The Physics of the Dark Photon by Marco Fabbrichesi & Emidio Gabrielli & Gaia Lanfranchi

Author:Marco Fabbrichesi & Emidio Gabrielli & Gaia Lanfranchi
Language: eng
Format: epub
ISBN: 9783030625191
Publisher: Springer International Publishing

(2.68)

which is not related to the dark photon and its coupling because it comes from the box-diagram insertion of the dark scalars and fermions.

The limit in Eq. (2.68) is obtained by requiring that the messenger contribution to the box diagram for the - mixing does not exceed the experimental value of the mixing parameter [62]. Due to chirality arguments, the leading contribution to the box diagram in Eq. (2.68) does not depend on the dark fermion mass, which is assumed to be much smaller than the corresponding messenger mass in the down sector and therefore very weakly on the loop function.

The limit in Eq. (2.68) applies specifically to the off-diagonal term in the Yukawa coupling of d-s quark mixing and the corresponding messenger state. A similar but weaker bound can be found from B-meson mixing.

As displayed in the equations above, all these limit can be made weaker by taking (or ) sufficiently light or by varying the corresponding mixing parameters , . In the UV model is thus possible to play with the parameters to make room for larger values of the dipole coefficient by absorbing part of the suppression in the connection between the scale and the mass ratios and . For instance a scale TeV for the new physics of the dark sector is still allowed by the stringent bound in Eq. (2.35) if we take sufficiently small. This way, there is some additional freedom in comparing limits from different processes as compared to the model-independent case where the scale is taken to be the same for all bounds.

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