arXiv subjects

Sechul Oh

Publications and source records attributed to Sechul Oh.

At least 19 recordsLinked to original sources

arXiv2024

Spontaneous Symmetry Breaking and Panic Escape

Panic-induced herding in individuals often leads to social disasters, resulting in people being trapped and trampled in crowd stampedes triggered by panic. We introduce a novel approach that offers fresh insights into studying the phenomenon of asymmetrical panic-induced escape. Our approach is based on the concept of Spontaneous Symmetry Breaking (SSB), a fundamental governing mechanism in the Physical Sciences. By applying the principles of SSB, we conjecture that the onset of disastrous effects of panic can be understood as a SSB phenomenon, and we formulate the process accordingly. We highlight that this way of understanding panic escape leads to simple general measures of preventing catastrophic situations, by considering two crucial parameters: \emph{population density} and \emph{external information}. The interplay of these two parameters is responsible for either breaking or restoring the symmetry of a system. We describe how these parameters are set by design conditions as well as crowd control. Based on these parameters, we discuss strategies for preventing potential social disasters caused by asymmetrical panic escape.

physics.soc-ph↗

arXiv2019

Probing sterile neutrino in $B$ ($D$) meson decays at Belle II (BESIII)

We present, how a systematic study of $B \to D\ell N$ ($D \to K \ell N$) decays with $\ell=\mu,\tau$, at Belle II (BESIII) can provide unambiguous signature of a heavy neutrino $N$ and/or constrain its mixing with active neutrinos $\nu_\ell$, which is parameterized by $|U_{\ell N}|^2$. Our constraint on $|U_{\mu N}|^2$ that can be achieved from the full Belle II data is comparable with what can be obtained from the much larger data set of the upgraded LHCb. Additionally, our method offers better constraint on $|U_{\mu N}|^2$ for mass of sterile neutrino $m_N < 2$ GeV. We can also probe the Dirac and Majorana nature of $N$ by observing the sequential decay of $N$, including suppression from observation of a displaced vertex as well as helicity flip, for Majorana $N$.

hep-ph↗

arXiv2017

Anomalies in (semi)-leptonic $B$ decays $B^{\pm} \to \tau^{\pm} \nu$, $B^{\pm} \to D \tau^{\pm} \nu$ and $B^{\pm} \to D^* \tau^{\pm} \nu$, and possible resolution with sterile neutrino

The universality of the weak interactions can be tested in semileptonic $b \to c$ transitions, and in particular in the ratios $R(D^{(*)}) \equiv \Gamma(B \rightarrow D^{(*)} \tau \nu )/\Gamma(B \rightarrow D^{(*)} \ell \nu )$ (where $\ell = \mu$ or $e$). Due to the recent differences between the experimental measurements of these observables by BaBar, Belle and LHCb on the one hand and the Standard Model predicted values on the other hand, we study the predicted ratios $R(D^{(*)}) = \Gamma(B \rightarrow D^{(*)} \tau +$ "missing" $)/\Gamma(B \rightarrow D^{(*)} \ell \nu )$ in scenarios with an additional sterile heavy neutrino of mass $\sim 1$ GeV. Further, we evaluate the newly defined ratio $R(0) \equiv \Gamma(B \to \tau +$ "missing" $)/\Gamma(B \to \mu \nu )$ in such scenarios, in view of the future possibilities of measuring the quantity at Belle-II.

hep-ph↗

arXiv2015

Model-Independent Analysis of CP Violation in Charmed Meson Decays

We present a model-independent analysis of CP violation, inspired by recent experimental observations, in charmed meson decays. The topological diagram approach is used to study direct CP asymmetries for singly Cabibbo-suppressed two-body hadronic decays of charmed mesons. We extract the magnitudes and relative phases of the corresponding topological amplitudes from available experimental information. In order to get more precise and reliable estimates of direct CP asymmetries, we take into account contributions from all possible strong penguin amplitudes, including the internal $b$-quark penguin contributions. We also study flavor SU(3) symmetry breaking effects in these decay modes and consequently, predict direct CP asymmetries of unmeasured modes.

