arXiv subjects

Jisuke Kubo

Publications and source records attributed to Jisuke Kubo.

At least 37 records · Page 2Linked to original sources

arXiv2018

Non-perturbative electroweak-scalegenesis on the test bench of dark matter detection

We revisit a recently proposed scale invariant extension of the standard model, in which the scalar bi-linear condensate in a strongly interacting hidden sector dynamically breaks scale symmetry, thereby triggering electroweak symmetry breaking. Relaxing the previously made assumption on $U(N_f)$ flavor symmetry we find that the presence of the would-be dark matter candidate opens a new annihilation process of dark matter at finite temperature, such that the model can satisfy stringent constraints of the future experiments of the dark matter direct detection.

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arXiv2017

Multicomponent Dark Matter in Radiative Seesaw Models

We discuss radiative seesaw models, in which an exact $Z_2\times Z_2'$ symmetry is imposed. Due to the exact $Z_2\times Z_2'$ symmetry, neutrino masses are generated at a two-loop level and at least two extra stable electrically neutral particles are predicted. We consider two models: one has a multi-component dark matter system and the other one has a dark radiation in addition to a dark matter. In the multi-component dark matter system, non-standard dark matter annihilation processes exist. We find that they play important roles in determining the relic abundance and also responsible for the monochromatic neutrino lines resulting from the dark matter annihilation process. In the model with the dark radiation, the structure of the Yukawa coupling is considerably constrained and gives an interesting relationship among cosmology, lepton flavor violating decay of the charged leptons and the decay of the inert Higgs bosons.

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arXiv2017

Gravitational Waves from Hidden QCD Phase Transition

Drastic changes in the early universe such as first-order phase transition can produce a stochastic gravitational wave (GW) background. We investigate the testability of a scale invariant extension of the standard model (SM) using the GW background produced by the chiral phase transition in a strongly interacting QCD-like hidden sector, which, via a SM singlet real scalar mediator, triggers the electroweak phase transition. Using the Nambu--Jona-Lasinio method in a mean field approximation we estimate the GW signal and find that it can be tested by future space based detectors.

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arXiv2016

Scale genesis and gravitational wave in a classically scale invariant extension of the standard model

We assume that the origin of the electroweak (EW) scale is a gauge-invariant scalar-bilinear condensation in a strongly interacting non-abelian gauge sector, which is connected to the standard model via a Higgs portal coupling. The dynamical scale genesis appears as a phase transition at finite temperature, and it can produce a gravitational wave (GW) background in the early Universe. We find that the critical temperature of the scale phase transition lies above that of the EW phase transition and below few $O(100)$ GeV and it is strongly first-order. We calculate the spectrum of the GW background and find the scale phase transition is strong enough that the GW background can be observed by DECIGO.

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arXiv2016

Genesis of electroweak and dark matter scales from a bilinear scalar condensate

The condensation of scalar bilinear in a classically scale invariant strongly interacting hidden sector is used to generate the electroweak scale, where the excitation of the condensate is identified as dark matter. We formulate an effective theory for the condensation of the scalar bilinear and find in the self-consistent mean field approximation that the dark matter mass is of $O(1)$ TeV with the spin-independent elastic cross section off the nucleon slightly below the LUX upper bound.

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arXiv2015

Scale and electroweak first-order phase transitions

We consider phase transitions in the standard model (SM) without the Higgs mass term, which is coupled through a Higgs portal term to an SM singlet, classically scale-invariant gauge sector with SM singlet scalar fields. At lower energies the gauge-invariant scalar bilinear in the hidden sector forms a condensate, dynamically creating a robust energy scale, which is transmitted through the Higgs portal term to the SM sector. A scale phase transition is a transition between phases with zero and nonzero condensates. An interplay between the EW and scale phase transitions is therefore expected. We find that in a certain parameter space both the electroweak (EW) and scale phase transitions can be a strong first-order phase transition. The result is obtained by means of an effective theory for the condensation of scalar bilinear in the mean field approximation.

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arXiv2015

Nambu-Goldstone Dark Matter in a Scale Invariant Bright Hidden Sector

We consider a scale invariant extension of the standard model (SM) with a combined breaking of conformal and electroweak symmetry in a strongly interacting hidden $SU(n_c)$ gauge sector with $n_f$ vector-like hidden fermions. The (pseudo) Nambu-Goldstone bosons that arise due to dynamical chiral symmetry breaking are dark matter (DM) candidates. We focus on $n_f=n_c=3$, where $SU(3)$ is the largest symmetry group of hidden flavor which can be explicitly broken into either $U(1) \times U(1)$ or $SU(2)\times U(1)$. We study DM properties and discuss consistent parameter space for each case. Because of different mechanisms of DM annihilation the consistent parameter space in the case of $SU(2)\times U(1)$ is significantly different from that of $SU(3)$ if the hidden fermions have a SM $U(1)_Y$ charge of $O(1)$.

