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P. Q. Hung

Publications and source records attributed to P. Q. Hung.

At least 19 recordsLinked to original sources
arXiv2024

A model of light pseudoscalar dark matter

The EW-$ν_R$ model was constructed in order to provide a seesaw scenario operating at the Electroweak scale $Λ_{EW} \sim 246$ GeV, keeping the same SM gauge structure. In this model, right-handed neutrinos are non-sterile and have masses of the order of $Λ_{EW}$. They can be searched for at the LHC along with heavy mirror quarks and leptons, the lightest of which have large decay lengths. The seesaw mechanism requires the existence of a complex scalar which is singlet under the SM gauge group. The imaginary part of this complex scalar denoted by $A^{0}_s$ is proposed to be the sub-MeV dark matter candidate in this manuscript. We find that the sub-MeV scalar can serve as a viable non-thermal feebly interacting massive particle (FIMP)-DM candidate. This $A_s^0$ can be a naturally light sub-MeV DM candidate due to its nature as a pseudo-Nambu-Goldstone (PNG) boson in the model. We show that the well-studied freeze out mechanism falls short in this particular framework producing DM overabundance. We identify that the freeze in mechanism produce the correct order of relic density for the sub-MeV DM candidate satisfying all applicable constraints. We then discuss the DM parameter space allowed by the current bounds from the direct and indirect searches for this sub-MeV DM. This model has a very rich scalar sector, consistent with various experimental constraints, predicts a $\sim 125$ GeV scalar with the SM Higgs characteristics satisfying the current LHC Higgs boson data.

hep-ph↗
arXiv2024

MoEDAL search in the CMS beam pipe for magnetic monopoles produced via the Schwinger effect

We report on a search for magnetic monopoles (MMs) produced in ultraperipheral Pb--Pb collisions during Run-1 of the LHC. The beam pipe surrounding the interaction region of the CMS experiment was exposed to 184.07 \textmu b$^{-1}$ of Pb--Pb collisions at 2.76 TeV center-of-mass energy per collision in December 2011, before being removed in 2013. It was scanned by the MoEDAL experiment using a SQUID magnetometer to search for trapped MMs. No MM signal was observed. The two distinctive features of this search are the use of a trapping volume very close to the collision point and ultra-high magnetic fields generated during the heavy-ion run that could produce MMs via the Schwinger effect. These two advantages allowed setting the first reliable, world-leading mass limits on MMs with high magnetic charge. In particular, the established limits are the strongest available in the range between 2 and 45 Dirac units, excluding MMs with masses of up to 80 GeV at 95\% confidence level.

nucl-ex↗
arXiv2023

A new look at the Dirac quantization condition

The angular momentum of any quantum system should be {\it unambiguously} quantized. We show that such a quantization fails for a pure Dirac monopole due to a previously overlooked field angular momentum from the monopole-electric charge system coming from the magnetic field of the Dirac string and the electric field of the charge. Applying the point-splitting method to the monopole-charge system yields a total angular momentum which obeys the standard angular momentum algebra, but which is gauge {\it variant}. In contrast it is possible to properly quantize the angular momentum of a topological 't Hooft-Polyakov monopole plus charge. This implies that pure Dirac monopoles are not viable -- only 't Hooft-Polyakov monopoles are theoretically consistent with angular momentum quantization and gauge invariance.

hep-th↗
arXiv2023

All in the Family: the quintessential kinship between Inflation and Dark Energy

A unified dynamical model of dark energy and inflation is presented, in which both phenomena are driven by axion-like fields-quintessences-of spontaneously broken global $U(1)_A$'s symmetries whose potentials are induced by instantons of the QCD gauge group $SU(3)_c$ for inflation and of a new strongly interacting gauge group $SU(2)_Z$ for dark energy. It is shown that $SU(3)_c$ and $SU(2)_Z$ fit snugly into a unified gauge group $SU(5)_Z$, {\em Ischyr$\acute{o}$s Unification Theory} or {\em IUT}, which is spontaneously broken down to $SU(3)_c \times SU(2)_Z \times U(1)_X$. A judicious choice of $SU(5)_Z$ representations leads to the $SU(3)_c$ and $SU(2)_Z$ couplings growing strong at $Λ_{QCD} \sim 200 \mev$ and $Λ_Z \sim 10^{-3} eV$ respectively. The model predicts particles carrying $SU(2)_Z$ quantum numbers which can be searched for at colliders such as the LHC and which, as a result, might indirectly reveal the nature of dark energy and perhaps inflation in a laboratory. In addition, the fermionic spectrum of the model contains a possible candidate for dark matter.

