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Bumseok Kyae

Publications and source records attributed to Bumseok Kyae.

At least 73 records · Page 4Linked to original sources
arXiv2004

Self-tuning of the cosmological constant and Einstein Gravity on the brane

We show that a self-tuning mechanism of the cosmological constant could work in 5D non-compact space-time. The standard model matter fields live only on the 4D brane. The change of vacuum energy on the brane just gives rise to dynamical shifts of the profiles of the background metric and a bulk scalar field in the extra dimension, keeping 4D space-time flat. To obtain the Newtonian potential on the brane, we introduce an additional brane-localized 4D Einstein-Hilbert term.

hep-ph↗
arXiv2004

Inflationary Cosmology with Five Dimensional SO(10)

We discuss inflationary cosmology in a five dimensional SO(10) model compactified on $S^1/(Z_2\times Z_2')$, which yields $SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)_X$ below the compactification scale. The gauge symmetry $SU(5)\times U(1)_X$ is preserved on one of the fixed points, while ``flipped'' $SU(5)'\times U(1)'_X$ is on the other fixed point. Inflation is associated with $U(1)_X$ breaking, and is implemented through $F$-term scalar potentials on the two fixed points. A brane-localized Einstein-Hilbert term allows both branes to have positive tensions during inflation. The scale of $U(1)_X$ breaking is fixed from $δT/T$ measurements to be around $10^{16}$ GeV, and the scalar spectral index $n=0.98-0.99$. The inflaton field decays into right-handed neutrinos whose subsequent out of equilibrium decay yield the observed baryon asymmetry via leptogenesis.

hep-ph↗
arXiv2003

Inflation and Leptogenesis in Five Dimensional SO(10)

We discuss five dimensional (5D) supersymmetric SO(10) compactified on the orbifold $S^1/(Z_2\times Z_2')$ such that the SO(10) gauge symmetry is broken on the fixed point(s) to its maximal subgroup(s). The MSSM gauge symmetry is recovered by the usual Higgs mechanism, and inflation is associated with the Higgs mechanism, implemented through F-term scalar potentials on the two fixed points. The spontaneous breaking scale is fixed from $δT/T$ measurements to be around $10^{16}$ GeV, and the scalar spectral index $n=0.98-0.99$. The inflaton field decays into right-handed neutrinos whose subsequent out of equilibrium decay yield the observed baryon asymmetry via leptogenesis.

hep-ph↗
arXiv2003

Grand Unified Inflation Confronts WMAP

In a class of realistic four and five dimensional supersymmetric grand unified models, the scalar spectral index is found to be $n_s=0.98 (\pm 0.01)$, in excellent agreement with the values determined by several previous experiments and most recently by the Wilkinson Microwave Anisotropy Probe (WMAP). The models predict $dn_s/d{\rm ln}k\sim 10^{-3}$ and a negligible tensor-to-scalar ratio $r\sim 10^{-8}$. A new five dimensional supersymmetric SO(10) model along these is presented in which inflation is associated with the breaking of SO(10) to SU(5) at scale $M$, with $δT/T\propto (M/M_{\rm Planck})^2$, so that $M\simeq 10^{16}$ GeV. The inflaton decay leads to the observed baryon asymmetry via leptogenesis. We also discuss how the monopole problem is solved without the use of non-renormalizable terms.

astro-ph↗
arXiv2003

F-term Inflation and Leptogenesis with 5D SO(10)

We discuss a five dimensional inflationary scenario based on a supersymmetric SO(10) model compactified on $S^1/(Z_2\times Z_2')$. Inflation is implemented through scalar potentials on four dimensional branes, and a brane-localized Einstein-Hilbert term is essential to make both brane vacuum energies positive during inflation. The orbifold boundary conditions break the SO(10) gauge symmetry to $SU(4)_c\times SU(2)_L\times SU(2)_R$ ($\equiv H$). The inflationary scenario yields $δT/T\propto (M/M_{\rm Planck})^2$, which fixes $M$, the symmetry breaking scale of $H$ to be close to the SUSY GUT scale of $10^{16}$ GeV. The scalar spectral index $n$ is $0.98-0.99$, and the tensor to scalar ratio $r$ is $\lapproxeq 10^{-4}$. The inflaton decay into the lightest right handed neutrinos yields the observed baryon asymmetry via leptogenesis.

