26,665 research outputs found
Anisotropic flows from colour strings: Monte-Carlo simulations
By direct Monte-Carlo simulations it is shown that the anisotropic flows can
be successfully described in the colour string picture with fusion and
percolation provided anisotropy of particle emission from the fused string is
taken into account. Quenching of produced particles in the strong colour field
of the string is the basic mechanism for this anisotropy. The concrete
realization of this mechanism is borrowed from the QED. Due to dependence of
this mechanism on the external field strength the found flows grow with energy,
with values for at LHC energies greater by ~15% than at RHIC energies.Comment: New version with a non-static distribution of string
Cumulative particle production as a rare event
The generalization of the Glauber formula for cumulative production events is
derived. On its basis the multiplicity distribution in such events is related
to the one in the minimum bias events. As compared to the rare events of type
, the formula involves a shift in the arguments determined by the
multiplicity from a collision with a cluster of several nucleons.Comment: 11 pages, LaTe
On the Phase Structure of QCD in a Finite Volume
The chiral phase transition in QCD at finite chemical potential and
temperature can be characterized for small chemical potential by its curvature
and the transition temperature. The curvature is accessible to QCD lattice
simulations, which are always performed at finite pion masses and in finite
simulation volumes. We investigate the effect of a finite volume on the
curvature of the chiral phase transition line. We use functional
renormalization group methods with a two flavor quark-meson model to obtain the
effective action in a finite volume, including both quark and meson fluctuation
effects. Depending on the chosen boundary conditions and the pion mass, we find
pronounced finite-volume effects. For periodic quark boundary conditions in
spatial directions, we observe a decrease in the curvature in intermediate
volume sizes, which we interpret in terms of finite-volume quark effects. Our
results have implications for the phase structure of QCD in a finite volume,
where the location of a possible critical endpoint might be shifted compared to
the infinite-volume case.Comment: 11 pages, 3 figures, 4 tables; minor text corrections, one figure
added, appendix added, references added, matches PLB versio
The WSRT wide-field HI survey: II. Local Group features
We have used the WSRT to carry out an unbiased wide-field survey of HI
emission features, achieving an RMS sensitivity of about 18 mJy/Beam at a
velocity resolution of 17 km/s over 1800 deg^2. In this paper we present our HI
detections at negative velocities which could be distinguished from the
Galactic foreground. Fully 29% of the entire survey area has high velocity HI
emission with N_HI exceeding our 3 sigma limit of about 1.5x10^17cm^-2 over 30
km/s. A faint population of discrete HVCs is detected in the immediate vicinity
of M31 which spans a large fraction of the M31 rotation velocity. This class of
features is confined to about 12 deg (160 kpc) projected radius of M31 and
appears to be physically associated. We detect a diffuse northern extension of
the Magellanic Stream (MS) from at least Dec=+20 to +40 deg., which then loops
back toward the south. Recent numerical simulations had predicted just such an
MS extension corresponding to the apo-galacticon portion of the LMC/SMC orbit
at a distance of 125 kpc. A faint bridge of HI emission appears to join the
systemic velocities of M31 with that of M33 and continues beyond M31 to the
north-west. This may be the first detection of HI associated with the warm-hot
intergalactic medium (WHIM). The distribution of peculiar velocity HI
associated with M31 can be described by a projected exponential of 25 kpc
scale-length and 5x10^17cm^-2 peak column density. We present the distribution
function of N_HI in the extended M31 environment, which agrees well with the
low red-shift QSO absorption line data over the range log(N_HI)=17.2 to 21.9.
Our data extend this comparison about two orders of magnitude lower than
previously possible and provide the first image of the Lyman limit absorption
system associated with an L* galaxy. (abridged)Comment: 16 pages, 12 figures, accepted for publication in A&
High-resolution imaging of compact high-velocity clouds (II)
We have imaged five compact high-velocity clouds in HI with arcmin angular-
and km/s spectral-resolution using the WSRT. Supplementary total-power data,
which is fully sensitive to both the cool and warm components of HI, is
available for comparison for all the sources, albeit with angular resolutions
that vary from 3' to 36'. The fractional HI flux in compact CNM components
varies from 4% to 16% in our sample. All objects have at least one local peak
in the CNM column which exceeds about 10^19 cm^-2 when observed with arcmin
resolution. It is plausible that a peak column density of 1-2x10^19 cm^-2 is a
prerequisite for the long-term survival of these sources. One object in our
sample, CHVC120-20-443 (Davies' cloud), lies in close projected proximity to
the disk of M31. This object is characterized by exceptionally broad linewidths
in its CNM concentrations (more than 5 times greater than the median value).
These CNM concentrations lie in an arc on the edge of the source facing the M31
disk, while the diffuse HI component of this source has a position offset in
the direction of the disk. All of these attributes suggest that CHVC120-20-443
is in a different evolutionary state than most of the other CHVCs which have
been studied. Similarly broad CNM linewidths have only been detected in one
other object, CHVC111-07-466, which also lies in the Local Group barycenter
direction and has the most extreme radial velocity known. A distinct
possibility for Davies' cloud seems to be physical interaction of some type
with M31. The most likely form of this interaction might be the ram-pressure or
tidal- stripping by either one of M31's visible dwarf companions, M32 or
NGC205, or else by a dark companion with an associated HI condensation.Comment: 12 pages, 11 (low res.) png figs, accepted for pub. in A&
String Percolation and the Glasma
We compare string percolation phenomenology to Glasma results on particle
rapidity densities, effective string or flux tube intrinsic correlations, the
ridge phenomena and long range forward-backward correlations. Effective strings
may be a tool to extend the Glasma to the low density QCD regime. A good
example is given by the minimum of the negative binomial distribution parameter
k expected to occur at low energy/centrality.Comment: Submitted to Phys. Lett
Density saturation and the decrease of the normalised width of the multiplicity distribution in high energy pp collisions
It is experimentally observed that the width of the KNO multiplicity
distribution --or the negative binomial parameter 1/k-- for pp collisions, in
the energy region 10 to 1800 GeV, is an increasing function of the energy. We
argue that in models with parton or string saturation such trend will necessary
change: at some energy the distribution will start to become narrower. In the
framework of percolating strings, we have estimated the change to occur at an
energy of the order of 5--10 TeV.Comment: 10 pages, 4 figures, uses elsart and amsmath; comparison with some
other models was added; version accepted by PL
Supply shocks, demand shocks, and labor market fluctuations
The authors use structural vector autoregressions to analyze the responses of worker flows, job flows, vacancies, and hours to demand and supply shocks. They identify these shocks by restricting the short-run responses of output and the price level. On the demand side, they disentangle a monetary and nonmonetary shock by restricting the response of the interest rate. The responses of labor market variables are similar across shocks: Expansionary shocks increase job creation, the job-finding rate, vacancies, and hours; and they decrease job destruction and the separation rate. Supply shocks have more persistent effects than demand shocks. Demand and supply shocks are equally important in driving business cycle fluctuations of labor market variables. The authors' findings for demand shocks are robust to alternative identification schemes involving the response of labor productivity at different horizons. Supply shocks identified by restricting productivity generate a higher fraction of impulse responses inconsistent with standard search and matching models.Labor supply ; Labor market ; Business cycles
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