142 research outputs found
Extracting m_s From Flavor Breaking in Hadronic Tau Decays
New finite energy sum rules (FESR's) for extracting m_s from hadronic tau
decay data are constructed which (1) significantly reduce potential theoretical
uncertainties present in existing sum rule analyses and (2) remove problems
associated with both the poor convergence of the OPE representation of the
longitudinal part of the vector and axial vector correlators and the large
statistical errors in the spectral data above the K^* region.Comment: 4 pages, 1 figure. Report of presentations to International
Conference on Quark Nuclear Physics, Adelaide, Feb. 21-25, 2000, 16th
International Conference on Problems in Few-Body Physics, Taipei, March 6-10,
2000, and 7th Conference on the Intersections of Particle and Nuclear
Physics, Quebec City, May 22-28, 200
Two-loop analysis of axial vector current propagators in chiral perturbation theory
We perform a calculation of the isospin and hypercharge axial vector current propagators [ΔA3μν(q) and ΔA8μν(q)] to two loops in SU(3)×SU(3) chiral perturbation theory. A large number of O(p6) divergent counterterms are fixed, and complete two-loop renormalized expressions for the pion and eta masses and decay constants are obtained. The calculated isospin and hypercharge axial vector polarization functions are used as input in new chiral sum rules, valid to second order in the light quark masses. Some phenomenological implications of these sum rules are considered
Final State Interactions and Khuri-Treiman Equations in η → 3π decays
Using extended Khuri-Treiman equations, we evaluate the final state interactions due to two-pion rescatterings to the decays η → (π^0)(π^+)(π^-) and η → (π^0)(π^0)(π^0). As subtraction to the dispersion relation we take the one-loop chiral perturbation theory result of Gasser and Leutwyler. The calculated corrections are moderate and amount to about 14% in the amplitude at the center of the decay region. A careful analysis of the errors inherent to our approach is given. As a consequence, the experimental rate of the decay can only be reproduced if the double quark mass ratio Q^(-2) ≡ (m_d - m_u)/(m_s - m̂) * (m_d + m_u)/(m_s + m̂) is increased from the usual value of 1/(24.1)^2 to 1/(22.4 ± 0.9)^2. We have also calculated the ratio of the rates of the two decays and various Dalitz Plot parameters. In particular, the linear slope a in the charged decay is different from the one-loop value and agrees better with experiment
Systematic 1/M expansion for spin 3/2 particles in baryon chiral perturbation theory
Starting from a relativistic formulation of the pion-nucleon-delta system, the most general structure of 1/M corrections for a heavy baryon chiral lagrangian including spin 3/2 resonances is given. The heavy components of relativistic nucleons and delta fields are integrated out and their contributions to the next-to-leaing order lagrangians are constructed explicitly. The effective theory obtained admits a systematic expansion in terms of soft momenta, the pion mass and the delta-nucleon mass difference . As an application, we consider neutral pion photoproduction at threshold to third order in this small scale expansion
K -> 3 pi Final State Interactions at NLO in CHPT and Cabibbo's Proposal to Measure a_0-a_2
We present the analytical results for the K -> 3 pi final state interactions
at next-to-leading order (NLO) in CHPT. We also study the recent Cabibbo's
proposal to measure the pi-pi scattering lenghts combination a_0-a_2 from the
cusp effect in the pi^0-pi^0 energy spectrum at threshold for K^+ -> pi^0 pi^0
pi^+ and K_L -> pi^0 pi^0 pi^0$, and give the relevant formulas to describe it
at NLO. For that, we use the NLO CHPT expression to fit the real part of K -> 3
pi to data while the pi-pi scattering lenghts are treated non-perturbatively.
Using them, we make a quantitative estimate of the theoretical uncertaintity of
the a_0-a_2 determination at NLO in our approach and obtain that it is not
smaller than 5 % if added quadratically and 7 % if linearly for K^+ -> pi^0
pi^0 pi^+. One gets similar theoretical uncertainties if the neutral K_L ->
pi^0 pi^0 pi^0 decay data below threshold are used instead. For this decay,
there are very large theoretical uncertainties above threshold due to
cancellations and data above threshold cannot be used to get the scattering
lenghts. All the numbers we present are in the isospin limit apart of two-pion
phase space factors which are physical. We compare our results for the cusp
effect with Cabibbo and Isidori's results and discuss the differences and
agreements.
We also comment on the apperance of the singularity at the K -> 3 pi
pseudo-threshold s=(m_K-m_pi)^2 in the discontinuity that defines the cusp.Comment: 31 pages, 8 figures. v2=v3 Added the full contributions to the cusp
from the real part of the discontinuity. v4 Improved text. Matches published
versio
Strong rescattering in K-> 3pi decays and low-energy meson dynamics
We present a consistent analysis of final state interactions in
decays in the framework of Chiral Perturbation Theory.
The result is that the kinematical dependence of the rescattering phases cannot
be neglected. The possibility of extracting the phase shifts from future
interference experiments is also analyzed.Comment: 14 pages in RevTex, 3 figures in postscrip
The Chiral Anomaly in Non-Leptonic Weak Interactions
The interplay between the chiral anomaly and the non-leptonic weak
Hamiltonian is studied. The structure of the corresponding effective Lagrangian
of odd intrinsic parity is established. It is shown that the factorizable
contributions (leading in ) to that Lagrangian can be calculated without
free parameters. As a first application, the decay K^+ \ra \pi^+ \pi^0 \gamma
is investigated.Comment: 10 pages, LaTe
Dispersion relations and soft pion theorems for K -> pi pi
We propose a new method to obtain the K -> pi pi amplitude from K -> pi which
allows one to fully account for the effects of final state interactions. The
method is based on a set of dispersion relations for the K -> pi pi amplitude
in which the weak Hamiltonian carries momentum. The soft pion theorem, which
relates this amplitude to the K -> pi amplitude, can be used to determine one
of the two subtraction constants - the second constant is at present known only
to leading order in chiral perturbation theory. We solve the dispersion
relations numerically and express the result in terms of the unknown higher
order corrections to this subtraction constant.Comment: Latex, 10 pages, 1 figure. Typo in eqs. (13,14) corrected, some
rephrasing in the introductio
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