hep-ph↗
arXiv2022

Search for Highly-Ionizing Particles in pp Collisions at the LHC's Run-1 Using the Prototype MoEDAL Detector

A search for highly electrically charged objects (HECOs) and magnetic monopoles is presented using 2.2 fb-1 of p - p collision data taken at a centre of mass energy (ECM) of 8 TeV by the MoEDAL detector during LHC's Run-1. The data were collected using MoEDAL's prototype Nuclear Track Detector array and the Trapping Detector array. The results are interpreted in terms of Drell-Yan pair production of stable HECO and monopole pairs with three spin hypotheses (0, 1/2 and 1). The search provides constraints on the direct production of magnetic monopoles carrying one to four Dirac magnetic charges (4gD) and with mass limits ranging from 590 GeV/c^2 to 1 TeV/c^2. Additionally, mass limits are placed on HECOs with charge in the range 10e to 180e, where e is the charge of an electron, for masses between 30 GeV/c^2 and 1 TeV/c^2.

hep-ex↗
arXiv2022

First experimental search for production of magnetic monopoles via the Schwinger mechanism

Schwinger showed that electrically-charged particles can be produced in a strong electric field by quantum tunnelling through the Coulomb barrier. By electromagnetic duality, if magnetic monopoles (MMs) exist, they would be produced by the same mechanism in a sufficiently strong magnetic field. Unique advantages of the Schwinger mechanism are that its rate can be calculated using semiclassical techniques without relying on perturbation theory, and the finite MM size and strong MM-photon coupling are expected to enhance their production. Pb-Pb heavy-ion collisions at the LHC produce the strongest known magnetic fields in the current Universe, and this article presents the first search for MM production by the Schwinger mechanism. It was conducted by the MoEDAL experiment during the 5.02 TeV/nucleon heavy-ion run at the LHC in November 2018, during which the MoEDAL trapping detectors (MMTs) were exposed to 0.235 nb$^{-1}$ of Pb-Pb collisions. The MMTs were scanned for the presence of magnetic charge using a SQUID magnetometer. MMs with Dirac charges 1$g_D$ $\leq$ $g$ $\leq$ 3$g_D$ and masses up to 75 GeV/c$^2$ were excluded by the analysis. This provides the first lower mass limit for finite-size MMs from a collider search and significantly extends previous mass bounds.

hep-ex↗
arXiv2021

An Electroweak Monopole, Dirac Quantization and the Weak Mixing Angle

We consider an extension of the Standard Model that was proposed recently by one of the current authors (PQH), which admits magnetic monopoles with a mass of order of a few TeV. We impose, in addition to topological quantization in the SU(2) sector of the model, the Dirac Quantization Condition (DQC) required for consistency of the quantum theory of a charged electron in the presence of the monopole. This leads to the prediction ${\rm sin}^2θ_W = 1/4$, where $θ_W$ is the weak mixing angle at the energy scale set by the monopole mass. A leading-order renormalization-group analysis yields the value of ${\rm sin}^2 θ_W \simeq 0.231$ at the $Z$-boson mass, as measured by experiment, under suitable conditions on the spectrum of the extra particles in the model.

hep-ph↗
arXiv2021

The Weak Eightfold Way: $SU(3)_W$ unification of the electroweak interactions

In a recent work, a successful prediction has been made for $\sin^2 θ_W$ at an energy scale of O(TeV) based on the Dirac quantization condition of an electroweak monopole of the EW-$ν_R$ model. The fact that such a prediction can be made has prompted the following question: Can $SU(2)$ be unified with $U(1)$ at O(TeV) scale since a prediction for $\sin^2 θ_W$ necessarily relates the $U(1)$ coupling $g^{\prime}$ to the $SU(2)$ weak coupling $g$? It is shown in this manuscript that this can be accomplished by embedding $SU(2) \times U(1)$ into $SU(3)_W$ (The Weak Eightfold Way) with the following results: 1) The same prediction of the weak mixing angle is obtained; 2) The scalar representations of $SU(3)_W$ contain all those that are needed to build the the EW-$ν_R$ model and, in particular, the real Higgs triplet used in the construction of the electroweak monopole. 3) Anomaly freedom requires the existence of mirror fermions present in the EW-$ν_R$ model. 4) Vector-Like Quarks (VLQ) with unconventional electric charges are needed to complete the $SU(3)_W$ representations containing the right-handed up-quarks, with interesting experimental implications such as the prediction of doubly-charged hybrid mesons.