hep-ph↗
arXiv2003

GUT Scale And Leptogenesis From 5D Inflation

We discuss a five dimensional inflationary scenario based on a supersymmetric SO(10) model compactified on $S^1/(Z_2\times Z_2')$. Inflation is implemented through scalar potentials on four dimensional branes, and a brane-localized Einstein-Hilbert term is essential to make both brane vacuum energies positive during inflation. The orbifold boundary conditions break the SO(10) gauge symmetry to $SU(4)_c\times SU(2)_L\times SU(2)_R$ ($\equiv H$). The inflationary scenario yields $δT/T\propto (M/M_{\rm Planck})^2$, which fixes $M$, the symmetry breaking scale of $H$ to be close to the SUSY GUT scale of $10^{16}$ GeV. The scalar spectral index $n$ is $0.98-0.99$, while the gravitational wave contribution to the quadrupole anisotropy is negligible ($\lapproxeq 1 {%}$). The inflaton decay into the lightest right handed neutrinos yields the observed baryon asymmetry via leptogenesis.

hep-ph↗
arXiv2002

Non-universal Soft Parameters in Brane World and the Flavor Problem in Supergravity

We consider gravity mediated supersymmetry (SUSY) breaking in 5D spacetime with two 4D branes B1 and B2 separated in the extra dimension. Using an off-shell 5D supergravity (SUGRA) formalism, we argue that the SUSY breaking scales could be non-universal even at the fundamental scale in a brane world setting, since SUSY breaking effects could be effectively localized. As an application, we suggest a model in which the two light chiral MSSM generations reside on B1, while the third generation is located on B2, and the Higgs multiplets as well as gravity and gauge multiplets reside in the bulk. For SUSY breaking of the order of 10--20 TeV caused by a hidden sector localized at B1, the scalars belonging to the first two generations can become sufficiently heavy to overcome the SUSY flavor problem. SUSY breaking on B2 from a different localized hidden sector gives rise to the third generation soft scalar masses of the order of 1 TeV. Gaugino masses are also of the order of 1 TeV if the size of the extra dimension is $\sim 10^{-16}$ ${\rm GeV}^{-1}$. As in 4D effective supersymmetric theory, an adjustment of TeV scale parameters is needed to realize the 100 GeV electroweak symmetry breaking scale.

hep-ph↗
arXiv2002

A model with bulk and brane gauge kinetic terms and SUSY breaking without hidden sector

We derive various solutions for the gauge field and the gaugino when there are both 5D bulk kinetic terms and 4D brane kinetic terms. Below the compactification scale $1/y_c$, gauge interaction by the massless mode is universal, independent of the locations of sources, but above $1/y_c$, the interaction distinguishes their locations. We consider the $S^1/(Z_2\times Z_2')$ orbifold compactification, in which N=2 SUSY and SU(2) gauge symmetry break down to N=1 and U(1), respectively. While the odd parity gauge fields under $Z_2$, $A^1_μ$ and $A^2_μ$, interact with the bulk gauge coupling $g^2$, $A^3_μ$ at low energy interacts with $e^2g^2/(e^2+g^2)$ due to the brane kinetic term with the coupling $e^2$. Even if $g^2$, which is asymptotically free, blew up at the scale $1/y_c<μ< Λ_{\rm cutoff}$, $e^2g^2/(e^2+g^2)$ could remain small at low energy by brane matter fields' contribution. The condensations of the gauginos $Ψ^1$ and $Ψ^2$ generate soft mass term of $Ψ^3$ by gravity mediation.

hep-th↗
arXiv2002

Family Unification in Five and Six Dimensions

In family unification models, all three families of quarks and leptons are grouped together into an irreducible representation of a simple gauge group, thus unifying the Standard Model gauge symmetries and a gauged family symmetry. Large orthogonal groups, and the exceptional groups $E_7$ and $E_8$ have been much studied for family unification. The main theoretical difficulty of family unification is the existence of mirror families at the weak scale. It is shown here that family unification without mirror families can be realized in simple five-dimensional and six-dimensional orbifold models similar to those recently proposed for SU(5) and SO(10) grand unification. It is noted that a family unification group that survived to near the weak scale and whose coupling extrapolated to high scales unified with those of the Standard model would be evidence accessible in principle at low energy of the existence of small (Planckian or GUT-scale) extra dimensions.

hep-ph↗
arXiv2001

Branes and Inflationary Cosmology

We discuss a brane based inflationary scenario in which an initially non-supersymmetric configuration involving a D4 brane is dynamically transformed into a supersymmteric one in a background space-time geometry determined by a stack of D6 branes. Inflation is realized in the effective four dimensional theory and ends after reaching a stable BPS configuration. The scalar spectral index turns out to be 0.98. Under some simplifying assumption the reheat temperature, Hubble constant and the string scale are estimated to be of order $10^{8}$ GeV, $10^{12}$ GeV and $10^{16}$ GeV, respectively.

