arXiv subjects

C. S. Lim

Publications and source records attributed to C. S. Lim.

48 records · Page 3Linked to original sources

arXiv2003

How precisely can we reduce the three-flavor neutrino oscillation to the two-flavor one only from (δm^2_{12})/(δm^2_{13}) <~ 1/15 ?

We derive the reduction formula, which expresses the survival rate for the three-flavor neutrino oscillation by the two-flavor one, to the next-to-leading order in case there is one resonance due to the matter effect. We numerically find that the next-to-leading reduction formula is extremely accurate and the improvement is relevant for the precision test of solar neutrino oscillation and the indirect measurment of CP violation in the leptonic sector. We also derive the reduction formula, which is slightly different from that previously obtained, in case there are two resonances. We numerically verify that this reduction formula is quite accurate and is valid for wider parameter region than the previously obtained ones are.

hep-ph↗

arXiv2002

The Hosotani Mechanism in Bulk Gauge Theories with an Orbifold Extra Space S^1/Z_2

We pursue the possibility of the scenario in which the Higgs field is identified with the extra-space component of a bulk gauge field. The space-time we take is M$^{4}$ $\otimes$ S$^1$/Z$_2$. We show that a non-trivial Z$_2$-parity assignment allows some of the extra-space component to have radiatively induced VEV, which strongly modifies the mass spectrum and gauge symmetry of the theory, realized by oribifolding. In particular we investigate the dynamical mass generation of zero-mode fermion and spontaneous gauge symmetry breaking due to the VEV. The gauge theories we adopt are a prototype model SU(2) and SU(3) model, of special interest as the realistic minimal scheme to incorporate the standard model SU(2) $\times$ U(1).

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arXiv2000

Pseudo-Dirac Scenario for Neutrino Oscillations

We argue how pseudo-Dirac scenario for neutrinos leads to rich neutrino oscillation phenomena, including oscillation inside each generation. The pseudo-Dirac scenario is generalized by incorporating generation mixings and formulae for the various neutrino oscillations are derived. As the application we compare the formulae with the corresponding data. We find that observed pattern of mixings, such as almost maximal mixing in the atmospheric neutrino oscillation, is naturally explained in the generalized Pseudo-Dirac scenario with small generation mixings. We, however, also point out that there remain some problems to be settled for this scenario to be viable. The possible theoretical framework to realize the pseudo-Dirac scenario is also briefly commented on.

hep-ph↗

arXiv2000

Implications of sigma models in the standard model and beyond

After a brief introduction to the sigma model in QCD, we discuss how the sigma model can be relevant in the Standard Model. It is shown to be useful in the analysis of weak processes, such as the study of $Δ{I} = 1/2$ rule, and in the analysis of the Higgs sector as well. The sigma model description is also shown to be quite useful in searching for the effects of New Physics via gauge boson self-interactions.

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arXiv1999

Effective Action Approach to Heavy Particle Contributions and Wilsonian Renormalization

We work in theories with both light and heavy particles. A method to obtain an effective low energy action with respect to the light particle is presented. Thanks to Wilsonian renormalization, we obtain effective actions with finite number of local operators describing possible non-decoupling effects of heavy particles. The validity of the method is first checked by explicit computation of a specific observable, the $ρ$ - parameter, in the framework of effective theory. Then we discuss a procedure to obtain the full effective action with respect to light particles in a typical example of the system of (t, b) doublet, gauge bosons and Higgs doublet, regarding only t quark as a heavy particle.

