arXiv subjects

Wee Hao Ng

Publications and source records attributed to Wee Hao Ng.

7 recordsLinked to original sources

arXiv2018

Re-visiting the bounds on hydrogen-antihydrogen oscillations from diffuse $γ$-ray surveys

Surveys of diffuse $γ$-ray in the interstellar medium (ISM) can be used to probe hydrogen-antihydrogen oscillations, by detecting the $γ$-ray emission from antihydrogen annihilation. A bound on the oscillation parameter $δ$ was originally derived by Feinberg, Goldhaber and Steigman (1978). In this paper, we re-visit the original derivation by performing a more detailed analysis that (1) incorporates suppression effects from additional elastic and inelastic processes, (2) treats the ISM as a multi-phase medium, and (3) utilises more recent $γ$-ray data from the Fermi Large Area Telescope. We find that suppression from elastic scattering plays a more important role than previously thought, while the multi-phase nature of the ISM affects how the $γ$-ray data should be utilised. We derive a more accurate bound on the oscillation period that is about an order of magnitude weaker than the older bound.

hep-ph↗

arXiv2016

Co-Decaying Dark Matter

We propose a new mechanism for thermal dark matter freezeout, termed Co-Decaying Dark Matter. Multi-component dark sectors with degenerate particles and out-of-equilibrium decays can co-decay to obtain the observed relic density. The dark matter density is exponentially depleted through the decay of nearly degenerate particles, rather than from Boltzmann suppression. The relic abundance is set by the dark matter annihilation cross-section, which is predicted to be boosted, and the decay rate of the dark sector particles. The mechanism is viable in a broad range of dark matter parameter space, with a robust prediction of an enhanced indirect detection signal. Finally, we present a simple model that realizes co-decaying dark matter.

hep-ph↗

arXiv2016

Probing a slepton Higgs on all frontiers

We study several aspects of supersymmetric models with a $U(1)_R$ symmetry where the Higgs doublet is identified with the superpartner of a lepton. We derive new, stronger bounds on the gaugino masses based on current measurements, and also propose ways to probe the model up to scales of $\mathcal{O}(10\, \textrm{TeV})$ at future $e^+e^-$ colliders. Since the $U(1)_R$ symmetry cannot be exact, we analyze the effects of $R$-symmetry breaking on neutrino masses and proton decay. In particular, we find that getting the neutrino mixing angles to agree with experiments in a minimal model requires a UV cutoff for the theory at around $ 10 \text{ TeV} $.

hep-ph↗

arXiv2015

A 2 TeV $W_R$, Supersymmetry, and the Higgs Mass

A recent ATLAS search for diboson resonances and a CMS search for $eejj$ resonances which both show excesses with significance around 3 sigma have generated interest in $SU(2)_R$ gauge extensions of the Standard Model with a $W'$ mass around 2 TeV. We investigate the possibility that an $SU(2)_R$ gauge extension of the MSSM compatible with an explanation of the diboson anomaly might give rise to a significant enhancement of the Higgs mass above the MSSM tree level bound $m_{h, \text{tree}} < 90 \; \text{GeV}$ due to non-decoupling D-terms. This model contains a vector-like charge -1/3 $SU(2)_R$ singlet quark for each generation which mixes significantly with the $SU(2)_R$ doublet quarks, affecting the $W_R$ phenomenology. We find that it is possible to achieve $m_{h, \text{tree}} > 110 \; \text {GeV}$, and this requires that the $Z'$ mass is close to 3 TeV.

hep-ph↗

arXiv2015

Sneutrino Higgs models explain lepton non-universality in CMS excesses

Recent searches for first-generation leptoquarks and heavy right-handed $W_R$ bosons have seen excesses in final states with electrons and jets. A bizarre property of these excesses is that they appear to violate lepton universality. With these results in mind, we study the phenomenology of supersymmetric models in which the Higgs arises as the sneutrino in an electron supermultiplet. Since the electron is singled out in this approach, one can naturally account for the lepton flavor structure of the excesses. In this work, we show that in such a framework, one can significantly alleviate the tension between the Standard Model and the data and yet evade current constraints from other searches. Lastly we point out that correlated excesses are expected to be seen in future multilepton searches.

hep-ph↗

arXiv2015

Nonzero $θ_{13}$ in $SO(3) \rightarrow A_4$ lepton models

The simplest neutrino mass models based on $A_4$ symmetry predict $θ_{13} = 0$ at tree level, a value that contradicts recent data. We study models that arise from the spontaneous breaking of an $SO(3)$ symmetry to its $A_4$ subgroup, and find that such models can naturally accommodate a nonzero $θ_{13}$ at tree level. Standard Model charged leptons mix with additional heavy ones to generate a $θ_{13}$ that scales with the ratio of the $A_4$-breaking to $SO(3)$-breaking scales. A suitable choice of energy scales hence allows one to reproduce the correct lepton mixing angles. We also consider an alternative approach where we modify the alignment of flavons associated with the charged lepton masses, and find that the effects on $θ_{13}$ are enhanced by a factor that scales as $m_τ/m_μ$.

hep-ph↗

arXiv2013

Truncated channel representations for coupled harmonic oscillators

Coupled quantum harmonic oscillators, studied by many authors using many different techniques over the decades, are frequently used toy-models to study open quantum systems. In this manuscript, we explicitly study the simplest oscillator model -- a pair of initially decoupled quantum harmonic oscillators interacting with a spring-like coupling, where the bath oscillator is initially in a thermal-like state. In particular, we treat the completely positive and trace preserving map on the system as a quantum channel, and study the truncation of the channel by truncating its Kraus set and its output dimension. We thereby derive the truncated transition amplitudes of the corresponding truncated channel. Finally, we give a computable approximation for these truncated transition amplitudes with explicit error bounds, and perform a case study of the oscillators in the off-resonant and weakly-coupled regime numerically. We demonstrate explicitly that the substantial leakage error can be mitigated via quantum error correction.

quant-ph↗