1,595 research outputs found
Antibaryon density in the central rapidity region of a heavy ion collision
We consider (anti-)baryons production in heavy ion collisions as production
of topological defects during the chiral phase transition. Non-zero quark
masses which explicitly break chiral symmetry supress the (anti-)baryon
density. Hardly any (anti-)baryons will be produced in the central rapidity
region of a heavy ion collision.Comment: 3 pages in RevTex, 3 .ps file
Dynamic prediction in breast cancer:proving feasibility in clinical practice using the TEAM trial
The Johnson-Segalman model with a diffusion term in Couette flow
We study the Johnson-Segalman (JS) model as a paradigm for some complex
fluids which are observed to phase separate, or ``shear-band'' in flow. We
analyze the behavior of this model in cylindrical Couette flow and demonstrate
the history dependence inherent in the local JS model. We add a simple gradient
term to the stress dynamics and demonstrate how this term breaks the degeneracy
of the local model and prescribes a much smaller (discrete, rather than
continuous) set of banded steady state solutions. We investigate some of the
effects of the curvature of Couette flow on the observable steady state
behavior and kinetics, and discuss some of the implications for metastability.Comment: 14 pp, to be published in Journal of Rheolog
Quarkonium momentum distributions in photoproduction and B decay
According to our present understanding many production processes
proceed through a coloured state followed by the emission of soft
particles in the quarkonium rest frame. The kinematic effect of soft particle
emission is usually a higher-order effect in the non-relativistic expansion,
but becomes important near the kinematic endpoint of quarkonium energy
(momentum) distributions. In an intermediate region a systematic resummation of
the non-relativistic expansion leads to the introduction of so-called `shape
functions'. In this paper we provide an implementation of the kinematic effect
of soft gluon emission which is consistent with the non-relativistic shape
function formalism in the region where it is applicable and which models the
extreme endpoint region. We then apply the model to photoproduction of
and production in meson decay. A satisfactory description of
decay data is obtained. For inelastic charmonium photoproduction we conclude
that a sensible comparison of theory with data requires a transverse momentum
cut larger than the currently used 1 GeV.Comment: latex, 45 pages; (v2) some typos corrected, version to appear in PR
QCD analysis of inclusive B decay into charmonium
We compute the decay rates and -energy distributions of mesons into
the final state , where can be any one of the -wave or -wave
charmonia, at next-to-leading order in the strong coupling. We find that a
significant fraction of the observed , and must be
produced through pairs in a colour octet state and should therefore
be accompanied by more than one light hadron. At the same time we obtain
stringent constraints on some of the long-distance parameters for colour octet
production.Comment: 40 pages, RevTeX, 4 figure
Hyperon Polarization in the Constituent Quark Model
We consider mechanism for hyperon polarization in inclusive production. The
main role belongs to the orbital angular momentum and polarization of the
strange quark-antiquark pairs in the internal structure of the constituent
quarks. We consider a nucleon as a core consisting of the constituent quarks
embedded into quark condensate. The nonperturbative hadron structure is based
on the results of chiral quark models.Comment: 14 pages, LaTeX, 2 Figures, References adde
The properties of the local spiral arms from RAVE data: two-dimensional density wave approach
Using the RAVE survey, we recently brought to light a gradient in the mean
galactocentric radial velocity of stars in the extended solar neighbourhood.
This gradient likely originates from non-axisymmetric perturbations of the
potential, among which a perturbation by spiral arms is a possible explanation.
Here, we apply the traditional density wave theory and analytically model the
radial component of the two-dimensional velocity field. Provided that the
radial velocity gradient is caused by relatively long-lived spiral arms that
can affect stars substantially above the plane, this analytic model provides
new independent estimates for the parameters of the Milky Way spiral structure.
Our analysis favours a two-armed perturbation with the Sun close to the inner
ultra-harmonic 4:1 resonance, with a pattern speed \Omega_p=18.6^{+0.3}_{-0.2}
km/s/kpc and a small amplitude A=0.55 \pm 0.02% of the background potential
(14% of the background density). This model can serve as a basis for numerical
simulations in three dimensions, additionally including a possible influence of
the galactic bar and/or other non-axisymmetric modes.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Plasmon oscillations in ellipsoid nanoparticles: beyond dipole approximation
The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have
been studied within the framework of the quasistatic approximation. A general
method has been proposed for finding the analytical expressions describing the
potential and frequencies of the plasmon oscillations of an arbitrary
multipolarity order. The analytical expressions have been derived for an
electric potential and plasmon oscillation frequencies of the first 24 modes.
Other higher orders plasmon modes are investigated numerically.Comment: 33 pages, 12 figure
Lattice QCD at the physical point: Simulation and analysis details
We give details of our precise determination of the light quark masses
m_{ud}=(m_u+m_d)/2 and m_s in 2+1 flavor QCD, with simulated pion masses down
to 120 MeV, at five lattice spacings, and in large volumes. The details concern
the action and algorithm employed, the HMC force with HEX smeared clover
fermions, the choice of the scale setting procedure and of the input masses.
After an overview of the simulation parameters, extensive checks of algorithmic
stability, autocorrelation and (practical) ergodicity are reported. To
corroborate the good scaling properties of our action, explicit tests of the
scaling of hadron masses in N_f=3 QCD are carried out. Details of how we
control finite volume effects through dedicated finite volume scaling runs are
reported. To check consistency with SU(2) Chiral Perturbation Theory the
behavior of M_\pi^2/m_{ud} and F_\pi as a function of m_{ud} is investigated.
Details of how we use the RI/MOM procedure with a separate continuum limit of
the running of the scalar density R_S(\mu,\mu') are given. This procedure is
shown to reproduce the known value of r_0m_s in quenched QCD. Input from
dispersion theory is used to split our value of m_{ud} into separate values of
m_u and m_d. Finally, our procedure to quantify both systematic and statistical
uncertainties is discussed.Comment: 45 page
Covariant and Heavy Quark Symmetric Quark Models
There exist relativistic quark models (potential or MIT-bag) which satisfy
the heavy quark symmetry (HQS) relations among meson decay constants and form
factors. Covariant construction of the momentum eigenstates, developed here,
can correct for spurious center-of-mass motion contributions.Proton form factor
and M1 transitions in quarkonia are calculated. Explicit expression for the
Isgur-Wise function is found and model determined deviations from HQS are
studied. All results depend on the model parameters only. No additional ad hoc
assumptions are needed.Comment: 34 pages (2 figures not included but avaliable upon request), LATEX,
(to be published in Phys.Rev.D
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