arXiv subjects

Bumseok Kyae

Publications and source records attributed to Bumseok Kyae.

At least 55 records · Page 3Linked to original sources

arXiv2007

Cosmic D- and DF-strings from D3Dbar3: Black Strings and BPS Limit

We study D- and DF-strings in a D3${\bar {\rm D}}3$ system by using Dirac-Born-Infeld type action. In the presence of an electric flux from the transverse direction, we discuss gravitating thick D-string solutions of a spatial manifold, ${\rm S}^{2}\times {\rm R}^{1}$, in which straight D-strings stretched along the R${}^{1}$ direction are attached to the south and north poles of the two-sphere. There is a horizon along its equator, which means the structure of black strings is formed. We also discuss the BPS limit for thin parallel D- and DF-strings in both flat and curved spacetime. We obtain the BPS sum rule for an arbitrarily-separated multi-string configuration with a Gaussian type tachyon potential. At the site of each thin BPS D(F)-string, the pressure takes a finite value. We find that there exists a maximum deficit angle $π$ in the conical geometry induced by thin BPS D- and DF-strings.

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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.

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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 $sin^2θ_W^0={3/14}$.

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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.

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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

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

Flipped SU(5) Predicts $δT/T$

We discuss hybrid inflation in supersymmetric flipped SU(5) model such that the cosmic microwave anisotropy $δT/T$ is essentially proportional to $(M /M_{P})^2$, where $M$ denotes the symmetry breaking scale and $M_{P}$ ($=2.4\times 10^{18}$ GeV) is the reduced Planck mass. The magnitude of $M$ determined from $δT/T$ measurements can be consistent with the value inferred from the evolution of SU(3) and SU(2) gauge couplings. In other words, one could state that flipped SU(5) predicts (more precisely `postdicts') $δT/T$. The scalar spectral index $n_s = 0.993\pm 0.007$, the scalar to tensor ratio satisfies $r \lapproxeq 10^{-6}$, while $dn_s/d{\rm ln}k \lapproxeq 4\times 10^{-4}$.

hep-ph↗

arXiv2006

DF-strings from D3${\bar {\bf D}}$3 as Cosmic Strings

We study Dirac-Born-Infeld type effective field theory of a complex tachyon and U(1)$\times$U(1) gauge fields describing a D3${\bar {\rm D}}$3 system. Classical solutions of straight global and local DF-strings with quantized vorticity are found and are classified into two types by the asymptotic behavior of the tachyon amplitude. For sufficiently large radial distances, one has linearly-growing tachyon amplitude and the other logarithmically-growing tachyon amplitude. A constant radial electric flux density denoting the fundamental-string background makes the obtained DF-strings thick. The other electric flux density parallel to the strings is localized, which represents localization of fundamental strings in the D1-F1 bound states. Since these DF-strings are formed in the coincidence limit of the D3${\bar {\rm D}}$3, these cosmic DF-strings are safe from inflation induced by the approach of the separated D3 and ${\bar {\rm D}}3$.

hep-th↗

arXiv2005

Flat-Directions in Grand Unification With $U(1)_R$ Symmetry

It is shown that in SO(10) and SU(5) models having a $U(1)_R$ symmetry, the requirement of breaking the unified group to the Standard Model leads to flat directions in the scalar potential. These can lead to a ``cosmological modulus problem". This is relevant to grand unified models of inflation, where $U(1)_R$ symmetries are often used to insure the flatness of the inflaton potential. A way that the modulus problem might be avoided is discussed.

hep-ph↗

arXiv2005

Inflation With A Realistic SO(10) Model

We implement inflation within a realistic supersymmetric SO(10) model in which the doublet-triplet splitting is realized through the Dimopoulos-Wilczek mechanism, the MSSM $μ$ problem is resolved, and higgsino mediated dimension five nucleon decay is heavily suppressed. The cosmologically unwanted topological defects are inflated away, and from $δT/ T$, the $B-L$ breaking scale is estimated to be of order $10^{16}-10^{17}$ GeV. Including supergravity corrections, the scalar spectral index $n_s = 0.99\pm 0.01$, with $|dn_s/ d{\rm ln}k| \lapproxeq 10^{-3}$.

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arXiv2005

Inflation With Realistic Supersymmetric SO(10)

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arXiv2005

Global and Local D-vortices

Codimension-two objects on a system of brane-antibrane are studied in the context of Born-Infeld type effective field theory with a complex tachyon and U(1)$\times$U(1) gauge fields. When the radial electric field is turned on in D2${\bar {\rm D}}$2, we find static regular global and local D-vortex solutions which could be candidates of straight cosmic D-strings in a superstring theory. A natural extension to DF-strings is briefly discussed.

