Adding Flavor to the SMEFT

Abstract

We study the flavor structure of the lepton and baryon number-conserving dimension-6 operators in the Standard Model effective field theory (SMEFT). Building on the work of [1], we define several well-motivated flavor symmetries and symmetry-breaking patterns that serve as competing hypotheses about the ultraviolet (UV) dynamics beyond the SM, not far above the TeV scale. In particular, we consider four different structures in the quark sector and seven in the charged lepton sector. The set of flavor-breaking spurions is (almost) always taken to be the minimal one needed to reproduce the observed charged fermion masses and mixings. For each case, we explicitly construct and count the operators to the first few orders in the spurion expansion, providing ready-for-use setups for phenomenological studies and global fits. We provide a Mathematica package SMEFTflavor (https://github.com/aethomsen/SMEFTflavor) to facilitate similar analyses for flavor symmetries not covered in this work.

The scale of new physics from the Higgs couplings to γγ and γZ

“…The experimental limits Br(µ → eγ) < 4.2 × 10 −13 [34] can be used in the decays ( 9), (10) and (11). Notice that bounds obtained here are roughly an order of magnitude weaker than the bounds obtained from l → 3l ′ decays.…”

“…These operators can be mapped to EFT frameworks, such as the HEFT and the SMEFT, at the level of dimension six operator (see for example, [4][5][6][7] and the references therein). The study of FV in EFTs has been performed in many works in the literature, see for example [8][9][10][11][12][13][14][15]. To the best of our knowledge, non-minimal FV di-Higgs couplings have never been studied previously in the literature, as in most cases, these h 2 f f operators are either avoided entirely, or assumed to be proportional the Yukawa couplings by imposing (minimal) flavor symmetries [16,17].…”

Building blocks of the flavourful SMEFT RG

“…This structure represents important information about the SMEFT, since when diagonalised the anomalous dimension matrix tells us which directions in parameter space are enhanced or suppressed in the IR relative to their naive scaling dimension of six. Combined with a broad and model-independent prior on the important coefficients at the UV scale (for example based on the space of tree level weakly coupled UV completions [15], and/or on flavour and CP symmetries [16,17]), an understanding of these directions can thus point to motivated search strategies for new physics in LHC and flavour data.…”

“…Since the blocks are labelled in terms of Clebsch-Gordan coefficients of the SM flavour group, it is also easy to identify the appropriate subsystems when specific symmetry-based flavour structures [16,17] are imposed on the SMEFT from the UV. This could be used as a starting point for a more in-depth study of the behaviour of flavour assumptions under RG flow.…”

Resolving the flavor structure in the MFV-SMEFT

“…The flavor problem in SMEFT has been recently addressed by constructing flavor patterns for the Wilson coefficients that preserve the fermion masses and mixings in the Standard Model. Viable flavor patterns include Minimal Flavor Violation (MFV) [16,17,19,20], U(2) or U(3) symmetries [21][22][23], flavor alignment [1,24], and Froggatt-Nielsen scenarios including leptoquark couplings [18,[25][26][27]. Assuming such an underlying pattern reduces the number of independent flavor parameters in the SMEFT and allows us to perform a global analysis of phenomenologically viable flavor structures in the first place.…”