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Jihn E. Kim

Publications and source records attributed to Jihn E. Kim.

At least 127 records · Page 7Linked to original sources
arXiv2008

Kaluza-Klein masses in nonprime orbifolds: Z(12-I) compactification and threshold correction

Analyzing the one-loop partition function, we discuss possible Kaluza-Klein (KK) states in the orbifold compactification of the heterotic string theory, toward the application to the threshold correction. The KK massive states associated with (relatively) large extra dimensions can arise only in non-prime orbifolds. The GSO projection condition by a shift vector $V^I$ is somewhat relaxed above the compactification scale 1/R. We also present the other condition on Wilson line $W$, $P\cdot W={\rm integer}$. With the knowledge of the partition function, we obtain the threshold corrections to gauge couplings, which include the Wilson line effects. We point out the differences in string and field theoretic orbifolds.

hep-th↗
arXiv2007

Axion as a CDM component

I discuss the essential features of the QCD axion: the strong CP solution and hence its theoretical necessity. I also review the effects of the QCD axion on astrophysics and cosmology, in particular with emphasis on its role in the dark matter component together with its supersymmetric partner axino. It is pointed out that string theory may or may not give a detectable QCD axion.

hep-ph↗
arXiv2007

SO(10)-like Superstring Standard Model with R-parity from the Heterotic String

We construct a supersymmetric standard model in the context of the Z_{12-I} orbifold compactification of the E_8 x E_8' heterotic string theory. The gauge group is SU(3)_c x SU(2)_L x U(1)_Y x U(1)^4 x [SO(10) x U(1)^3]' with sin^2θ_W = 3/8. We obtain three families of SO(10) spinor-like chiral matter states, and Higgs doublets. All other extra states are exactly vector-like under the standard model gauge symmetry. There are numerous standard model singlets, many of which get VEVs such that only the standard model gauge symmetry survives and desired Yukawa couplings can be generated at lower energies. In particular, all vector-like exotic states achieve superheavy masses and the R-parity can be preserved.

hep-th↗
arXiv2007

GMSB at a stable vacuum and MSSM without exotics from heterotic string

We show that it is possible to introduce the confining hidden sector gauge group SU(5)' with the chiral matter 10 plus 5-bar, which are neutral under the standard model gauge group, toward a gauge mediated supersymmetry breaking (GMSB) in a Z_{12-I} orbifold compactification of E_8xE_8 heterotic string. Three families of MSSM result without exotics. We also find a desirable matter parity P (or R-parity) assignment. We note that this model contains the spectrum of the Lee-Weinberg model which has a nice solution of the mu problem.

hep-ph↗
arXiv2007

Z_{12-I} Orbifold Compactification toward SUSY Standard Model

We explain the orbifold compactification in string models and present a Z_{12-I} orbifold compactification toward supersymmetric standard models. We also point out an effective R-parity from this string construction. The VEVs of gauge singlets are chosen such that phenomenological constraints are satisfied.

hep-ph↗
arXiv2007

Gauge mediated supersymmetry breaking without exotics in orbifold compactification

We suggest SU(5)$'$ in the hidden sector toward a possible gauge mediated supersymmetry breaking scenario for removing the SUSY flavor problem, with an example constructed in $\Z_{12-I}$ with three families. The example we present has the Pati-Salam type classification of particles in the observable sector and has no exotics at low energy. We point out that six or seven very light pairs of ${\bf 5}'$ and $\bar{\bf 5}'$ out of ten vectorlike $\five'$ and $\fiveb'$ pairs of SU(5)$'$ is achievable, leading to a possibility of an unstable supersymmetry breaking vacuum. The possibility of different compactification radii of three two tori toward achieving the needed coupling strength is also suggested.

hep-ph↗
arXiv2007

Superstring standard model from Z_{12-I} orbifold compactification with and without exotics, and effective R-parity

