Closing in on new chiral leptons at the LHC

Current measurements of the h→Zγ signal strength invite us to speculate about possible new physics interactions that exclusively affect μZγ without altering the other signal strengths. Additional consideration of tree unitarity enables us to correlate the nonstandard values of μZγ with an upper limit on the scale of new physics. We find that even when μZγ deviates from the Standard Model value by only 20%, the scale of new physics should be well within the reach of the LHC. Published by the American Physical Society 2024

New physics interpretations for nonstandard values of h→Zγ

Boto,

Das,

Romão

et al. 2024

Vector dark matter with Higgs portal in type II seesaw framework

Das,

Jha,

Nanda

2024

We study the phenomenology of a vector dark matter (VDM) in a U(1)X gauged extension of the Standard Model (SM), which is set in a type II seesaw framework. When this U(1)X symmetry is spontaneously broken by the vacuum expectation value (VEV) of a newly introduced complex scalar singlet, the gauge boson Z′ becomes massive. The stability of the dark matter (DM) is ensured by the presence of an exact charge conjugation symmetry resulting from the structure of the Lagrangian. On the other hand, the SU(2)L triplet scalar facilitates light neutrino masses via the type II seesaw mechanism. We have studied the phenomenology of the usual WIMP DM, considering all possible theoretical and experimental constraints that are applicable. Due to the presence of a triplet scalar, the present framework can also accommodate the observed 2σ deviation in h→Zγ decay rate, recently measured at the LHC. The possibility of nonthermal production of DM from the decay of the singlet scalar has also been briefly discussed. Published by the American Physical Society 2024

Interpretation of excess in H→Zγ using a light axionlike particle

Cheung,

Ouseph

2024

We interpret the recent excess in a rare decay of the Higgs boson, H→Zγ, using a light axionlike particle (ALP) in the mass range 0.05–0.1 GeV. The dominant decay of such a light ALP is into a pair of collimated photons, whose decay is required to happen before reaching the ECAL detector, such that it mimics a single photon in the detector. It can explain the excess with a coupling CaZHeff/Λ∼4×10−5 GeV−1, while the decay of the ALP before reaching the ECAL requires the diphoton coupling Cγγeff/Λ≥0.35 TeV−1(0.1 GeV/ma)2. A potential test would be the rare decay of the Z boson Z→aH*→a(bb¯) at the Tera-Z option of the future FCC and CEPC. However, it has a branching ratio of only O(10−12), and thus barely testable. The production cross section for pp→Z*→aH via the same coupling CaZHeff/Λ at the LHC is too small for detection. Published by the American Physical Society 2024