arXiv subjects

Bumseok Kyae

Publications and source records attributed to Bumseok Kyae.

At least 19 recordsLinked to original sources

arXiv2019

A model of dynamical SUSY breaking

Supersymmetric (SUSY) models and dynamical breaking of symmetries have been used to explain hierarchies of mass scales. We find that a chiral representation, $\overline{\bf 10}\, \oplus\, \overline{\bf 5}\, \oplus\, 2\cdot{\bf 5}$ in SUSY SU(5) in the hidden sector, breaks global SUSY dynamically, by producing a composite field $ϕ$ below the SU(5) confinement scale. This dynamincal SUSY breaking can have two important applications, one in particle physics and the other in cosmology. Gavitational effects transmit this dynamical breaking to the standard model(SM) superpartners and the quintessential vacuum energy. The SM superpartners feel the effects just by the magnitude of the gravitino mass while the smallness of the quintessential vacuum energy is due to the composite nature of a singlet field $ϕ$. The composite $ϕ$ carries a global charge which is hardly broken in SUSY and hence its phase can be used toward a quintessential axion for dark energy of the Universe.

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arXiv2018

Electroweak symmetry breaking by a neutral sector: Dynamical relaxation of the little hierarchy problem

We propose a new dynamical relaxation mechanism of the little hierarchy problem, based on a singlet extension of the minimal supersymmetric standard model (MSSM). In this scenario, the small soft mass parameter of an MSSM singlet is responsible for the electroweak symmetry breaking and the non-zero Higgs vacuum expectation value, whereas the effect of the large soft mass parameter of the Higgs boson, -m_{h_u}^2 is dynamically compensated by a flat direction of the MSSM singlets. The small singlet's soft mass and the Z boson mass can be protected, even if the stop mass is heavier than 10 or 20 TeV, since the gravity-mediated supersymmetry breaking effects and the relevant Yukawa couplings are relatively small. A "focus point" of the singlet's soft mass parameter can emerge around the stop mass scale, and so various fine-tuning measures can reduce well below 100. Due to the relatively large gauge-mediated effects, the MSSM superpartners are much heavier than the experimental bounds, and the unwanted flavor changing processes are adequately suppressed.

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arXiv2017

The anomalous U(1) global symmetry and flavors from an SU(5) x SU(5)$'$ GUT in $Z_{12-I}$ orbifold compactification

In string compactifications, frequently there appears the anomalous U(1) gauge symmetry which belonged to E8$\times$E8 of the heterotic string. This anomalous U(1) gauge boson obtains mass at the compactification scale, just below $10^{18\,}$GeV, by absorbing one pseudoscalar (corresponding to the model-independent axion) from the second rank anti-symmetric tensor field $B_{MN}$. Below the compactification scale, there results a global symmetry U(1)$_{\rm anom}$ whose charge $Q_{\rm anom}$ is the original gauge U(1) charge. This is the most natural global symmetry, realizing the "invisible" axion. This global symmetry U(1)$_{\rm anom}$ is suitable for a flavor symmetry. In the simplest compactification model with the flipped SU(5) grand unification, we calculate all the low energy parameters in terms of the vacuum expectation values of the standard model singlets.

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arXiv2017

Hairs of discrete symmetries and gravity

Gauge symmetries are known to be respected by gravity because gauge charges carry flux lines, but global charges do not carry flux lines and are not conserved by gravitational interaction. For discrete symmetries, they are spontaneously broken in the Universe, forming domain walls. Since the realization of discrete symmetries in the Universe must involve the vacuum expectation values of Higgs fields, a string-like configuration (hair) at the intersection of domain walls in the Higgs vacua can be realized. Therefore, we argue that discrete charges are also respected by gravity.

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arXiv2016

A possible relation between leptogenesis and PMNS phases

We propose a new scenario for baryogenesis through leptogenesis, where the CP phase relevant for leptogenesis is connected directly to the PMNS phase(s) in the light neutrino mixing matrix. The scenario is realized in case only one CP phase appears in the full theory, originating from the complex vacuum expextation value of a standard model singlet field. In order to realize this scheme, the electroweak symmetry is required to be broken during the leptogenesis era and a new loop diagram with an intermediate $W$ boson exchange including the low energy neutrino mixing matrix should play the dominant contribution to the CP violation for leptogenesis. In this letter, we discuss the new basic mechanism, which we call type-II leptogenesis, and give an estimate for maximally reachable baryon asymmetry depending on the PMNS phases.

