861 research outputs found
Properties of effective massive Yang-Mills theory in the limit of vanishing vector boson mass
Two-loop corrections to the pole mass of the vector boson and the pole masses
and the magnetic moments of fermions are calculated in the framework of an
effective field theory of massive Yang-Mills fields interacting with fermions.
It is shown that the limit of vanishing vector boson mass is finite for all
these quantities. Implications of the obtained results are discussed.Comment: 12 pages, 4 figure
Once more on the Higgs decay into two photons
We comment on the recently reiterated claim that the contribution of the
W-boson loop to the Higgs boson decay into two photons leads to different
expressions in the gauge and the unitary gauge. By applying a
gauge-symmetry preserving regularization with higher-order covariant
derivatives we reproduce once again the "classical" gauge-independent result.Comment: 6 pages, 1 figur
Cusps in K --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays. As
has recently been pointed out by Cabibbo and Isidori, an accurate measurement
of the cusp may allow one to pin down the S-wave pi pi scattering lengths to
high precision. Here, we present and illustrate an effective field theory
framework that allows one to determine the structure of this cusp in a
straightforward manner. The strictures imposed by analyticity and unitarity are
respected automatically.Comment: 14 pages, 3 figures, uses Elsevier styl
Vacuum energy in the effective field theory of general relativity
In the framework of an effective field theory of general relativity a model
of scalar and vector bosons interacting with the metric field is considered. It
is shown in the framework of a two-loop order calculation that for the
cosmological constant term which is fixed by the condition of vanishing vacuum
energy the graviton remains massless and there exists a self-consistent
effective field theory of general relativity coupled to matter fields defined
on a flat Minkowski background. This result is obtained under the assumption
that the energy-momentum tensor of the gravitational field is given by the
pseudotensor of Landau-Lifshitz's classic textbook. Implications for the
cosmological constant problem are also briefly discussed.Comment: 11 pages, 4 figure
Chiral unitary meson-baryon dynamics in the presence of resonances: Elastic pion-nucleon scattering
We develop a novel approach to chiral meson-baryon dynamics incorporating
unitarity constraints and explicit resonance fields. It is based on the most
general structure of any pion-nucleon partial wave amplitude neglecting the
unphysical cuts as derived from the N/D method. This amplitude is then matched
to the one-loop heavy baryon chiral perturbation theory result at third order
and to tree level exchanges of baryon- and meson states in the s,t and u
channels. This generates the left-hand cuts. The unitarization procedure does
not involve form factors or regulator functions. The resonance parameters are
determined from fits to the S- and P-wave pion-nucleon partial wave amplitudes
for energies up to 1.3 GeV. In particular, the is accurately
reproduced whereas scalar and vector meson couplings are less precisely pinned
down. We also obtain a satisfactory description of the N threshold
parameters. Further extensions of this method to coupled channels and the
three-flavor case are briefly discussed.Comment: 23 pp, LaTeX2e, 10 fig
Triviality of quantum electrodynamics revisited
Quantum electrodynamics is considered to be a trivial theory. This is based
on a number of evidences, both numerical and analytical. One of the strong
indications for triviality of QED is the existence of the Landau pole for the
running coupling. We show that by treating QED as the leading order
approximation of an effective field theory and including the next-to-leading
order corrections, the Landau pole is removed. Therefore, we conclude that the
conjecture, that for reasons of self-consistency, QED needs to be trivial is a
mere artefact of the leading order approximation to the corresponding effective
field theory.Comment: 3 pages, 2 figure
Derivation of spontaneously broken gauge symmetry from the consistency of effective field theory II: Scalar field self-interactions and the electromagnetic interaction
We extend our study of deriving the local gauge invariance with spontaneous
symmetry breaking in the context of an effective field theory by considering
self-interactions of the scalar field and inclusion of the electromagnetic
interaction. By analyzing renormalizability and the scale separation conditions
of three-, four- and five-point vertex functions of the scalar field, we fix
the two couplings of the scalar field self-interactions of the leading order
Lagrangian. Next we add the electromagnetic interaction and derive conditions
relating the magnetic moment of the charged vector boson to its charge and the
masses of the charged and neutral massive vector bosons to each other and the
two independent couplings of the theory. We obtain the bosonic part of the
Lagrangian of the electroweak Standard Model as a unique solution to the
conditions imposed by the self-consistency conditions of the considered
effective field theory.Comment: 11 pp, 3 fig
Near threshold ppbar enhancement in the J/psi -> omega ppbar decay
The near-threshold behavior of the ppbar invariant mass spectrum from the
J/psi -> omega ppbar decay reported recently by the BES Collaboration is
analyzed. Contrary to the statement made by the BES Collaboration itself our
study demonstrates that there is indeed a noticeable enhancement in the ppbar
invariant mass spectrum near threshold. Moreover, this enhancement is nicely
reproduced by the final state interaction in the relevant 11S0 ppbar partial
wave as given by the Julich nucleon--antinucleon model. Therefore, and again
contrary to the statement by the BES Collaboration, their new data on J/psi ->
omega ppbar decay in fact strongly support the FSI interpretation of the ppbar
enhancement, seen also in other decay reactions.Comment: 3 pages, 2 figure
Wilsonian renormalization group and the Lippmann-Schwinger equation with a multitude of cutoff parameters
The Wilsonian renormalization group approach to the Lippmann-Schwinger
equation with a multitude of cutoff parameters is introduced. A system of
integro-differential equations for the cutoff-dependent potential is obtained.
As an illustration, a perturbative solution of these equations with two cutoff
parameters for a simple case of an S-wave low-energy potential in the form of a
Taylor series in momenta is obtained. The relevance of the obtained results for
the effective field theory approach to nucleon-nucleon scattering is discussed.Comment: 6 pages, no figure
Wilsonian renormalization group versus subtractive renormalization in effective field theories for nucleon--nucleon scattering
We compare the subtractive renormalization and the Wilsonian renormalization
group approaches in the context of an effective field theory for the
two-nucleon system. Based on an exactly solvable model of contact interactions,
we observe that the standard Wilsonian renormalization group approach with a
single cutoff parameter does not cover the whole space spanned by the
renormalization scale parameters of the subtractive formalism. In particular,
renormalization schemes corresponding to Weinberg's power counting in the case
of an unnaturally large scattering length are beyond the region covered by the
Wilsonian renormalization group approach. In the framework of pionless
effective field theory, also extended by the inclusion of a long-range
interaction of separable type, we demonstrate that Weinberg's power counting
scheme is consistent in the sense that it leads to a systematic order-by-order
expansion of the scattering amplitude.Comment: 23 pages, 2 figure
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