Abstract
The Littlest Higgs model with T-parity (LHT) belongs to the simplest new physics scenarios with new sources of flavour and CP violation. The latter originate in the interactions of ordinary quarks and leptons with heavy mirror quarks and leptons that are mediated by new heavy gauge bosons. Also a heavy fermionic top partner is present in this model which communicates with the SM fermions by means of standard W^pm and Z^0 gauge bosons. We present a new analysis of quark flavour observables in the LHT model in view of the oncoming flavour precision era. We use all available information on the CKM parameters, lattice QCD input and experimental data on quark flavour observables and corresponding theoretical calculations, taking into account new lower bounds on the symmetry breaking scale and the mirror quark masses from the LHC. We investigate by how much the branching ratios for a number of rare K and B decays are still allowed to depart from their SM values. This includes K^+rightarrow pi ^+nu bar{nu }, K_{L}rightarrow pi ^0nu bar{nu }, K_Lrightarrow mu ^+mu ^-, Brightarrow X_sgamma , B_{s,d}rightarrow mu ^+mu ^-, Brightarrow K^{(*)}ell ^+ell ^-, Brightarrow K^{(*)}nu bar{nu }, and varepsilon '/varepsilon . Taking into account the constraints from Delta F=2 processes, significant departures from the SM predictions for K^+rightarrow pi ^+nu bar{nu } and K_{L}rightarrow pi ^0nu bar{nu } are possible, while the effects in B decays are much smaller. In particular, the LHT model favours mathcal {B}(B_{s}rightarrow mu ^+mu ^-) ge mathcal {B}(B_{s}rightarrow mu ^+mu ^-)_mathrm{SM}, which is not supported by the data, and the present anomalies in Brightarrow K^{(*)}ell ^+ell ^- decays cannot be explained in this model. With the recent lattice and large N input the imposition of the varepsilon '/varepsilon constraint implies a significant suppression of the branching ratio for K_{L}rightarrow pi ^0nu bar{nu } with respect to its SM value while allowing only for small modifications of K^+rightarrow pi ^+nu bar{nu }. Finally, we investigate how the LHT physics could be distinguished from other models by means of indirect measurements and discuss the consequences for quark flavour observables of not finding any LHT state in the coming years.
Highlights
Elementary Particle Physics stands at the threshold of big discoveries
We present a new analysis of quark flavour observables in the Littlest Higgs model with T-parity (LHT) model in view of the oncoming flavour precision era
While the indirect constraints from electroweak precision (EWP) physics are largely unchanged with respect to our earlier analyses, major improvements have been achieved on direct bounds thanks to the first LHC run
Summary
Elementary Particle Physics stands at the threshold of big discoveries. The completion of the Standard Model (SM) through the Higgs discovery in 2012 [1,2] has shown that we are on the right track towards the fundamental theory. Very importantly the NA62 experiment at CERN should provide in the years a new measurement of B(K + → π +νν), which will be an important test of the LHT model in view of very small theoretical uncertainties in this decay In view of these developments the two main goals of our present analysis are:. We investigate what size of new flavour-violating effects will still be possible if we do not find any LHT state during the LHC run This means setting the masses of new gauge bosons and mirror quarks to be several TeV. 3 we collect the relevant expressions for quark flavour observables that can be compactly written in terms of these master functions This will allow us to indicate the changes in the CKM input and in non-perturbative parameters as well as QCD corrections that took place since our 2009 analysis. Excellent reviews of Little Higgs models can be found in [40,41]
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