arXiv subjects

Gwo-Guang Wong

Publications and source records attributed to Gwo-Guang Wong.

15 recordsLinked to original sources

arXiv2021

Self-interacting Dark Matter with Scalar Dilepton Mediator

The cold dark matter (CDM) candidate with weakly interacting massive particles can successfully explain the observed dark matter relic density in cosmic scale and the large-scale structure of the Universe. However, a number of observations at the satellite galaxy scale seem to be inconsistent with CDM simulation. This is known as the small-scale problem of CDM. In recent years, it has been demonstrated that self-interacting dark matter (SIDM) with a light mediator offers a reasonable explanation for the small-scale problem. We adopt a simple model with SIDM and focus on the effects of Sommerfeld enhancement. In this model, the dark matter candidate is a leptonic scalar particle with a light mediator. We have found several regions of the parameter space with proper masses and coupling strength generating a relic density that is consistent with the observed CDM relic density. Furthermore, this model satisfies the constraints of recent direct searches and indirect detection for dark matter as well as the effective number of neutrinos and the observed small-scale structure of the Universe. In addition, this model with the favored parameters can resolve the discrepancies between astrophysical observations and $N$-body simulations.

hep-ph↗

arXiv2019

Scalar leptoquark effects on $B \to μ\barν$ decay

Purely leptonic $B$ meson decays provide unique probes for physics Beyond the Standard Model. We study the impact of a scalar leptoquark, $S_1$, on $B \to μ\barν$ decay. We find that, for $m_{S_1}\sim 1$ TeV, the $S_1$ leptoquark can modify the $B \to μ\barν$ rate significantly. Such a leptoquark can in prinicple also alter the $B \to τ\barν$ rate. However, current searches from LHC and low energy physics provide some constraints on the parameter space.

hep-ph↗

arXiv2019

Enhanced $B \to μ\barν$ Decay at Tree Level as Probe of Extra Yukawa Couplings

With no New Physics seen at the LHC, a second Higgs doublet remains attractive and plausible. The ratio ${\cal R}_B^{μ/τ} = {\cal B}(B \to μ\barν)/{\cal B}(B \to τ\barν)$ is predicted at 0.0045 in both the Standard Model and the type II two Higgs doublet model, but it can differ if extra Yukawa couplings exist in Nature, which we deem an experimental issue. Considering recent Belle update on $B \to μ\barν$, we show that in the general two Higgs doublet model, the ratio could be up by a factor of two, which can be probed by the Belle~II experiment with just a few ab$^{-1}$.

hep-ph↗

arXiv2017

Time-independent Green's Function of a Quantum Simple Harmonic Oscillator System and Solutions with Additional Generic Delta-Function Potentials

The one-dimensional time-independent Green's function $G_0$ of a quantum simple harmonic oscillator system ($V_0(x)=m ω^2 x^2/2$) can be obtained by solving the equation directly. It has a compact expression, which gives correct eigenvalues and eigenfunctions easily. The Green's function $G$ with an additional delta-function potential can be obtained readily. The same technics of solving the Green's function $G_0$ can be used to solve the eigenvalue problem of the simple harmonic oscillator with an generic delta-function potential at an arbitrary site, i.e. $V_1(x)\propto δ(x-a)$. The Wronskians play an important and interesting role in the above studies. Furthermore, the approach can be easily generalized to solve the quantum system of a simple harmonic oscillator with two or more generic delta-function potentials. We give the solutions of the case with two additional delta-functions for illustration.

quant-ph↗

arXiv2017

Confronting Dirac Fermionic Dark Matter with Recent Data

We study Dirac fermionic dark matter (DM, $χ^0$) and confront it with recent data. To evade the stringent direct search limits from PandaX-II, XENON1T and LUX experiments, the quantum numbers of the Dirac DM are taken to be $I_3=Y=0$ to remove the tree-level $Z$-exchange diagram. Loop amplitudes can contribute to the elastic scattering cross section. We find that there are cancellations in the one-loop diagrams, which largely reduce the cross section and make the Dirac DM viable in the direct search. For a generic isospin $I$, we survey the Dirac DM mass constrained by the latest results of PandaX-II, XENON1T and LUX experiments, the observed DM relic density, and the H.E.S.S. and the Fermi-LAT astrophysical observations. Sommerfeld enhancement effects on DM annihilation processes are investigated. We find that the cross section of $χ^0\barχ^0$ annihilating to the standard model (SM) gauge bosons are in general significantly enhanced, and the Fermi-LAT, the H.E.S.S. upper limits on $\langleσv\rangle({W^+W^-,γγ})$ and the observed relic density become serious constraints on the Dirac DM mass. The $I<4$ cases are ruled out and for $I\geq 4$, the lower bound on Dirac DM mass are forced to be $\gtrsim$ 60 TeV. The elastic scattering cross section for $m_χ$ of few tens TeV with a generic $I$ is found to be $σ^{SI}\simeq I^2(I+1)^2\times7\times10^{-49}$~cm$^2$. The predicted $\langleσ(χ^0\barχ^0\to Z^0Z^0, Z^0γ, γγ)v\rangle$ and $σ^{SI}$ are sizable and they will be useful to search for DM in astrophysical observation and in direct search in near future.

