arXiv subjects

J. N. Ng

Publications and source records attributed to J. N. Ng.

At least 19 recordsLinked to original sources

arXiv2020

Consequences of Neutrinoless Double Decays Dominated by Short Range Interactions

We investigate some consequences if neutrinoless double beta decays of nuclei are dominated by short range interactions. To illustrate our results, we assume that such decays proceed mainly through short range interactions involving two-W-bosons exchanges and confine ourselves to only include new scalars without new gauge interactions for SM fermions. For the neutrino mass problem we propose to solve it by adopting that the active light neutrinos have predominantly Dirac masses and the small Majorana masses induced by the new scalars render them pseudo(quasi)-Dirac particles. This particular aspect of neutrinos may be detectable in the next generation of neutrino oscillation experiments and/or neutrino telescopes. If so this opens a new connection between neutrinoless double beta decays and neutrino physics. We also noted the new physics signals such as high charged scalar states that can be explored in hadron colliders. In particular, we find that a high energy e^- e^- collider will be very useful in testing the origin of lepton number violation which complements neutrinoless double decays studies.

hep-ph↗

arXiv2016

Doubly cvharged vector leptons and the Higgs portal

Using a bottom up phenomenological approach we constructed a simple doubly charged vector lepton $E^{\pm\pm}$ model for the possible 750 GeV diphoton resonance $Φ$ at the LHC assuming it to be a scalar particle. Since no stable doubly charged leptons are seen, to facilitate their decays we complete the model by adding a charged SM electroweak scalar $S^\pm$. $Φ$ is a SM singlet and can be either an inert scalar or a Higgs field. In the inert case more than one vector lepton are required to account for the photon fusion production of the resonance if the model is to remain perturbative. For a Higgssed case $S^\pm$ can assist the production mechanism without using more than one such lepton. We also found that precision measurements constrain the couplings of $E^{\pm\pm}$ and $S^\pm$ to SM particles to be small. This raises the possibility that they can be fairly long lived and can give rise to displaced vertices if produced at the LHC.

hep-ph↗

arXiv2007

CPT conserving cosmological birefringence

We demonstrate that the cosmological birefringence can arise from CPT conserving effect, originated from the CPT-even dimension-six Chern-Simons-like term. We show that a sizable rotation polarization angle in the data of the cosmic microwave background radiation polarization can be induced.

astro-ph↗

arXiv2007

Cosmological birefringence induced by neutrino current

We review our recent work on the cosmological birefringence. We propose a new type of effective interactions in terms of the $CPT$-even dimension-six Chern-Simons-like term to generate the cosmological birefringence. We use the neutrino number asymmetry to induce a non-zero rotation polarization angle in the data of the cosmic microwave background radiation polarization.

astro-ph↗

arXiv2007

Neutrino number asymmetry and cosmological birefringence

We study a new type of effective interactions in terms of the $CPT$-even dimension-six Chern-Simons-like term, which could originate from superstring theory, to generate the cosmological birefringence. We use the neutrino number asymmetry to induce a sizable rotation polarization angle in the data of the cosmic microwave background radiation polarization. The combined effect of the new term and the neutrino asymmetry provides an alternative way to understand the birefringence.

astro-ph↗

arXiv2007

Testing Radiative Neutrino Mass Generation at the LHC

We have investigated in detail a model that contains an additional SU(2) singlet and triplet scalar fields than the Standard Model (SM). This allows the radiative generation of Majorana neutrino masses at two-loop order with the help of doubly charged Higgs bosons that arise from the extended Higgs sector. We studied in detail the phenomenology of the Higgs and neutrino sectors of the model. We give the analytical form of the masses of scalar and pseudoscalar bosons and their mixings, and the structure of the active neutrino mass matrix. It is found that the model accommodates only normal neutrino mass hierarchy, and that there is a large parameter space where the doubly charged Higgs can be observed at the LHC, thereby making it testable at the LHC. Furthermore, the neutrino-less double beta ($\nonu$) decays arise predominantly from exchange processes involving the doubly charged Higgs, whose existence is thus unmistakable if $\nonu$ decays are observed. The production and decays of the doubly charged Higgs are analyzed, and distinct and distinguishing signals are discussed.

