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Norimi Yokozaki

Publications and source records attributed to Norimi Yokozaki.

At least 37 records · Page 2Linked to original sources

Muon $g-2$ in Higgs-anomaly mediation

A simple model for the explanation of the muon anomalous magnetic moment was proposed by the present authors within the context of the minimal supersymmetric standard model [1607.05705, 1608.06618]: "Higgs-anomaly mediation". In the setup, squarks, sleptons, and gauginos are massless at tree-level, but the Higgs doublets get large negative soft supersymmetry (SUSY) breaking masses squared $m_{H_u}^2 \simeq m_{H_d}^2 < 0$ at a certain energy scale, $M_{\rm inp}$. The sfermion masses are radiatively generated by anomaly mediation and Higgs-loop effects, and gaugino masses are solely determined by anomaly mediation. Consequently, the smuons and bino are light enough to explain the muon $g-2$ anomaly while the third generation sfermions are heavy enough to explain the observed Higgs boson mass. The scenario avoids the SUSY flavor problem as well as various cosmological problems, and is consistent with the radiative electroweak symmetry breaking. In this paper, we show that, although the muon $g-2$ explanation in originally proposed Higgs-anomaly mediation with $M_{\rm inp}\sim 10^{16}\,$GeV is slightly disfavored by the latest LHC data, the muon $g-2$ can still be explained at $1σ$ level when Higgs mediation becomes important at the intermediate scale, $M_{\rm inp} \sim 10^{12}\,$GeV. The scenario predicts light SUSY particles that can be fully covered by the LHC and future collider experiments. We also provide a simple realization of $m_{H_u}^2 \simeq m_{H_d}^2 < 0$ at the intermediate scale.

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A Complete Solution to the Strong CP Problem: a SUSY Extension of the Nelson-Barr Model

We present a supersymmetric solution to the strong CP problem based on spontaneous CP violation which simultaneously addresses the affects coming from supersymmetry breaking. The generated CP violating phase is communicated to the quark sector by interacting with a heavy quark a la Nelson-Barr. The Majorana mass of the right handed neutrinos is generated by interactions with the CP violating sector and so does not conserve CP. This gives the neutrino sector a non-trivial CP violating phase which can then generate the baryon asymmetry of the universe through leptogeneis. The problematic phase in the supersymmetry breaking parameters are suppressed by appealing to a particular gauge mediation model which naturally suppresses the phases of the tree-level gluino mass. This suppression plus the fact that in gauge mediation all loop generated flavor and CP violation is of the minimal flavor violation variety allows for a complete and consistent solution to the strong CP problem.

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Proton Decay and Axion Dark Matter in SO(10) Grand Unification via Minimal Left-Right Symmetry

We study the proton lifetime in the $SO(10)$ Grand Unified Theory (GUT), which has the left-right (LR) symmetric gauge theory below the GUT scale. In particular, we focus on the minimal model without the bi-doublet Higgs field in the LR symmetric model, which predicts the LR-breaking scale at around $10^{10\text{--}12}$ GeV. The Wilson coefficients of the proton decay operators turn out to be considerably larger than those in the minimal $SU(5)$ GUT model especially when the Standard Model Yukawa interactions are generated by integrating out extra vector-like multiplets. As a result, we find that the proton lifetime can be within the reach of the Hyper-Kamiokande experiment even when the GUT gauge boson mass is in the $10^{16\text{--}17}$ GeV range. We also show that the mass of the extra vector-like multiplets can be generated by the Peccei-Quinn symmetry breaking in a consistent way with the axion dark matter scenario.

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Bino-wino coannihilation as a prediction in the $E_7$ unification of families

We study the phenomenological consequences of the supersymmetric (SUSY) $E_7/SU(5)\times U(1)^3$ non-linear sigma model coupled to supergravity, where the three generations of quark and lepton chiral multiplets appear as (pseudo) Nambu Goldstone (NG) multiplets, that is, the origin of the three families is explained. To break SUSY, we introduce a SUSY breaking field charged under some symmetry avoiding the Polonyi problem. The gaugino mass spectrum is almost uniquely determined when one requires the electroweak vacuum to be (meta)stable: it would be a miracle that the mass difference between the bino and wino turns out to be within $O(1)\%$ at the low energy. Thus, a bino-wino coannihilation is naturally predicted, which can explain the correct relic abundance of dark matter. Moreover, we find that the bottom-tau Yukawa couplings and the gauge couplings are unified up to $O(1)\%$ in most of the viable region. This scenario can be fully tested at the LHC and future collider experiments since the gauginos and some of the pseudo-NG bosons are light. An axion-like multiplet, which can be identified with the QCD axion, is also predicted.

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Gaugino Mediation Scenarios for Muon $g-2$ and Dark Matter

We explore the possibility that the muon $g-2$ anomaly and the nature of dark matter can be simultaneously explained within the framework of gaugino mediation, focusing on bino-like dark matter where the observed abundance is obtained via co-annihilations. The minimal model with non-universal gaugino masses is excluded by stau vacuum instability, although this constraint can be somewhat relaxed via the addition of a universal soft scalar mass (or $B-L$ gaugino mediation). A more promising alternative is gaugino+Higgs mediation, which significantly raises the soft masses of the third generation sfermions leading to a split spectrum. In this framework, the muon $g-2$ can be easily explained and the dark matter abundance obtained through either bino-wino or bino-slepton co-annihilations.