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arXiv2014

Reduction of couplings and its application in particle physics, Finite theories, Higgs and top mass predictions

In this report we tell the story of the notion "reduction of couplings" as we witnessed it in the course of time. Born as an innocent child of renormalization theory it first served the study of asymptotic behavior of several couplings in a given model. Reduced couplings appeared as functions of a primary one, compatible with the renormalization group equation and thus solutions of a specific set of ordinary differential equations. If these functions have the form of power series the respective theories resemble standard renormalizable ones and thus widen considerably the area covered until then by symmetries as a tool for constraining the number of couplings consistently. Still on the more abstract level reducing couplings enabled one to construct theories with beta-functions vanishing to all orders of perturbation theory. Reduction of couplings became physicswise truely interesting and phenomenologically important when applied to the standard model and its possible extensions. In particular in the context of supersymmetric theories it became the most powerful tool known today once it was learned how to apply it also to couplings having dimension of mass and to mass parameters. Technically this all relies on the basic property that reducing couplings is a renormalization scheme independent procedure. Predictions of top and Higgs mass prior to their experimental finding highlight the fundamental physical significance of this notion. Twenty-two original articles and one set of lectures are being commented, put into historical perspective and interrelated with each other.

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arXiv2014

Multicomponent Dark Matter in Radiative Seesaw Model and Monochromatic Neutrino Flux

We consider a two loop radiative seesaw model with an exact $Z_2 \times Z'_2$ symmetry, which can stabilize two or three dark matter particles. The model is a simple extension of the inert scalar model of Ma, where the lepton-number violating mass term of the inert scalar, which is required to be small for small neutrino masses, is generated at the one-loop level. The semi-annihilation processes of different dark matter particles, which are present when there exist more than three different dark matter particles, not only play an important role for their relic densities, but also are responsible for the monochromatic neutrino lines resulting from the dark matter annihilation processes. The monochromatic neutrinos do not suffer from a chiral suppression, and we investigate the observational possibility of the monochromatic neutrino flux from the Sun.

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arXiv2014

Electroweak Symmetry Breaking via QCD

We propose a new mechanism to generate the electroweak scale within the framework of QCD, which is extended to include conformally invariant scalar degrees of freedom belonging to a larger irreducible representation of $SU(3)_c$. The electroweak symmetry breaking is triggered dynamically via the Higgs portal by the condensation of the colored scalar field around 1 TeV. The mass of the colored boson is restricted to be 350 GeV $\lesssim m_S\lesssim $ 3 TeV, with the upper bound obtained from perturbative renormalization group evolution. This implies that the colored boson can be produced at LHC. If the colored boson is electrically charged, the branching fraction of the Higgs decaying into two photons can slightly increase, and moreover, it can be produced at future linear colliders. Our idea of non-perturbative EW scale generation can serve as a new starting point for more realistic model building in solving the hierarchy problem.

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arXiv2014

Gamma-ray Line from Nambu-Goldstone Dark Matter in a Scale Invariant Extension of the Standard Model

A recently proposed scale invariant extension of the standard model is modified such that it includes a Dark Matter candidate which can annihilate into gamma-rays. For that a non-zero $U(1)_Y$ hypercharge $Q$ is assigned to the fermions in a QCD-like hidden sector. The Nambu-Goldstone bosons, that arise due to dynamical chiral symmetry breaking in the hidden sector, are cold Dark Matter candidates, and the extension allows them to annihilate into two photons, producing a gamma-ray line spectrum. We find that the gamma-ray line energy must be between 0.7 TeV and 0.9 TeV with the velocity-averaged annihilation cross section $10^{-30}\sim 10^{-26}$ cm^3/s for $Q=1/3$. With a non-zero hypercharge $Q$, the hidden sector is no longer completely dark and can be directly probed by collider experiments.

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arXiv2014

Electroweak and Conformal Symmetry Breaking by a Strongly Coupled Hidden Sector

The LHC and other experiments show so far no sign of new physics and long-held beliefs about naturalness should be critically reexamined. We discuss therefore in this paper a model with a combined breaking of conformal and electroweak symmetry by a strongly coupled hidden sector. Even though the conformal symmetry is anomalous, this may still provide an explanation of the smallness of electroweak scale compared to the Planck scale. Specifically we start from a classically conformal model, in which a strongly coupled hidden sector undergoes spontaneous chiral symmetry breaking. A coupling via a real scalar field transmits the breaking scale to the Standard Model Higgs and triggers electroweak symmetry breaking. The model contains dark matter candidates in the form of dark pions, whose stability is being guaranteed by the flavor symmetry of hidden quark sector. We study its relic abundance and direct detection prospects with the Nambu-Jona-Lasinio method and discuss the phase transition in the dark sector as well as in the electroweak sector.