hep-ph↗

arXiv2007

Study of $B\to p\bar{p}K^*$ and $B\to p\bar{p}ρ$

We study the three-body baryonic B decays of $B\to p\bar{p}(K^{*},ρ)$ in the standard model. The baryonic matrix elements are calculated in terms of the SU(3) flavor symmetry and the QCD power counting rules within the the perturbative QCD. We find that the decay branching ratios, angular and direct CP asymmetries of ($B^{-}\to p\bar{p}K^{*-}, \bar{B}^{0}\to p\bar{p}K^{*0}, B^{-}\to p\bar{p}ρ^{-}$) are around $(6,1,30)\times 10^{-6}$, $(13,-27,11)%$ and $(22,1,-3)%$, which are consistent with the current BaBar and Belle data, respectively. The large values of the branching ratio in $B^{-}\to p\bar{p}ρ^{-}$ and the direct CP asymmetry in $B^{\pm}\to p\bar{p}K^{*\pm}$ are useful to test the standard model and search for new physics.

hep-ph↗

arXiv2007

Unconventional Neutrino Mass Generation, Neutrinoless Double Beta Decays, and Collider Phenomenology

We study a model in which lepton number violation is solely triggered by a dimension 4 hard breaking term in the scalar potential. A minimal model which contains a SU(2) triplet with hypercharge Y=2, and a pair of singlet doubly charged scalar fields in addition to the Standard Model (SM) Higgs doublet is constructed. The model is technically natural in the sense that lepton number is preserved in the limit that the hard term vanishes. SM phenomenology restricts the vacuum expectation value of the triplet scalar field $v_T<5.78$ GeV. Neutrino masses controlled by $v_T$ are generated at the two loop level and are naturally to the sub-eV range. In general they exhibit normal hierarchy structure. Here the neutrino mass term does not dominate neutrinoless double beta decays of nuclei. Instead the short distance physics with doubly charged Higgs exchange gives the leading contribution. We expect weak scale singly and doubly charged Higgs bosons to make their appearances at the LHC and the ILC.

hep-ph↗

arXiv2006

Direct CP violation in $B^\pm\to p \bar{p} K^{(*)\pm}$

We study the direct CP violation in $B^\pm\to p\bar p K^{(*)\pm}$ decays in the standard model. We point out that these three-body baryonic B decays can be important tools for detecting the direct CP violation in the charged $B$ system, in which there are no conclusive signatures yet. In particular, we show that the direct CP violating asymmetry in $B^\pm\to p\bar p K^{*\pm}$ is around 22% which supports the recent data by the BABAR Collaboration.

hep-ph↗

arXiv2002

T violation in $Λ_b\toΛ\ell^+\ell^-$ decays

We examine the T-odd transverse lepton and $Λ$ polarizations in the baryonic decays of $Λ_b\toΛl^+l^- (l=e ,μ)$ to study the T violating effects. We show that the lepton polarizations are suppressed but the $Λ$ ones can be as large as 50% in CP violating theories beyond the standard model such as the SUSY models, which can be tested in various future hadron colliders.

hep-ph↗

arXiv2002

CP Violation in the Decay $η\toπ^+π^-γ$

We study the CP violating effects in the decay of $η\toπ^+π^-γ$. We show that to have CP violation in the decay, one has to consider both linear and circular photon polarizations. In the standard model, the polarizations are vanishingly small. However, model-independently, i.e. using only experimental constraint imposed by the limit on $Br(η\toπ^+π^-)$ it can be up to $O(10%)$. We also explore various possible operators and we find that the tensor type operator, possibly arising from a nonzero CP violating electric dipole moment of the strange quark, can induce a sizable linear photon polarization.

hep-ph↗

arXiv2002

T violation in $Λ_b\to Λ\ell^+\ell^-$ decays with polarized $Λ$

We study the T violating effects in the baryonic decays of $Λ_b\toΛl^+l^- (l=e ,μ)$ with polarized $Λ$. We show that the transverse $Λ$ polarizations in these baryonic decays could be as large as 50% in CP violating theories beyond the standard model such as the SUSY models, which can be tested in various future hadron colliders.

