arXiv subjects

Yuta Orikasa

Publications and source records attributed to Yuta Orikasa.

66 records · Page 4Linked to original sources

arXiv2014

X-ray line in Radiative Neutrino Model with Global $U(1)$ Symmetry

We study a three loop induced radiative neutrino model with global $U(1)$ symmetry at TeV scale, in which we consider two component dark matter particles. We discuss the possibility to explain the X-ray line signal at about 3.55 keV recently reported by XMN-Newton X-ray observatory using data of various galaxy clusters and Andromeda galaxy. Subsequently, we also discuss to show that sizable muon anomalous magnetic moment, a discrepancy of the effective number of neutrino species $ΔN_{\rm eff}\approx$ 0.39, and scattering cross section detected by direct detection searches can be derived.

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arXiv2014

Dark matter in the $SO(5)\times U(1)$ gauge-Higgs unification

In the $SO(5) \times U(1)$ gauge-Higgs unification the lightest, neutral component of $n_F$ $SO(5)$-spinor fermions (dark fermions), which are relevant for having the observed unstable Higgs boson, becomes the dark matter of the universe. We show that the relic abundance of the dark matter determined by WMAP and Planck data is reproduced, below the bound placed by the direct detection experiment by LUX, by a model with one light and three heavier ($n_F=4$) dark fermions with the lightest one of a mass from 2.3$\,$TeV to 3.1$\,$TeV. The corresponding Aharonov-Bohm phase $θ_H$ in the fifth dimension ranges from 0.097 to 0.074. The case of $n_F=3$ ($n_F = 5, 6$) dark fermions yields the relic abundance smaller (larger) than the observed limit.

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arXiv2014

LHC signals of the $SO(5)\times U(1)$ gauge-Higgs unification

Signatures of the $SO(5)\times U(1)$ gauge-Higgs unification at LHC and future colliders are explored. The Kaluza-Klein (KK) mass spectra of $γ, Z, Z_R$ and the Higgs self-couplings obey universality relations with the Aharonov-Bohm (AB) phase $θ_H$ in the fifth dimension. The current data at low energies and at LHC indicate $θ_H <0.2$. Couplings of quarks and leptons to KK gauge bosons are determined. Three neutral gauge bosons, the first KK modes $Z_R^{(1)}$, $Z^{(1)}$, and $γ^{(1)}$, appear as $Z'$ bosons in dilepton events at LHC. For $θ_H = 0.114$, the mass and decay width of $Z_R^{(1)}$, $Z^{(1)}$, and $γ^{(1)}$ are (5.73TeV, 482GeV), (6.07TeV, 342GeV), and (6.08TeV, 886GeV), respectively. For $θ_H = 0.073$ their masses are 8.00TeV$\sim$8.61TeV. An excess of events in the dilepton invariant mass should be observed in the $Z'$ search at the upgraded LHC at 14TeV.

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arXiv2014

Radiative Symmetry Breaking from Flat Potential in various U(1)' models

We investigate a radiative electroweak gauge symmetry breaking scenario via the Coleman-Weinberg mechanism starting from a completely flat Higgs potential at the Planck scale ("flatland scenario"). In our previous paper, we showed that the flatland scenario is possible only when an inequality K<1 among the coefficients of the beta functions is satisfied. In this paper, we calculate the number K in various models with an extra U(1) gauge sector in addition to the SM particles. We also show the renormalization group (RG) behaviors of a couple of the models as examples.

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arXiv2014

Radiative symmetry breaking at the Fermi scale and flat potential at the Planck scale

We investigate a possibility of the "flatland scenario", in which the electroweak gauge symmetry is radiatively broken via the Coleman-Weinberg mechanism starting from a completely flat Higgs potential at the Planck scale. We show that the flatland scenario is realizable only when an inequality K<1 among the coefficients of the beta-functions is satisfied. We show several models satisfying the condition.

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arXiv2013

Classically conformal B-L extended Standard Model and phenomenology

Bardeen has argued that once the classically conformal invariance and its minimal violation by quantum anomalies are imposed on the SM, it can be free from the quadratic divergences and hence the gauge hierarchy problem. Under the hypothesis, We investigated the minimal B-L extended SM with a flat Higgs potential at the Planck scale. In this model, the B-L symmetry is radiatively broken at TeV scale. We studied phenomenology and detectability of the model at LHC and the ILC.

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arXiv2013

Novel universality and Higgs decay H -> γγ, gg in the SO(5) x U(1) gauge-Higgs unification

The SO(5) x U(1) gauge-Higgs unification in the Randall-Sundrum warped space with the Higgs boson mass m_H=126 GeV is constructed. An universal relation is found between the Kaluza-Klein (KK) mass scale $m_{KK}$ and the Aharonov-Bohm (AB) phase $θ_H$ in the fifth dimension; $m_{KK} \sim 1350 GeV/(sin θ_H)^{0.787}$. The cubic and quartic self-couplings of the Higgs boson become smaller than those in the standard model (SM), having universal dependence on $θ_H$. The decay rates H -> γγ, gg are evaluated by summing contributions from KK towers. Corrections coming from KK excited states are finite and about 0.2% (2%) for $θ_H= 0.12 (0.36)$, branching fractions of various decay modes of the Higgs boson remaining nearly the same as in the SM. The signal strengths of the Higgs decay modes relative to the SM are $\sim cos^2 θ_H$. The mass of the first KK $Z$ is predicted to be $5.9 (2.4)$TeV for $θ_H= 0.12 (0.36)$. We also point out the possible enhancement of $Γ(H -> γγ)$ due to the large $U(1)_X$ charge of new fermion multiplets.

