arXiv subjects

Eung Jin Chun

Publications and source records attributed to Eung Jin Chun.

At least 109 records · Page 6Linked to original sources

arXiv2006

String Cosmology of the D-brane Universe

We analyze homogeneous anisotropic cosmology driven by the dilaton and the self-interacting ``massive'' antisymmetric tensor field which are indispensable bosonic degrees with the graviton in the NS-NS sector of string theories with D-branes. We found the attractor solutions for this system, which show the overall features of general solutions, and confirmed it through numerical analysis. The dilaton possesses the potential due to the presence of the D-brane and the curvature of extra dimensions. In the presence of the non-vanishing antisymmetric tensor field, the homogeneous universe expands anisotropically while the D-brane term dominates. The isotropy is recovered as the dilaton rolls down and the curvature term dominates. With the stabilizing potential for the dilaton, the isotropy can also be recovered.

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arXiv2006

Axino Light Dark Matter and Neutrino Masses with R-parity Violation

Motivated by the recent observation of the 511 keV $γ$-ray line emissions from the galactic bulge and an explanation for it by the decays of light dark matter particles, we consider the light axino whose mass can be in the 1-10 MeV range, particularly, in the context of gauge-mediated supersymmetry breaking models. We discuss the production processes and cosmological constraints for the light axino dark matter. It is shown that the bilinear R-parity violating terms provide an appropriate mixing between the axino and neutrinos so that the light axino decays dominantly to $e^+ e^- ν$. We point out that the same bilinear R-parity violations consistently give both the lifetime of the axino required to explain the observed 511 keV $γ$-rays and the observed neutrino masses and mixing.

hep-ph↗

arXiv2006

Cosmological Aspects of the D-brane World

The D-brane world is an idea that we are living on the D-brane imbedded in a 10- or 11-dimensional spacetime of string theories, aiming at the construction of realistic models from string theories. We investigate the cosmological aspects of the D-brane world, focusing on homogeneous anisotropic cosmology driven by the dilaton and the NS-NS 2-form field which becomes massive in the presence of the D-brane. The dilaton possesses the potential due to the presence of the D-brane, various form field fluxes, and the curvature of extra dimensions. In the absence of stabilizing potential, we found the attractor solutions for this system which show the overall features of general solutions. In the presence of the non-vanishing NS-NS 2-form field, the homogeneous universe expands anisotropically while the D-brane term dominates. The isotropy is recovered as the dilaton rolls down and the curvature term dominates. With the stabilizing potential for the dilaton, the anisotropy developed by the initial NS-NS 2-form field flux is erased as the NS-NS 2-form field begins to oscillate around the minimum, forming the B-matter, and the isotropic matter-dominated universe is obtained.

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arXiv2006

Cosmological implication of antisymmetric tensor field on D-brane

We discuss the cosmological implications of an antisymmetric tensor field when it experiences a kind of ``Higgs mechanism,'' including nonlocal interaction terms, on D-branes. Even when a huge magnetic-condensation-inducing anisotropy is assumed in the early universe, the expansion of the universe leads to an isotropic $B$-matter-dominated universe.

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arXiv2005

Testing Neutrino Mass Models

The existence of the neutrino masses and mixing would be an important window into the nature of physics beyond the Standard Model, which will be searched for in the forthcoming experiments such as LHC. In this talk, we discuss some examples of neutrino mass models which are testable through the observation of lepton flavor violating processes and/or electric dipole moments correlated with the neutrino mass structure.

hep-ph↗

arXiv2005

TeV leptogenesis in Z-prime models and its collider probe

We show that the U(1)-prime models linked with the seesaw mechanism at TeV scale can lead to a successful baryogenesis through soft leptogenesis with a resonant behavior in the B parameter. Such a consideration constrains the Z-prime mass to be larger than 2-3 TeV depending on the seesaw scale and the spharelon rate. Together with multi-TeV Z-prime, large sneutrino-antisneutrino mixing and CP violating phenomena required by TeV leptogenesis could be searched for in future colliders by observing the distinct same-sign dilepton--dichargino as well as dislepton--diHiggs signatures.

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arXiv2005

A Predictive Seesaw Scenario for EDMs

The generation of electric dipole moments (EDMs) is addressed in the supersymmetric seesaw scenario realized through the exchange of SU(2)_W triplet states. In particular, we show that the triplet soft-breaking bilinear term can induce finite contributions to lepton and quark EDMs. Moreover, the peculiar flavour structure of the model allows us to predict the EDM ratios d_e/d_mu and d_mu/d_tau only in terms of the neutrino parameters.

