Hajime Fukuda

Diboson Resonance as a Portal to Hidden Strong Dynamics

A bstractWe propose a new explanation for excess events observed in the search for a high-mass resonance decaying into dibosons by the ATLAS experiment. The resonance is identified as a composite spin-0 particle that couples to the Standard Model gauge bosons via dimension-5 operators. The excess events can be explained if the dimension-5 operators are suppressed by a mass scale of O1−10

Flavor-Changing Neutral-Current Decays in Top-Specific Variant Axion Model

\mathcal{O}\left(1-10\right)

A "gauged"

TeV. We also construct a model of hidden strong gauge dynamics which realizes the spin-0 particle as its lightest composite state, with appropriate couplings to Standard Model gauge bosons.

U(1)

We pursue a class of visible axion models where the axion mass is enhanced by strong dynamics in a mirrored copy of the Standard Model in the line of the idea put forward by Rubakov. In particular, we examine the consistency of the models with laboratory, astrophysical, and cosmological constraints. As a result, viable parameter regions are found, where the mass of the axion is of O(100)  MeV or above while the Peccei-Quinn breaking scale is at around 103–5  GeV.

Peccei–Quinn symmetry

A bstractThe invisible variant axion model is very attractive as it is free from the domain wall problem. This model requires two Higgs doublets at the electroweak scale where one Higgs doublet carries a nonzero Peccei-Quinn (PQ) charge and the other is neutral under the PQ U(1) symmetry. We consider the most interesting and less constrained scenario of the variant axion model, where only the right-handed top quark is charged under the PQ symmetry and couples with the PQ-charged Higgs doublet. As a result, the top quark can decay to the observed standard-model-like Higgs boson h and the charm or up quark, t → h c/u, which is testable soon at the LHC Run-II. Moreover, we propose a method to probe the chiral nature of the Higgs flavor-changing interaction using the angular distribution of t → ch decays if a sufficient number of such events are observed. We also show that our model has the capacity to explain the h → τ μ decay reported by the CMS collaboration, if the right-handed tau lepton also carries a PQ charge and couples to the PQ-charged Higgs boson.

Seminatural Gauge Mediation from Product Group Unification

Abstract Higgsino in supersymmetric standard models is known to be a promising candidate for dark matter in the Universe. Its phenomenological property is strongly affected by the gaugino fraction in the Higgsino-like state. If this is sizable, in other words, if gaugino masses are less than O ( 10 ) TeV, we may probe the Higgsino dark matter in future non-accelerator experiments such as dark matter direct searches and measurements of electric dipole moments. On the other hand, if gauginos are much heavier, then it is hard to search for Higgsino in these experiments. In this case, due to a lack of gaugino components, the mass difference between the neutral and charged Higgsinos is uniquely determined by electroweak interactions to be around 350 MeV, which makes the heavier charged state rather long-lived, with a decay length of about 1 cm. In this letter, we argue that a charged particle with a flight length of O ( 1 ) cm can be probed in disappearing-track searches if we require only two hits in the pixel detector. Even in this case, we can reduce background events with the help of the displaced-vertex reconstruction technique. We study the prospects of this search strategy at the LHC and future colliders for the Higgsino dark matter scenario. It is found that an almost pure Higgsino is indeed within the reach of the future 33 TeV collider experiments. We then discuss that the interplay among collider and non-accelerator experiments plays a crucial role in testing the Higgsino dark matter scenarios. Our strategy for disappearing-track searches can also enlarge the discovery potential of pure wino dark matter as well as other electroweak-charged dark matter candidates.

Asymmetric dark matter in early Universe chemical equilibrium always leads to an antineutrino signal

Abstract The Peccei–Quinn (PQ) solution to the strong CP problem requires an anomalous global U ( 1 ) symmetry, the PQ symmetry. The origin of such a convenient global symmetry is quite puzzling from the theoretical point of view in many aspects. In this paper, we propose a simple prescription which provides an origin of the PQ symmetry. There, the global U ( 1 ) PQ symmetry is virtually embedded in a gauged U ( 1 ) PQ symmetry. Due to its simplicity, this mechanism can be implemented in many conventional models with the PQ symmetry.

Gauged Peccei-Quinn symmetry — A case of simultaneous breaking of SUSY and PQ symmetry

We propose a focus point gauge mediation model based on the product group unification (PGU), which solves the doublet-triplet splitting problem of the Higgs multiplets. In the focus point gauge mediation, the electroweak symmetry breaking scale can be naturally explained even for multi-TeV stops. It is known that the focus point behavior appears if a ratio of the number of SU(2) doublet messengers to that of SU(3) triplet messengers is close to 5/2. Importantly, this ratio (effectively) appears in our scenario based on the PGU, if the messenger field is an adjoint representation of SU(5) gauge group. Therefore, our focus point scenario is very predictive. It is also pointed out the gravitino can be dark matter without spoiling the success of the thermal leptogenesis. The absence of the SUSY CP-problem is guaranteed in the case that the Higgs B-term vanishes at the messenger scale.