hep-ph↗

arXiv2016

Study of Majorana Fermionic Dark Matter

We construct a generic model of Majorana fermionic dark matter (DM). Starting with two Weyl spinor multiplets $η_{1,2}\sim (I,\mp Y)$ coupled to the Standard Model (SM) Higgs, six additional Weyl spinor multiplets with $(I\pm 1/2, \pm(Y\pm 1/2))$ are needed in general. It has 13 parameters in total, five mass parameters and eight Yukawa couplings. The DM sector of the minimal supersymmetric standard model (MSSM) is a special case of the model with $(I,Y)=(1/2,1/2)$. Therefore, this model can be viewed as an extension of the neutralino DM sector. We consider three typical cases: the neutralino-like, the reduced and the extended cases. For each case, we survey the DM mass $m_χ$ in the range of $(1,2500)$ GeV by random sampling from the model parameter space and study the constraints from the observed DM relic density, the direct search of LUX, XENON100 and PICO experiments, and the indirect search of Fermi-LAT data. We investigate the interplay of these constraints and the differences among these cases. It is found that the direct detection of spin-independent DM scattering off nuclei and the indirect detection of DM annihilation to $W^+W^-$ channel are more sensitive to the DM searches in the near future. The allowed mass for finding $\tilde H$-, $\tilde B$-, $\tilde W$- and non neutralino-like DM particles and the predictions on $\langleσ(χχ\rightarrow ZZ, ZH, t{\bar t}) v\rangle$ in the indirect search are given.

hep-ph↗

arXiv2003

Accounting for Slow J/psi from B Decay

A slow J/psi excess exists in the inclusive B -> J/psi+X spectrum, and is indicative of some hadronic effect. From color octet nature of c cbar pair in b-> c cbar s decay, one such possibility would be B -> J/psi+ K_g decay, where K_g is a hybrid resonance with sbar g q constituents. We show that a K_g resonance of ~ 2 GeV mass and suitably broad width could be behind the excess.

hep-ph↗

arXiv2002

The Glueball Spectrum from a Potential Model

The spectrum of two-gluon glueballs below 3 GeV is investigated in a potential model with dynamical gluon mass using variational method. The short distance potential is approximated by one-gluon exchange, while the long distance part is taken as a breakable string. The mass and size of the radial as well as orbital excitations up to principle quantum number n=3 are evaluated. The predicted mass ratios are compared with experimental and lattice results.

hep-ph↗

arXiv2001

Glueball States in a Constituent Gluon Model

In a model with dynamical gluon mass, we investigate the bound states of two and three gluons via a Schrödinger equation. The short distance potential is approximated by one-gluon-exchange while the long distance part is assumed to be of a breakable string. We estimate the masses and in particular the {\it sizes} of low-lying bound states with no orbital angular momentum. By considering quantum-mechanical smearing of the gluon fields and normalizing to lattice results on $M_{0^{++}}$ and $M_{2^{++}}$, we find that the $0^{++}$ glueball is rather small in size compared with the others. The fitted gluon mass is of order 600 to 700 MeV, which is reasonable. The 3-gluon glueballs $0^{-+}$, $1^{--}$ and $3^{--}$ states are nearly degenerate, and their mass ratio with $2^{++}$ is largely independent of all parameters and consistent with lattice calculations. We estimate the mass of $1^{--}$ glueball to be $3.1-3.7$ GeV, which is close to the mass of $J/ψ$ and $ψ^\prime$.

hep-ph↗

arXiv1995

Magnetic Field Dependence of Muonium-antimuonium Conversion

We study the magnetic field dependence of muonium--antimuonium conversion induced by neutral (pseudo)scalar bosons. Only the $SS$ operator contributes to the conversion of polarized muonium, but it gets quenched by a magnetic field of strength 0.1 Gauss or stronger. Conversion induced by $SS$ couplings for unpolarized muonium is independent of magnetic field. Magnetic fields of 0.1 Tesla or stronger starts to suppress conversion induced by $PP$ interactions in the lowest Breit-Rabi level, but gets partially compensated by a rise in conversion probability in the other unpolarized level. The effects of $(S\mp P)(S\mp P)$ and $(S\mp P)(S\pm P)$ operators behave in the same way as $(V\mp A)(V\mp A)$ and $(V\mp A)(V\pm A)$ operators, respectively.