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arXiv2004

Time-varying Quark Masses and Cosmological Axion Energy

The possibility is examined that the masses of the light quarks $u$ and $d$ have varied over the course of the universe's evolution. Such a variation would have an effect on axion cosmology, and can be the basis of a solution of the so-called axion energy problem. If this is the case, a scalar force somewhat weaker than gravity could exist that has a range of order 1 km.

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arXiv2004

$δT/T$ and Neutrino Masses in SU(5)

We implement inflation in a supersymmetric SU(5) model with U(1) R-symmetry such that the cosmic microwave anisotropy $δT/T$ is proportional to $(M/M_{\rm Planck})^2$, where $M\sim M_{GUT}=2-3\times 10^{16}$ GeV, the SU(5) breaking scale, and $M_{\rm Planck}=2.4\times 10^{19}$ GeV. The presence of a global $U(1)_X$ symmetry, spontaneously broken also at scale $M_{GUT}$, provides an upper bound $M_{GUT}^2/M_{\rm Planck}\sim 10^{14}$ GeV on the masses of SU(5) singlet right handed neutrinos, which explains the mass scale associated with atmospheric neutrino oscillations. The SU(5) monopoles and $U(1)_X$ cosmic strings are inflated away. Although the doublet-triplet splitting requires fine-tuning, the MSSM $μ$ problem is resolved and dimension five proton decay is strongly suppressed.

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arXiv2004

Brane gravity, massless bulk scalar and self-tuning of the cosmological constant

We show that a self-tuning mechanism of the cosmological constant could work in 5D non-compact space-time with a $Z_2$ symmetry in the presence of a massless scalar field. The standard model matter fields live only on the 4D brane. The change of vacuum energy on the brane (brane cosmological constant) by, for instance, electroweak and QCD phase transitions, just gives rise to dynamical shifts of the profiles of the background metric and the scalar field in the extra dimension, keeping 4D space-time flat without any fine-tuning. To avoid naked singularities in the bulk, the brane cosmological constant should be negative. We introduce an additional brane-localized 4D Einstein-Hilbert term so as to provide the observed 4D gravity with the non-compact extra dimension. With a general form of brane-localized gravity term allowed by the symmetries, the low energy Einstein gravity is successfully reproduced on the brane at long distances. We show this phenomenon explicitly for the case of vanishing bulk cosmological constant.

hep-th↗

arXiv2004

A General Analysis of Corrections to the Standard See-saw Formula in Grand Unified Models

In realistic grand unified models there are typically extra vectorlike matter multiplets at the GUT scale that are needed to explain the family hierarchy. These contain neutrinos that, when integrated out, can modify the usual neutrino see-saw formula. A general analysis is given. It is noted that such modifications can explain why the neutrinos do not exhibit a strong family hierarchy like the other types of fermions.

hep-ph↗

arXiv2004

Einstein Gravity on a Brane in 5D Non-compact Flat Spacetime -DGP model revisited-

We revisit the 5D gravity model by Dvali, Gabadadze, and Porrati (DGP). Within their framework it was shown that even in 5D non-compact Minkowski space $(x^μ,z)$, the Newtonian gravity can emerge on a brane at short distances by introducing a brane-localized 4D Einstein-Hilbert term $δ(z)M_4^2\sqrt{|\bar{g}_4|}\bar{R}_4$ in the action. Based on this idea, we construct simple setups in which graviton standing waves can arise, and we introduce brane-localized $z$ derivative terms as a correction to $δ(z)M_4^2\sqrt{|\bar{g}_4|}\bar{R}_4$. We show that the gravity potential of brane matter becomes $-\frac{1}{r}$ at {\it long} distances, because the brane-localized $z$ derivative terms allow only a smooth graviton wave function near the brane. Since the bulk gravity coupling may be arbitrarily small, strongly interacting modes from the 5D graviton do not appear. We note that the brane metric utilized to construct $δ(z)M_4^2\sqrt{|\bar{g}_4|}\bar{R}_4$ can be relatively different from the bulk metric by a conformal factor, and show that the graviton tensor structure that the 4D Einstein gravity predicts are reproduced in DGP type models.

hep-th↗

arXiv2004

Low Energy Consequences of Five Dimensional SO(10)

We consider 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 both fixed points (branes), and the residual gauge symmetry is $SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)_X$. We explore one example in which the gauge symmetries on the two branes are respectively $SU(5)\times U(1)_X$ and $SU(4)_c\times SU(2)_L\times SU(2)_R$, and the MSSM gauge symmetry is recovered by the usual Higgs mechanism. We discuss how fermion masses and mixings can be understood in this framework by introducing a flavor $U(1)_F$ symmetry. Unification of the MSSM gauge couplings and proton stability are also considered. An order of magnitude increase in sensitivity could reveal proton decay.

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