hep-ph↗

arXiv2011

An extension of tribimaximal lepton mixing

Harrison, Perkins and Scott have proposed simple charged lepton and neutrino mass matrices that lead to the tribimaximal mixing $U_{\rm TBM}$. We consider in this work an extension of the mass matrices so that the leptonic mixing matrix becomes $U_{\rm PMNS}=V_L^{\ell\dagger}U_{\rm TBM}W$, where $V_L^\ell$ is a unitary matrix needed to diagonalize the charged lepton mass matrix and $W$ measures the deviation of the neutrino mixing matrix from the bimaximal form. Hence, corrections to $U_{\rm TBM}$ arise from both charged lepton and neutrino sectors. Following our previous work to assume a Qin-Ma-like parametrization $V_{\rm QM}$ for the charged lepton mixing matrix $V_L^\ell$ in which the {\it CP}-odd phase is approximately maximal, we study the phenomenological implications in two different scenarios: $V_L^\ell=V_{\rm QM}^\dagger$ and $V_L^\ell=V_{\rm QM}$. We find that the latter is more preferable, though both scenarios are consistent with the data within $3\sigma$ ranges. The predicted reactor neutrino mixing angle $\theta_{13}$ in both scenarios is consistent with the recent T2K and MINOS data. The leptonic {\it CP} violation characterized by the Jarlskog invariant $J_{\rm CP}$ is generally of order $10^{-2}$.

hep-ph↗

arXiv2011

Wolfenstein Parametrization at Higher Order: Seeming Discrepancies and Their Resolution

In different Wolfenstein parametrizations derived from different exact parametrizations of the Cabibbo-Kobayashi-Maskawa matrix, we explicitly study seeming discrepancies between the matrix elements at the higher order of the expansion parameter $\lambda$. A systematic way of resolving the seeming discrepancies is proposed. We find that most of the discrepancies can be naturally resolved by a proper redefinition of the numerically small (of order $\lambda$) parameters. Our approach is further applied to the cases for the Wolfenstein-{\it like} parametrizations, such as the Qin-Ma parametrization.

hep-ph↗

arXiv2011

Recent Neutrino Data and a Realistic Tribimaximal-like Neutrino Mixing Matrix

In light of the recent neutrino experimental results from Daya Bay and RENO Collaborations, we construct a realistic tribimaximal-like Pontecorvo-Maki-Nakagawa-Sakata (PMNS) leptonic mixing matrix. Motivated by the Qin-Ma (QM) parametrization for the quark mixing matrix in which the CP-odd phase is approximately maximal, we propose a simple ansatz for the charged lepton mixing matrix, namely, it has the QM-like parametrization, and assume the tribimaximal mixing (TBM) pattern for the neutrino mixing matrix. The deviation of the leptonic mixing matrix from the TBM one is then systematically studied. While the deviation of the solar and atmospheric neutrino mixing angles from the corresponding TBM values, i.e. $\sin^2\theta_{12}=1/3$ and $\sin^2\theta_{23}=1/2$, is fairly small, we find a nonvanishing reactor mixing angle given by $\sin\theta_{13}\approx \lambda/\sqrt{2}$ ($\lambda\approx 0.22$ being the Cabibbo angle). Specifically, we obtain $\theta_{13}\simeq 9.2^{\circ}$ and $\delta_{CP} \simeq \delta_{\rm QM} \simeq {\cal O}(90^{\circ})$. Furthermore, we show that the leptonic \CP violation characterized by the Jarlskog invariant is $|J^{\ell}_{CP}|\simeq \lambda/6$, which could be tested in the future experiments such as the upcoming long baseline neutrino oscillation ones.

