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Daniel Ng

Publications and source records attributed to Daniel Ng.

At least 19 recordsLinked to original sources
arXiv2026

Orbax: Distributed Checkpointing with JAX

In a landscape of high-performance distributed ML systems, JAX has emerged as a framework of choice. However, JAX's modular design philosophy leaves it without a standardized checkpointing solution. In this paper, we introduce Orbax, a modular, JAX-native checkpointing library that abstracts the complexities of distributed accelerator systems while also providing flexibility for user-friendly checkpoint manipulations throughout the ML model lifecycle. We demonstrate performance exceeding comparable PyTorch competitors by up to 3.5$\times$ for saving and 2$\times$ for loading. The library is available at https://github.com/google/orbax.

cs.DC↗
arXiv1995

A note on Majorana neutrinos, leptonic CKM and electron electric dipole moment

The electric dipole moment of the electron, $d_e$, is known to vanish up to thre e-loops in the standard model with massless neutrinos. However, if neutrinos are massive Majorana particles, we obtain the result that $d_e$ induced by leptonic CKM mechanism is non-vanishing at two-loop order, and it applies to all massive Majorana neutrino models.

hep-ph↗
arXiv1995

The $Z \to b \bar b$ Excess and Top Decay

The apparent excess of $Z \rightarrow b \bar b$ events at LEP may be an indication of new physics beyond the standard model. However, in either the two-Higgs-doublet model or the minimal supersymmetric standard model, any explanation would lead to an important new decay mode of the top quark and suppresses the $t \rightarrow W b$ branching fraction, which goes against what has been observed at the Tevatron. In the two-Higgs-doublet model, the branching fraction of $Z \rightarrow b \bar b$ + a light boson which decays predominantly into $b \bar b$ would be at least of order 10$^{-4}$.

hep-ph↗
arXiv1995

The $R_b$ Excess at LEP: Clue to New Physics at the TEVATRON?

If the $R_b$ excess at LEP is real, then any explanation in terms of renormalizable loop corrections leads to important new decay modes of the $t$ quark and suppresses the $t \to bW$ branching ratio. In the two-Higgs-doublet model, the branching ratio of $Z \to b \bar b$ + a light boson which decays itself predominantly into $b \bar b$ is at least of order $10^{-4}$.

hep-ph↗
arXiv1994

Muon Number Violating Processes in Single Particle Extensions of the Standard Model

We study the one-loop induced muon number processes when the standard model is minimally extended to include a $\rm SU(2)$ singlet of a charged scalar $h^+$ and a neutral fermion $N$. We find that $μ\rightarrow e γ$ is more sensitive for the former model whereas $μ-e$ conversion in nuclei for the latter. Effects of a scalar leptoquark $y^{1/3}$ and a heavy vector fermion $E^-$, which induce tree level rare muon decays, are also discussed.

hep-ph↗
arXiv1994

Phenomenological Consequences of Singlet Neutrinos

In this paper, we study the phenomenology of right-handed neutrino isosinglets. We consider the general situation where the neutrino masses are not necessarily given by $m_D^2/M$, where $m_D$ and $M$ are the Dirac and Majorana mass terms respectively. The consequent mixing between the light and heavy neutrinos is then not suppressed, and we treat it as an independent parameter in the analysis. It turns out that $μ-e$ conversion is an important experiment in placing limits on the heavy mass scale ($M$) and the mixing. Mixings among light neutrinos are constrained by neutrinoless double beta decay, as well as by solar and atmospheric neutrino experiments. Detailed one-loop calculations for lepton number violating vertices are provided.

hep-ph↗
arXiv1994

Lepton flavor changing processes and CP violation in the 331 model

By extending the electroweak gauge group to $SU(3)_L\times U(1)_Y$, the 331 model incorporates dilepton gauge bosons $Y$ which do not respect individual lepton family number. We point out that, in addition to family diagonal couplings such as $Y$--$e$--$e$ that change lepton family number by two units, dileptons may also have family non-diagonal couplings such as $Y$--$μ$--$e$. The latter coupling violates lepton family number by a single unit and manifests itself via lepton flavor changing decays such as $μ\to3e$ and $μ\to eγ$. The family non-diagonal interaction can be CP violating and typically generates extremely large leptonic electric dipole moments. We demonstrate a natural mechanism for eliminating both single unit lepton flavor violation and large leptonic CP violation. Although we focus on the 331 model, our results are applicable to other dilepton models as well, including $SU(15)$ grand unification.

hep-ph↗
arXiv1993

Can $μ$--$e$ Conversion in Nuclei be a Good Probe for Lepton-Number Violating Higgs Couplings ?

