28 research outputs found
On the minimality of the order p^6 chiral Lagrangian
A method to find relations between the operators in the mesonic Lagrangian of
Chiral Perturbation Theory at order p^6 is presented. The procedure can be used
to establish if the basis of operators in the Lagrangian is minimal. As an
example, we apply the method to the two-flavour case in the absence of scalar
and pseudo-scalar sources (s=p=0), and conclude that the minimal Lagrangian
contains 27 independent operators.Comment: 14 pages, 2 figure
Renormalization Group Analysis in NRQCD for Colored Scalars
The vNRQCD Lagrangian for colored heavy scalar fields in the fundamental
representation of QCD and the renormalization group analysis of the
corresponding operators are presented. The results are an important ingredient
for renormalization group improved computations of scalar-antiscalar bound
state energies and production rates at next-to-next-to-leading-logarithmic
(NNLL) order.Comment: 19 pages, 8 figures; revtex4. References added; version to appear in
Phys. Rev.
The Upsilon -> X gamma photon spectrum in the soft-energy region
The dominant contribution of the next-to-leading order perturbative QCD
corrections to the Upsilon -> X gamma photon energy spectrum for photon
energies w ~ m_b alpha_s can be obtained trivially from the knowledge of the
corresponding O(alpha) correction to the positronium decay spectrum in the same
region. The latter can be obtained from the NRQED computation of the
orthopositronium photon spectrum, or by applying the threshold expansion to the
1-loop QED amplitude, as it is explained in this talk.Comment: 7 pages, 5 figures. Contribution to the proceedings of EFT'09 -
International Workshop on Effective Field Theories: from the Pion to the
Upsilon-, 1-6 February 2009, Valencia (Spain
Integrating out heavy particles with functional methods: a simplified framework
We present a systematic procedure to obtain the one-loop low-energy effective
Lagrangian resulting from integrating out the heavy fields of a given
ultraviolet theory. We show that the matching coefficients are determined
entirely by the hard region of the functional determinant involving the heavy
fields. This represents an important simplification with respect the
conventional matching approach, where the full and effective theory
contributions have to be computed separately and a cancellation of the infrared
divergent parts has to take place. We illustrate the method with a descriptive
toy model and with an extension of the Standard Model with a heavy real scalar
triplet. A comparison with other schemes that have been put forward recently is
also provided.Comment: 24 pages. Uses feynMF packag