hep-ph↗

arXiv2011

Remarks on the Qin-Ma Parametrization of Quark Mixing Matrix

Recently, Qin and Ma (QM) have advocated a new Wolfenstein-like parametrization of the quark mixing matrix based on the triminimal expansion of the Cabibbo-Kobayashi-Maskawa (CKM) parametrization. The CP-odd phase in the QM parametrization is around $90^\circ$ just as that in the CKM parametrization. We point out that the QM parametrization can be readily obtained from the Wolfenstein parametrization after appropriate phase redefinition for quark fields and that the phase $\delta$ in both QM and CKM parametrizations is related to the unitarity angles $\alpha$, $\beta$ and $\gamma$, namely, $\delta= \beta+\gamma$ or $\pi-\alpha$. We show that both QM and Wolfenstein parametrizations can be deduced from the CKM and Chau-Keung-Maiani ones. By deriving the QM parametrization from the Fritzsch-Xing (FX) parametrization of the quark mixing matrix, we find that the phase of the FX form is in the vicinity of $-270^\circ$ and hence $\sin\delta\approx 1$. We discuss the seeming discrepancy between the Wolfenstein and QM parametrizations at the high order of $\lambda\approx |V_{us}|$.

hep-ph↗

arXiv2011

Flavor SU(3) symmetry and QCD factorization in $B \to PP$ and $PV$ decays

Using flavor SU(3) symmetry, we perform a model-independent analysis of charmless $\bar B_{u,d} (\bar B_s) \to PP, ~PV$ decays. All the relevant topological diagrams, including the presumably subleading diagrams, such as the QCD- and EW-penguin exchange diagrams and flavor-singlet weak annihilation ones, are introduced. Indeed, the QCD-penguin exchange diagram turns out to be important in understanding the data for penguin-dominated decay modes. In this work we make efforts to bridge the (model-independent but less quantitative) topological diagram or flavor SU(3) approach and the (quantitative but somewhat model-dependent) QCD factorization (QCDF) approach in these decays, by explicitly showing how to translate each flavor SU(3) amplitude into the corresponding terms in the QCDF framework. After estimating each flavor SU(3) amplitude numerically using QCDF, we discuss various physical consequences, including SU(3) breaking effects and some useful SU(3) relations among decay amplitudes of $\bar B_s \to PV$ and $\bar B_d \to PV$.

hep-ph↗

arXiv2011

Recent Neutrino Data and Type III Seesaw with Discrete Symmetry

In light of the recent neutrino experiment results from Daya Bay and RENO Collaborations, we study phenomenology of neutrino mixing angles in the Type III seesaw model with an discrete $A_4 \times Z_2$ symmetry, whose spontaneously breaking scale is much higher than the electroweak scale. At tree level, the tri-bimaximal (TBM) form of the lepton mixing matrix can be obtained from leptonic Yukawa interactions in a natural way. We introduce all possible effective dimension-5 operators, invariant under the Standard Model gauge group and $A_4 \times Z_2$, and explicitly show that they induce a deviation of the lepton mixing from the TBM mixing matrix, which can explain a large mixing angle $\theta_{13}$ together with small deviations of the solar and atmospheric mixing angles from the TBM. Two possible scenarios are investigated, by taking into account either negligible or sizable contributions from the light charged lepton sector to the lepton mixing matrix. Especially it is found in the latter scenario that all the neutrino experimental data, including the recent best-fit value of $\theta_{13} = 8.68^{\circ}$, can be accommodated. The leptonic CP violation characterized by the Jarlskog invariant $J_{CP}$ has a non-vanishing value, indicating a signal of maximal CP violation.

hep-ph↗

arXiv2011

Constraints on a New Light Spin-One Particle from Rare b -> s Transitions

The anomalously large like-sign dimuon charge asymmetry in semileptonic b-hadron decays recently measured by the D0 Collaboration may be hinting at the presence of CP-violating new physics in the mixing of B_s mesons. It has been suggested that the effect of a nonstandard spin-1 particle lighter than the b quark with flavor-changing couplings to b and s quarks can reproduce the D0 result within its one-sigma range. Here we explore the possibility that the new particle also couples to charged leptons l=e,mu and thus contributes to rare b -> s processes involving the leptons. We consider in particular constraints on its couplings from existing experimental data on the inclusive B -> X_s l^+ l^- and exclusive B -> K^{(*)} l^+ l^- decays, as well as the anomalous magnetic moments of the leptons. We find that there is parameter space of the particle that is allowed by the current data. Future measurements of these B transitions and rare decays of the B_s meson, such as B_s -> (phi,eta,eta') l^+ l^- and B_s -> l^+ l^-, at LHCb and next-generation B factories can probe its presence or couplings more stringently.

