The $B$ Anomalies and non-SMEFT New Physics

Abstract

The modern viewpoint is that the Standard Model is the leading part of an effective field theory that obeys the symmetry $SU(3{)}_C\times SU(2{)}_L\times U(1{)}_Y$. Since the discovery of the Higgs boson, it is generally assumed that this symmetry is realized linearly (SMEFT), but a nonlinear realization (e.g., HEFT) is still possible. The two differ in their predictions for the size of certain low-energy dimension-6 four-fermion operators: for these, HEFT allows $O(1)$ couplings, while in SMEFT they are suppressed by a factor $v^2/{\Lambda }_{\mathrm{NP}}^2$, where $v$ is the Higgs vev. In this talk, I argue that (i) such non-SMEFT operators contribute to both $b\to s{\ell }^{+}{\ell }^{-}$ and $b\to c{\tau }^{-}{\bar{\nu }}_{\tau }$, transitions involved in the present-day $B$ anomalies, (ii) the contributions to $b\to s{\ell }^{+}{\ell }^{-}$ are constrained to be small, at the SMEFT level, and (iii) the contribution to $b\to c{\tau }^{-}{\bar{\nu }}_{\tau }$ can be sizeable. I show that the angular distribution in $\bar{B}\to D^{\ast }(\to D{\pi }^{\prime }){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau }){\bar{\nu }}_{\tau }$ contains enough information to extract the coefficients of all new-physics operators. The measurement of this angular distribution can tell us if non-SMEFT new physics is present.

Comments: 4 pages, 1 figure. Talk given at FPCP2022, Oxford Mississippi, May 23-27, 2022