hep-ph↗
arXiv2020

Topologically stable, finite-energy electroweak-scale monopoles

The existence of a magnetic monopole, if it exists, remains elusive. Experimental searches have been carried out and are continuing in this quest. Of great uncertainty is the mass of the monopole which is model-dependent and ranging from some Grand Unified scale to the electroweak scale. In this paper, we propose a model where topologically stable, finite-energy monopoles {\em à la} 't Hooft-Polyakov could exist with a mass proportional to the electroweak scale. This comes about in a model of neutrino masses where right-handed neutrinos are {\em non-sterile} whose electroweak-scale Majorana masses are obtained by the coupling to a complex {\em triplet} Higgs field. Custodial symmetry which insures $M_W=M_Z \cos θ_W$ requires the introduction of another triplet Higgs field but {\em real} this time. It is this {\em real Higgs triplet} that is at the core of our proposal.

hep-ph↗
arXiv2019

The Lifetime Frontier: Search for New Physics with Long-Lived Particles

The search for new physics with long-lived particles is an ongoing and thriving effort in the High Energy Physics community which necessitates new search strategies such as novel algorithms, novel detectors, etc...For these reasons, one could perhaps add another frontier, the Lifetime Frontier, to the standard three (Energy, Intensity and Cosmic). In this talk, I will describe a BSM physics model whose characteristic signatures are decays of new (mirror) fermions at displaced vertices, a domain belonging to the Lifetime Frontier. It is a model of {\em non-sterile} right-handed neutrinos whose masses are proportional to the electroweak scale $Λ_{EW} \sim 246 \, GeV$. The model proposed a solution to the strong CP problem with a surprising connection between the sizes of the neutrino masses and the $θ$-angle which contributes to the neutron electric dipole moment.

hep-ph↗
arXiv2018

Mirror fermions and the strong CP problem: A new axionless solution and experimental implications

A new solution to the strong CP problem with distinct experimental signatures (long-lived particles) at the LHC is proposed. It is based on the Yukawa interactions between mirror quarks, Standard Model (SM) quarks and Higgs singlets. (Mirror quarks and leptons which include non-sterile right-handed neutrinos whose Majorana masses are proportional to the electroweak scale, form the basis of the EW-$ν_R$ model.) The aforementioned Yukawa couplings can in general be complex and can contribute to $Arg\, Det M$ ($\barθ = θ_{QCD} + Arg\, Det M$) at tree-level. The model contains a Peccei-Quinn-type global symmetry which allows it to rotate away $θ_{QCD}$.The crux of matter in this manuscript is the fact that {\em no matter how large} the CP-violating phases in the Yukawa couplings might be, $Arg\, Det M$ can remain small i.e. $\barθ < 10^{-10}$ for reasonable values of the Yukawa couplings and, in fact, vanishes when the VEV of the Higgs singlet (responsible for the Dirac part of the neutrino mass in the seesaw mechanism) vanishes. The smallness of the contribution to $\barθ$ is {\em principally due} to the smallness of the ratio of the two mass scales in the seesaw mechanism: the Dirac and Majorana mass scales.

hep-ph↗
arXiv2018

Constraints from the S-parameter on models with scalar triplets

Models with scalar triplets can have a large impact on the electroweak precision S-parameter and have to be dealt "with extreme prejudice". Such models, and in particular the Georgi-Machacek (GM) model, involve a complex triplet scalar containing doubly-charged Higgses plus a real triplet and are of recent phenomenological interests. It turns out that large mass splittings within the triplet will not be allowed by the S-parameter in the absence of extra fermionic degrees of freedom. Simply speaking, having only an extra triplet of scalars severely restricts the mass splitting within that triplet even with the present precision on the S-parameter which will further be improved with the proposed Higgs factories.

hep-ph↗
arXiv2018

Expression of Interest for Evolution of the Mu2e Experiment

We propose an evolution of the Mu2e experiment, called Mu2e-II, that would leverage advances in detector technology and utilize the increased proton intensity provided by the Fermilab PIP-II upgrade to improve the sensitivity for neutrinoless muon-to-electron conversion by one order of magnitude beyond the Mu2e experiment, providing the deepest probe of charged lepton flavor violation in the foreseeable future. Mu2e-II will use as much of the Mu2e infrastructure as possible, providing, where required, improvements to the Mu2e apparatus to accommodate the increased beam intensity and cope with the accompanying increase in backgrounds.

