4,624 research outputs found
Quenched chiral perturbation theory to one loop
We calculate the divergences of the generating functional of quenched chiral perturbation theory at one loop, and renormalize the theory by an appropriate definition of the counterterms. We show that the quenched chiral logarithms can be accounted for by defining a renormalized B0 parameter which, at lowest order, is proportional to the vacuum expectation value of the scalar quark density. Finally, we calculate several quantities at one loop to better analyze the modifications induced by quenching in the ultraviolet finite part of the one-loop corrections. We point out that some of the finite loop corrections may diverge in the chiral limit.
Isospin dependence of the three-nucleon force
We classify --nucleon forces according to their isospin dependence and
discuss the most general isospin structure of the three--nucleon force. We
derive the leading and subleading isospin--breaking corrections to the
three--nucleon force using the framework of chiral effective field theory.Comment: 21 pages, 6 figure
Resonances, Chiral Symmetry, Coupled Channel Unitarity and Effective Lagrangians
By means of a coupled channel non-perturbative unitary approach, it is
possible to extend the strong constrains of Chiral Perturbation Theory to
higher energies. In particular, it is possible to reproduce the lowest lying
resonances in meson-meson scattering up to 1.2 GeV using the parameters of the
O(p^2) and O(p^4) Chiral Lagrangian. We report on an update of these results
examining their possible relevance for meson spectroscopy.Comment: To appear in the proceedings of the 8th International Conference on
Hadron Spectroscopy, HADROn 99, August 24-28, 1999, Beijing, China. Four
pages, uses espcrc1.sty (included
A Non-Perturbative Chiral Approach for Meson-Meson Interactions
A non-perturbative method which combines constraints from chiral symmetry
breaking and coupled channel unitarity is used to describe meson-meson
interactions up to \sqrt{s}\lesssim 1.2 GeV, extending in this way the range of
applicability of the information contained in Chiral Perturbation Theory (\chi
PT), since this perturbative series is typically restricted to \sqrt{s}\lesssim
500 MeV. The approach uses the O(p^2) and O(p^4) \chiPT Lagrangians. The seven
free parameters resulting from the O(p^4) Lagrangian are fitted to the
experimental data. The approach makes use of the expansion of T^{-1} instead of
the amplitude itself as done in \chiPT. The former expansion is suggested by
analogy with the effective range approximation in Quantum Mechanics and it
appears to be very useful. The results, in fact, are in good agreement with a
vast amount of experimental analyses.Comment: 4 pages, 2 figures, LaTeX, Talk given at PANIC99, Uppsala (Sweden),
June 10-16, 199
Critical Analysis of Baryon Masses and Sigma-Terms in Heavy Baryon Chiral Perturbation Theory
We present an analysis of the octet baryon masses and the and
--terms in the framework of heavy baryon chiral perturbation theory. At
next-to-leading order, , knowledge of the baryon masses and
allows to determine the three corresponding finite
low--energy constants and to predict the the two --terms
. We also include the spin-3/2 decuplet in the
effective theory. The presence of the non--vanishing energy scale due to the
octet--decuplet splitting shifts the average octet baryon mass by an infinite
amount and leads to infinite renormalizations of the low--energy constants. The
first observable effect of the decuplet intermediate states to the baryon
masses starts out at order . We argue that it is not sufficient to retain
only these but no other higher order terms to achieve a consistent description
of the three--flavor scalar sector of baryon CHPT. In addition, we critically
discuss an SU(2) result which allows to explain the large shift of via intermediate states.Comment: 18 pp, TeX, BUTP-93/05 and CRN-93-0
Thermal reaction of Pt film with 110 GaN epilayer
Backscattering spectrometry, x-ray diffractometry, and scanning electron microscopy have been used to study the reaction of a thin Pt film with an epilayer of [110] GaN on [110] sapphire upon annealing at 450, 550, 650, 750, and 800 degrees C for 30 min. A Ga concentration of 2 at. % is detected by MeV He-4(++) backscattering spectrometry in the Pt layer at 550 degrees C. By x-ray diffraction, structural changes are observed already at 450 degrees C. At 650 OC, textured Ga2Pt appears as reaction product. The surface morphology exhibits instabilities by the formation of blisters at 650 degrees C and voids at 800 degrees C
Hadronic Correlators from All-point Quark Propagators
A method for computing all-point quark propagators is applied to a variety of
processes of physical interest in lattice QCD. The method allows, for example,
efficient calculation of disconnected parts and full momentum-space 2 and 3
point functions. Examples discussed include: extraction of chiral Lagrangian
parameters from current correlators, the pion form factor, and the unquenched
eta-prime.Comment: LATTICE01(Algorithms and Machines
pi-N charge exchange and pi(+)-pi(0) scattering at low energies
pi-N and pi-pi interactions near threshold are uniquely sensitive to the
chiral symmetry breaking part of the strong interaction. The pi-N sigma-term
value with its implications for nucleon quark structure and the recent
controversy concerning the size of the scalar quark condensate have renewed the
experimental interest in these two fundamental systems. We report new
differential cross sections for the reaction at 27.5 MeV
pion incident kinetic energy, measured between and
. Our results are in excellent agreement with the existing
comprehensive pi-N phase shift analysis. We also report on a Chew-Low analysis
of exclusive data at 260 MeV pion incident energy.Comment: Talk given by D. Pocanic at QULEN97, Osaka, 20-23 May 1997; 4 pages,
2 PostScript figures, writen in LaTeX 2e, uses packages "epsfig" and
"espcrc1
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