hep-ph↗

arXiv2011

Quark-lepton complementarity and tribimaximal neutrino mixing from discrete symmetry

The quark-lepton complementarity (QLC) relations indicate a deep structure that interrelates quarks and leptons. We propose new scenarios, in a seesaw framework with discrete $A_4$ flavor symmetry, which can accommodate the QLC relations and the nonzero neutrino mixing angle $\theta_{13}$ together with all the available neutrino experimental data, in a consistent way to generate the Cabibbo-Kobayashi-Maskawa (CKM) matrix for the quark mixing. Certain effective dimension-5 operators are introduced, which induce a deviation of the lepton mixing matrix from the tribimaximal mixing (TBM) pattern and lead the quark mixing matrix to the CKM one in form. We explicitly demonstrate three different possibilities of constructing the charged lepton mixing matrix and point out that the {\it phases} of whose elements play a crucial role to satisfy the QLC relations. We find that for the reactor mixing angle $\theta_{13}$ its possible values can vary around the center value $\sin \theta_{13} \simeq \lambda /\sqrt{2}$ ($\lambda \simeq 0.22$ being the Cabbibo angle) and have the lower bound $\theta_{13} \gtrsim 3.5^{\circ}$. We also show that sizable leptonic CP violation characterized by the Jarlskog invariant $|J_{\rm CP}|\sim{\cal O}(10^{-2})$ is allowed, which is expected to be tested in the future experiments such as the upcoming long baseline neutrino oscillation ones.

hep-ph↗

arXiv2010

Anomalous CP-Violation in B_s-Bbar_s Mixing Due to a Light Spin-One Particle

The recent measurement of the like-sign dimuon charge asymmetry in semileptonic b-hadron decays by the D0 Collaboration is about 3 sigmas away from the standard-model prediction, hinting at the presence of CP-violating new physics in the mixing of B_s mesons. We consider the possibility that this anomalous result arises from the contribution of a light spin-1 particle. Taking into account various experimental constraints, we find that the effect of such a particle with mass below the b-quark mass can yield a prediction consistent with the anomalous D0 measurement within its one-sigma range.

hep-ph↗

arXiv2009

Rare B Decays with a HyperCP Particle of Spin One

In light of recent experimental information from the CLEO, BaBar, KTeV, and Belle collaborations, we investigate some consequences of the possibility that a light spin-one particle is responsible for the three Sigma^+ -> p mu^+ mu^- events observed by the HyperCP experiment. In particular, allowing the new particle to have both vector and axial-vector couplings to ordinary fermions, we systematically study its contributions to various processes involving b-flavored mesons, including B-Bbar mixing as well as leptonic, inclusive, and exclusive B decays. Using the latest experimental data, we extract bounds on its couplings and subsequently estimate upper limits for the branching ratios of a number of B decays with the new particle. This can serve to guide experimental searches for the particle in order to help confirm or refute its existence.

hep-ph↗

arXiv2009

Lepton FCNC in Type III Seesaw Model

In Type III seesaw model, there are tree level flavor changing neutral currents (FCNC) in the lepton sector, due to mixing of charged particles in the leptonic triplet introduced to realize seesaw mechanism, with the usual charged leptons. In this work we study these FCNC effects in a systematic way using available experimental data. Several FCNC processes have been studied before. The new processes considered in this work include: lepton flavor violating processes $τ\to P l$, $τ\to V l$, $V \to l \bar l'$, $P \to l \bar l'$, $M\to M' l \bar l'$ and muonium-antimuonium oscillation. Results obtained are compared with previous results from $l_i \to l_j l_k \bar l_l$, $l_i \to l_j γ$, $Z \to l \bar l'$ and $μ- e$ conversion. Our results show that the most stringent constraint on the $e$-to-$τ$ FCNC effect comes from $τ\to π^0 e$ decay. $τ\to ρ^0 μ$ and $τ\to π^0 μ$ give very stringent constraints on the $μ$-to-$τ$ FCNC effect, comparable with that obtained from $τ\to μ\bar μμ$ studied previously. The constraint on the $e$-to-$μ$ FCNC effect from processes considered in this work is much weaker than that obtained from processes studies previously, in particular that from $μ- e$ conversion in atomic nuclei. We find that in the canonical seesaw models the FCNC parameters, due to tiny neutrino masses, are all predicted to be much smaller than the constraints obtained here, making such models irrelevant. However, we also find that in certain special circumstances the tiny neutrino masses do not directly constrain the FCNC parameters. In these situations, the constraints from the FCNC studies can still play important roles.

