arXiv subjects

Nobuhito Maru

Publications and source records attributed to Nobuhito Maru.

At least 37 records · Page 2Linked to original sources

arXiv2021

Extranatural Flux Inflation

We propose a new inflation scenario in flux compactification, where a zero mode scalar field of extra components of the higher dimensional gauge field is identified with an inflaton. The scalar field is a pseudo Nambu-Goldstone boson of spontaneously broken translational symmetry in compactified spaces. The inflaton potential is non-local and finite, which is protected against the higher dimensional non-derivative local operators by quantum gravity corrections thanks to the gauge symmetry in higher dimensions and the shift symmetry originated from the translation in extra spaces. We give an explicit inflation model in a six dimensional scalar QED, which is shown to be consistent with Planck 2018 data.

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arXiv2021

The strong CP problem and higher dimensional gauge theories

We discuss a natural scenario to solve the strong CP problem in the framework of the higher dimensional gauge theory. An axion-like field $A_y$ has been built-in as the extra-space component of the higher dimensional gauge field. The coupling of $A_y$ with gluons is attributed to the radiatively induced "Chern-Simons" (CS) term. We adopt a toy model with some unknown gauge symmetry U(1)$_X$. The CS term is obtained in two ways: first by a concrete 1-loop calculation and next by use of the Fujikawa's method to deal with the chiral anomaly in 4D space-time. The obtained results are identical, which implies that the radiative correction to the CS term is "1-loop exact" and is also free from UV-divergence even though the theory itself is non-renormalizable. As a novel feature of this scenario, such obtained CS term is no longer linear in the field $A_y$ as in the usually discussed CS term in 5D space-time but a periodic function of $A_y$, since $A_y$ has a physical meaning as the Wilson-loop phase. We argue how such novel feature of this scenario causes the modification of the ordinary solutions of the strong CP problem based on the axion fields.

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arXiv2021

Non-Gaussianity from $X, Y$ gauge bosons in Cosmological Collider Physics

Heavy fields of Hubble scale order present during inflation contribute to the non-Gaussian signature for the three-point function of the inflaton. Taking into account that Hubble scale is around the scale of grand unified theory (GUT), this opens a possibility that the GUT scale signatures, which are very hard to be discovered at collider, might be detectable by using information from the precise observations of cosmic microwave background. We discuss a detactability of the $X, Y$ gauge boson present in any GUT in a framework of cosmological collider physics. Calculating one-loop contributions of $X, Y$ gauge bosons to the inflaton three-point functions, we find a remarkable result that one-loop diagram with interactions originated from the mass terms of $X, Y$ gauge bosons provides an enhancement factor expressed by the ratio between the $X, Y$ gauge boson mass and Hubble scale as $(m_X/H)^4$. In an estimation of the non-Gaussianity, this factor is crucial and its impact on the detactability of $X, Y$ gauge bosons is discussed.

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arXiv2020

Cancellation of One-loop Corrections to Scalar Masses in Flux Compactification with Higher Dimensional Operators

We further study the cancellation of the one-loop corrections to the scalar mass in a six dimensional SU(2) gauge theory with higher dimensional operators, which is compactified on a torus with magnetic flux. Higher dimensional operators also contribute to the corrections to the scalar mass nontrivially. We explicitly show by the diagrammatic calculations that the corrections are exactly cancelled even with the leading terms of the higher dimensional operators.

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arXiv2020

Improving Fermion Mass Hierarchy in Grand Gauge-Higgs Unification with Localized Gauge Kinetic Terms

Grand gauge-Higgs unification of five dimensional SU(6) gauge theory on an orbifold S^1/Z_2 with localized gauge kinetic terms is discussed. The Standard model (SM) fermions on one of the boundaries and some massive bulk fermions coupling to the SM fermions on the boundary are introduced, so that they respect an SU(5) symmetry structure. The SM fermion masses including top quark are reproduced by mild tuning the bulk masses and parameters of the localized gauge kinetic terms. Gauge coupling universality is not guaranteed by the presence of the localized gauge kinetic terms and it severely constrains the Higgs vacuum expectation value. Higgs potential analysis shows that the electroweak symmetry breaking occurs by introducing additional bulk fermions in simplified representations.The localized gauge kinetic terms enhance the magnitude of the compactification scale, which helps Higgs boson mass large. Indeed the observed Higgs boson mass 125 GeV is obtained.

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arXiv2019

Strong First Order Electroweak Phase Transition in Gauge-Higgs Unification at Finite Temperature

We analyze the electroweak phase transition at finite temperature in a model of gauge-Higgs unification where the fermion mass hierarchy including top quark mass, a viable electroweak symmetry breaking and an observed Higgs mass are successfully reproduced. To study the phase transition, we derive the general formula of the 1-loop effective potential at finite temperature by using the $ζ$ function regularization method. It is remarkable that the functions determining the Kaluza-Klein mass spectrum have only to be necessary in calculations. This potential can be applicable to any higher dimensional theory in flat space where one extra spatial dimension is compactified. Applying to our model of gauge-Higgs unification, the strong first phase transition compatible with 125 GeV Higgs mass is found to happen.

