is
concluded that the origin of 56Ni in hypernovae associated with GRBs is not the
explosive nucleosynthesis in the jet. We consider that the idea that the origin
is the explosive nucleosynthesis in the accretion disk is more promising. We
also show that the explosion becomes bi-polar naturally due to the effect of
the deformed progenitor. This fact suggests that the 56Ni synthesized in the
accretion disk and conveyed as outflows are blown along to the rotation axis,
which will explain the line features of SN 1998bw and double peaked line
features of SN 2003jd. Some fraction of the gamma-ray lines from 56Ni decays in
the jet will appear without losing their energies because the jet becomes
optically thin before a considerable amount of 56Ni decays as long as the jet
is a relativistic flow. We show that abundance of nuclei whose mass number \sim
40 in the ejecta depends sensitively on the energy deposition rate. So it may
be determined by observations of chemical composition in metal poor stars which
model is the proper one as a model of a gamma-ray burst accompanied by a
hypernova.Comment: 29 pages with 16 figures. ApJ, accepte
Numerical Study on GRB-Jet Formation in Collapsars
Two-dimensional magnetohydrodynamic simulations are performed using the
ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB
jet, taking account of realistic equation of state, neutrino cooling and
heating processes, magnetic fields, and gravitational force from the central
black hole and self gravity. It is found that neutrino heating processes are
not so efficient to launch a jet in this study. It is also found that a jet is
launched mainly by B_\phi fields that are amplified by the winding-up effect.
However, since the ratio of total energy relative to the rest mass energy in
the jet is not so high as several hundred, we conclude that the jets seen in
this study are not be a GRB jet. This result suggests that general relativistic
effects, which are not included in this study, will be important to generate a
GRB jet. Also, the accretion disk with magnetic fields may still play an
important role to launch a GRB jet, although a simulation for much longer
physical time (\sim 10-100 s) is required to confirm this effect. It is shown
that considerable amount of 56Ni is synthesized in the accretion disk. Thus
there will be a possibility for the accretion disk to supply sufficient amount
of 56Ni required to explain the luminosity of a hypernova. Also, it is shown
that neutron-rich matter due to electron captures with high entropy per baryon
is ejected along the polar axis. Moreover, it is found that the electron
fraction becomes larger than 0.5 around the polar axis near the black hole by
\nu_e capture at the region. Thus there will be a possibility that r-process
and r/p-process nucleosynthesis occur at these regions. Finally, much neutrons
will be ejected from the jet, which suggests that signals from the neutron
decays may be observed as the delayed bump of afterglow or gamma-rays.Comment: 54 pages with 19 postscript figures. Accepted for publication in ApJ.
High resolution version is available at
http://www2.yukawa.kyoto-u.ac.jp/~nagataki/collapsar.pd
NLO merging in tt+jets
In this talk the application of the recently introduced methods to merge NLO
calculations of successive jet multiplicities to the production of top pairs in
association with jets will be discussed, in particular a fresh look is taken at
the top quark forward-backward asymmetries. Emphasis will be put on the
achieved theoretical accuracy and the associated perturbative and
non-perturbative error estimates.Comment: 6 pages, 3 figures, proceedings contribution for EPS 2013, Stockholm,
17-24 Jul
QCD Radiation in the Production of High s-hat Final States
In the production of very heavy final states - high Mandelstam s-hat - extra
QCD radiation can play a significant role. By comparing several different
parton shower approximations to results obtained with fixed-order perturbation
theory, we quantify the degree to which these approaches agree (or disagree),
focussing on initial state radiation above pT = 50 GeV, for top pair production
at the Tevatron and at the LHC, and for SUSY pair production at the LHC.
