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Search Results: 1 - 10 of 210873 matches for " P. Q. Hung "
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Implications of right-handed neutrinos with electroweak-scale masses
Hung, P. Q.
High Energy Physics - Phenomenology , 2007,
Abstract: The possibility of constructing a model in which right-handed neutrinos have electroweak-scale masses as well as being {\em non-sterile} was espoused in Ref. 1. In this talk, I will review the ideas and results of Ref. 1 and discuss its implications for colliders such as the Tevatron, LHC and ILC.
Shadow vacuum alignment and dark energy
Hung, P. Q.
High Energy Physics - Phenomenology , 2007,
Abstract: In a recent model of dark energy (with several phenomenological consequences), the universe is assumed to be trapped in a false vacuum with an energy density of the order of (10^{-3} eV)^4, mimicking the presently successful $\Lambda CDM$ scenario. This involves a new gauge group SU(2)_Z, {\em the shadow sector}, which becomes strong at a scale $\Lambda_Z \sim 10^{-3} eV$. The model is described by the SU(2)_Z instanton-induced potential of an axion-like scalar field, a_Z, with two degenerate vacuua. The false (metastable) vacuum appears as a result of an phenomenological (ad-hoc) soft breaking term linear in a_Z which explicitely breaks that degeneracy. In this paper, we discuss a possible dynamical origin for this soft breaking term as coming from the alignment of the vacuum along a direction in which the condensate of the shadow fermions, $<\bar{\psi}^{(Z)}_{i} i \gamma_{5} \psi^{(Z)}_{i}>$ which breaks spontaneously both P and CP, is non-vanishing. The present universe lives in a vacuum which violates both P and CP in the shadow SU(2)_Z sector!
$Z \to b {\bar b}$ in a composite model of fermions
P. Q. Hung
Physics , 1996,
Abstract: A composite model of fermions is proposed to explain the "anomaly" in $Z \rightarrow b {\bar b}$ and, to a lesser extent, in $Z \rightarrow c {\bar c}$. It contains a {\em nonsequential} fourth family whose mass of one member (the charge -1/3 quark) is constrained to be between 47 GeV and 49 GeV. The charge +2/3 quark is constrained to lie between 67 GeV and 107 GeV. This opens up the exciting prospect for near-future discoveries at LEP2 and possibly at the Tevatron.
A phenomenological Theory of Fermion Masses and Mixings
P. Q. Hung
Physics , 1994, DOI: 10.1142/S0217732394001593
Abstract: A phenomenological theory of fermion masses and mixings is constructed within the framework of a four- family symmetry. It is found that the most favored set of relevant CKM elements are $|V_{us}|\approx 0.222$, $|V_{cb}|\approx 0.044$, $|V_{ub}/V_{cb}|\approx 0.082$, $|V_{ud}|\approx 0.974$, $|V_{cs}|\approx 0.9736$, $|V_{cd}|\approx 0.224$ with $\hat{B}_K \approx 0.8$. The top quark mass is predicted to be 258 GeV at 1 GeV with its physical mass approximately equal to 153 GeV. The Majorana scale associated with the fourth neutrino is bound from above to be 6.4 TeV.
Electroweak-scale mirror fermions, $μ\to e γ$ and $τ\to μ γ$
P. Q. Hung
Physics , 2007, DOI: 10.1016/j.physletb.2007.12.005
Abstract: The Lepton Flavour Violating (LFV) processes $\mu \to e \gamma$ and $\tau \to \mu \gamma$ are estimated in a model of electroweak-scale right-handed neutrinos. The present bounds on the branching ratios, $B(\mu \to e \gamma)< 1.2 \times 10^{-11}$, $B(\tau \to \mu \gamma) < 6.8 \times 10^{-8}$ (BaBar) and $< 4.5 \times 10^{-8}$ (Belle), puts strong constraints on the parameters of the model. This constraint links low energy rare decay processes to high-energy phenomena (e.g. decay lengths of the mirror charged leptons which are important in the search for the telltale like-sign dilepton events present in the model of electroweak-scale right-handed neutrinos).
On Neutrino Masses and Family Replication
P. Q. Hung
Physics , 1998, DOI: 10.1103/PhysRevD.59.113008
Abstract: The old issue of why there are more than one family of quarks and leptons is reinvestigated with an eye towards the use of anomaly as a tool for constraining the number of families. It is found that, by assuming the existence of right-handed neutrinos (which would imply that neutrinos will have a mass) and a new chiral SU(2) gauge theory, strong constraints on the number of families can be obtained. In addition, a model, based on that extra SU(2), is constructed where it is natural to have one "very heavy" fourth neutrino and three almost degenerate light neutrinos whose masses are all of the Dirac type.
Teeny, tiny Dirac neutrino masses: an unorthodox point of view
P. Q. Hung
Physics , 2000, DOI: 10.1063/1.1328878
Abstract: There are now strong hints suggesting that neutrinos do have a mass after all. If they do have a mass, it would have to be tiny. Why is it so? Is it Dirac or Majorana? Can one build a model in which a teeny, tiny Dirac neutrino mass arises in a natural way? Can one learn something else other than just neutrino masses? What are the extra phenomenological consequences of such a model? These are the questions that I will try to focus on in this talk.
A Model of Quark and Lepton Masses I: The Neutrino Sector
P. Q. Hung
Physics , 2000, DOI: 10.1103/PhysRevD.62.053015
Abstract: If neutrinos have masses, why are they so tiny? Are these masses of the Dirac type or of the Majorana type? We are already familiar with the mechanism of how to obtain a tiny Majorana neutrino mass by the famous see-saw mechanism. The question is: Can one build a model in which a tiny Dirac neutrino mass arises in a more or less "natural" way? What would be the phenomenological consequences of such a scenario, other than just merely reproducing the neutrino mass patterns for the oscillation data? In this article, a systematic and detailed analysis of a model is presented, with, as key components, the introduction of a family symmetry as well as a new SU(2) symmetry for the right-handed neutrinos. In particular, in addition to the calculations of light neutrino Dirac masses, interesting phenomenological implications of the model will be presented.
Minimal SU(5) Resuscitated by Higgs Coupling Fixed Points
P. Q. Hung
Physics , 1997,
Abstract: The issue of gauge unification in the (non-supersymmetric) Standard Model is reinvestigated. It is found that with just an additional fourth generation of quarks and leptons, $SU(3) \otimes SU(2) \otimes U(1)$ gauge couplings converge to a common point $\sim 2.65 \times 10^{15}$ GeV ($\tau_p \sim 10^{34 \pm 1}$ years) provided the Higgs boson has a mass of at least 210 GeV. The presence of ultraviolet fixed points for the Yukawa and Higgs quartic couplings is found to be the origin of such unification.
See-Sawless Neutrino Masses
P. Q. Hung
Physics , 1998,
Abstract: An alternative to the famous see-saw mechanism is proposed to explain the smallness of the neutrino masses (if present). This model involves a fourth family which mixes very little with the other three. It contains one heavy neutrino (mN > mZ /2) and three very light neutrinos whose masses are radiatively induced. In contrast with the see-saw mechanism, all neutrino masses are Dirac masses. In one particular scenario, the three light neutrinos are almost degenerate in mass and are found to be consistent with fits to the Solar and Atmospheric neutrino deficits. They might even account for the Hot Dark Matter.
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