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Register a new userMonophoton signals in electron-positron colliders in a simplified E6SSM
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The mono-photon signature emerging in an E6 Supersymmetric Standard Model (E6SSM) from inert higgsino Dark Matter (DM) is analyzed at future $e^+e^-$ colliders. As the inert neutral and charged higgsinos are nearly degenerate, the inert chargino is a rather long lived particle and the charged particle associated with its decay to the inert higgsino is quite soft. We show that the pair production of inert charginos at a 500 GeV electron-positron collider with an initial or final state photon is the most promising channel for probing the inert higgsino as one DM candidate within the E6SSM. We also emphasize that this signal has no chance of being observed at the Large Hadron Collider with higher energy and/or luminosity. Finally, we remark that, combined with a DM signal produced in Direct Detection experiments involving an active higgsino state as the second DM candidate, this dual evidence could point to a two-component DM version of the E6SSM.
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An electron-positron linear collider in the energy range between 500 and 1000 GeV is of crucial importance to precisely test the Standard Model and to explore the physics beyond it. The physics program is complementary to that of the Large Hadron Collider. Some of the main physics goals and the expected accuracies of the anticipated measurements at such a linear collider are discussed. A short review of the different collider designs presently under study is given including possible upgrade paths to the multi-TeV region. Finally a framework is presented within which the realisation of such a project could be achieved as a global international project.
In recent years there have been many proposals for new electron-positron colliders, such as the Circular Electron-Positron Collider, the International Linear Collider, and the Future Circular Collider in electron-positron mode. Much of the motivation for these colliders is precision measurements of the Higgs boson and searches for new electroweak states. Hence, many of these studies are focused on energies above the $h,Z$ threshold. However, there are proposals to run these colliders at the lower $WW$ threshold and $Z$-pole energies. In this paper, we propose a new search for Higgs physics accessible at lower energies: $e^+e^-rightarrow h,Z_d$, where $Z_d$ is a new light gauge boson such as a dark photon or dark-$Z$. Such searches can be conducted at the $WW$ threshold, i.e. energies below the $h,Z$ threshold where exotic Higgs decays can be searched for in earnest. Additionally, due to very good angular and energy resolution at future electron-positron colliders, these searches will be sensitive to $Z_d$ masses below 1 GeV, which is lower than the current direct LHC searches. We will show that at $sqrt{s}=160$ GeV with 10 ab$^{-1}$, a search for $e^+e^-rightarrow h,Z_d$ is sensitive to $h-Z-Z_d$ couplings of $deltasim 8times 10^{-3}$ and cross sections of $sim 1-2$ ab for $Z_d$ masses below 1 GeV. The results are similar at $sqrt{s}=240$ GeV with 5 ab$^{-1}$.
There is a recent proposal of identifying the Higgs particle of the Standard Model as a pseudo Nambu-Goldstone boson. This new broken symmetry introduces new particles and new interactions. Among these new interactions a central role to get a new physics is played by the new neutral gauge boson. We have studied the new neutral currents in the Littlest Higgs model and compared with other extended models. For high energy $e^+ + e^-$ colliders we present a clear signature for new neutral gauge bosons that can indicate the theoretical origin of these particles. Previous analysis by other authors were done at collider energies equal to the new gauge boson mass $M_{A_H}$. In this paper we show that asymmetries in fermion anti-fermion production can display model differences in the case $M_{A_H} > sqrt{s}$. For $M_{A_H} < sqrt{s}$ we show that the hard photon energy distribution in $e^+ + e^- lra gamma + f + bar f$ can present a model dependence. New bounds for the new neutral gauge boson masses are also presented.
Flavor symmetries are useful to realize fermion flavor structures in the standard model. In particular, discrete $A_4$ symmetry is used to realize lepton flavor structures, and some scalars which are called flavon are introduced to break this symmetry. In many models, flavons are assumed to be much heavier than the electroweak scale. However, our previous work showed that flavon mass around 100 GeV is allowed by experimental constraints in the $A_4$ symmetric model with residual $Z_3$ symmetry. In this paper, we discuss collider search of such a light flavon $varphi_T$. We find that an electron - photon collision, as a considerable option at the international linear collider, has advantages to search for the signals. At the electron - photon collider flavons are produced as $e^-gamma to l^- varphi_T$ and decay into two charged leptons. Then we analyze signals of flavor-conserving final-state $tau^+ tau^- e^-$, and flavor-violating final-states $tau^+ mu^- mu^-$ and $mu^+ tau^- tau^-$ by carrying out numerical simulation. For the former final-state, SM background can be strongly suppressed by imposing cuts on the invariant masses of final-state leptons. For the later final-states, SM background is extremely small, because in the SM there are no such flavor-violating final-states. We then find that sufficient discovery significance can be obtained, even if flavons are heavier than the lower limits from flavor physics.
The review of using of compton backscattering method for determination of the beam energy in collider experiments is given.
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