physics.ins-det↗
arXiv2018

Electron Electric Dipole Moment in Mirror Fermion Model with Electroweak Scale Non-sterile Right-handed Neutrinos

The electric dipole moment of the electron is studied in detail in an extended mirror fermion model with the following unique features of (a) right-handed neutrinos are non-sterile and have masses at the electroweak scale, and (b) a horizontal symmetry of the tetrahedral group is used in the lepton and scalar sectors. We study the constraint on the parameter space of the model imposed by the latest ACME experimental limit on electron electric dipole moment. Other low energy experimental observables such as the anomalous magnetic dipole moment of the muon, charged lepton flavor violating processes like muon decays into electron plus photon and muon-to-electron conversion in titanium, gold and lead are also considered in our analysis for comparison. In addition to the well-known CP violating Dirac and Majorana phases in the neutrino mixing matrix, the dependence of additional phases of the new Yukawa couplings in the model is studied in detail for all these low energy observables.

hep-ph↗
arXiv2017

Top Quark Rare Decays via Loop-Induced FCNC Interactions in Extended Mirror Fermion Model

Flavor changing neutral current (FCNC) interactions for a top quark $t$ decays into $Xq$ with $X$ represents a neutral gauge or Higgs boson, and $q$ a up- or charm-quark are highly suppressed in the Standard Model (SM) due to the Glashow-Iliopoulos-Miami mechanism. Whilst current limits on the branching ratios of these processes have been established at the order of $10^{-4}$ from the Large Hadron Collider experiments, SM predictions are at least nine orders of magnitude below. In this work, we study some of these FCNC processes in the context of an extended mirror fermion model, originally proposed to implement the electroweak scale seesaw mechanism for non-sterile right-handed neutrinos. We show that one can probe the process $t \to Zc$ for a wide range of parameter space with branching ratios varying from $10^{-6}$ to $10^{-8}$, comparable with various new physics models including the general two Higgs doublet model with or without flavor violations at tree level, minimal supersymmetric standard model with or without $R$-parity, and extra dimension model.

hep-ph↗
arXiv2017

A non-vanishing neutrino mass and the strong CP problem: A new solution from the perspective of the EW-$ν_R$ model

The EW-$ν_R$ model was constructed to provide a scenario in which right-handed neutrinos are non-sterile and have masses proportional to the electroweak scale, providing an opportunity to test the seesaw mechanism at the LHC. What was hidden in the model until recently is the chiral symmetry which helps solve the strong CP problem by using it to rotate $θ_{QCD}$ to zero. It turns out the contribution from the electroweak sector to the effective $\barθ$ is proportional to the light neutrino masses and is naturally small, satisfying the constraint coming from the present absence of the neutron electric dipole moment, and without the need for an axion. Talk presented at the APS Division of Particles and Fields Meeting (DPF 2017), July 31-August 4, 2017, Fermilab. C170731

hep-ph↗
arXiv2017

What does a non-vanishing neutrino mass have to say about the strong CP problem?

A new solution to the strong CP problem with distinct experimental signatures at the LHC is proposed. It is based on the Yukawa interactions between mirror quarks, Standard Model (SM) quarks and Higgs singlets. (Mirror quarks and leptons which include non-sterile right-handed neutrinos whose Majorana masses are proportional to the electroweak scale, form the basis of the EW-$ν_R$ model.) The aforementioned Yukawa couplings can in general be complex and can contribute to $Arg\, Det M$ ($\barθ = θ_{QCD} + Arg\, Det M$) at tree-level. The crux of matter in this manuscript is the fact that {\em no matter how large} the CP-violating phases in the Yukawa couplings might be, $Arg\, Det M$ can remain small i.e. $\barθ < 10^{-10}$ for reasonable values of the Yukawa couplings and, in fact, vanishes when the VEV of the Higgs singlet (responsible for the Dirac part of the neutrino mass in the seesaw mechanism) vanishes. The smallness of the contribution to $\barθ$ is {\em principally due} to the smallness of the ratio of the two mass scales in the seesaw mechanism: the Dirac and Majorana mass scales.

hep-ph↗