hep-ph↗
arXiv2001

Wave function of the radion in the brane background with a massless scalar field and a self-tuning problem

We consider flat solutions in the brane background with a massless scalar field appearing in 5D $H^2_{MNPQ}$. Since there exist bulk singularities or arises the divergent 4D Planck mass, we should introduce a compact extra dimension, the size of which is then fixed by brane tension(s) and a bulk cosmological constant. Inspecting scalar perturbations around the flat solutions, we find that the flat solutions are stable vacua from the positive mass spectrum of radion. We show that the massless radion mode is projected out by the boundary condition arising in cutting off the extra dimension. Thus, the fixed extra dimension is not alterable, which is not useful toward a self-tuning of the cosmological constant.

hep-th↗
arXiv2001

Localized gravity and mass hierarchy in D=6 with the Gauss-Bonnet term

We obtain the localized gravity on the intersection of two orthogonal non-solitonic or solitonic 4-branes in D=6 in the presence of the Gauss-Bonnet term. The tension of the intersection is allowed to exist unlike the case without the Gauss-Bonnet term. We show that gravity could be confined to the solitonic 4-branes for a particular choice of the Gauss-Bonnet coupling. If the extra dimensions are compactified with the $T^2/(Z_2\times Z_2)$ orbifold symmetry, the mass hierarchy between the Planck scale and the weak scale can be explained by putting our universe at the TeV intersection of positive tension located at the orbifold fixed point.

hep-th↗
arXiv2001

Model for self-tuning the cosmological constant

The vanishing cosmological constant in the four dimensional space-time is obtained in a 5D Randall-Sundrum model with a brane (B1) located at $y=0$. The matter fields can be located at the brane. For settling any vacuum energy generated at the brane to zero, we need a three index antisymmetric tensor field $A_{MNP}$ with a specific form for the Lagrangian. For the self-tuning mechanism, the bulk cosmological constant should be negative.

hep-th↗
arXiv2001

Self-tuning solution of the cosmological constant problem with antisymmetric tensor field

We present a self-tuning solution of the cosmological constant problem with one extra dimension which is curved with a warp factor. To separate out the extra dimension and to have a self-tuning solution, a three index antisymmetric tensor field is introduced with the $1/H^2$ term in the Lagrangian. The standard model fields are located at the $y=0$ brane. The existence \cite{kklcc} of the self-tuning solution (which results without any fine tuning among parameters in the Lagrangian) is crucial to obtain a vanishing cosmological constant in a 4D effective theory. The de Sitter and anti de Sitter space solutions are possible. The de Sitter space solutions have horizons. Restricting to the spaces which contain the $y=0$ brane, the vanishing cosmological constant is chosen in the most probable universe. For this interpretaion to be valid, the existence of the self-tuning solution is crucial in view of the phase transitions. In this paper, we show explicitly a solution in case the brane tension shifts from one to another value. We also discuss the case with the $H^2$ term which leads to one-fine-tuning solutions at most.

hep-th↗
arXiv2000

The $μ$ and soft masses from the intermediate scale brane with non-factorizable geometry

The proton decay problem and the negative brane tension problem in the original Randall-Sundrum model can be resolved by interpreting the Planck scale brane as the visible sector brane. The hierarchy problem is resolved with supersymmetry, and the TeV scales for soft masses and $μ$ in supersymmetric models are generated by the physics at the intermediate scale ($\sim 10^{11-13}$ GeV) brane.

hep-ph↗
arXiv2000

Cosmology and Modulus Stabilization in the Randall-Sundrum Setup with Bulk Matter

We provide the exact time-dependent cosmological solutions in the Randall-Sundrum (RS) setup with bulk matter, which may be smoothly connected to the static RS metric. In the static limit of the extra dimension, the solutions are reduced to the standard Friedmann equations. In view of our solutions, we also propose an explanation for how the extra dimension is stabilized in spite of a flat modulus potential at the classical level.

hep-th↗
arXiv2000

The radion contribution to the weak mixing angle

In the Randall-Sundrum (RS) compactification, the gap between two branes is stabilized by the vacuum expectation value of a scalar field called {\it radion}, $ϕ$. This radion behaves like a weak interaction singlet scalar field, coupling to matter through the trace of the energy momentum tensor. We find that it can induce a sizable correction to the weak mixing angle if the vacuum expectation value and the mass of the radion is around TeV. We also comment on the contribution to the $K_L-K_S$ mass difference and to $(g-2)_μ$.

hep-ph↗