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Muon $g-2$ in Split-Family SUSY in light of LHC Run II

The Split-Family supersymmetry is a model in which the sfermion masses of the first two generations are in $\mathcal{O}(100\text{-}1000)$ GeV while that of the third one is in $\mathcal{O}(10)$TeV. With such a hierarchical spectrum, the deviation of the muon $g-2$ and the observed Higgs boson mass are explained simultaneously. In this paper, we revisit the Split-Family SUSY model in light of the updated LHC constraints. We also study the flavor changing neutral current problems in the model. As we will show, the problems do not lead to stringent constraints when the Cabibbo-Kobayashi-Maskawa matrix is the only source of the flavor mixing. We also study how large flavor mixing in the supersymmetry breaking parameters is allowed.

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Focus Point Gauge Mediation without a Severe Fine-tuning

We consider focus point gauge mediation within the framework of the next-to-minimal supersymmetric standard model, which substantially reduces the degree of fine-tuning for the electroweak symmetry breaking. The milder fine-tuning is realized by a messenger field in the adjoint representation of $SU(5)$ gauge group with $SU(3)_c$ octet being heavy. Our model has a simple ultraviolet completion. The fine-tuning measure $Δ$ can be as small as 40-50 without any contradiction with LHC constraints.

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Heavy Gravitino from Dynamical Generation of Right-Handed Neutrino Mass Scale, and Gravitational Waves

The absence of supersymmetric particles at the weak scale is a puzzle if supersymmetry solves the gauge hierarchy problem. We show that, if the right-handed neutrino masses arise from hidden gaugino condensation via GUT-suppressed operators, successful thermal leptogenesis leads to the lower bound on the gravitino mass, which may explain the little hierarchy problem. If domain walls associated with the gaugino condensation are formed after inflation, they annihilate when $H \sim m_{3/2}$. We address the possibility that observable gravitational wave signals might emerge from the domain wall annihilation.

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An extended gauge mediation for muon $(g-2)$ explanation

It is increasingly becoming difficult, within a broad class of supersymmetric models, to satisfactorily explain the discrepancy between the measured $(g-2)_μ$ and its standard model prediction, and at the same time satisfy all the other constraints. In this paper we propose a new scheme of gauge mediation by introducing new soft supersymmetry breaking mass parameters for the Higgs sector in a minimal setup containing only a pair of $({\bf 5} + \bar{\bf 5})$ messenger fields of SU(5). This enables us to explain the $(g-2)_μ$ discrepancy while avoiding all the existing constraints. We also provide possible dynamical origin of the new soft mass parameters. The wino and higgsino weighing below 500 GeV constitute the smoking gun signal at the (high luminosity) LHC.

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Flavor-Safe Light Squarks in Higgs-Anomaly Mediation

We consider a simple setup with light squarks which is free from the gravitino and SUSY flavor problems. In our setup, a SUSY breaking sector is sequestered from the matter and gauge sectors, and it only couples to the Higgs sector directly with $\mathcal{O}(100)\,$TeV gravitino. Resulting mass spectra of sfermions are split: the first and second generation sfermions are light as $\mathcal{O}(1)\,$TeV while the third generation sfermions are heavy as $\mathcal{O}(10)\,$TeV. The light squarks of $\mathcal{O}(1)\,$TeV can be searched at the (high-luminosity) LHC and future collider experiments. Our scenario can naturally avoid too large flavor-changing neutral currents and it is consistent with the $ε_K$ constraint. Moreover, there are regions explaining the muon $g-2$ anomaly and bottom-tau/top-bottom-tau Yukawa coupling unification simultaneously.

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Enhanced axion-photon coupling in GUT with hidden photon

We show that the axion coupling to photons can be enhanced in simple models with a single Peccei-Quinn field, if the gauge coupling unification is realized by a large kinetic mixing $χ= {\cal O}(0.1)$ between hypercharge and unbroken hidden U(1)$_H$. The key observation is that the U(1)$_H$ gauge coupling should be rather strong to induce such large kinetic mixing, leading to enhanced contributions of hidden matter fields to the electromagnetic anomaly. We find that the axion-photon coupling is enhanced by about a factor of 10-100 with respect to the GUT-axion models with $E/N = 8/3$.

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Light Higgsino and Gluino in $R$-invariant Direct Gauge Mediation

We provide a simple solution to the $μ$-$B_μ$ problem in the "$R$-invariant direct gauge mediation model". With the solution, the Higgsino and gluino are predicted to be light as $\mathcal{O}(100)$GeV and $\mathcal{O}(1)$TeV, respectively. Those gluino and Higgsino can be accessible at the LHC and future collider experiments. Moreover, dangerous dimension five operators inducing rapid proton decays are naturally suppressed by the $R$-symmetry.