We construct a supersymmetric standard model in the context of the $Z_{12-I}$ orbifold compactification of the heterotic string theory. The gauge group is $SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)^4\times[SO(10)\times U(1)^3]'$. We obtain three chiral families, $3\times\{Q,d^c,u^c,L,e^c,ν^c\}$, and Higgs doublets. There are numerous neutral singlets many of which can have VEVs so that low energy phenomenology on Yukawa couplings can be satisfied. In one assignment (Model E) of the electroweak hypercharge, we obtain the string scale value of $sin^2θ_W^0={3/8}$ and another exactly massless {\it exphoton} (in addition to the photon) coupling to exotic particles only. There are color triplet and anti-triplet exotics, $α$ and $\barα$, $SU(2)_L$ doublet exotics, $δ$ and $\barδ$, and $SU(3)_c\times SU(2)_L$ singlet but $Y={2/3},-{1/3},-{2/3},{1/3}$ exotics, $ξ,η,\barξ, \barη$. We show that all these vector-like exotics achieve heavy masses by appropriate VEVs of neutral singlets. One can find an effective R-parity between light (electroweak scale) particles so that proton and the LSP can live sufficiently long. In another assignment (Model S) of the electroweak hypercharge, there does not appear any exotic particle but $sin^2θ_W^0={3/14}$.

hep-ph↗
arXiv2007

String compactification, QCD axion and axion-photon-photon coupling

It is pointed out that there exist a few problems to be overcome toward an observable sub-eV QCD axion in superstring compactification. We give a general expression for the axion decay constant. For a large domain wall number $N_{DW}$, the axion decay constant can be substantially lowered from a generic value of a scalar singlet VEV. The Yukawa coupling structure in the recent $Z_{12-I}$ model is studied completely, including the needed nonrenormalizable terms toward realistic quark and lepton masses. In this model we find an approximate global symmetry and vacuum so that a QCD axion results but its decay constant is at the GUT scale. The axion-photon-photon coupling is calculated for a realistic vacuum satisfying the quark and lepton mass matrix conditions. It is the first time calculation of $c_{aγγ}$ in realistic string compactifications: $c_{aγγ}={5/3}-1.93\simeq -0.26$.

hep-ph↗
arXiv2007

Harmless R-parity violation from Z_{12-I} compactification of E_8 X E_8' heterotic string

In a recent $\Z_{12-I}$ orbifold model, an approximate $Z_2$ symmetry which forbids the baryon number violating operators up to sufficiently high orders is found. The dimension-4 $ΔB\ne 0$ operators of the MSSM fields occur at dimension 10. The effective dimension-5 $ΔB\ne 0$ operators derived from these are harmless if some VEVs of neutral singlets are O(1/10) times the string scale. The main reason for forbidding these $ΔB\ne 0$ operators up to such a high order is the large order N=12 of $\Z_N$ since the $H$-momentum rule is $(-1,1,1)$ mod (12, 3, 12). For a lower order $N<12$, the $ΔB\ne 0$ operators would appear at lower dimensions.

hep-ph↗
arXiv2006

Axions: Past, Present, and Future

The current status of axion physics is presented. There still exists the axion window 10^9 GeV < F_a < 10^{12} GeV. The recent CAST solar axion search experiment on the axion-photon-photon coupling strength has to be improved by a factor of 100 to reach down to the region of superstring axions. The calculable theta and m_u=0 cases for strong CP solutions, and axino cosmology in SUSY extension of axion are also commented.

hep-ph↗
arXiv2006

Flipped SU(5) from Z_{12-I} orbifold with Wilson line

We construct a three family flipped SU(5) model from the heterotic string theory compactified on the $\Z_{12-I}$ orbifold with one Wilson line. The gauge group is $\rm SU(5)\times U(1)_X\times U(1)^2\times[SU(2)\times SO(10)\times U(1)^2]^\prime$. This model does not derive any nonabelian group except SU(5) from $E_8$, which is possible only for two cases in case of one shift $V$, one in ${\bf Z}_{12-I}$ and the other in ${\bf Z}_{12-II}$. We present all possible Yukawa couplings. We place the third quark family in the twisted sectors and two light quark families in the untwisted sector. From the Yukawa couplings, the model provides the R-parity, the doublet-triplet splitting, and one pair of Higgs doublets. It is also shown that quark and lepton mixings are possible. So far we have not encountered a serious phenomenological problem. There exist vectorlike flavor SU(5) exotics (including \Qem=$\pm\frac16$ color exotics and \Qem=$\pm\frac12$ electromagnetic exotics) and SU(5) vectorlike singlet exotics with \Qem=$\pm\frac12$ which can be removed near the GUT scale. In this model, ${\rm sin}^2θ_W^0={3/8}$ at the full unification scale.

