Search results for "Effective Field Theory"
showing 10 items of 212 documents
Effective Field Theory for Jet Processes
2015
Processes involving narrow jets receive perturbative corrections enhanced by logarithms of the jet opening angle and the ratio of the energies inside and outside the jets. Analyzing cone-jet processes in effective field theory, we find that in addition to soft and collinear fields their description requires degrees of freedom which are simultaneously soft and collinear to the jets. These collinear-soft particles can resolve individual collinear partons, leading to a complicated multi-Wilson-line structure of the associated operators at higher orders. Our effective field theory provides, for the first time, a factorization formula for a cone-jet process, which fully separates the physics at …
Weak Interactions at Low Energy
1985
In this series of lectures, I would like to discuss the basic aspects of the standard electroweak theory, as well as some alternatives. The phenomenology associated with charged and neutral currents weak interaction will show the success of the standard theory in giving a quantitative account of the existing data. The framework of most of our considerations will be that of an effective theory at low momentum transfer, low with respect to the masses of the intermediate vector bosons, 80–90 GeV. As an extension of the standard theory for the leptonic sector, I will contemplate the possibility of massive neutrinos being described by Majorana fields, leading to exotic phenomena induced by lepto…
A one-loop study of matching conditions for static-light flavor currents
2012
Heavy Quark Effective Theory (HQET) computations of semi-leptonic decays, e.g. B -> pi l nu, require the knowledge of the parameters in the effective theory for all components of the heavy-light flavor currents. So far non-perturbative matching conditions have been employed only for the time component of the axial current. Here we perform a check of matching conditions for the time component of the vector current and the spatial component of the axial vector current up to one-loop order of perturbation theory and to lowest order of the 1/m-expansion. We find that the proposed observables have small higher order terms in the 1/m-series and are thus excellent candidates for a non-perturbat…
Dispersive evaluation of the Lamb shift in muonic deuterium from chiral effective field theory
2020
We merge the dispersive relation approach and the ab initio method to compute nuclear structure corrections to the Lamb shift in muonic deuterium. We calculate the deuteron response functions and corresponding uncertainties up to next-to-next-to-next-to-leading order in chiral effective field theory and compare our results to selected electromagnetic data to test the validity of the theory. We then feed response functions calculated over a wide range of kinematics to the dispersion-theory formalism and show that an improved accuracy is obtained compared to that with the use of available experimental data in the dispersive analysis. This opens up the possibility of applying this hybrid metho…
Recent developments in effective field theory
2007
We will give a short introduction to the one-nucleon sector of chiral perturbation theory and will address the issue of a consistent power counting and renormalization. We will discuss the infrared regularization and the extended on-mass-shell scheme. Both allow for the inclusion of further degrees of freedom beyond pions and nucleons and the application to higher-loop calculations. As applications we consider the chiral expansion of the nucleon mass to order O(q^6) and the inclusion of vector and axial-vector mesons in the calculation of nucleon form factors.
The polarizability of the pion: no conflict between dispersion theory and chiral perturbation theory
2008
Recent attempts to determine the pion polarizability by dispersion relations yield values that disagree with the predictions of chiral perturbation theory. These dispersion relations are based on specific forms for the absorptive part of the Compton amplitudes. The analytic properties of these forms are examined, and the strong enhancement of intermediate-meson contributions is shown to be connected with spurious singularities. If the basic requirements of dispersion relations are taken into account, the results of dispersion theory and effective field theory are not inconsistent.
Electromagnetic transition form factors of the Roper resonance in a phenomenological field theory
2014
We analyze the form factors of the electromagnetic nucleon-to-Roper-resonance transition in the framework of a low-energy phenomenological field theory. A systematic power-counting procedure is generated by applying the complex-mass scheme. Within this power counting we calculate the form factors to next-to-next-to-leading order and fit the results to empirical data.
Factorization and NNLL Resummation for Higgs Production with a Jet Veto
2012
Using methods of effective field theory, we derive the first all-order factorization theorem for the Higgs-boson production cross section with a jet veto, imposed by means of a standard sequential recombination jet algorithm. Like in the case of small-q_T resummation in Drell-Yan and Higgs production, the factorization is affected by a collinear anomaly. Our analysis provides the basis for a systematic resummation of large logarithms log(m_H/p_T^veto) beyond leading-logarithmic order. Specifically, we present predictions for the resummed jet-veto cross section and efficiency at next-to-next-to-leading logarithmic order. Our results have important implications for Higgs-boson searches at the…
Factorization and resummation for jet broadening
2011
Jet broadening is an event-shape variable probing the transverse momenta of particles inside jets. It has been measured precisely in e+e- annihilations and is used to extract the strong coupling constant. The factorization of the associated cross section at small values of the broadening is afflicted by a collinear anomaly. Based on an analysis of this anomaly, we present the first all-order expressions for jet-broadening distributions, which are free of large perturbative logarithms in the two-jet limit. Our formulae reproduce known results at next-to-leading logarithmic order but also extend to higher orders.
The magnetic moment of the ρ-meson
2014
The magnetic moment of the \rho-meson is calculated in the framework of a low-energy effective field theory of the strong interactions. We find that the complex-valued strong interaction corrections to the gyromagnetic ratio are small leading to a value close to the real leading tree level result, g_\rho = 2. This is in a reasonably good agreement with the available lattice QCD calculations for this quantity.