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arXiv2013

Two-loop radiative seesaw with multicomponent dark matter explaining the possible gamma excess in the Higgs boson decay and at the Fermi LAT

A non-supersymmetric model of a two-loop radiative seesaw is proposed. The model contains, in addition to the standard model (SM) Higgs boson, an inert SU(2)_L doublet scalar eta and two inert singlet scalars phi and chi. The lepton number is softly broken by a dimension-two operator, and the tree-level Dirac mass is forbidden by Z_2 x Z_2' (or D_{2N}), which predicts the existence of two or three dark matter particles. The scalar sector is minimal; none of the scalar fields can be suppressed for the radiative seesaw mechanism to work. There are by-products: The SM Higgs boson decay into two gamma's is slightly enhanced by eta^+ (the charged component of eta) circulating in one-loop diagrams for h to gamma gamma. The 135 GeV gamma-ray line observed at the Fermi LAT can be also explained by the annihilation of chi dark matter. We employ a mechanism of temperature-dependent annihilation cross section to suppress the continuum gamma rays and the production of antiprotons. The explanation can survive even down to the XENON1T sensitivity limit.

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arXiv2012

Multi-Component Dark Matter Systems and Their Observation Prospects

Conversions and semi-annihilations of dark matter (DM) particles in addition to the standard DM annihilations are considered in a three-component DM system. We find that the relic abundance of DM can be very sensitive to these non-standard DM annihilation processes, which has been recently found for two-component DM systems. To consider a concrete model of a three-component DM system, we extend the radiative seesaw model of Ma by adding a Majorana fermion χand a real scalar boson ϕ, to obtain a Z_2 \times Z'_2 DM stabilizing symmetry, where we assume that the DM particles are the inert Higgs boson, χand ϕ. It is shown how the allowed parameter space, obtained previously in the absence of χand ϕ, changes. The semi-annihilation process in this model produces monochromatic neutrinos. The observation rate of these monochromatic neutrinos from the Sun at IceCube is estimated. Observations of high energy monochromatic neutrinos from the Sun may indicate a multi-component DM system.

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arXiv2012

Super Flavorsymmetry with Multiple Higgs Doublets

The meaning of non-abelian super flavorsymmetry in the presence of Multiple Higgs Doublets is twofold: The first one is to order the Yukawa sector of the standard model, while generating the Cheng-Sher suppression of tree-level Flavor Changing Neutral Currents (FCNCs), and the second one is to soften the fine tuning problem in the scalar potential and at the same time to suppress FCNCs coming from the soft breaking of supersymmetry. If spontaneous CP violation is combined with non-abelian super flavorsymmetry the CP phases in the soft supersymmetry breaking sector can disappear. This feature of super flavorsymmetry is reviewed and elaborated in a supersymmetric model of flavor based on the finite group Q6. The predictions of the model in ferimion mass and mixing, and flavor and CP violation can be tested in future experiments.

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arXiv2012

Vanishing Minors in the Neutrino Mass Matrix from Abelian Gauge Symmetries

Augmenting the Standard Model by three right-handed neutrinos allows for an anomaly-free gauge group extension G_max = U(1)_(B-L) x U(1)_(L_e-L_mu) x U(1)_(L_mu-L_tau). While simple U(1) subgroups of G_max have already been discussed in the context of approximate flavor symmetries, we show how two-zero textures in the right-handed neutrino Majorana mass matrix can be enforced by the flavor symmetry, which is spontaneously broken very economically by singlet scalars. These zeros lead to two vanishing minors in the low-energy neutrino mass matrix after the seesaw mechanism. This study may provide a new testing ground for a zero-texture approach: the different classes of two-zero textures with almost identical neutrino oscillation phenomenology can in principle be distinguished by their different Z' interactions at colliders.

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arXiv2011

Impact of Inert Higgsino Dark Matter

We consider a recently proposed supersymmetric radiative seesaw model which is coupled with the minimal supergravity. The conventional R parity and $Z_2$ invariance are imposed, which ensures the existence of a multi-component dark matter system. We assume that the pair of the lightest neutralino $\tildeχ$ and the fermionic component $\tildeξ$ of the inert Higgs supermultiplet is dark matter. If $\tildeξ$ is lighter than $\tildeχ$, and the lightest neutral inert Higgs boson is kinematically forbidden to decay (third dark matter), the allowed region in the $m_0{\rm \mathchar`-}M_{1/2}$ plane increases considerably, where $m_0$ and $M_{1/2}$ are the universal soft-supersymmetry-breaking scalar and gaugino mass, respectively, although the dominant component of the multi-component dark matter system is $\tildeχ$. There is a wide allowed region above the recent LHC limit.

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arXiv2011

Variations on the Supersymmetric Q6 Model of Flavor

We observe that a recently proposed supersymmetric model with Q6 flavor symmetry admits a new CP violating ground state. A new sum rule for the quark mixing parameters emerges, which is found to be consistent with data. Simple extensions of the model to the neutrino sector suggest an inverted hierarchical mass spectrum with nearly maximal CP violation (|delta_{MNS}| simeq pi/2). Besides reducing the number of parameters in the fermion sector, these models also provide solutions to the SUSY flavor problem and the SUSY CP problem. We construct a renormalizable scalar potential that leads to the spontaneous breaking of CP symmetry and the family symmetry.

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