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arXiv2019

Cancellation of One-loop Corrections to Scalar Masses in Yang-Mills Theory with Flux Compactification

We calculate one-loop corrections to the mass for the zero mode of scalar field in a six-dimensional Yang-Mills theory compactified on a torus with magnetic flux. It is shown that these corrections are exactly cancelled thanks to a shift symmetry under the translation in extra spaces. This result is expected from the fact that the zero mode of scalar field is a Nambu-Goldstone boson of the translational invariance in extra spaces.

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arXiv2019

Fermion Mass Hierarchy in Grand Gauge-Higgs Unification

Grand gauge-Higgs unification of five dimensional $SU(6)$ gauge theory on an orbifold $S^1/Z_2$ is discussed. The Standard model (SM) fermions are introduced on one of the boundaries and some massive bulk fields are also introduced so that they couple to the SM fermions through the mass terms on the boundary. Integrating out the bulk fields generates the SM fermion masses with exponentially small bulk mass dependences. The SM fermion masses except for top quark are shown to be reproduced by mild tuning the bulk masses. One-loop Higgs potential is calculated and it is shown that the electroweak symmetry breaking occurs by introducing additional bulk fields. Higgs boson mass is also computed.

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arXiv2018

Triple Higgs Boson Coupling in Gauge-Higgs Unification

We consider the triple coupling of the Higgs boson in the context of the gauge-Higgs unification scenario. We show that the triple coupling of the Higgs boson in this scenario generically deviates from SM prediction since the Higgs potential in this scenario has a periodicity. We calculate the coupling in the five-dimensional $SU(3)$ x $U(1)_X$ gauge-Higgs unification model and obtain 70% deviation from the SM prediction.

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arXiv2018

$SU(2)_L$ Doublet Vector Dark Matter from Gauge-Higgs Unification

A new vector dark matter (DM) scenario in the context of the gauge-Higgs unification (GHU) is proposed. The DM particle is identified with an electric-charge neutral component in an $SU(2)_L$ doublet vector field with the same quantum number as the Standard Model Higgs doublet. Since such an $SU(2)_L$ doublet vector field is incorporated in any models of the GHU scenario, it is always a primary and model-independent candidate for the DM in the scenario. The observed relic density is reproduced through a DM pair annihilations into the weak gauge bosons with a TeV-scale DM mass, which is nothing but the compactification scale of extra-dimensions. Due to the higher-dimensional gauge structure of the GHU scenario, a pair of the DM particles has no direct coupling with a single $Z$-boson/Higgs boson, so that the DM particle evades the severe constraint from the current direct DM search experiments.

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arXiv2018

Revisiting Electroweak Symmetry Breaking and Higgs Mass in Gauge-Higgs Unification

We propose a new model of 5D $SU(3)\otimes U(1)_X$ gauge-Higgs unification with a successful electroweak symmetry breaking and a realistic Higgs boson mass. In our model, the representations of the fermions are very simple, the ${\bf 3}, \overline{\bf 3}$ and $\bf \overline{15}$ representations of $SU(3)$ gauge group. Employing the anti-periodic boundary conditions for $\bf \overline{15}$ reduces massless exotic fermions and simplifies the brane localized mass terms. We calculate the 1-loop Higgs potential in detail and find that a realistic electroweak symmetry breaking and the observed Higgs mass are obtained.

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arXiv2017

Fermionic Minimal Dark Matter in 5D Gauge-Higgs Unification

We propose a Minimal Dark Matter (MDM) scenario in the context of a simple gauge-Higgs Unification (GHU) model based on the gauge group SU(3) x U(1)' in 5-dimensional Minkowski space with a compactification of the 5th dimension on S^1/Z_2 orbifold. A pair of vector-like SU(3) multiplet fermions in a higher-dimensional representation is introduced in the bulk, and the DM particle is identified with the lightest mass eigenstate among the components in the multiplets. In the original model description, the DM particle communicates with the Standard Model (SM) particles only through the bulk gauge interaction, and hence our model is the GHU version of the MDM scenario. There are two typical realizations of the DM particle in 4-dimensional effective theory: (i) the DM particle is mostly composed of the SM SU(2)_L multiplets, or (ii) the DM is mostly composed of the SM SU(2)_L singlets. Since the case (i) is very similar to the original MDM scenario, we focus on the case (ii), which is a realization of the Higgs-portal DM scenario in the context of the GHU model. We identify an allowed parameter region to be consistent with the current experimental constraints, which will be fully covered by the direct dark matter detection experiments in the near future. In the presence of the bulk multiplet fermions in higher-dimensional $SU(3)$ representations, we reproduce the 125 GeV Higgs boson mass through the renormalization group evolution of Higgs quartic coupling with the compactification scale of 10-100 TeV.

