Topics in Effective Field Theories
In recent years. our understanding of the structure of quantum field theories has benefitted greatly from the introduction and development of effective field theory (EFT) techniques. The EFT language allows for a systematic characterization of interactions between degrees of freedom relevant in a given energy range, even when some of these interactions are induced by new physics at a higher energy, whose details may be complicated or unknown. In situations where the higher energy theory is well understood, it is nevertheless very useful to be able to describe the behavior of fields that are of interest in a given energy regime, without making reference to degrees of freedom present at different energy scales. In particular, this allows for a relatively straightforward comparison of the effects on low energy modes of different high energy interactions. We present here two previously published papers, in each of which the EFT concept plays a central role. In Chapter 1, nonperturbative (instanton) contributions to EFT scattering amplitudes are studied. It is found that when the high energy theory requires all fermions (heavy and light) to participate in such tunneling processes, instantons involving only the light fields are naturally absent in the effective theory. This is true even though no explicit mention of the heavy fermions which have been "integrated out" is made in the effective theory description. The resolution of what had been an apparent paradox in the literature is testimony to the generality and consistency of EFT techniques. In Chapter 2. EFT methods are applied to a problem of immediate practical and experimental interest--the possibility of quark compositeness. Top quark substructure, associated with new interactions present at scales above the top quark mass, but unrelated to electroweak physics, is examined with regard to possible effects on experimentally accessible production and decay rates of known particles. It is found that such new physics is indeed consistent with presently available experimental data, so long as only right handed quark fields participate in the new interactions.
- Pub Date:
- QUARK SUBSTRUCTURE;
- Physics: Elementary Particles and High Energy