hep-th↗
arXiv2006

Baryogenesis by Heavy Quarks: Q-genesis

In this talk, I present a new mechanism for baryogenesis the Q-genesis in which the heavy quarks are the source of baryon number. There exists a narrow allowed region for the Q-genesis.

hep-ph↗
arXiv2006

String MSSM through flipped SU(5) from Z_{12} orbifold

In a $Z_{12-I}$ orbifold compactification through an intermediate flipped SU(5), the string MSSM (${\cal S}$MSSM) spectra (three families, one pair of Higgs doublets, and neutral singlets) are obtained with the Yukawa coupling structure. The GUT $\sin^2θ_W^0=\frac38$, even with exotics in the twisted sector, can be run to the observed electroweak scale value by mass parameters of vectorlike exotics near the GUT scale. We also obtain R-parity and doublet-triplet splitting.

hep-th↗
arXiv2006

Modification of Decay Constants of Superstring Axions: Effects of Flux Compactification and Axion Mixing

We study possibilities for lowering the decay constants of superstring axions. In the heterotic Calabi-Yau compactification, a localized model-dependent axion can appear at a nearly collapsing 2-cycle. The effect of flux can be used for generating warp factor suppression of the axion decay constant. We also point out that the hidden sector instanton potential much higher than the QCD instanton potential picks up the larger effective axion decay constant as that of the QCD axion. We show that this can be converted by introducing many hidden-sector quarks so that the decay constant of the QCD axion turns out to be much smaller than the string scale.

hep-th↗
arXiv2006

Quantum numbers of heavy neutrinos, tri-bi-maximal mixing through double seesaw with permutation symmetry, and comment on $θ_{\rm sol}+θ_c\simeq \fracπ{4}$

Using the family symmetry, in the neutrino mass matrix we remove the Yukawa coupling (arising in the Dirac type mass between the heavy neutrinos and light lepton doublets) dependence in the double seesaw mechanism so that it is directly proportional to the mass matrix $m^{(nn)}$ of heavy Majorana neutrinos. The family symmetry is supposed to be broken spontaneously at high energy scale so that the neutrino mass matrix is given by the family symmetry at high energy scale. With the permutation symmetry $S_3$, we note a variety of possible mass hierarchies arising distinctly in neutrinos, charged leptons, $Q_{\rm em}=-\frac13$ quarks, and $Q_{\rm em}=\frac23$ quarks. Distinguishing these hierarchies, we obtain a relation between the CKM angles and the MNS angles. Finally, we comment on the approximate relation $θ_{\rm sol}+θ_c\simeq \fracπ{4}$.

hep-ph↗
arXiv2005

Gauge Unification via Stable Brane Recombination

We study the transition between parallel and intersecting branes on a torus. Spontaneous symmetry breaking of nonabelian gauge symmetry is understood as brane separation, and a more general intermediate deformation is discussed. We argue that there exists supersymmetry preserving transition and we can always have parallel branes as a final state. The transition is interpreted due to dynamics of the F- and D-string junctions and their generalization to (F, D$p$) bound states. The gauge group and coupling unification is achieved, also as a result of supersymmetry. From the tadpole cancelation condition, we naturally have some class of intersecting brane models as broken phases of Type I theory with SO(32) gauge group.

hep-th↗
arXiv2005

Gauges in the Bulk II: Models with Bulk Scalars

Extending previous work in Randall-Sundrum type models, we construct low-energy effective actions for braneworlds with a bulk scalar field, with special attention to the case of BPS branes. Holding the branes at fixed coordinate position with a general ansatz for the bulk metric, and imposing the Einstein frame as a gauge condition, we obtain a scalar-tensor theory with only one scalar degree of freedom related to the proper brane separation. The formalism is applicable even when there is direct coupling of the bulk scalar and brane matter, as in the Horava-Witten model. We further show that the usual moduli space approximation actually describes a non-BPS three-brane system.

hep-th↗