Malaphoric Z′ models for b→sℓ+ℓ- anomalies

Abstract

Abstract We study some phenomenological effects of kinetic mixing between the hypercharge field and a new U(1) gauge field in specific $$Z^\prime $$

Z ′

models that ameliorate the tensions between measurements and Standard Model predictions in

$$b \rightarrow s\ell ^+ \ell ^-$$

b → s

ℓ +

ℓ -

decays. To this end, we rederive the dimension-6 SMEFT coefficients resulting from integrating out the kinetically-mixed (‘malaphoric’)

$$Z^\prime $$

Z ′

field. The kinetic mixing provides a family-universal component to the couplings of the

$$Z^\prime $$

Z ′

field, which can improve fits to lepton flavour universality observables. We show how kinetic mixing improves the best fit of the

$$B_3-L_2$$

B 3

-

L 2

model to

$$b\rightarrow s$$

b → s

data by 7.0 units of

$$\chi ^2$$

χ 2

while remaining compatible with other relevant data sets such as electroweak precision observables and measurements of

$$e^+ e^- \rightarrow \ell ^+ \ell ^-$$

e +

e -

→

ℓ +

ℓ -

at LEP2.