Project

chiral perturbation theory; dispersion relations; finite size effects; supersymmetry; flavour mixing; CP violation; Standard Model of Particle Physics; Strong interactions; Effective Field Theories

Lead
Lay summary
IIn particle physics there is a general effort worldwide to find effects which cannot be explained by the "standard model" - the generally accepted theory of particle interactions. This effort is carried out along two mainalleys: the high-energy and the high-precision ones. By increasing the energy of the events observed in laboratory one tries to produce new particles, not present in the standard model. By increasing the precision of the measurements of the decays of known particles one tries to see deviations from what the standard model predicts -- in this case the evidence of new particles is only indirect.The goal of this project is to improve the precision of the theoretical calculations of decay modes of known particles and so to match the increasing experimental precision in the corresponding measurements. Only in this manner one can obtain convincing evidence of new effects from experimental measurements. The difficulty of the theoretical calculations lies in the presence of strong interactions -- although we have a theory which we believe describes them exactly (quantum chromodynamics, QCD), we are not yet able to calculate observables, within this theory, to the desired level of precision. With this aim we will use methods like effective field theories or dispersion relations and collaborate with colleagues which use the numerical approach to deal with the strong interactions (lattice QCD).Moreover we will study in which specific processes one should expect new effects, by considering a popular extension of the standard model which incorporates a new, yet unobserved symmetry, called supersymmetry. According to the latter, every particle present in the standard model and observed so far should have a partner with spin changed by half a unit. Moreover, instead of only one Higgs doublet (the only particle in the standard model which is yet unobserved), there should be two. If supersymmetry were exact, these new particles should have the same mass as their standard model partner, but it is expected that supersymmetry is broken and that the new particles are all heavier. Through quantum effects, however, their effects would be visible even in the decays of the observed standard model particles. One of the goal of this project is to predict where one should see some of these effects and once these are seen, to draw conclusions about the spectrum (the masses) of the new particles.In this manner one can connect the high-precision and the high-energy frontiers in experimental particle physics.This project is intertwined with the activity of the European network FLAVIAnet, whose web page can be found here:http://ific.uv.es/flavianet/

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

In particle physics there is a general effort worldwide to find effectswhich cannot be explained by the standard model (SM) - the generally accepted theory of particle interactions. This effort is carried out along two main alleys: the high-energy and the high-precision ones. By increasing theenergy of the events observed in laboratory one tries to produce newparticles, not present in the standard model. By increasing the precisionof the measurements of the decays of known particles one tries to seedeviations due to the effect of virtual particles from what the standard model predicts - in this case the evidence of new particles is only indirect.The last few years of activity in the field of experimental particlephysics have shown that more patience and perseverance are needed in thesearch for new physics. This is due both to the delayed start of the LHCand to the continuing success of the SM in describingprecision experiments - despite the steady accumulation of new data andincrease in precision. Hints of possible failures of the SM are beingdiscussed right now, as always in the last several years, but these are far from being conclusive yet. The big picture of particle physics has not changedwith respect to two years ago, when we submitted the application for aresearch project of which the present one represents the continuation.Our first goal is to improve our understanding of strong-interactionphenomena, both per se and in order to extract from experimentinformation about fundamental parameters of the SM. The tools to deal withstrong interactions are: chiral perturbation theory (CHPT), dispersionrelations, and numerical lattice calculations. Although we do not directlyperform the latter, we make CHPT calculations which help in doing thenecessary extrapolations before one can use the numerical results inconnection with phenomenology.Our second line of research concerns the interpretation of new physicssignals in low energy experiments. In this research project we adopt asupersymmetric extension of the SM as the framework in which to discussthese issues, and in particular assume that the flavor structure of thelatter is not fully arbitrary, but respects the principle of minimalflavor violation (MFV). According to this, the only sources of flavorviolations are represented by the Yukawa matrices, even in extensions ofthe SM. In this way it is possible to have controlled flavor violations(as required by experiments) without fully specifying the supersymmetricmodel.This is the line of research which provides the bridge to theLHC physics: in the framework we work in, new physics effects are providedby loops of new particles. Their masses and coupling constants determinethe size of the effects and low energy precision experiments excluderegions in the parameter space. If supersymmetry is relevant below the TeVregion, then one should find new particles in the regions of parameterspace which are allowed by low energy experiments. Conversely, once the LHC will find new particles it will be easy to predict what kind of effects toexpect in precision experiments at low energy.