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arXiv2005

Cosmology of Antisymmetric Tensor Field in D-brane Universe

We analyze homogeneous, anisotropic cosmology driven by a self-interacting ``massive'' antisymmetric tensor field $B_{μν}$ which is present in string theories with D-branes. Time-dependent magnetic $B$ field existing in the early universe can lead to the Bianchi type I universe. Evolutions of such a tensor field are solved exactly or numerically in the universe dominated by vacuum energy, radiation, and $B$ field itself. The matter-like behavior of the $B$ field (dubbed as ``$B$-matter'') ensures that the anisotropy disappears at late time and thus becomes unobservable in a reasonable cosmological scenario. Such a feature should be contrasted to the cosmology of the conventional massless antisymmetric tensor field.

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arXiv2004

Neutrino Mass from R-parity Violation in Split Supersymmetry

We investigate how the observed neutrino data can be accommodated by R-parity violation in Split Supersymmetry. The atmospheric neutrino mass and mixing are explained by the bilinear parameters $ξ_i$ inducing the neutrino-neutralino mixing as in the usual low-energy supersymmetry. Among various one-loop corrections, only the quark-squark exchanging diagrams involving the order-one trilinear couplings $λ'_{i23,i32}$ can generate the solar neutrino mass and mixing if the scalar mass $m_S$ is not larger than $10^9$ GeV. This scheme requires an unpleasant hierarchical structure of the couplings, e.g., $λ_{i23,i32}\sim 1$, $λ'_{i33} \lesssim 10^{-4}$ and $ξ_i \lesssim 10^{-6}$. On the other hand, the model has a distinct collider signature of the lightest neutralino which can decay only to the final states, $l_i W^{(*)}$ and $νZ^{(*)}$, arising from the bilinear mixing. Thus, the measurement of the ratio; $Γ(e W^{(*)}) : Γ(μW^{(*)}) : Γ(τW^{(*)})$ would provide a clean probe of the small reactor and large atmospheric neutrino mixing angles as far as the neutralino mass is larger than 62 GeV.

hep-ph↗

arXiv2004

Curvaton and QCD Axion in Supersymmetric Theories

A pseudo Nambu-Goldstone boson as curvaton avoids the eta-problem of inflation which plagues most curvaton candidates. We point out that a concrete realization of the curvaton mechanism with a pseudo Nambu-Goldstone boson can be found in the supersymmetric Peccei-Quinn mechanism resolving the strong CP problem. In the flaton models of Peccei-Quinn symmetry breaking, the angular degree of freedom associated with the QCD axion can naturally be a flat direction during inflation and provides successful curvature perturbations. In this scheme, the preferred values of the axion scale and the Hubble parameter during inflation turn out to be about 10^{10} GeV and 10^{12} GeV, respectively. Moreover, it is found that a significant isocurvature component, (anti)correlated to the overall curvature perturbation, can be generated, which is a smoking-gun for the curvaton scenario. Finally, non-Gaussianity in the perturbation spectrum at potentially observable level is also possible.

hep-ph↗

arXiv2004

Neutrino Oscillations and Collider Test of the R-parity Violating Minimal Supergravity Model

We study the R-parity violating minimal supergravity models accounting for the observed neutrino masses and mixing, which can be tested in future collider experiments. The bi-large mixing can be explained by allowing five dominant tri-linear couplings $ λ'_{1,2,3}$ and $λ_{1,2}$. The desired ratio of the atmospheric and solar neutrino mass-squared differences can be obtained in a very limited parameter space where the tree-level contribution is tuned to be suppressed. In this allowed region, we quantify the correlation between the three neutrino mixing angles and the tri-linear R-parity violating couplings. Qualitatively, the relations $| λ'_1 | < | λ'_2| \sim | λ'_3|$, and $|λ_1| \sim |λ_2|$ are required by the large atmospheric neutrino mixing angle $θ_{23}$ and the small angle $θ_{13}$, and the large solar neutrino mixing angle $θ_{12}$, respectively. Such a prediction on the couplings can be tested in the next linear colliders by observing the branching ratios of the lightest supersymmetric particle (LSP). For the stau or the neutralino LSP, the ratio $|λ_1|^2: |λ_2|^2: |λ_1|^2 + |λ_2|^2$ can be measured by establishing $Br(eν): Br(μν) : Br(τν)$ or $Br(νe^\pm τ^\mp ): Br(νμ^\pmτ^\mp) : Br(ντ^\pmτ^\mp)$, respectively. The information on the couplings $λ'_i$ can be drawn by measuring $Br(l_i t \bar{b}) \propto |λ'_i|^2$ if the neutralino LSP is heavier than the top quark.