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arXiv2012

Minimal Flavor Violation in the Minimal U(1)_{B-L} Model and Resonant Leptogenesis

We investigate the resonant leptogenesis scenario in the minimally $U(1)_{B-L}$ extended standard model with minimal flavor violation. In our model, the $U(1)_{B-L}$ gauge symmetry is broken at the TeV scale and standard model singlet neutrinos gain Majorana masses of order TeV. In addition, we introduce a flavor symmetry on the singlet neutrinos at a scale higher than TeV. The flavor symmetry is explicitly broken by the neutrino Dirac Yukawa coupling, which induces splittings in the singlet neutrino Majorana masses at lower scales through renormalization group evolutions. We call this setup "minimal flavor violation". The mass-splittings are proportional to the tiny Dirac Yukawa coupling, and hence they automatically enhance the CP asymmetry parameter necessary for the resonant leptogenesis mechanism. In this paper, we calculate the baryon number yield by solving the Boltzmann equations, including the effects of $U(1)_{B-L}$ gauge boson that also has TeV scale mass and causes washing-out of the singlet neutrinos in the course of thermal leptogenesis. The Dirac Yukawa coupling for neutrinos is fixed in terms of neutrino oscillation data and an arbitrary $3 \times 3$ complex-valued orthogonal matrix. We show that the right amount of baryon number asymmetry can be achieved through thermal leptogenesis in the context of the minimal flavor violation with singlet neutrinos and $U(1)_{B-L}$ gauge boson at the TeV scale. These particles can be discovered at the LHC in the near future.

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arXiv2012

Dark matter in the classically conformal B-L model

When the classically conformal invariance is imposed on the minimal gauged B-L extended Standard Model (SM), the B-L gauge symmetry is broken by the Coleman-Weinberg mechanism naturally at the TeV scale. Introducing a new Z_2 parity in the model, we investigate phenomenology of a right-handed neutrino dark matter whose stability is ensured by the parity. We find that the relic abundance of the dark matter particle can be consistent with the observations through annihilation processes enhanced by resonances of either the SM Higgs boson, the B-L Higgs boson or the B-L gauge boson (Z' boson). Therefore, the dark matter mass is close to half of one of these boson masses. Due to the classically conformal invariance and the B-L gauge symmetry breaking via the Coleman-Weinberg mechanism, Higgs boson masses, Z' boson mass and the dark matter mass are all related, and we identify the mass region to be consistent with experimental results. We also calculate the spin-independent cross section of the dark matter particle off with nucleon and discuss implications for future direct dark matter search experiments.

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arXiv2011

Resonant Leptogenesis in the Minimal B-L Extended Standard Model at TeV

We investigate the resonant leptogenesis scenario in the minimal B-L extended standard model(SM) with the B-L symmetry breaking at the TeV scale. Through detailed analysis of the Boltzmann equations, we show how much the resultant baryon asymmetry via leptogenesis is enhanced or suppressed, depending on the model parameters, in particular, the neutrino Dirac Yukawa couplings and the TeV-scale Majorana masses of heavy degenerate neutrinos. In order to consider a realistic case, we impose a simple ansatz for the model parameters and analyze the neutrino oscillation parameters and the baryon asymmetry via leptogenesis as a function of only a single CP-phase. We find that for a fixed CP-phase all neutrino oscillation data and the observed baryon asymmetry of the present universe can be simultaneously reproduced.

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arXiv2009

The minimal B-L model naturally realized at TeV scale

In a previous paper, we have proposed the minimal B-L extended standard model as a phenomenologically viable model that realizes the Coleman-Weinberg-type breaking of the electroweak symmetry. Assuming the classical conformal invariance and stability up to the Planck scale, we will show in this paper that the model naturally predicts TeV scale B-L breaking as well as a light standard-model singlet Higgs boson and light right-handed neutrinos around the same energy scale. We also study phenomenology and detectability of the model at the Large Hadron Collider (LHC) and the International Linear Collider (ILC).

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arXiv2009

Classically Conformal B-L extended Standard Model

Under a hypothesis of classically conformal theories, we investigate the minimal B-L extended Standard Model, which naturally provides the seesaw mechanism for explaining tiny neutrino masses. In this setup, the radiative gauge symmetry breaking is successfully realized in a very simple way: The B-L gauge symmetry is broken through the conformal anomaly induced by quantum corrections in the Coleman-Weinberg potential. Associated with this B-L symmetry breaking, the Higgs mass parameter is dynamically generated, by which the electroweak symmetry breaking is triggered. We find that a wide range of parameter space can satisfy both the theoretical and experimental requirements.

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