Abstract
We study associated Higgs production with a photon at electron-positron colliders, $e^+e^-\to h\gamma$, in various extended Higgs models, such as the inert doublet model (IDM), the inert triplet model (ITM) and the two Higgs doublet model (THDM). The cross section in the standard model (SM) is maximal around $\sqrt{s}=$250 GeV, and we present how and how much the new physics can enhance or reduce the production rate. We also discuss the correlation with the $h\to\gamma\gamma$ and $h\to Z\gamma$ decay rates. We find that, with a sizable coupling to a SM-like Higgs boson, charged scalars can give considerable contributions to both the production and the decay if their masses are around 100 GeV. Under the theoretical constraints from vacuum stability and perturbative unitarity as well as the current constraints from the Higgs measurements at the LHC, the production rate can be enhanced from the SM prediction at most by a factor of two in the IDM. In the ITM, in addition, we find a particular parameter region where the $h\gamma$ production significantly increases by a factor of about six to eight, but the $h\to\gamma\gamma$ decay still remains as in the SM. In the THDM, possible deviations from the SM prediction are minor in the viable parameter space.
Highlights
In the inert triplet model, in addition, we find a particular parameter region where the hγ production significantly increases by a factor of about 6 to 8, but the h → γγ decay still remains as in the standard model (SM)
High-energy eþe− colliders as a Higgs factory have been discussed for a long time in order to identify the Higgs sector; i.e., a mechanism of electroweak symmetry breaking and its relation to physics beyond the standard model (SM)
Instead of a doublet field as in the inert doublet model (IDM), we introduce an isospin triplet field Δ with hypercharge Y 1⁄4 1 and impose an exact Z2 symmetry under which Δ is odd while all the other SM fields are even [43,44]
Summary
High-energy eþe− colliders as a Higgs factory have been discussed for a long time in order to identify the Higgs sector; i.e., a mechanism of electroweak symmetry breaking and its relation to physics beyond the standard model (SM). 240–250 GeV has been extensively studied for realization of the International Linear Collider (ILC) [1,2,3] as well as the lepton collision option of the Future Circular Collider [4] and the Circular Electron Positron Collider [5] Such collision energies are optimal for studying associated Higgs production with a Z boson, eþpe−ffiffi → hZ, where the total cross section is maximal around s 1⁄4 250 GeV in the SM. We study how and how much new physics can enhance (or reduce) the hγ signal at future eþe− colliders. We note that the relative magnitudes between the triangle and box contributions are rather different at different energies, and new physics can affect the energies, e.g., btoettawlereanteps ffisdffi i1⁄4ffe2re5n0tlyanadt different collision 500 GeV, as seen below. We study such effects in each extended Higgs model
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