714 research outputs found
Perturbative QCD Fragmentation Functions for Production of P-wave Mesons with Charm and Beauty
We calculate the leading order QCD fragmentation functions for the production
of -wave charmed beauty mesons. Long-distance effects are factored into two
nonperturbative parameters: the derivative of the radial wavefunction at the
origin and a second parameter related to the probability for a
heavy quark pair that is produced in a color-octet -wave state to form a
color-singlet -wave bound state. The four states and those states
which lie below the flavor threshold eventually all decay into the
ground state through hadronic cascades or by emitting photons. The total
fragmentation probabilities for production of the ground state from
the cascades of the and states are about and
respectively. Thus the direct production of the -wave
states via fragmentation may account for a significant fraction of the
inclusive production rate of the at large transverse momentum in high
energy colliders. Our analytic results for the -wave fragmentation functions
disagree with those obtained earlier in the literature.Comment: 31 pages, Latex file, 1 figure (postscript file appended at the end
Generalized forward scattering amplitudes in QCD at high temperature
We extend to a general class of covariant gauges an approach which relates
the thermal Green functions to forward scattering amplitudes of thermal
particles. A brief discussion of the non-transversality of the thermal gluon
polarization tensor is given in this context. This method is then applied to
the calculation of the ln(T) contributions associated with general
configurations of 2 and 3-point gluon functions. The results are Lorentz
covariant and have the same structure as the ultraviolet divergent
contributions which occur at zero temperature.Comment: 10 pages, 3 figure
Correlation effects in the ground state of trapped atomic Bose gases
We study the effects of many-body correlations in trapped ultracold atomic
Bose gases. We calculate the ground state of the gas using a ground-state
auxiliary-field quantum Monte Carlo (QMC) method [Phys. Rev. E 70, 056702
(2004)]. We examine the properties of the gas, such as the energetics,
condensate fraction, real-space density, and momentum distribution, as a
function of the number of particles and the scattering length. We find that the
mean-field Gross-Pitaevskii (GP) approach gives qualitatively incorrect result
of the kinetic energy as a function of the scattering length. We present
detailed QMC data for the various quantities, and discuss the behavior of GP,
modified GP, and the Bogoliubov method under a local density approximation.Comment: 11 pages, 12 figures, as typeset using REVTEX4. Submitted to Phys.
Rev.
The Free Energy of High Temperature QED to Order From Effective Field Theory
Massless quantum electrodynamics is studied at high temperature and zero
chemical potential. We compute the Debye screening mass to order and
the free energy to order } by an effective field theory approach,
recently developed by Braaten and Nieto. Our results are in agreement with
calculations done in resummed perturbation theory. This method makes it
possible to separate contributions to the free energy from different momentum
scales (order and ) and provides an economical alternative to
computations in the full theory which involves the dressing of internal
propagators.Comment: 10 pages Latex, 6 figure
Hadronic Production of S-wave and P-wave Charmed Beauty Mesons via Heavy Quark Fragmentation
At hadron colliders the dominant production mechanism of mesons
with large transverse momentum is due to parton fragmentation. We compute the
rates and transverse momentum spectra for production of S-wave and P-wave
mesons at the Tevatron via the direct fragmentation of the bottom
antiquark as well as the Altarelli-Parisi induced gluon fragmentation. Since
all the radially and orbitally excited mesons below the
flavor threshold will cascade into the pseudoscalar ground state through
electromagnetic and/or hadronic transitions, they all contribute to the
inclusive production of . The contributions of the excited S-wave and
P-wave states to the inclusive production of are 58 and 23\%,
respectively, and hence significant.Comment: Changes are made in the Discussio
Helicity Probabilities For Heavy Quark Fragmentation Into Excited Mesons
In the fragmentation of a heavy quark into a heavy meson whose light degrees
of freedom have angular momentum , all the helicity probabilities are
completely determined in the heavy quark limit up to a single probability
. We point out that this probability depends on the longitudinal
momentum fraction of the meson and on its transverse momentum
relative to the jet axis. We calculate as a function of scaling
variables corresponding to and for the heavy quark limit of the
perturbative QCD fragmentation functions for quark to fragment into mesons. In this model, the light degrees of freedom prefer to have
their angular momentum aligned transverse to, rather than along, the jet axis.
Implications for the production of excited heavy mesons, like and
, are discussed.Comment: 10 pages, Latex file plus 3 figures with postscript files appended at
the en
Nonuniversal Effects in the Homogeneous Bose Gas
Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te
Power counting and effective field theory for charmonium
We hypothesize that the correct power counting for charmonia is in the
parameter Lambda_QCD/m_c, but is not based purely on dimensional analysis (as
is HQET). This power counting leads to predictions which differ from those
resulting from the usual velocity power counting rules of NRQCD. In particular,
we show that while Lambda_QCD/m_c power counting preserves the empirically
verified predictions of spin symmetry in decays, it also leads to new
predictions which include: A hierarchy between spin singlet and triplet octet
matrix elements in the J/psi system. A quenching of the net polarization in
production at large transverse momentum. No end point enhancement in radiative
decays. We discuss explicit tests which can differentiate between the
traditional and new theories of NRQCD.Comment: 18 pages, 1 figure Replaced plot of the psi polarization parameter
alpha as a function of transverse momentum. Alpha is now closer to zero for
large transverse moment
Semiclassical Corrections to a Static Bose-Einstein Condensate at Zero Temperature
In the mean-field approximation, a trapped Bose-Einstein condensate at zero
temperature is described by the Gross-Pitaevskii equation for the condensate,
or equivalently, by the hydrodynamic equations for the number density and the
current density. These equations receive corrections from quantum field
fluctuations around the mean field. We calculate the semiclassical corrections
to these equations for a general time-independent state of the condensate,
extending previous work to include vortex states as well as the ground state.
In the Thomas-Fermi limit, the semiclassical corrections can be taken into
account by adding a local correction term to the Gross-Pitaevskii equation. At
second order in the Thomas-Fermi expansion, the semiclassical corrections can
be taken into account by adding local correction terms to the hydrodynamic
equations
Finite temperature formalism for nonabelian gauge theories in the physical phase space
We establish a new framework of finite temperature field theory for
Yang-Mills theories in the physical phase space eliminating all unphysical
degrees of freedoms. Relating our method to the imaginary time formalism of
James and Landshoff in temporal axial gauge, we calculate the two-loop pressure
and provide a systematic and unique method to construct the additional vertices
encountered in their approach.Comment: 18 pages, 5 postscript figures, uses revtex, eps
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