10,231 research outputs found
Iterated Monoidal Categories
We develop a notion of iterated monoidal category and show that this notion
corresponds in a precise way to the notion of iterated loop space. Specifically
the group completion of the nerve of such a category is an iterated loop space
and free iterated monoidal categories give rise to finite simplicial operads of
the same homotopy type as the classical little cubes operads used to
parametrize the higher H-space structure of iterated loop spaces. Iterated
monoidal categories encompass, as a special case, the notion of braided tensor
categories, as used in the theory of quantum groups.Comment: 55 pages, 3 PostScript figure
Shadowing and Absorption Effects on J/psi Production in dA Collisions
We study medium modifications of J/psi production in cold nuclear media in
deuterium-nucleus collisions. We discuss several parameterizations of the
modifications of the parton densities in the nucleus, known as shadowing, an
initial-state effect. We also include absorption of the produced J/psi by
nucleons, a final-state effect. Both spatially homogeneous and inhomogeneous
shadowing and absorption are considered. We use the number of binary
nucleon-nucleon collisions as a centrality measure. Results are presented for
d+Au collisions at sqrt{S_{NN}} = 200 GeV and for d+Pb collisions at
sqrt{S_{NN}} = 6.2 TeV. To contrast the centrality dependence in pA and dA
collisions, we also present pPb results at sqrt{S_{NN}} = 8.8 TeV.Comment: 22 pages, 11 figures, uses revte
Dissociation rates of J/psi's with comoving mesons - thermal vs. nonequilibrium scenario
We study J/psi dissociation processes in hadronic environments. The validity
of a thermal meson gas ansatz is tested by confronting it with an alternative,
nonequilibrium scenario. Heavy ion collisions are simulated in the framework of
the microscopic transport model UrQMD, taking into account the production of
charmonium states through hard parton-parton interactions and subsequent
rescattering with hadrons. The thermal gas and microscopic transport scenarios
are shown to be very dissimilar. Estimates of J/psi survival probabilities
based on thermal models of comover interactions in heavy ion collisions are
therefore not reliable.Comment: 12 pages, 6 figure
The last orbit of binary black holes
We have used our new technique for fully numerical evolutions of orbiting
black-hole binaries without excision to model the last orbit and merger of an
equal-mass black-hole system. We track the trajectories of the individual
apparent horizons and find that the binary completed approximately one and a
third orbits before forming a common horizon. Upon calculating the complete
gravitational radiation waveform, horizon mass, and spin, we find that the
binary radiated 3.2% of its mass and 24% of its angular momentum. The early
part of the waveform, after a relatively short initial burst of spurious
radiation, is oscillatory with increasing amplitude and frequency, as expected
from orbital motion. The waveform then transitions to a typical `plunge'
waveform; i.e. a rapid rise in amplitude followed by quasinormal ringing. The
plunge part of the waveform is remarkably similar to the waveform from the
previously studied `ISCO' configuration. We anticipate that the plunge
waveform, when starting from quasicircular orbits, has a generic shape that is
essentially independent of the initial separation of the binary.Comment: 5 pages, 5 figures, revtex
Chromospheric CaII Emission in Nearby F, G, K, and M stars
We present chromospheric CaII activity measurements, rotation periods and
ages for ~1200 F-, G-, K-, and M- type main-sequence stars from ~18,000
archival spectra taken at Keck and Lick Observatories as a part of the
California and Carnegie Planet Search Project. We have calibrated our
chromospheric S values against the Mount Wilson chromospheric activity data.