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Muon g-2 in MSSM Gauge Mediation Revisited

The Higgs boson of 125 GeV requires large stop masses, leading to the large $μ$-parameter in most cases of gauge mediation. On the other hand, the explanation for the muon $g-2$ anomaly needs small slepton and neutralino/chargino masses. Such disparity in masses may be obtained from a mass splitting of colored and non-colored messenger fields. However, even if the required small slepton and neutralino/chargino masses are realized, all parameter regions consistent with the muon g-2 are excluded by the recent updated ATLAS result on the wino search in the case that the messenger fields are in ${\bf 5}+\bar {\bf 5}$ representations of SU(5). It is also revealed that the messenger fields in ${\bf 10} + \overline{\bf 10}$ or ${\bf 24}$ representation can not explain the muon g-2 anomaly. We show, giving a simple example model, that the above confliction is solved if there is an additional contribution to the Higgs soft mass which makes the $μ$-parameter small. We also show that the required Higgs B-term for the electroweak symmetry breaking is consistently generated by radiative corrections from gaugino loops.

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Splitting Mass Spectra and Muon g-2 in Higgs-Anomaly Mediation

We propose a scenario where only the Higgs multiplets have direct couplings to a supersymmetry (SUSY) breaking sector. The standard model matter multiplets as well as the gauge multiples are sequestered from the SUSY breaking sector; therefore, their masses arise via anomaly mediation at the high energy scale with a gravitino mass of $\sim$100 TeV. Due to renormalization group running effects from the Higgs soft masses, the masses of the third generation sfermions become O(10) TeV at the low energy scale, while the first and second generation sfermion masses are O(0.1-1) TeV, avoiding the tachyonic slepton problem and flavor changing neutral current problem. With the splitting mass spectrum, the muon g-2 anomaly is explained consistently with the observed Higgs boson mass of 125 GeV. Moreover, the third generation Yukawa couplings are expected to be unified in some regions.

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Gravitational waves from domain walls and their implications

We evaluate the impact of domain-wall annihilation on the currently ongoing and planned gravitational wave experiments, including a case in which domain walls experience a frictional force due to interactions with the ambient plasma. We show the sensitivity reach in terms of physical parameters, namely, the wall tension and the annihilation temperature. We find that a Higgs portal scalar, which stabilizes the Higgs potential at high energy scales, can form domain walls whose annihilation produces a large amount of gravitational waves within the reach of the advanced LIGO experiment (O5). Domain wall annihilation can also generate baryon asymmetry if the scalar is coupled to either SU(2)$_L$ gauge fields or the $(B-L)$ current. This is a variant of spontaneous baryogenesis, but it naturally avoids the isocurvature constraint due to the scaling behavior of the domain-wall evolution. We delineate the parameter space where the domain-wall baryogenesis works successfully and discuss its implications for the gravitational wave experiments.

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Gauge Coupling Unification with Hidden Photon, and Minicharged Dark Matter

We show that gauge coupling unification is realized with a greater accuracy in the presence of a massless hidden photon which has a large kinetic mixing with hypercharge. We solve the renormalization group equations at two-loop level and find that the GUT unification scale is around $10^{16.5}$ GeV which sufficiently suppresses the proton decay rate, and that the unification is essentially determined by the kinetic mixing only, and it is rather insensitive to the hidden gauge coupling or the presence of vector-like matter fields charged under U(1)$_H$ and/or SU(5). Matter fields charged under the unbroken hidden U(1)$_H$ are stable and they contribute to dark matter. Interestingly, they become minicharged dark matter which carries a small but non-zero electric charge, if the hidden gauge coupling is tiny. The minicharged dark matter is a natural outcome of the gauge coupling unification with a hidden photon.

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Nambu-Goldstone Boson Hypothesis for Squarks and Sleptons in Pure Gravity Mediation

We point out that a hypothesis of squarks and sleptons being Nambu-Goldstone (NG) bosons is consistent with pure gravity mediation or minimal split supersymmetry (SUSY). As a concrete example, we consider a SUSY $E_7/SU(5) \times U(1)^3$ non-linear sigma model in the framework of pure gravity mediation. The model accommodates three families of the quark and lepton chiral multiplets as (pseudo) NG multiplets of the Kahler manifold, which may enable us to understand the origin and number of the families. We point out that squarks in the first and second generations are likely to be as light as a few TeV if the observed baryon asymmetry is explained by the thermal leptogenesis; therefore, these colored particles can be discovered at the LHC Run-2 or at the high luminosity LHC.

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Upper Bound on the Gluino Mass in Supersymmetric Models with Extra Matters

We discuss the upper bound on the gluino mass in supersymmetric models with vector-like extra matters. In order to realize the observed Higgs mass of 125 GeV, the gluino mass is bounded from above in supersymmetric models. With the existence of the vector-like extra matters at around TeV, we show that such an upper bound on the gluino mass is significantly reduced compared to the case of minimal supersymmetric standard model. This is due to the fact that radiatively generated stop masses as well the stop trilinear coupling are enhanced in the presence of the vector-like multiplets. In a wide range of parameter space of the model with extra matters, the gluino is required to be lighter than $\sim 3$ TeV, which is likely to be within the reach of forthcoming LHC experiment.

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