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arXiv2015

Naturalness-guided Gluino Mass Bound from the Minimal Mixed Mediation of SUSY Breaking

In order to significantly reduce the fine-tuning associated with the electroweak symmetry breaking in the minimal supersymmetric standard model (MSSM), we consider not only the minimal gravity mediation effects but also the minimal gauge mediation ones for a common supersymmetry breaking source at a hidden sector. In this "Minimal Mixed Mediation model," the minimal forms for the Kahler potential and the gauge kinetic function are employed at tree level. The MSSM gaugino masses are radiatively generated through the gauge mediation. Since a "focus point" of the soft Higgs mass parameter, m_{h_u}^2 appears around 3-4 TeV energy scale in this case, m_{h_u}^2 is quite insensitive to stop masses. Instead, the naturalness of the small m_{h_u}^2 is more closely associated with the gluino mass rather than the stop mass unlike the conventional scenario. As a result, even a 3-4 TeV stop mass, which is known to explain the 125 GeV Higgs mass at three-loop level, can still be compatible with the naturalness of the electroweak scale. On the other hand, the requirements of various fine-tuning measures much smaller than 100 and |μ| < 600 GeV constrain the gluino mass to be 1.6 TeV < M_3 < 2.2 TeV, which is well-inside the discovery potential range of LHC RunII.

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arXiv2015

Shifted focus point scenario from the minimal mixed mediation of SUSY breaking

We employ both the minimal gravity- and the minimal gauge mediations of supersymmetry breaking at the grand unified theory (GUT) scale in a single supergravity framework, assuming the gaugino masses are generated dominantly by the minimal gauge mediation effects. In such a "minimal mixed mediation model," a "focus point" of the soft Higgs mass parameter, m_{h_u}^2 emerges at 3-4 TeV energy scale, which is exactly the stop mass scale needed for explaining the 126 GeV Higgs boson mass without the "A-term" at the three loop level. As a result, m_{h_u}^2 in the MSSM can be quite insensitive to various trial stop masses at low energy, reducing the fine-tuning measures to be much smaller than 100 even for a 3-4 TeV low energy stop mass and -0.5 < A_t / m_0 < +0.1 at the GUT scale. The $μ$ parameter is smaller than 600 GeV. The gluino mass is predicted to be about 1.7 TeV, which could readily be tested at LHC run2.

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arXiv2015

Shifted focus point of the Higgs mass parameter from the minimal mixed mediation of SUSY breaking

We employ both the minimal gravity- and the minimal gauge mediations of supersymmetry breaking at the grand unified theory (GUT) scale in a single supergravity framework, assuming the gaugino masses are generated dominantly by the minimal gauge mediation effects. In such a "minimal mixed mediation model," a "focus point" of the soft Higgs mass parameter, m_{h_u}^2 emerges at 3-4 TeV energy scale, which is exactly the stop mass scale needed for explaining the 126 GeV Higgs boson mass without the "A-term" at the three loop level. As a result, m_{h_u}^2 can be quite insensitive to various trial stop masses at low energy, reducing the fine-tuning measures to be much smaller than 100 even for a 3-4 TeV low energy stop mass and -0.5 < A_t/m_0 < +0.1 at the GUT scale. The gluino mass is predicted to be about 1.7 TeV, which could readily be tested at LHC run2.

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arXiv2015

Perspective on completing natural inflation

We present a perspective on the inflation paths in 2-, 3-,,, N-flation models based on the ultraviolet completion in heterotic string theory, where a number of grand unification scale axions are used. The number of non-Abelian gauge groups for a natural inflation is restricted in string compactification, and we argue that the most plausible completion of natural inflation from a theory perspective is the 2-flation.

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arXiv2014

Precise focus point scenario for a natural Higgs boson in the MSSM

A small Higgs mass parameter m_{h_u}^2 can be insensitive to various trial heavy stop masses, if a universal soft squared mass is assumed for the chiral superpartners and the Higgs boson at the grand unification (GUT) scale, and a focus point (FP) of m_{h_u}^2 appears around the stop mass scale. The challenges in the FP scenario are (1) a too heavy stop mass (~ 5 TeV) needed for the 126 GeV Higgs mass and (2) the too high gluino mass bound (> 1.4 TeV). For a successful FP scenario, we consider (1) a superheavy right-hand (RH) neutrino and (2) the first and second generations of hierarchically heavier chiral superpartners. The RH neutrino can move a FP in the higher energy direction in the space of (Q, m_{h_u}^2(Q)), where Q denotes the renormalization scale. On the other hand, the hierarchically heavier chiral superpartners can lift up a FP in that space through two-loop gauge interactions. Precise focusing of m_{h_u}^2(Q) is achieved with the RH neutrino mass of ~ 10^{14} GeV together with an order one (0.9-1.2) Dirac Yukawa coupling to the Higgs boson, and the hierarchically heavy masses of 15-20 TeV for the heavier generations of superpartners, when the U(1)_R breaking soft parameters, m_{1/2} and A_0 are set to be 1 TeV at the GUT scale. Those values can naturally explain the small neutrino mass through the seesaw mechanism, and suppress the flavor violating processes in supersymmetric models.

