790 research outputs found
The NJL-jet model for quark fragmentation functions
A description of fragmentation functions which satisfy the momentum and
isospin sum rules is presented in an effective quark theory. Concentrating on
the pion fragmentation function, we first explain why the elementary (lowest
order) fragmentation process q --> q \pi is completely inadequate to describe
the empirical data, although the "crossed" process \pi --> q \bar{q} describes
the quark distribution functions in the pion reasonably well. Taking into
account cascade-like processes in a generalized jet-model approach, we then
show that the momentum and isospin sum rules can be satisfied naturally,
without the introduction of ad hoc parameters. We present results for the
Nambu--Jona-Lasinio (NJL) model in the invariant mass regularization scheme and
compare them with the empirical parametrizations. We argue that the NJL-jet
model, developed herein, provides a useful framework with which to calculate
the fragmentation functions in an effective chiral quark theory.Comment: 21 pages, 7 figure
Quark-Jet model for transverse momentum dependent fragmentation functions
In order to describe the hadronization of polarized quarks, we discuss an
extension of the quark-jet model to transverse momentum dependent fragmentation
functions. The description is based on a product ansatz, where each factor in
the product represents one of the transverse momentum dependent splitting
functions, which can be calculated by using effective quark theories. The
resulting integral equations and sum rules are discussed in detail for the case
of inclusive pion production. In particular, we demonstrate that the
3-dimensional momentum sum rules are satisfied naturally in this transverse
momentum dependent quark-jet model. Our results are well suited for numerical
calculations in effective quark theories, and can be implemented in Monte-Carlo
simulations of polarized quark hadronization processes.Comment: 19 pages, 4 figure
Calculating Kaon Fragmentation Functions from NJL-Jet Model
The Nambu--Jona-Lasinio (NJL) - Jet model provides a sound framework for
calculating the fragmentation functions in an effective chiral quark theory,
where the momentum and isospin sum rules are satisfied without the introduction
of ad hoc parameters. Earlier studies of the pion fragmentation functions using
the NJL model within this framework showed qualitative agreement with the
empirical parameterizations. Here we extend the NJL-Jet model by including the
strange quark. The corrections to the pion fragmentation functions and
corresponding kaon fragmentation functions are calculated using the elementary
quark to quark-meson fragmentation functions from NJL. The results for the kaon
fragmentation functions exhibit a qualitative agreement with the empirical
parameterizations, while the unfavored strange quark fragmentation to pions is
shown to be of the same order of magnitude as the unfavored light quark's. The
results of these studies are expected to provide important guidance for the
analysis of a large variety of semi-inclusive data.Comment: 9 pages, 14 figure
Liquid-gas phase transition in nuclear matter including strangeness
We apply the chiral SU(3) quark mean field model to study the properties of
strange hadronic matter at finite temperature. The liquid-gas phase transition
is studied as a function of the strangeness fraction. The pressure of the
system cannot remain constant during the phase transition, since there are two
independent conserved charges (baryon and strangeness number). In a range of
temperatures around 15 MeV (precise values depending on the model used) the
equation of state exhibits multiple bifurcates. The difference in the
strangeness fraction between the liquid and gas phases is small when they
coexist. The critical temperature of strange matter turns out to be a
non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure
Spin dependent parton distributions and structure functions
Nuclear parton distributions and structure functions are determined in an
effective chiral quark theory. We also discuss an extension of our model to
fragmentation functions.Comment: To appear in the proceedings of the 20th European Conference on
Few-Body Problems in Physics, Pisa, September 10-14, 200
Stellar Velocity Dispersion Measurements in High-Luminosity Quasar Hosts and Implications for the AGN Black Hole Mass Scale
We present new stellar velocity dispersion measurements for four luminous
quasars with the NIFS instrument and the ALTAIR laser guide star adaptive
optics system on the Gemini North 8-m telescope. Stellar velocity dispersion
measurements and measurements of the supermassive black hole masses in luminous
quasars are necessary to investigate the coevolution of black holes and
galaxies, trace the details of accretion, and probe the nature of feedback. We
find that higher-luminosity quasars with higher-mass black holes are not offset
with respect to the MBH-sigma relation exhibited by lower-luminosity AGNs with
lower-mass black holes, nor do we see correlations with galaxy morphology. As
part of this analysis, we have recalculated the virial products for the entire
sample of reverberation-mapped AGNs and used these data to redetermine the mean
virial factor hfi that places the reverberation data on the quiescent
M_BH-sigma relation. With our updated measurements and new additions to the AGN
sample, we obtain = 4.31 +/- 1.05, which is slightly lower than, but
consistent with, most previous determinations.Comment: Accepted for publication in ApJ. For a brief video highlighting the
results of this paper, see: http://www.youtube.com/watch?v=Mxx80aOVw1
A Revised Broad-Line Region Radius and Black Hole Mass for the Narrow-Line Seyfert 1 NGC 4051
We present the first results from a high sampling rate, multi-month
reverberation mapping campaign undertaken primarily at MDM Observatory with
supporting observations from telescopes around the world. The primary goal of
this campaign was to obtain either new or improved Hbeta reverberation lag
measurements for several relatively low luminosity AGNs. We feature results for
NGC 4051 here because, until now, this object has been a significant outlier
from AGN scaling relationships, e.g., it was previously a ~2-3sigma outlier on
the relationship between the broad-line region (BLR) radius and the optical
continuum luminosity - the R_BLR-L relationship. Our new measurements of the
lag time between variations in the continuum and Hbeta emission line made from
spectroscopic monitoring of NGC 4051 lead to a measured BLR radius of R_BLR =
1.87 (+0.54 -0.50) light days and black hole mass of M_BH = 1.73 (+0.55 -0.52)
x 10^6 M_sun. This radius is consistent with that expected from the R_BLR-L
relationship, based on the present luminosity of NGC 4051 and the most current
calibration of the relation by Bentz et al. (2009a). We also present a
preliminary look at velocity-resolved Hbeta light curves and time delay
measurements, although we are unable to reconstruct an unambiguous
velocity-resolved reverberation signal.Comment: 38 pages, 7 figures, accepted for publication in ApJ, changes from v1
reflect suggestions from anonymous refere
- …