Model-independent constraints on ΔF= 2 operators and the scale of new physics

Abstract

Froggatt-Nielsen mechanism in a model with SU(3)c×SU(3)L×U (1) Abstract: We update the constraints on new-physics contributions to ∆F = 2 processes from the generalized unitarity triangle analysis, including the most recent experimental developments. Based on these constraints, we derive upper bounds on the coefficients of the most general ∆F = 2 effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of new physics that contributes to these low-energy effective interactions. We point out that, due to the enhancement in the renormalization group evolution and in the matrix elements, the coefficients of non-standard operators are much more constrained than the coefficient of the operator present in the Standard Model. Therefore, the scale of new physics in models that generate new ∆F = 2 operators, such as next-to-minimal flavour violation, has to be much higher than the scale of minimal flavour violation, and it most probably lies beyond the reach of direct searches at the LHC.

Kaon mixing beyond the SM from Nf = 2 tmQCD and model independent constraints from the UTA

“…A generalization of the UT analysis, which allows for NP effects by including the most significant flavour constraints on NP available at the time was performed in ref. [9]. The result was a simultaneous determination of the CKM parameters and the size of NP contributions to ∆F = 2 processes in the neutral kaon and B d,s meson sectors.…”

“…They hence represent a significant progress with respect to the input values used in the UT analysis performed in ref. [9], where quenched lattice numbers (without a systematic continuum limit extrapolation analysis) computed more than five years ago in refs. [6] and [7] were employed.…”

“…For this reason, we present here an update of the analysis of ref. [9] based on our new values of the ∆S = 2 B-parameters. The new ingredients entering the analysis are collected in tables 1 and 2.…”

“…Following ref. [9], in deriving the lower bounds on the NP scale Λ, we assume L i = 1, that corresponds to strongly-interacting and/or tree-level coupled NP. Two other interesting possibilities are given by loop-mediated NP contributions proportional to either α 2 s or α 2 W .…”

“…Section 2 contains a brief description of the ∆S = 2 matrix elements of the effective weak Hamiltonian describing the most general pattern of K 0 −K 0 oscillations. In section 3, based on the results of this work for the ∆S = 2 B-parameters, we discuss the implications for NP of our updated Unitarity Triangle (UT) analysis [9]. In section 4 we illustrate the main theoretical features of the lattice setup employed in our simulations (twisted mass lattice QCD [10,11]) and we describe the strategy for obtaining accurate numerical estimates of the B-parameters as well as ratios of kaon four-fermion matrix elements.…”