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arXiv2014

Large tensor spectrum of BICEP2 in the natural SUSY hybrid model

The large tensor spectrum recently observed by the BICEP2 Collaboration requires a super-Planckian field variation of the inflaton in the single-field inflationary scenario. The required slow-roll parameter ε\approx 0.01 would restrict the e-folding number to around 7 in (sub-)Planckian inflationary models. To overcome such problems, we consider a two-field scenario based on the natural assisted supersymmetric (SUSY) hybrid model ("natural SUSY hybrid inflation" [1]), which combines the SUSY hybrid and the natural inflation models. The axionic inflaton field from the natural inflation sector can admit the right values for the tensor spectrum as well as a spectral index of 0.96 with a decay constant smaller than the Planck scale, f \lesssim M_P. On the other hand, the vacuum energy of 2 x 10^{16} GeV with 50 e-folds is provided by the inflaton coming from the SUSY hybrid sector, avoiding the eta problem. These are achieved by introducing both the U(1)_R and a shift symmetry, and employing the minimal Kahler potential.

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arXiv2014

Primordial gravitational wave of BICEP2 from dynamical double hybrid inflation

BICEP2 has observed a primordial gravitational wave corresponding to the tensor-to-scalar ratio of 0.16. It seems to require a super-Planckian inflationary model. In this paper, we propose a double hybrid inflation model, where the inflaton potential dynamically changes with the evolution of the inflaton fields. During the first phase of inflation over 7 e-folds, the power spectrum can be almost constant by a large linear term in the hybrid potential, which is responsible also for the large tensor-to-scalar ratio. In the second phase of 50 e-folds, the dominant potential becomes dynamically changed to the logarithmic form as in the ordinary supersymmetric hybrid inflation, which is performed by the second inflaton field. In this model, the sub-Planckian field values (~0.9 M_P) can still yield the correct cosmic observations with the sufficient e-folds.

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arXiv2014

Light dark matter for Fermi-LAT and CDMS observations

Light fermionic/scalar dark matter (DM) (m_DM ~ 8 GeV) neutral under the standard model can be responsible for the CDMS and CoGeNT signals, and the Fermi-LAT gamma-ray excesses. In order to explain them in a relatively simple framework, we have explored various DM annihilation and scattering processes, discussing important phenomenological constraints coming from particle physics. Assuming that the two independent observations have a common DM origin and the processes arise through a common mediator, DM should annihilate into tau/anti-tau lepton pairs through an s-channel, and scatter with nuclei through a t-channel process. To avoid the p-wave suppression, a new Higgs-like scalar field with a mass of O(1) TeV is necessary as a common mediator of both the processes. We propose a supersymmetric model realizing the scenario.

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arXiv2014

Inert Higgs extension of the NMSSM

We introduce one pair of inert Higgs doublets {H_d, H_u} and singlets {N^c, N}, and consider their couplings with the Higgs doublets of the minimal supersymmetric standard model (MSSM), W \supset y_N N^c h_u H_d + y_N' N h_d H_u. We assign extra U(1)_{Z'} gauge charges only to the extra vector-like superfields, and so all the MSSM superfields remain neutral under the new U(1)_{Z'}. They can be an extension of the "λterm," W \supset λS h_u h_d in the next-to-MSSM (NMSSM). Due to the U(1)_{Z'}, the maximally allowed low energy value of y_N can be lifted up to 0.85, avoiding a Landau-pole (LP) below the grand unification scale. Such colorless vector-like superfields remarkably enhance the radiative MSSM Higgs mass particularly for large tanβthrough the y_N term and the corresponding holomorphic soft term. As a result, the lower bound of λand the upper bound of tanβcan be relaxed to disappear from the restricted parameter space of the original NMSSM, 0.6 < λ< 0.7 and 1< tanβ< 3. Thus, the valid parameter space significantly expands up to 0 < λ< 0.7, 0 < y_N < 0.85, and 2 < tanβ< 50, evading the LP problem and also explaining the 126 GeV Higgs mass naturally.

