Constraining the axion portal with $B\to K{\ell }^{+}{\ell }^{-}$

We investigate the bounds on axionlike states from flavor-changing neutral current $b\to s$ decays, assuming the axion couples to the standard model through mixing with the Higgs sector. Such GeV-scale axions have received renewed attention in connection with observed cosmic ray excesses. We find that existing $B\to K{\ell }^{+}{\ell }^{-}$ data impose stringent bounds on the axion decay constant in the multi-TeV range, relevant for constraining the “axion portal” model of dark matter. Such bounds also constrain light Higgs scenarios in the next-to-minimal supersymmetric standard model. These bounds can be improved by dedicated searches in $B$-factory data and at LHCb.

Figure 1

Bounds on $f_a$ as a function of $\tan \beta$ and $m_H$ for $n=1$ in Eq. (8), for $m_a^2\ll m_B^2$. For each displayed value of $f_a$ there are two contour lines, and the region between them is allowed for $f_a$ below the shown value. The bound disappears along the dashed curve, and gets generically weaker for larger $\tan \beta$.

Figure 2

The shaded regions of $f_a{tan}^2\beta$ are excluded in the large $\tan \beta$ limit. To indicate the region of validity of the large $\tan \beta$ approximation, the dashed (dotted) curve shows the bound for $\tan \beta =3$ ($\tan \beta =1$).

Figure 3

Bounds on ${sin}^2\theta \mathrm{Br}(a\to {\mu }^{+}{\mu }^{-})$ as a function of $\tan \beta$ and $m_H$. Similar to Fig. 1, the successively darker regions going away from the dashed curve are allowed for ${sin}^2\theta \mathrm{Br}(a\to {\mu }^{+}{\mu }^{-})$ above the indicated values. When $m_a$ is not small compared to $m_B$, these bounds should be modified by Eq. (18), but this is a small effect.

Figure 4

Bounds on ${sin}^2\theta \mathrm{Br}(a\to {\mu }^{+}{\mu }^{-})/{tan}^2\beta$ in the large $\tan \beta$ limit. The shaded region is excluded, and the dashed (dotted) curve shows $\tan \beta =3$ ($\tan \beta =1$).