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arXiv2017

Fermion Dark Matter in Gauge-Higgs Unification

We propose a Majorana fermion dark matter in the context of a simple gauge-Higgs Unification (GHU) scenario based on the gauge group $SU(3)$ x $U(1)'$ in 5-dimensional Minkowski space with a compactification of the 5th dimension on $S^1/Z_2$ orbifold. The dark matter particle is identified with the lightest mode in $SU(3)$ triplet fermions additionally introduced in the 5-dimensional bulk. We find an allowed parameter region for the dark matter mass around a half of the Standard Model Higgs boson mass, which is consistent with the observed dark matter density and the constraint from the LUX 2016 result for the direct dark matter search. The entire allowed region will be covered by, for example, the LUX-ZEPLIN dark matter experiment in the near future. We also show that in the presence of the bulk $SU(3)$ triplet fermions the 125 GeV Higgs boson mass is reproduced through the renormalization group evolution of Higgs quartic coupling with the compactification scale of around $10^8$ GeV.

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arXiv2017

Anomalous Higgs Yukawa Couplings and Recent LHC Data

Very recently, the CMS collaboration has reported a search for the production for a Standard Model (SM) Higgs boson in association with a top quark pair ($t bar{t} H$) at the LHC Run-2 and a best fit $t bar{t} H$ yield of $1.5 pm 0.5$ times the SM prediction with an observed significance of $3.3 sigma$. We study a possibility of whether or not this observed deviation can be explained by anomalous Higgs Yukawa couplings with the top and the bottom quarks, along with the LHC Run-1 data for the Higgs boson properties. We find that anomalous top and bottom Yukawa couplings with about $0-20$% and $10-40$% reductions from their SM values, respectively, can simultaneously fit the recent CMS result and the LHC Run-1 data.

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arXiv2016

Predictions of the Higgs mass and the weak mixing angle in the 6D gauge-Higgs unification

In the gauge-Higgs unification with multiple extra spaces, the Higgs self-coupling is of the order of $g^2$ and Higgs is predicted to be light, being consistent with the LHC results. When the gauge group is simple, the weak mixing angle is also predictable. We address a question whether there exists a model of gauge-Higgs unification in 6-dimensional space-time, which successfully predicts the mass ratios of the Higgs boson and weak gauge bosons. First, by use of a useful formula we give a general argument on the condition to get a realistic prediction of the weak mixing angle $sin^{2}theta_{W} = 1/4$, and find that triplet and sextet representations of the minimal SU(3) gauge group lead to the realistic prediction. Concerning the Higgs mass, we notice that in the models with one Higgs doublet, the predicted Higgs mass is always the same: $M_H = 2 M_W$. However, by extending our discussion to the models with two Higgs doublets, the situation changes: we obtain an interesting prediction $M_{H} leq 2M_{W}$ at the leading order of the perturbation. Thus it is possible to recover the observed Higgs mass, 125 GeV, for a suitable choice of the parameter. The situation is in clear contrast to the case of the minimal supersymmetric standard model, where $M_{H} leq M_{Z}$ at the classical level and the predicted Higgs mass cannot recover the observed value.

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arXiv2016

Perturbative unification of gauge couplings in supersymmetric $E_6$ models

We study gauge coupling unification in supersymmetric $E_6$ models where an additional $\mathrm{U}(1)'$ gauge symmetry is broken near the TeV scale and a number of exotic matter fields from the $\bm{27}$ representations have $O(\mathrm{TeV})$ mass. Solving the 2-loop renormalization group equations of gauge couplings and a kinetic mixing coupling between the $\mathrm{U}(1)'$ and $\mathrm{U}(1)_Y$ gauge fields, we find that the gauge couplings fall into the non-perturbative regime below the GUT scale. We examine threshold corrections on the running of gauge couplings from both light and heavy ($\sim$ GUT scale) particles and show constraints on the size of corrections to achieve the perturbative unification of gauge couplings.

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arXiv2016

Trilinear gauge boson couplings in the gauge-Higgs unification

We examine trilinear gauge boson couplings (TGCs) in the context of the $SU(3)_W\otimes U(1)'$ gauge-Higgs unification scenario. The TGCs play important roles in the probes of the physics beyond the standard model, since they are highly restricted by the experiments. We discuss mass spectrum of the neutral gauge boson with brane-localized mass terms carefully and find that the TGCs and $ρ$ parameter may deviate from standard model predictions. Finally we put a constraint from these observables and discuss the possible parameter space.

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arXiv2016

Anomalous Top and Bottom Yukawa Couplings and LHC Run 1 Data

In some extensions of the Standard Model, Yukawa couplings of the physical Higgs boson can be deviated from those in the Standard Model. We study a possibility whether or not such anomalous Yukawa couplings are consistent with the LHC Run 1 data. It is found that sizable deviations of top and bottom (and tau) Yukawa couplings from the Standard Model predictions can nicely fit the data. New physics beyond the Standard Model can be revealed through more precise measurements of such anomalous Yukawa couplings at the LHC Run 2 in the near future. We also discuss a simple setup which can leads to anomalous Yukawa couplings.

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