Contributions of flavor violating couplings of a Higgs boson to pp→WWpp\to WW

We study contributions to $pp\to W^+W^- \to \ell\nu_\ell \ell^\prime\nu_{\ell^\prime}$ in models with a new Higgs boson, $H$, and a neutral lepton, $\nu_{4}$, with couplings $H-\nu_{4}-\nu_{\mu}$ and $W-\nu_{4}-\mu$ through the process $pp \to H \to \nu_4 \nu_\mu \to W \mu \nu_\mu \to \ell\nu_\ell \mu \nu_\mu$. Contrary to naive expectations, we find that contributions to $pp\to WW$ can be very large while satisfying constraints from standard $H\to WW$ and $H\to\gamma\gamma$ searches. Even the excess observed by ATLAS in $pp\to WW$, if taken at face value, can be easily accommodated. The various kinematic distributions fit nicely the experimentally determined ones. This scenario can arise for example in a two Higgs doublet model with vectorlike leptons.Comment: 16 pages, 5 figure

Dark Matter "Collider" from Inelastic Boosted Dark Matter

We propose a novel dark matter (DM) detection strategy for the models with non-minimal dark sector. The main ingredients in the underlying DM scenario are a boosted DM particle and a heavier dark sector state. The relativistic DM impinged on target material scatters off inelastically to the heavier state which subsequently decays into DM along with lighter states including visible (Standard Model) particles. The expected signal event, therefore, accompanies a visible signature by the secondary cascade process associated with a recoiling of the target particle, differing from the typical neutrino signal not involving the secondary signature. We then discuss various kinematic features followed by DM detection prospects at large volume neutrino detectors with a model framework where a dark gauge boson is the mediator between the Standard Model particles and DM.Comment: 6 pages, 4 figures, 2 table

Searching for Boosted Dark Matter via Dark-Strahlung

We propose a new search channel for boosted dark matter (BDM) signals coming from the present universe, which are distinct from simple neutrino signals including those coming from the decay or pair-annihilation of dark matter. The signal process is initiated by the scattering of high-energetic BDM off either an electron or a nucleon. If the dark matter is dark-sector U(1)-charged, the scattered BDM may radiate a dark gauge boson (called "dark-strahlung") which subsequently decays to a Standard Model fermion pair. We point out that the existence of this channel may allow for the interpretation that the associated signal stems from BDM, not from the dark-matter-origin neutrinos. Although the dark-strahlung process is generally subleading compared to the lowest-order simple elastic scattering of BDM, we find that the BDM with a significant boost factor may induce an O(10-20%) event rate in the parameter regions unreachable by typical beam-produced dark-matter. We further find that the dark-strahlung channel may even outperform the leading-order channel in the search for BDM, especially when the latter is plagued by substantial background contamination. We argue that cosmogenic BDM searches readily fall in such a case, hence taking full advantage of dark-strahlung. As a practical application, experimental sensitivities expected in the leading-order and dark-strahlung channels are contrasted in dark gauge boson parameter space, under the environment of DUNE far-detectors, revealing usefulness of dark-strahlung.Comment: 9 pages, 4 figures, Journal-submitted versio

Collider probes of singlet fermionic dark matter scenarios for the Fermi gamma-ray excess

We investigate the collider signatures of the three benchmark points in the singlet fermionic dark matter model. The benchmark points, which were introduced previously to explain the Fermi gamma-ray excess by dark matter (DM) pair annihilation at the Galactic center, have definite predictions for future collider experiments such as the International Linear Collider and the High-Luminosity LHC. We consider four collider observables: (1) Higgs signal strength (essentially $hZZ$ coupling), (2) triple Higgs coupling, (3) exotic Higgs decay, and (4) direct production of a new scalar particle. The benchmark points are classified by the final states of the DM annihilation process: a pair of $b$ quarks, SM-like Higgs bosons, and new scalar particles. Each benchmark scenario has detectable new physics signals for the above collider observables that can be well tested in the future lepton and hadron colliders.Comment: 14 pages, 1 figure, 1 tabl

D0 dimuon charge asymmetry from B_s system with Z' couplings and the recent LHCb result

The D0 collaboration has announced the observation of the like-sign dimuon charge asymmetry since 2010, which has more than 3\sigma deviation from the Standard Model prediction. One of the promising explanation is considering the existence of flavor changing Z' couplings to the b and s quarks which can contribute to the off-diagonal decay width in the B_s - \bar{B}_s mixing. Model construction is highly constrained by the recent LHCb data of 1fb^{-1} integrated luminosity . In this paper, we analyze the experimental constraints in constructing new physics models to explain the dimuon charge asymmetry from the CP violation of the B_s system. We present limits on Z' couplings and show that it is impossible to obtain the 1\sigma range of the dimuon charge asymmetry without the new contribution in the B_d system. Even with arbitrary contribution in the B_d system, the new couplings must be in the fine tuned region.Comment: 34 pages, 12 figures, Additional analyses and references are updated. (Conclusion unchanged.