7,625 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
Deformation and annealing study of Nicraly
Extensive experiments were carried out on the ODS alloy Nicraly, (an alloy prepared by mechanical alloying and consolidating a powder blend consisting of 16% chromium, 4% aluminum, 2-3% yttria, balance nickel), in efforts to develop methods of controlling the grain size and grain shape of the material. The experiments fell into two general categories: variations in the annealing parameters using the as-extruded material as it was received, and various thermomechanical processing schedules (various combinations of cold work and annealing). Success was achieved in gaining grain size and grain shape control by annealing of the as-extruded material. By proper selection of annealing temperature and cooling rates, the grain size of the as-received material was increased almost two orders of magnitude (from an average grain dimension of 0.023 mm to 1.668 mm) while the aspect ratio was increased by some 50% (from 20:1 to 30:1). No success was achieved in gaining significant control of the grain size and shape of the material by thermo-mechanical processing
Mesons and diquarks in neutral color superconducting quark matter with -equilibrium
The spectrum of meson and diquark excitations in cold color-superconducting
(2SC) quark matter is investigated under local color and electric neutrality
constraints with -equilibrium. A 2-flavored Nambu--Jona-Lasinio type
model including a baryon , color , and electric chemical
potentials is used. Two relations between coupling constants and in the
diquark- and quark-antiquark channels, correspondingly, are treated,
and . At the gapless- and at the gapped neutral color
superconductivity is realized. It is shown that color and electrical neutrality
together with -equilibrium lead to a strong mass splitting within the
pion isotriplet in the 2SC phase (both gapped and gapless), in contrast with
non--neutral matter. It is also shown that the properties of the physical
-singlet diquark excitation in the 2SC ground state varies for
different parameterization schemes. Thus, for one finds a heavy
resonance with mass 1100 MeV in the non--neutral (gapped) case, whereas,
if neutrality is imposed, a stable diquark with mass 200 MeV
appears in the gapless 2SC phase. For , there is again a resonance (with
the mass 300 MeV) in the neutral gapped 2SC phase. Hence, the existence
of the stable massive SU(2)-singlet diquark excitation is a new peculiarity
of the gapless 2SC.Comment: 18 pages, 9 figures; version accepted for publication in PR
Elevated temperature deformation of thoria dispersed nickel-chromium
The deformation behavior of thoria nickel-chromium (TD-NiCr) was examined over the temperature range 593 C (1100 F) to 1260 C (2300 F) in tension and compression and at 1093 C (2000 F) in creep. Major emphasis was placed on: (1) the effects of the material and test related variables (grain size, temperature, stress and strain rate) on the deformation process; and (2) the evaluation of single crystal TD-NiCr material produced by a directional recrystallization process. Elevated temperature yield strength levels and creep activation enthalpies were found to increase with increasing grain size reaching maximum values for the single crystal TD-NiCr. Stress exponent of the steady state creep rate was also significantly higher for the single crystal TD-NiCr as compared to that determined for the polycrystalline materials. The elevated temperature deformation of TD-NiCr was analyzed in terms of two concurrent, parallel processes: diffusion controlled grain boundary sliding, and dislocation motion
Ab-initio calculation of the Gilbert damping parameter via linear response formalism
A Kubo-Greenwood-like equation for the Gilbert damping parameter is
presented that is based on the linear response formalism. Its implementation
using the fully relativistic Korringa-Kohn-Rostoker (KKR) band structure method
in combination with Coherent Potential Approximation (CPA) alloy theory allows
it to be applied to a wide range of situations. This is demonstrated with
results obtained for the bcc alloy system FeCo as well as for a
series of alloys of permalloy with 5d transition metals.
To account for the thermal displacements of atoms as a scattering mechanism,
an alloy-analogy model is introduced. The corresponding calculations for Ni
correctly describe the rapid change of when small amounts of
substitutional Cu are introduced
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
Massive quark propagator and competition between chiral and diquark condensate
The Green-function approach has been extended to the moderate baryon density
region in the framework of an extended Nambu--Jona-Lasinio model, and the
thermodynamic potential with both chiral and diquark condensates has been
evaluated by using the massive quark propagator. The phase structure along the
chemical potential direction has been investigated and the strong competition
between the chiral and diquark condensate has been analyzed by investigating
the influence of the diquark condensate on the sharp Fermi surface. The
influence of the diquark condensate on the quark properties has been
investigated, even though the quarks in the color breaking phase are very
different from that in the chiral breaking phase, the difference between quarks
in different colors is very small.Comment: Revtex, 34 pages, 7 figures, section V revised, accepted by PR
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