Special attention is paid to ambiguities associated with the choice of the
maximum value of the ordering variable in parton shower models.Comment: Invited talk at 2005 International Linear Collider Physics and
Detector Workshop and Second ILC Accelerator Workshop, Snowmass, CO
(Snowmass05), 5 pages, LaTeX, 3 eps figure
Constraints on non-thermal Dark Matter from Planck lensing extraction
Distortions of CMB temperature and polarization anisotropy maps caused by
gravitational lensing, observable with high angular resolution and sensitivity,
can be used to constrain the sterile neutrino mass, offering several advantages
against the analysis based on the combination of CMB, LSS and Ly\alpha forest
power spectra. As the gravitational lensing effect depends on the matter
distribution, no assumption on light-to-mass bias is required. In addition,
unlike the galaxy clustering and Ly\alpha forest power spectra, the projected
gravitational potential power spectrum probes a larger range of angular scales,
the non-linear corrections being required only at very small scales. Taking
into account the changes in the time-temperature relation of the primordial
plasma and the modification of the neutrino thermal potential, we compute the
projected gravitational potential power spectrum and its correlation with the
temperature in the presence of DM sterile neutrino. We show that the
cosmological parameters are generally not biased when DM sterile neutrino is
included. From this analysis we found a lower limit on DM sterile neutrino mass
m_s >2.08 keV at 95% CL, consistent with the lower mass limit obtained from the
combined analysis of CMB, SDSS 3D power spectrum and SDSS Ly\alpha forest power
spectrum ( keV). We conclude that although the information that
can be obtained from lensing extraction is rather limited due to the high level
of the lensing noise of Planck experiment, weak lensing of CMB offers a
valuable alternative to constrain the dark matter sterile neutrino mass.Comment: 15 pages, 6 figure
Determinantes macroeconómicos de los flujos migratorios peruanos
The objective of this paper is to determine the variables associated with the weight that Peruvian immigration has in the total immigration in Chile for the period 2005-2014. The initial hypothesis is that the Peruvian migratory flow has a social and economic component. The results showed that an increase in the Human Development Index (HDI) in favor of Chile increases the migratory flow. On the other hand, a larger education budget in favor of Chile decreases the migratory flow of Peruvian citizens.El objetivo de este trabajo es determinar las variables asociadas al peso que la inmigración peruana tiene en el conjunto de la inmigración total en Chile para el período 2005-2014. La hipótesis de inicio es que el flujo migratorio peruano tiene un componente social y económico. Los resultados pusieron de manifiesto que un incremento en el Índice de Desarrollo Humano (IDH) a favor de Chile aumenta el flujo migratorio. Por otro lado, un mayor presupuesto en educación a favor de Chile, disminuye el flujo migratorio de ciudadanos peruanos
Report of the 2005 Snowmass Top/QCD Working Group
This report discusses several topics in both top quark physics and QCD at an
International Linear Collider (ILC). Issues such as measurements at the
threshold, including both theoretical and machine requirements, and
the determination of electroweak top quark couplings, are reviewed. New results
concerning the potential of a 500 GeV collider for measuring
couplings and the top quark Yukawa coupling are presented. The status of higher
order QCD corrections to jet production cross sections, heavy quark form
factors, and longitudinal gauge boson scattering, needed for percent-level
studies at the ILC, are reviewed. A new study of the measurement of the
hadronic structure of the photon at a collider is presented. The
effects on top quark properties from several models of new physics, including
composite models, Little Higgs theories, and CPT violation, are studied.Comment: 39 pages, many figs; typos fixed and refs added. Contributed to the
2005 International Linear Collider Physics and Detector Workshop and 2nd ILC
Accelerator Workshop, Snowmass, Colorado, 14-27 Aug 200
Constraining Light Gravitino Mass from Cosmic Microwave Background
We investigate the possibilities of constraining the light gravitino mass
m_{3/2} from future cosmic microwave background (CMB) surveys. A model with
light gravitino with the mass m_{3/2}<O(10) eV is of great interest since it is
free from the cosmological gravitino problem and, in addition, can be
compatible with many baryogenesis/leptogenesis scenarios such as the thermal
leptogenesis. We show that the lensing of CMB anisotropies can be a good probe
for m_{3/2} and obtain an expected constraint on m_{3/2} from precise
measurements of lensing potential in the future CMB surveys, such as the
PolarBeaR and CMBpol experiments. If the gravitino mass is m_{3/2}=1 eV, we
will obtain the constraint for the gravitino mass as m_{3/2} < 3.2 eV (95%
C.L.) for the case with Planck+PolarBeaR combined and
m_{3/2}=1.04^{+0.22}_{-0.26} eV (68% C.L.) for CMBpol. The issue of Bayesian
model selection is also discussed.Comment: 22 pages, 6 figures, 7 tables, references are added, accepted for
publication in JCA
Discovery of GeV Emission from the Circinus galaxy with the Fermi-LAT
We report the discovery of gamma-ray emission from the Circinus galaxy using
the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope.
Circinus is a nearby (~4 Mpc) starburst with a heavily obscured Seyfert-type
active nucleus, bipolar radio lobes perpendicular to the spiral disk, and
kpc-scale jet-like structures. Our analysis of 0.1-100 GeV events collected
during 4 years of LAT observations reveals a significant (~ 7.3 sigma) excess
above the background. We find no indications of variability or spatial
extension beyond the LAT point-spread function. A power-law model used to
describe the 0.1-100 GeV gamma-ray spectrum yields a flux of
(18.8+/-5.8)x10^{-9} ph cm^{-2} s^{-1} and photon index 2.19+/-0.12,
corresponding to an isotropic gamma-ray luminosity of 3 x 10^{40} erg s^{-1}.
This observed gamma-ray luminosity exceeds the luminosity expected from
cosmic-ray interactions in the interstellar medium and inverse Compton
radiation from the radio lobes. Thus the origin of the GeV excess requires
further investigation.Comment: 7 pages, 7 figures, accepted for publication in the Astrophysical
Journa
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