arXiv subjects
Publications and source records attributed to W. -Y. Keung.
We constrain the possibility of a new pseudoscalar coupling between the muon and proton using a recent measurement of the 2S hyperfine splitting in muonic hydrogen.
Stoponium, a bound state of top squark and its antiparticle in a supersymmetric model, may be found in the ongoing Higgs searches at the LHC. Its WW and ZZ detection ratios relative to the Standard Model Higgs boson can be more than unity from WW* threshold to the two Higgs threshold. The gamma gamma channel is equally promising. Some regions of the stoponium mass below 150 GeV are already being probed by the ATLAS and CMS experiments.
We describe a characteristic signature of dark matter (DM) annihilation or decay into gamma-rays. We show that if the total angular momentum of the initial DM particle(s) vanishes, and helicity suppression operates to prevent annihilation/decay into light fermion pairs, then the amplitude for the dominant 3-body final state f^+f^-γhas a unique form dictated by gauge invariance. This amplitude and the corresponding energy spectra hold for annihilation of DM Majorana fermions or self-conjugate scalars, and for decay of DM scalars, thus encompassing a variety of possibilities. Within this scenario, we analyze Fermi LAT, PAMELA and HESS data, and predict a hint in future Fermi gamma-ray data that portends a striking signal at atmospheric Cherenkov telescopes (ACTs).
We analyze new diffuse gamma-ray data from the Fermi Gamma-ray Space Telescope, which do not confirm an excess in the EGRET data at galactic mid-latitudes, in combination with measurements of electron and positron fuxes from PAMELA, Fermi and HESS within the context of three possible sources: dark matter (DM) annihilation or decay into charged leptons, and a continuum distribution of pulsars. We allow for variations in the backgrounds, consider several DM halo profiles, and account for systematic uncertainties in data where possible. We find that all three scenarios represent the data well. The pulsar description holds for a wide range of injection energy spectra. We compare with ATIC data and the WMAP haze where appropriate, but do not fit these data since the former are discrepant with Fermi data and the latter are subject to large systematic uncertainties. We show that for cusped halo profiles, Fermi could observe a spectacular gamma-ray signal of DM annihilation from the galactic center while seeing no excess at mid-latitudes.
Assuming that the positron excess in PAMELA satellite data is a consequence of annihilations of cold dark matter, we consider from a model-independent perspective if the data show a preference for the spin of dark matter. We then perform a general analysis of annihilations into two-body final states to determine what weighted combination of channels best describes the data.
New limits on couplings $λ^i_{jk}{''}$, which break both the baryon number and the $R$--parity, are derived by using a new mechanism that contributes to the neutron-anti-neutron oscillation. The constraints due to proton decay and its potential phenomenology are also reexamined.
We analyze the production of triple pseudoscalar Higgs bosons in the decay channel of $Z\rightarrow AAA$ for light pseudoscalar bosons when the corresponding scalar boson is too heavy to be produced by $Z$ decay. Analytic results are obtained both at the tree level and at the one--loop level. The branching fraction can be as large as $10^{-5}$ which should be detectable at LEP.
If sneutrinos are the lightest supersymmetry partners and $R$-parity is not conserved, the process $e^+e^- \to \tilde {\barν} \tilde ν$ can have striking signatures due to the decay modes $\tildeν\to\ell^+\ell'^-$ or $\tildeν\to q \bar q'$. We present cross section formulas and discuss event rates and detection at the upgraded $e^+e^-$ collider LEP. Four-lepton signals should be detectable up to sneutrino mass $\tilde {m}_ν= 80$ GeV and maybe beyond; four-jet signals should be detectable up to $\tilde {m}_ν= 70$ GeV, but would probably be obscured thereafter by $WW$ background.
If $R$-parity is not conserved, the SUSY-threshold production process $e^+e^- \to χ_1^0χ_1^0$ could be detectable with relatively low luminosity. Hence an interesting mass range for the lightest SUSY particle $χ_1^0$ could be explored at the CERN LEP collider during its intermediate energy development, even before the full LEP200 upgrade is completed. We present cross section formulas and discuss event rates and detection for the three distinct decay options: $χ_1^0\to 2\, {\rm charged \; leptons}\, +\, {\rm neutrino}$, $χ_1^0\to {\rm lepton}\, +2\, {\rm quarks}$, and $χ_1^0\to 3\, {\rm quarks}$.
We present a simple model in which CP symmetry is spontaneously broken only after the radiative corrections are taken into account. The model includes two Higgs-boson doublets and two right-handed singlet neutrinos which induce the necessary non-hermitian interaction. To evade the Georgi-Pais theorem, some fine-tuning of coupling constants is necessary. However, we show that such fine-tuning is natural in the technical sense as it is protected by symmetry. Some phenomenological consequences are also discussed.
The asymmetries ${\cal A}_k \equiv [Γ(\twddec) -Γ(\tbwddec)] /[Γ(\twddec) + Γ(\tbwddec)]$ in the partial widths of the top quark decays are discussed within the Standard Model (SM), the Two-Higgs-Doublet Model (2HDM) and supersymmetric extensions of the SM (SSM). The leading contributions to these asymmetries in the SM and in the 2HDM are induced by the up-type quark self-energy diagrams and are found to be very small. However, in the SSM, the asymmetry ${\cal A}_b$ can be substantial, ${\cal O}(α_{QCD})$, provided the CP-violating phase of gluino-top-stop couplings is not suppressed. Within the SSM ${\cal A}_b$ is generated by the vertex corrections.
The two--loop mechanism of Bjorken and Weinberg is used to constrain flavor changing neutral Higgs bosons. We calculate the complete set of two--loop diagrams for the rare decay $μ\rightarrow e + γ$ induced by such neutral Higgs bosons, for arbitrary Higgs and top masses. The analytic result is used to set limits on Higgs masses for some recent models with specific ansatz about the flavor changing couplings. For example, in the Cheng--Sher scenario of multi-Higgs doublet models, all neutral Higgs bosons possess flavor changing ($f_i \leftrightarrow f_j)$ couplings proportional to $\sqrt{m_i m_j}$. We find that the present limit on $μ\to eγ$ implies that, in such scheme, these neutral Higgs bosons should be heavier than $200$ GeV.
We investigate a potentially large CP violating asymmetry in the neutral Higgs boson decay into a heavy quark pair or a $W^+$--$W^-$ pair. The source of the CP nonconservation is in the Yukawa couplings of the Higgs boson which can contain both scalar and pseudoscalar pieces. One of the interesting consequence is the different rates of the Higgs boson decays into CP conjugate polarized states. The required final state interactions can be either the strong or the electroweak interactions. The CP violating asymmetry can manifests itself in the asymmetry in the energies of the secondary decay products of these heavy quarks and $W$ bosons. Such asymmetry can be measureable in the future colliders such as SSC or LHC.
In this paper we study the neutron electric dipole moment (EDM) due to Higgs boson exchange in Left-Right symmetric models. In pseudo-manifest Left-Right symmetric models, the neutral Higgs contribution is smaller than that from the charged Higgs. The charged Higgs contribution at the two loop level can be as large as the experimental upper bound. In non (pseudo) manifest Left-Right symmteric models, the neutral Higgs exchange contribution can reach the experimental upper bound. The Higgs exchange contributions can be more important than the ones from W-boson exchange due to $W_L - W_R$ mixing.