259 research outputs found
Bosonization in Particle Physics
Path integral techniques in collective fields are shown to be a useful
analytical tool to reformulate a field theory defined in terms of microscopic
quark (gluon) degrees of freedom as an effective theory of collective boson
(meson) fields. For illustrations, the path integral bosonization approach is
applied to derive a (non)linear sigma model from a Nambu-Jona-Lasinio (NJL)
quark model. The method can be extended to include higher order derivative
terms in meson fields or heavy-quark symmetries. It is also approximately
applicable to QCD.Comment: 12 pages, LaTeX, uses lamuphys.sty, 5 LaTeX figures, talk given at
the Workshop "Field Theoretical Tools in Polymer and Particle Physics",
University Wuppertal, June 17-19, 199
Weak decays of the B_c meson to charmonium and D mesons in the relativistic quark model
Semileptonic and nonleptonic decays of the B_c meson to charmonium and D
mesons are studied in the framework of the relativistic quark model. The decay
form factors are explicitly expressed through the overlap integrals of the
meson wave functions in the whole accessible kinematical range. The
relativistic meson wave functions are used for the calculation of the decay
rates. The obtained results are compared with the predictions of other
approaches.Comment: 27 pages, 17 figures, 1 figure and 1 reference added, version to
appear in Phys. Rev.
Quark and pion condensation in a chromomagnetic background field
The general features of quark and pion condensation in dense quark matter
with flavor asymmetry have been considered at finite temperature in the
presence of a chromomagnetic background field modelling the gluon condensate.
In particular, pion condensation in the case of a constant abelian
chromomagnetic field and zero temperature has been studied both analytically
and numerically. Under the influence of the chromomagnetic background field the
effective potential of the system is found to have a global minimum for a
finite pion condensate even for small values of the effective quark coupling
constant. In the strong field limit, an effective dimensional reduction has
been found to take place.Comment: 17 pages, 6 figure
The doubly heavy baryons
We present the results for the masses of the doubly heavy baryons
and where obtained in the framework of the simple
approximation within the nonperturbative string approach.Comment: 4 pages, 1 EPS fig., using espcrc2.sty package. Talk presented by
I.M.Narodetskii at the 5th International Conference on Hyperon, Charm and
Beauty Hadrons, Vancouver, Canada, June 200
The Influence of an External Chromomagnetic Field on Color Superconductivity
We study the competition of quark-antiquark and diquark condensates under the
influence of an external chromomagnetic field modelling the gluon condensate
and in dependence on the chemical potential and temperature. As our results
indicate, an external chromomagnetic field might produce remarkable qualitative
changes in the picture of the color superconducting (CSC) phase formation. This
concerns, in particular, the possibility of a transition to the CSC phase and
diquark condensation at finite temperature.Comment: 27 pages, RevTex, 8 figures; the version accepted for the publication
in PRD (few references added; new numerical results added; main conclusions
are not changed
Commissioning and performance characteristics of a pre-clinical image-guided radiotherapy system
Characteristics of a small-animal radiotherapy device, the X-RAD SmART, are described following commissioning of the
device for pre-clinical radiotherapy research. Performance characteristics were assessed using published standards and compared with previous results published for similar systems. Operational radiation safety was established. Device X-ray beam
quality and output dose-rate were found to be consistent with those reported for similar devices. Output steadily declined over
18 months though remained within tolerance levels. There is considerable variation in output factor across the international
installations for the smallest feld size (varying by more than 30% for 2.5 mm diameter felds). Measured depth dose and
profle data was mostly consistent with that published, with some diferences in penumbrae and generally reduced fatness.
Target localisation is achieved with an imaging panel and with automatic corrections for panel fex and device mechanical
instability, targeting within 0.2 mm is achievable. The small-animal image-guided radiotherapy platform has been implemented and assessed and found to perform as specifed. The combination of kV energy and high spatial precision make it
suitable for replicating clinical dose distributions at the small-animal scale, though dosimetric uncertainties for the narrowest
felds need to be acknowledged
Semileptonic B decays into even parity charmed mesons
By using a constituent quark model we compute the form factors relevant to
semileptonic transitions of B mesons into low-lying p-wave charmed mesons. We
evaluate the q^2 dependence of these form factors and compare them with other
model calculations. The Isgur-Wise functions tau(1/2) and tau(3/2) are also
obtained in the heavy quark limit of our results.Comment: 11 pages, 2 figure
Pion condensation of quark matter in the static Einstein universe
In the framework of an extended Nambu--Jona-Lasinio model we are studying
pion condensation in quark matter with an asymmetric isospin composition in a
gravitational field of the static Einstein universe at finite temperature and
chemical potential. This particular choice of the gravitational field
configuration enables us to investigate phase transitions of the system with
exact consideration of the role of this field in the formation of quark and
pion condensates and to point out its influence on the phase portraits. We
demonstrate the effect of oscillations of the thermodynamic quantities as
functions of the curvature and also refer to a certain similarity between the
behavior of these quantities as functions of curvature and finite temperature.
Finally, the role of quantum fluctuations for spontaneous symmetry breaking in
the case of a finite volume of the universe is shortly discussed.Comment: RevTex4; 15 pages, 10 figure
Study of Bc --> J/psi pi, etac pi decays with perturbative QCD approach
The Bc --> J/psi pi, etac pi decays are studied with the perturbative QCD
approach. It is found that form factors and branching ratios are sensitive to
the parameters w, v, f_J/psi and f_etac, where w and v are the parameters of
the charmonium wave functions for Coulomb potential and harmonic oscillator
potential, respectively, f_J/psi and f_etac are the decay constants of the
J/psi and etac mesons, respectively. The large branching ratios and the clear
signals of the final states make the Bc --> J/psi pi, etac pi decays to be the
prospective channels for measurements at the hadron collidersComment: 21 pages, revtex
Following Gluonic World Lines to Find the QCD Coupling in the Infrared
Using a parametrization of the Wilson loop with the minimal-area law, we
calculate the polarization operator of a valence gluon, which propagates in the
confining background. This enables us to obtain the infrared freezing (i.e.
finiteness) of the running strong coupling in the confinement phase, as well as
in the deconfinement phase up to the temperature of dimensional reduction. The
momentum scale defining the onset of freezing is found both analytically and
numerically. The nonperturbative contribution to the thrust variable,
originating from the freezing, makes the value of this variable closer to the
experimental one.Comment: 25 pages, 5 figure
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