hep-ph↗

arXiv1995

$μ^+e^- <---> μ^- e^+$ Transitions via Neutral Scalar Bosons

With $μ\to eγ$ decay forbidden by multiplicative lepton number conservation, we study muonium--antimuonium transitions induced by neutral scalar bosons. Pseudoscalars do not induce conversion for triplet muonium, while for singlet muonium, pseudoscalar and scalar contributions add constructively. This is in contrast to the usual case of doubly charged scalar exchange, where the conversion rate is the same for both singlet and triplet muonium. Complementary to muonium conversion studies, high energy $μ^+e^- \to μ^- e^+$ and $e^-e^- \to μ^- μ^-$ collisions could reveal spectacular resonance peaks for the cases of neutral and doubly charged scalars, respectively.

hep-ph↗

arXiv1994

Perspective on Quark Mass and Mixing Relations

Recent data indicate that $V_{ub}\cong λ^4 \cong (0.22)^4$, while $m_t$ seems to be $174$ GeV. The relations $m_d/m_s\sim m_s/m_b \sim δ\sim λ^2 \simeq \vert V_{cb}\vert$ and $m_u/m_c\sim m_c/m_t \sim δ^2 \sim λ^4 \sim \vert V_{ub}\vert$ suggest that %a plausible clean separation of the %origin of the quark mixing matrix: the down type sector is responsible for $\vert V_{us}\vert$ and $\vert V_{cb}\vert$, while $V_{ub}$ comes from the up type sector. Five to six parameters might suffice to account for the ten quark mass and mixing parameters, resulting in specific power series representations for the mass matrices. In this picture, $δ$ seems to be the more sensible expansion parameter, while $λ\cong \sqrt{m_d/m_s} \sim \sqrtδ$ is tied empirically to $(M_d)_{11} = 0$.

hep-ph↗

arXiv1994

Radiative Majorana Neutrino Masses

We present new radiative mechanisms for generating Majorana neutrino masses, within an extension of the standard model that successfully generates radiative charged lepton masses, order by order, from heavy sequential leptons. Only the new sequential neutral lepton has a right-handed partner, and its Majorana mass provides the seed for Majorana neutrino mass generation. Saturating the cosmological bound of $50$ eV with $m_{ν_τ}$, we find that $m_{ν_μ}$ and $m_{ν_e}$ could be at most $10^{-2}$, and $10^{-3}$ eV, respectively. The electron neutrino mass may vanish in the limit of degenerate charged Higgs bosons. Unfortunately, $ν_e - ν_τ$ mixing is also radiatively induced, and is too small for sake of solving the solar neutrino problem via the Mikheyev--Smirnov--Wolfenstein effect.

hep-ph↗

arXiv1994

Radiative Lepton Masses with Heavy Lepton Seed

We construct a $Z_8$ model for leptons where all Yukawa couplings are of order unity, but known lepton masses are generated radiatively, {\it order by order}. The seed is provided by fourth generation leptons $E$ and $N$, which receive (Dirac) mass in usual way. Two additional Higgs doublets with nontrivial $Z_8$ charge are introduced to give nearest neighbor Yukawa couplings. Hence, nonstandard Higgs bosons are flavor changing in an unusual way. Loop masses are generated when $Z_8$ is {\it softly} broken down to $Z_2$. However, $e$ and $μ$ mass generation require new Higgs bosons to be at weak scale. Neutral scalar mixing underlies $m_μ/m_τ\gg m_e/m_μ$, $m_τ/m_E$. The $Z_2$ symmetry forbids $μ\to eγ$ and $τ\to μγ$. The most stringent bound comes from $τ\to μμ^\pm e^\mp$. The model has interesting implications for $τ\to eγ$, $μ\bar e \to \barμe$ conversion, $μ\to eν_e\barν_μ$, and FCNC decays of $E$ and $N$ (such as $E\to τe^\pmμ^\mp$).

hep-ph↗

arXiv1993

Experimental and Theoretical Implications of New Sequential Leptons

If new sequential leptons $E^\pm$ and $N^0$ exist, the LEP bound implies $m_E$, $m_N > M_Z/2$. The heaviness of the neutral lepton breaks away from the pattern of the first three generations. The minimal model is to have 4 left-handed lepton doublets and 4 right-handed charged lepton singlets, but only one right-handed neutral lepton singlet. Since in general the 3rd and 4th generation should mix, and since $\vert m_N - m_E\vert$ should not be too large, neither $E$ nor $N$ would be stable, and both tend to decay via the Cabibbo suppressed $E\to ν_τ$ or $N\to τ$ charged currents. This leads to the interesting signature of like-sign $W$ pair production via $E^+N \to \barν_ττ^- W^+W^+$ at the SSC and LHC. The popular seesaw mechanism cannot plausibly accommodate the near masslessness of the light neutrinos and the heaviness of $N^0$ simultaneously. The representation structure poses a difficulty to the traditional approach of $SO(10)$-based grand unified theories. The discovery of such new heavy leptons would thus have rather wide ranging and far reaching implications.

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