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arXiv2013

U(1)_{B_1+B_2-2L_1} mediation for the natural SUSY and the anomalous muon g-2

We propose a U(1)^\prime mediated supersymmetry (SUSY) breaking, in which U(1)^\prime is identified with U(1)_{B_1+B_2-2L_1}. The U(1)_{B_1+B_2-2L_1} gauge symmetry, which is anomaly-free with the field contents of the minimal supersymmetric standard model, assigns \pm 1/3 charges to the first and second generations of the quarks, and \mp 2 to the first generation of the leptons. As a result, the first two generations of squarks acquire masses of about 7 TeV, and the first generation of the sleptons do those of 40 TeV, respectively, in the presence of one or three pairs of extra vector-like matter {{\bf 5},\bar{\bf 5}}. Non-observation on extra colored particles below 1 TeV at the large hadron collider, and also the flavor violations such as μ^-\rightarrow e^-γare explained. By virtue of such a gauge symmetry, proton stability can be protected. The other squarks and sleptons as well as the gauginos can obtain masses of order 10^{2-3} GeV through the conventional gravity or gauge mediated SUSY breaking mechanism. The relatively light smuon/sneutrino and the neutralino/chargino could be responsible for the (g-2)_μdeviated from the standard model prediction. The stop mass of \sim 500 GeV relieves the fine-tuning problem in the Higgs sector. Two-loop effects by the relatively heavy sfermions can protect the smallness of the stop mass from the radiative correction by the heavy gluino (\gtrsim 1 TeV). Extra vector-like matter can enhance the radiative corrections to the Higgs mass up to 126 GeV, and induce the desired mixing among the chiral fermions after U(1)_{B_1+B_2-2L_1} breaking.

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arXiv2013

Decaying WIMP dark matter for AMS-02 cosmic positron excess

For explaining the AMS-02 cosmic positron excess, which was recently reported, we consider a scenario of thermally produced and decaying dark matter (DM) into the standard model (SM) leptons with an extremely small decay rate, Γ_{DM} \sim 10^{-26} sec.^{-1}. Since the needed DM mass is relatively heavy (700 GeV < m_{DM} < 3000 GeV), we introduce another DM component apart from the lightest supersymmetric particle ("LSP"). For its (meta-) stability and annihilation into other particles, the new DM should be accompanied with another Z_2 symmetry apart from the R-parity. Sizable renormalizable couplings of the new DM with SM particles, which are necessary for its thermalization in the early universe, cannot destabilize the new DM because of the new Z_2 symmetry. Since the new DM was thermally produced, it can naturally explain the present energy density of the universe. The new DM can decay into the SM leptons (and the LSP) only through non-renormalizable operators suppressed by a superheavy squared mass parameter after the new symmetry is broken around TeV scale. We realize this scenario in a model of "gauged vector-like leptons," which was proposed recently for the naturalness of the Higgs boson.

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arXiv2013

Relaxing the Landau-pole constraint in the NMSSM with the Abelian gauge symmetries

In order to relax the Landau pole constraint on "λ", which is a coupling constant between a singlet S and the MSSM Higgs, λSh_uh_d in the next-to-MSSM (NMSSM), and also maintain the gauge coupling unification, we consider U(1) gauge extensions of the NMSSM. For relatively strong U(1) gauge interactions down to low energies, we assign U(1) charges only to the Higgs and the third family of the chiral matter among the MSSM superfields. In the U(1)_Z [U(1)_Z\times U(1)_X] extension, the low energy value of λcan be lifted up to 0.85-0.95 [0.9-1.0], depending on the employed charge normalizations, when λand the new gauge couplings are required not to blow up below the 10^{16} GeV energy scale. Introduction of extra vector-like superfields can induce the desired Yukawa couplings for the first two families of the chiral matter. We also discuss various phenomenological constraints associated with extra U(1) breaking.

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arXiv2013

Vector-like leptons and extra gauge symmetry for the natural Higgs boson

For raising the radiative Higgs mass without a serious fine-tuning in the Higgs sector, we introduce vector-like lepton doublets and neutral singlets {L,L^c; N,N^c}, and consider their order one Yukawa coupling to the Higgs, W \supset y_NLh_uN^c. The 125 GeV Higgs mass can be naturally explained with the stop mass squared of ~(500 GeV)^2 and even without the "A-term" contributions. It is possible because of the quartic power of y_N in the radiative Higgs mass correction, and much less stringent mass bounds on extra leptonic matter. In order to avoid blowup of y_N at higher energy scales, a non-Abelian gauge extension of the MSSM is attempted, under which {L,L^c; N,N^c} are charged, while all the ordinary MSSM superfields remain neutral. We discuss the gauge coupling unification. This mechanism can be applied also for enhancing h^0 \rightarrow γγwith W \supset y_EL^ch_uE, if the charged lepton singlets {E,E^c} are also introduced.

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