From these measurements we have calculated median activity levels and derived
R'HK, stellar ages, and rotation periods for 1228 stars, ~1000 of which have no
previously published S values. We also present precise time series of activity
measurements for these stars.Comment: 62 pages, 7 figures, 1 table. Second (extremely long) table is
available at http://astro.berkeley.edu/~jtwright/CaIIdata/tab1.tex Accepted
by ApJ
Sea flavor content of octet baryons and intrinsic five-quark Fock states
Sea quark contents of the octet baryons are investigated by employing an
extended chiral constituent quark approach, which embodies higher Fock
five-quark components in the baryons wave-functions. The well-known flavor
asymmetry of the nucleon sea , is used as input to predict the
probabilities of , and in the nucleon, ,
and baryons, due to the intrinsic five-quark components in the
baryons wave functions.Comment: 22 page
The Influence of Advection on the Short Term CO 2 -Budget in and Above a Forest Canopy
An experimental micrometeorological set-up was established at the CARBOEURO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation of the vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two auxiliary towers to measure horizontal and vertical CO2 and H2O gradients through the canopy, and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m was established. It is shown that under stable (nighttime) conditions the mean advective fluxes have magnitudes on the same order as the daily eddy covariance (EC) flux, which implies that they play a significant, but not yet fully understood, role in the carbon budget equation. The two advective fluxes are opposite and seem to cancel each other at night (at least for these measurements). During the day, vertical advection tends to zero, while horizontal advection is still present implying a flow of CO2 out of the control volume. From our measurements, a mean daily gain of 2.2 gC m−2 d−1 for the horizontal advection and a mean daily loss of 2.5 gC m−2d−1 for the vertical advection is calculated for a period of 20 days. However the large scatter of the advective fluxes has to be further investigated. It is not clear yet whether the large variability is natural or due to measurement errors and conceptual deficiencies of the experiment. Similar results are found in the few comparable studie
The influence of advection on the short term CO2 budget in and above a forest canopy
An experimental micrometeorological set-up was established at the CARBOEU-RO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation ofthe vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two aux-iliary towers to measure horizontal and vertical CO 2 and H 2 O gradients through the canopy,and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m wasestablished. It is shown that under stable (nighttime) conditions the mean advective fluxeshave magnitudes on the same order as the daily eddy covariance (EC) flux, which implies thatthey play a significant, but not yet fully understood, role in the carbon budget equation. Thetwo advective fluxes are opposite and seem to cancel each other at night (at least for thesemeasurements). During the day, vertical advection tends to zero, while horizontal advection isstill present implying a flow of CO 2 out of the control volume. From our measurements, amean daily gain of 2.2 gC m-2 d-1for the horizontal advection and a mean daily loss of2.5 gC m-2 d-1 for the vertical advection is calculated for a period of 20 days. However thelarge scatter of the advective fluxes has to be further investigated. It is not clear yet whether thelarge variability is natural or due to measurement errors and conceptual deficiencies of theexperiment. Similar results are found in the few comparable studies
Fireballs from Quark Stars in the CFL Phase: Application to Gamma Ray Bursters
Recent studies of photon-generation mechanisms in the color-superconducting
Color-Flavor Locked (CFL) phase of dense quark matter have found gamma-ray
emissivities in excess of ~ 10^{50} erg cm^{-3} s^{-1} for temperatures in the
10-30 MeV range. We suggest that this property can trigger gamma-ray bursts
(GRBs) and associated fireballs at the surface of hypothetical hot (newly born)
quark stars with an energy release of up to 10^{48}-10^{50} erg within a
fraction of a millisecond. If surrounded by an accretion disk following its
formation, the star's bursting activity can last from tens of milliseconds to
hundreds of seconds releasing up to 10^{52} erg in total energy. We discuss
typical features of observed GRBs within our model and explain how quark stars
in the CFL phase might constitute natural candidates for corresponding inner
engines.Comment: 8 journal pages, 6 figures. Accepted for publication in the
Astrophysical Journa
Research in particles and fields
The astrophysical aspects of cosmic and gamma rays and the radiation environment of the Earth and other planets investigated by means of energetic particle detector systems flown on spacecraft and balloons are discussed. The theory of particles and fields in space is also addressed with particular emphasis on models of Saturn's magnetic field
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