hep-ph↗

arXiv2009

Large Mixing of Light and Heavy Neutrinos in Seesaw Models and the LHC

In the type-I seesaw model the size of mixing between light and heavy neutrinos, nu and N, respectively, is of order the square root of their mass ratio, (m_nu/m_N)^(1/2), with only one generation of the neutrinos. Since the light-neutrino mass must be less than an eV or so, the mixing would be very small, even for a heavy-neutrino mass of order a few hundred GeV. This would make it unlikely to test the model directly at the LHC, as the amplitude for producing the heavy neutrino is proportional to the mixing size. However, it has been realized for some time that, with more than one generation of light and heavy neutrinos, the mixing can be significantly larger in certain situations. In this paper we explore this possibility further and consider specific examples in detail in the context of type-I seesaw. We study its implications for the single production of the heavy neutrinos at the LHC via the main channel q qbar' -> W^* -> l N involving an ordinary charged lepton l. We then extend the discussion to the type-III seesaw model, which has richer phenomenology due to presence of the charged partners of the heavy neutrinos, and examine the implications for the single production of these heavy leptons at the LHC. In the latter model the new kinds of solutions that we find also make it possible to have sizable flavor-changing neutral-current effects in processes involving ordinary charged leptons.

hep-ph↗

arXiv2008

Extracting the CKM phase angle γ(\equiv ϕ_3) from isospin analysis in B\to K πdecays

We propose a new method to extract the CKM phase angle γ(\equiv ϕ_3) from the isospin analysis in B \to K πdecays. Unlike previously proposed methods, we do not employ flavor SU(3) symmetry, so that this method is free from the hadronic uncertainty coming from the SU(3) breaking effect. Neither we adopt any Dalitz-plot analysis, which may involve multiple strong phases and large final state interactions. After including small CP violating terms in B^+ \to K^0 π^+ and color-suppressed electroweak penguin contribution in B^0 \to K^+ π^-, whose values are estimated from the QCD factorization, we obtain γ= ({70}^{+5 +1 +2}_{-14 -1 -3})^\circ \textrm{or} {106^\circ}< γ< {180^\circ}. The first error is due to the experimental errors mainly caused by mixing-induced CP asymmetry S_{{K_s} π^0}. The second and third errors come from the theoretical uncertainty for two above-mentioned small contributions, respectively. Since we utilize only the isospin relations in B \to K πdecays, this method will work well, regardless of possible new physics effects unless the isospin relations do not hold.

hep-ph↗

arXiv2008

Analytic Resolution of Puzzle in $B\to K π$ decays

We present a systematic method to extract each standard model (SM)-{\it like} hadronic parameter as well as new physics parameters in analytic way for $B\to Kπ$ decays. Using the analytic method to the currently available experimental data, we find two possible solutions analytically equivalent: one showing the large SM-{\it like} color-suppressed tree contribution and the other showing the large SM-{\it like} EWP contribution. The magnitude of the NP amplitude and its weak phase are quite large. For instance, we find $|P^{NP}/P| = 0.39\pm0.13$, $ϕ^{NP}=91^\circ\pm15^\circ$ and $δ^{NP}=8^\circ\pm27^\circ$, which are the ratio of the NP-to-SM contribution, the weak and the relative strong phase of the NP amplitude, respectively.

hep-ph↗