hep-ph↗

arXiv2001

Neutrino Oscillations via the Bulk

We investigate the possibility that the large mixing of neutrinos is induced by their large coupling to a five-dimensional bulk neutrino. In the strong coupling limit the model is exactly soluble. It gives rise to an oscillation amplitude whose squared-mass difference is independent of the channel, thus making it impossible to explain both the solar and the atmospheric neutrino oscillations simultaneously.

hep-ph↗

arXiv2000

The interplay between Weak and Strong Phases and Direct CP Violation from the Charmless B-meson Decays

We present a general analysis on charmless B-meson decays $B\to ππ$ and $πK$. It is noticed that the final state interactions and inelastic rescattering effects must be significant in order to understand the consistency of the current data. By using general isospin decompositions, the isospin amplitudes and the corresponding strong phases could be extracted from a global $χ^2$ fit of the experimental data. We emphasize that in general there are two, rather than one, relative strong phases in the decomposition. In the assumption of two equalstrong phases as considered in the literature, the current data, especially the ones concerning $B\to π^0 K^{0(\pm)}$decays, will imply a large isospin amplitude $|a^c_{3/2}| > 40 $, which is larger by a factor of five than the one from the naive factorization estimation. When two different strong phases are considered, all the isospin amplitudes can become, within the $1σ$-level, comparable with the theoretical values. We also show that the difference between the two strong phases cannot be too large and will be restricted by the most recent upper bound of $B\to π^0π^0$ decay. In any case, the strong phases are found to be large and the branching ratio of $B\to π^0π^0$ is likely to be enhanced by an order of magnitude in comparison with the one obtained from the naive factorization approach. Direct CP violations in all decay modes are also calculated and found to be close to the sensitivity of the present experiments.

hep-ph↗

arXiv2000

Neutrinos in Extra Dimensions and the Anomalous Magnetic Moments of Leptons

The use of extra dimensional scenarios as models for neutrino mass affects many low energy observables. We consider the implications of virtual bulk neutrinos in precision experiments of the anomalous magnetic moments of the muon and the electron. We consider neutrino models in factorizable geometry of the type M_4 x T as well as the sliced AdS_5 non-factorizable geometry. In both geometries we find finite contributions to g-2 after summing over the KK excitations of the bulk neutrinos. In the case of Randall-Sundrum geometry, we find that the muon experiment is approaching the precision necessary to probe these models.

hep-ph↗

arXiv2000

Bulk Higgs Boson Decays in Brane Localized Gravity

We embed the Standard Model in the Randall-Sundrum model of 5 dimensional brane localized gravity. The SM gauge and chiral fermion fields are restricted on the 4D visible brane whereas the Higgs and the right-handed neutrino are assumed to be 5D bulk fields. We calculate the effective couplings of the lowest mass Higgs field to the SM fermions and to the gauge bosons and find that the couplings are enhanced. Furthermore, the invisible decay width of a bulk Higgs of mass 150 GeV is shown to be large.

hep-ph↗

arXiv2000

The Use of Nuclear Beta-decay as a Test of Bulk Neutrinos in Extra Dimensions

Theories which include neutrinos in large extra dimensions can be constrained by nuclear beta decay experiments. We examine universality of beta decay strengths of Fermi transitions. From this we find that the extra dimensional Yukawa coupling for a higher dimensional scale of 10 TeV, and two extra dimensions can be constrained to y < 1. Kinematic implications are also discussed. In particular, an extra dimensional scenario will produce a tritium decay endpoint spectrum with a different shape than that for just one massive state.

nucl-th↗

arXiv1999

Astrophysical Implications of the Induced Neutrino Magnetic Moment from Large Extra Dimensions

Theories involving extra dimensions, a low (TeV) string scale and bulk singlet neutrinos will produce an effective neutrino magnetic moment which may be large (< 10^{-11} mu_B). The effective magnetic moment increases with neutrino energy, and therefore high energy reactions are most useful for limiting the allowed number of extra dimensions. We examine constraints from both neutrino-electron scattering and also astrophysical environments. We find that supernova energy loss considerations require a number of extra dimensions, n > 1, for an electron neutrino-bulk neutrino Yukawa coupling of order 1.

hep-ph↗