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Can extra dimensions accessible to the SM explain the recent measurement of anomalous magnetic moment of the muon?

K. Agashe, N. G. Deshpande, G. -H. Wu

TL;DR

This paper assesses whether flat extra dimensions with SM fields propagating in the bulk can significantly affect the muon anomalous magnetic moment, $a_\mu$. It systematically analyzes scenarios where fermions are brane-localized, where all SM fields reside in universal extra dimensions, and where colored fields propagate in a subspace of the bulk. The authors derive constraints from precision electroweak data, the $T$ parameter, hadronic $B$ decays, and $b \to s \gamma$, showing that in minimal setups the KK contributions to $a_\mu$ are typically smaller than the SM electroweak correction. However, by allowing colored fields to inhabit a smaller subspace and employing multi-Higgs-doublet sectors, they demonstrate parameter regions where KK-induced contributions to $a_\mu$ can be comparable to, or even reach, the SM electroweak size, highlighting the crucial role of Higgs sector structure and flavor constraints in these models.

Abstract

We investigate whether models with flat extra dimensions in which SM fields propagate can give a significant contribution to the anomalous magnetic moment of the muon (MMM). In models with only SM gauge and Higgs fields in the bulk, the contribution to the MMM from Kaluza-Klein (KK) excitations of gauge bosons is very small. This is due to the constraint on the size of the extra dimensions from tree-level effects of KK excitations of gauge bosons on precision electroweak observables such as Fermi constant. If the quarks and leptons are also allowed to propagate in the (same) bulk (``universal'' extra dimensions), then there are no contributions to precision electroweak observables at tree-level. However, in this case, the constraint from one-loop contribution of KK excitations of (mainly) the top quark to T parameter again implies that the contribution to the MMM is small. We show that in models with leptons, electroweak gauge and Higgs fields propagating in the (same) bulk, but with quarks and gluon propagating in a sub-space of this bulk, both the above constraints can be relaxed. However, with only one Higgs doublet, the constraint from the process b -> s gamma requires the contribution to the MMM to be smaller than the SM electroweak correction. This constraint can be relaxed in models with more than one Higgs doublet.

Can extra dimensions accessible to the SM explain the recent measurement of anomalous magnetic moment of the muon?

TL;DR

This paper assesses whether flat extra dimensions with SM fields propagating in the bulk can significantly affect the muon anomalous magnetic moment, . It systematically analyzes scenarios where fermions are brane-localized, where all SM fields reside in universal extra dimensions, and where colored fields propagate in a subspace of the bulk. The authors derive constraints from precision electroweak data, the parameter, hadronic decays, and , showing that in minimal setups the KK contributions to are typically smaller than the SM electroweak correction. However, by allowing colored fields to inhabit a smaller subspace and employing multi-Higgs-doublet sectors, they demonstrate parameter regions where KK-induced contributions to can be comparable to, or even reach, the SM electroweak size, highlighting the crucial role of Higgs sector structure and flavor constraints in these models.

Abstract

We investigate whether models with flat extra dimensions in which SM fields propagate can give a significant contribution to the anomalous magnetic moment of the muon (MMM). In models with only SM gauge and Higgs fields in the bulk, the contribution to the MMM from Kaluza-Klein (KK) excitations of gauge bosons is very small. This is due to the constraint on the size of the extra dimensions from tree-level effects of KK excitations of gauge bosons on precision electroweak observables such as Fermi constant. If the quarks and leptons are also allowed to propagate in the (same) bulk (``universal'' extra dimensions), then there are no contributions to precision electroweak observables at tree-level. However, in this case, the constraint from one-loop contribution of KK excitations of (mainly) the top quark to T parameter again implies that the contribution to the MMM is small. We show that in models with leptons, electroweak gauge and Higgs fields propagating in the (same) bulk, but with quarks and gluon propagating in a sub-space of this bulk, both the above constraints can be relaxed. However, with only one Higgs doublet, the constraint from the process b -> s gamma requires the contribution to the MMM to be smaller than the SM electroweak correction. This constraint can be relaxed in models with more than one Higgs doublet.

Paper Structure

This paper contains 6 sections, 10 equations, 1 figure.

Table of Contents

  1. Quarks and leptons confined to $4D$
  2. Universal extra dimensions
  3. Quarks and gluon in a subspace of the bulk
  4. Case $\delta _c = 0$: quarks and gluon on a brane
  5. Case $\delta _c \neq 0$
  6. Conclusions

Figures (1)

  • Figure 1: The contribution to the MMM from KK states of the electroweak gauge bosons relative to the SM electroweak correction as a function of the total number of KK states (see Eq. (\ref{['amukk3']})) and for $\delta = 3, 4, 5,$ and $6$, where $\delta$ is the number of extra dimensions in which the leptons and electroweak gauge bosons propagate. We assume $x =1$, $R^{-1} = 400$ GeV and do not impose the constraint from the process $b \rightarrow s \gamma$ since this constraint depends sensitively on the Higgs content (see text).