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arXiv2004

Late Leptogenesis from Radiative Soft Terms

We point out that the so-called ``soft leptogenesis'' can occur at TeV scale if the $B$ term is generated through radiative corrections which involve two-loop diagrams with the gaugino exchange. This mechasnism requires the non-trivial CP phase, ${Im}(A m_{1/2}^*)\neq 0$, and can naturally explain the observed baryon asymmetry of the universe associated with the TeV scale seesaw mechanism. Such a low scale leptogenesis would be a promising option in view of the tight upper limit on the reheat temperature avoiding the gravitino problem in supergravity models.

hep-ph↗

arXiv2004

Supersymmetric threshold corrections to Δm^2_{\odot}

For nearly degenerate neutrinos, quantum corrections can modify the tree-levelmasses via low energy supersymmetric threshold corrections comparable to the solar oscillation mass scale. We numerically calculate corrections to neutrino masses in minimal supergravity (mSugra) and Gauge Mediated Supersymmetry Breaking (GMSB) scenarios and identify parameter spaces in the high energy regime for which the solar neutrino mass splitting becomes too large compared to the LMA solution. We show that such considerations can give bounds on GMSB and mSugra models which can be useful. On the contrary, if we start from degenerate mass eigenvalues at the tree level, these threshold corrections being generation dependent, can also produce the required mass splitting at solar scale for regions of parameter space.

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arXiv2003

Neutrino Mass Matrix in the Minimal Supergravity Model: Bi-large Mixing with Trilinear R-parity Violation

We study the correlation between the neutrino oscillation and the production/decay of the lightest supersymmetric particle(LSP) in the context of the minimal supergravity model(mSUGRA) without R-parity. We show how the neutrino masses and mixing which are consistent with the recent neutrino data can be obtained in this model, and describe how to probe the model by observing the LSP decay at collider experiments. It is shown that the generic 1-loop contributions to neutrino masses are too small to account for the solar and atmospheric neutrino oscillations and thus some fine cancellation in tree-level contribution is required to severely constrain the viable parameter space. In most parameter space of mSUGRA, the neutralino or the stau is LSP. Examining both cases, we find that there is a simple correlation between the neutrino mixing angles and the LSP branching ratios in the small $\tanβ$ region so that the model can be clearly tested in the future colliders. In the large $\tanβ$ region, such a correlation is obscured by the large tau Yukawa contribution which makes it nontrivial to test the model.

hep-ph↗

arXiv2003

Wrong-sign Kaons in B decays and New Physics

New physics can possibly emerge in the B decays into wrong-sign kaons for which the standard model contributions are extremely suppressed. We analyze two-body decays of $\bar{B}^0$ and $B^-$ mesons involving the $b\to dd\bar{s}$ ($ΔS=-1$) and $b\to ss\bar{d}$ ($ΔS=+2$) transitions in a model independent way, and examine various wrong-sign kaon signals which are expected to be observed in the future $B$ experiments. Our analysis shows that it would be possible to identify the origin of new physics through the combined analysis of several B decay modes involving one or two wrong-sign $K^*$'s.

hep-ph↗

arXiv2003

Testing Higgs Triplet Model and Neutrino Mass Patterns

The observed neutrino oscillation data might be explained by new physics at a TeV scale, which is testable in the future experiments. Among various possibilities, the low-energy Higgs triplet model is a prime candidate of such new physics since it predicts clean signatures of lepton flavor violating processes directly related to the neutrino masses and mixing. It is discussed how various neutrino mass patterns can be discriminated by examining the lepton flavor violating decays of charged leptons as well as the collider signatures of a doubly charged Higgs boson in the model.

hep-ph↗

arXiv2001

CP Violation, Sneutrino Oscillation and Neutrino Masses in R-parity Violating Supersymmetric Standard Model

In supersymmetric theories, sneutrino--anti-sneutrino mixing can occur with the oscillation time $\sim 0.01$ ps corresponding the atmospheric neutrino mass scale $\sim 0.05$ eV. We explore the possibility of observing sneutrino oscillation phenomena and CP violation when R-parity violation explains the observed neutrino masses and mixing. It is shown for some parameter region in the bilinear model of R-parity violation that the tiny sneutrino mass splitting and time-dependent CP violating asymmetries could be measured in the future experiments if the tau sneutrino is the lightest supersymmetric particle.

hep-ph↗

arXiv2001

Bi-maximal neutrino mixing and small U_{e3} from Abelian flavor symmetry

Atmospheric neutrino data strongly suggests a near-maximal ν_μ-ν_τ mixing and also solar neutrino data can be nicely explained by another near-maximal ν_e-ν_μ or ν_e-ν_τ mixing. We examine the possibility that this bi-maximal mixing of atmospheric and solar neutrinos arises naturally, while keeping U_{e3} and Δm^2_{sol}/Δm^2_{atm} small enough, as a consequence of Abelian flavor symmetry. Two simple scenarios of Abelian flavor symmetry within supersymmetric framework are considered to obtain the desired form of the neutrino mass matrix and the charged lepton mass matrix parameterized by the Cabibbo angle λ\approx 0.2. Future experiments at a neutrino factory measuring the size of U_{e3} and the sign of Δm^2_{32} could discriminate those scenarios as they predict distinctive values of U_{e3} in connection with Δm^2_{sol}/Δm^2_{atm} and also with the order of the neutrino mass eigenvalues.

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