Motivated by the improving sensitivity, $R$, of experiments on $μ~Ti \rightarrow e~Ti$ and the enhanced Higgs nucleon interaction, we study this lepton number violating process induced by Higgs exchange. Taking the possible sensitivity, $R \simeq 10^{-16}$, we obtain the constraint on the Higgs-muon-electron vertex, $κ_{μe}$, to be less than $2.4\times10^{-7}$ if the masses of the Higgs scalar and $W$ gauge boson are the same. $κ_{μe}$ is also calculated for some models.

hep-ph↗
arXiv1993

New Supersymmetric Option for Two Higgs Doublets

If the standard electroweak gauge model is embedded in a larger theory which is supersymmetric and the latter breaks down to the former at some mass scale, then the reduced Higgs potential at the electroweak mass scale may differ from that of the well-known minimal supersymmetric extension. Specifically, if the larger theory is based on $\rm {SU(2)_L \times SU(2)_R \times U(1)}$, an interesting alternative exists for two Higgs doublets.

hep-ph↗
arXiv1993

SSC Phenomenology of the 331 Model of Flavor

The 331 model offers an explanation of flavor by anomaly cancellation between three families. It predicts three exotic quarks, $Q=D$, $S$, $T$, and five extra gauge bosons comprising an additional neutral $Z_2$ and four charged dileptonic gauge bosons $(Y^{--},Y^-)$, $(Y^{++},Y^+)$. Production of $Q\overline{Q}$, $QY$, $YY$ and $Z_2$ at the SSC is calculated, and signatures are discussed.

hep-ph↗
arXiv1993

Symmetry Remnants: Rationale for Having Two Higgs Doublets

There is a good reason why the standard electroweak SU(2) X U(1) gauge model may be supplemented by two Higgs scalar doublets. They may be remnants of the spontaneous breaking of an SU(2) X SU(2) X U(1) gauge symmetry at a much higher energy scale. In one case, the two-doublet Higgs potential has a custodial SU(2) symmetry and implies an observable scalar triplet. In another, a light neutral scalar becomes possible.

hep-ph↗
arXiv1992

The electroweak theory of SU(3) $\times$ U(1)

An electroweak model of SU(3) $\times$ U(1) gauge group is studied. {}From the group theoretical constraint, the symmetry breaking of this model to the standard model occurs at 1.7~TeV or lower. Hence the mass of the new neutral gauge boson is less than 1.7 TeV. The $Y^\pm$ and $Y^{\pm\pm}$ masses are found to be less than half of the $Z_2$ mass. Thus, the decays $Z_2 \to Y^{++} Y^{--}$ with $Y^{++} \to 2\ell^+ \: (\ell \!=\! e,μ,τ)$ is allowed, providing spectacular signatures at future colliders. {}From the flavor-changing neutral current processes, the representations of quarks can be uniquely determined. The neutrino-isoscalar scattering experiments are also considered.

hep-ph↗
arXiv1992

Search for Dileptons in Z decay

The lepton family number violation $Z$ boson decay, $Z \to e^-e^-μ^+μ^+$ or $e^+e^+μ^-μ^-$, mediated by a dilepton, e.g. from an SU(15) theory, is calculated. The branching ratio of such exotic decay for allowed dilepton masses is found to be smaller than 10$^{-10}$.

hep-ph↗
arXiv1992

Search for Heavy Leptons at Hadron Colliders

Four models are considered which contain heavy leptons beyond the three families of the standard model. Two are fourth-generation extensions of the standard model in which the right-handed heavy leptons are either isosinglets or in an isodoublet; the other two are motivated by the aspon model of CP violation. In all these models, the heavy neutrino can either be heavier than, or comparable in mass to, the charged lepton leading to the possibility that the charged lepton is very long-lived. Production cross section and signatures for the heavy leptons are computed for the SSC and LHC.

hep-ph↗
arXiv1992

Phenomenological Aspects of Supersymmetric Standard Models without Grand Unification

When the GUT relation on gaugino masses is relaxed, the mass and composition of the lightest neutralino are different from those in the GUT case. We discuss its phenomenological implications on the relic abundance of the neutralinos and on superparticle searches. In particular, we focus on the case where the neutral component of Winos dominates the lightest neutralino. It turns out the Wino-LSP is not a candidate for the dark matter.

hep-ph↗
arXiv1992

Dilepton Production in $e^- p$ and $e^+ e^-$ Colliders

In an $e^- p$ collider, a striking signature for a dilepton gauge boson is \ep \ ; this cross-section is calculated by using the helicity amplitude technique. At HERA, with center-of-mass energy $\sqrt s = 314 GeV$, a dilepton mass above $150 GeV$ is inaccessible but at LEPII-LHC, with a center-of-mass energy $\sqrt s = 1790 GeV $, masses up to 650 GeV can be discovered. In an $e^+ e^-$ collider, the signature is \ee \ . The cross-sections of this process are also calculated for the center-of-mass energies $\sqrt s = 200, 500$ and $1000 GeV$.

hep-ph↗