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arXiv1998

Lepton-Flavour Violation in Ordinary and Supersymmetric Grand Unified Theories

By an explicit calculation we show that in ordinary SU(5) logarithmic divergence in the amplitude of $μ\to eγ$ cancels among diagrams and remaining finite part is suppressed by at least $1/M_{GUT}^2$. In SUSY SU(5), when the effect of flavour changing wave function renormalization is taken into account such logarithmic correction disappears, provided a condition is met among SUSY breaking masses. In SUGRA-inspired SUSY GUT the remaining logarithmic effect is argued not to be taken as a prediction of the theory.

hep-ph↗

arXiv1998

The Gauge Hierarchy Problem and Higher Dimensional Gauge Theories

We report on an attempt to solve the gauge hierarchy problem in the framework of higher dimensional gauge theories. Both classical Higgs mass and quadratically divergent quantum correction to the mass are argued to vanish. Hence the hierarchy problem in its original sense is solved. The remaining finite mass correction is shown to depend crucially on the choice of boundary condition for matter fields, and a way to fix it dynamically is presented. We also point out that on the simply-connected space $S^2$ even the finite mass correction vanishes.

hep-th↗

arXiv1998

Grand Unified Theories and Lepton-Flavour Violation

Lepton-flavour violating processes, such as $μ\to eγ$, are studied in ordinary (non-SUSY) SU(5) and SUSY SU(5) grand unified theories. First given are some introductory argument on the mechanism of U.V. divergence cancellation in flavour changing neutral current processes and on the decoupling of particles with GUT scale masses . We next see that such general argument is confirmed by an explicit calculation of the amplitude of $μ\to eγ$ in ordinary SU(5), which shows that logarithmic divergence really cancels among diagrams and remaining finite part are suppressed by at least $1/M_{GUT}^2$. In SUSY SU(5), flavour changing slepton mass-squared term get a logarithmic correction, as recently claimed. However, when the effect of flavour changing wave function renormalization is also taken into account such logarithmic correction turns out to disappear, provided a condition is met among SUSY breaking soft masses. In SUGRA-inspired SUSY GUT, such condition is not satisfied. But the remaining logarithmic effect is argued not to be taken as a prediction of the theory associated with an irrelevant operator. We find that the log-correction should not exist in models with gauge mediated SUSY breaking.

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arXiv1997

Quaternionic Mass Matrices and CP Symmetry

A viable formulation of gauge theory with extra generations in terms of quaternionic fields is presented. For the theory to be acceptable, the number of generations should be equal to or greater than 4. The quark-lepton mass matrices are generalized into quaternionic matrices.It is concluded that explicit CP violation automatically disappears in both strong- and weak-interaction sectors.

hep-ph↗

arXiv1995

Non-decoupling Effects of Heavy Particles in Triple Gauge Boson Vertices

Non-decoupling effects of heavy particles present in beyond-the-standard models are studied for the triple gauge boson vertices $γW^+W^-$ and $Z^0W^+W^-$. We show from a general argument that the non-decoupling effects are described by four independent parameters, in comparison with the three parameters $S$, $T$ and $U$ in the oblique corrections. These four parameters of the effective triple gauge boson vertices are computed in two beyond-the-standard models. We also study the relation of the four parameters to the $S$, $T$, $U$ parameters, relying on an operator analysis.

hep-ph↗

arXiv1994

A Natural Explanation of All Solar Neutrino Data by Resonant Spin-Flavor Precession Scenario

It is emphasized that the $E_ν$ (neutrino energy) spectrum of the $ν_e$ survival probability in the Resonant Spin-Flavor Precession (RSFP) scenario has very desirable shape to reconcile all existing solar neutrino data. As the result, the RSFP scenario is shown to have rather broad allowed region to reconcile the data in the ($B,\ Δm^2$) plane, with $B$ being the magnetic field strength inside the Sun. The sensitivity of the allowed region on the different choices of the $B$ profile, and the time variations of the solar neutrino event rates in the RSFP scenario are also discussed in some detail.

hep-ph↗

arXiv1994

CP in Orbifold Models

We study CP in orbifold models. It is found that the orbifolds always have some automorphisms as CP symmetry. The symmetries are restricted non-trivially due to geometrical structure of the orbifolds. Explicit analysis on Yukawa couplings also shows that CP is not violated in orbifold models.

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