arXiv subjects

Shinya Kanemura

Publications and source records attributed to Shinya Kanemura.

At least 127 records · Page 7Linked to original sources

arXiv2015

LHC Run-I constraint on the mass of doubly charged Higgs bosons in the same-sign diboson decay scenario

In this Letter, we study the latest bound on the mass of doubly charged Higgs bosons, $H^{\pm\pm}$, assuming that they dominantly decay into a diboson. The new bound is obtained by comparing the inclusive searches for events with a same-sign dilepton by the ATLAS Collaboration using the latest 20.3 fb$^{-1}$ data at the LHC 8 TeV run with theoretical prediction based on the Higgs triplet model with next-to-leading order QCD corrections. We find that the lower mass bound on $H^{\pm\pm}$ is about 84 GeV.

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arXiv2014

Fingerprinting non-minimal Higgs sectors

After the discovery of the standard-model-like Higgs boson at the LHC, the structure of the Higgs sector remains unknown. We discuss how it can be determined by the combination of direct and indirect searches for additional Higgs bosons at future collider experiments. First of all, we evaluate expected excluded regions for the mass of additional neutral Higgs bosons from direct searches at the LHC with the 14 TeV collision energy in the two Higgs doublet models with a softly-broken $Z_2$ symmetry. Second, precision measurements of the Higgs boson couplings at future experiments can be used for the indirect search of extended Higgs sectors if measured coupling constant with the gauge boson slightly deviates from the standard model value. In particular, in the two Higgs doublet model with the softly-broken discrete symmetry, there are four types of Yukawa interactions, so that they can be discriminated by measuring the pattern of deviations in Yukawa coupling constants. Furthermore, we can fingerprint various extended Higgs sectors with future precision data by detecting the pattern of deviations in the coupling constants of the standard-model-like Higgs boson. We demonstrate how the pattern of deviations can be different among various Higgs sectors which predict the electroweak rho parameter to be unity; such as models with additional an isospin singlet, a doublet, triplets or a septet. We conclude that as long as the gauge coupling constant of the Higgs boson slightly differs from the standard model prediction but is enough to be detected at the LHC and its high-luminosity run or at the International Linear Collider, we can identify the non-minimal Higgs sector even without direct discovery of additional Higgs bosons at the LHC.

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arXiv2014

Novel Constraint on Parameter Space of the Georgi-Machacek Model by Current LHC Data

The same-sign diboson process $pp\to W^\pm W^\pm jj$ has been measured at the LHC using leptonic decay channels of the $W$ bosons, with production cross sections of two fiducial regions reported to be consistent with the standard model expectations within 1 sigma. These results constrain new physics models with a modified $W^+W^+W^-W^-$ vertex. We consider in particular the Georgi-Machacek model in which the quartic $W$ boson vertex is effectively modified due to mediations of new Higgs bosons in the model. The relevant gauge-gauge-scalar couplings are all proportional to the vacuum expectation value of the isospin triplets, which can be of $\mathcal{O}(10)$ GeV because of custodial vacuum alignment. Using the current 8-TeV data at the LHC, we exclude parameter space on the plane of the triplet vacuum expectation value and the new Higgs boson mass. The expected discovery reach at the 14-TeV LHC is also studied.

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arXiv2014

Complementarity in direct searches for additional Higgs bosons at the LHC and the International Linear Collider

We discuss complementarity of discovery reaches of heavier neutral Higgs bosons and charged Higgs bosons at the LHC and the International Linear Collider (ILC) in two Higgs doublet models (2HDMs). We perform a comprehensive analysis on their production and decay processes for all types of Yukawa interaction under the softly-broken discrete symmetry which is introduced to avoid flavour changing neutral currents, and we investigate parameter spaces of discovering additional Higgs bosons at the ILC beyond the LHC reach. We find that the 500 GeV run of the ILC with the integrated luminosity of 500 fb^{-1} shows an advantage for discovering the additional Higgs bosons in the region where the LHC cannot discover them with the integrated luminosity of 300 fb^{-1}. For the 1 TeV run of the ILC with the integrated luminosity of 1 ab^{-1}, production processes of an additional Higgs boson associated with the top quark can be useful as discovery channels in some parameter spaces where the LHC with the integrated luminosity of 3000 fb^{-1} cannot reach. It is emphasized that the complementary study at the LHC and the ILC is useful not only to survey additional Higgs bosons at the TeV scale, but also to discriminate types of Yukawa interaction in the 2HDM.

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arXiv2014

Bounds on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenario

A direct search for doubly-charged Higgs bosons $H^{\pm\pm}$ is one of the most important probe in the Higgs Triplet Model, which is motivated by generation mechanisms of tiny neutrino masses. There are two major decay modes of $H^{\pm\pm}$; i.e., the same-sign dilepton decay $H^{\pm\pm}\to\ell^\pm\ell^\pm$ and the same-sign diboson decay $H^{\pm\pm}\to W^{\pm(*)}W^{\pm(*)}$. For the case where the former decay mode is dominant, the lower limit on the mass of $H^{\pm\pm}$ has been set at about 400 GeV by ATLAS and CMS Collaborations. On the other hand, for the case where the latter decay mode is dominant, no dedicated search has been performed in the past. By taking into account characteristic signals of $H^{\pm\pm}$ in the diboson decay scenario at LEP and the LHC experiments, we find that the lower mass bound of 60-68 GeV can be obtained using the same-sign dilepton search performed by ATLAS Collaboration with 4.7 fb$^{-1}$ data at the collision energy of 7 TeV. We also show that the limit can be extended up to about 85-90 GeV, assuming the integrated luminosity of 20 fb$^{-1}$ and 7 TeV for the collision energy. We give detailed explanations on the decay properties of $H^{\pm\pm}$ for relatively small mass cases and also on production cross sections of $H^{\pm\pm}$ at the next-to-leading order of QCD at the LHC.

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arXiv2014

Neutrino Mass and Dark Matter from Gauged $U(1)_{B-L}$ Breaking

We propose a new model where the Dirac mass term for neutrinos, the Majorana mass term for right-handed neutrinos, and the other new fermion masses arise via the spontaneous breakdown of the $U(1)_{B-L}$ gauge symmetry. The anomaly-free condition gives four sets of assignment of the B-L charge to new particles, and three of these sets have an associated global $U(1)_{DM}$ symmetry which stabilizes dark matter candidates. The dark matter candidates contribute to generating the Dirac mass term for neutrinos at the one-loop level. Consequently, tiny neutrino masses are generated at the two-loop level via a Type-I-Seesaw-like mechanism. We show that this model can satisfy current bounds from neutrino oscillation data, the lepton flavor violation, the relic abundance of the dark matter, and the direct search for the dark matter. This model would be tested at future collider experiments and dark matter experiments.

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arXiv2014

Radiative neutrino mass, dark matter and electroweak baryogenesis from the supersymmetric gauge theory with confinement

We propose a simple model to explain neutrino mass, dark matter and baryogenesis based on the extended Higgs sector which appears in the low-energy effective theory of a supersymmetric gauge theory with confinement. We here consider the SU(2)$_H$ gauge symmetry with three flavours of fundamental representations which are charged under the standard SU(3)$_C\times$ SU(2)$_L\times$U(1)$_Y$ symmetry and a new discrete $Z_2$ symmetry. We also introduce $Z_2$-odd right-handed neutrino superfields in addition to the standard model matter superfields. The low-energy effective theory below the confinement scale contains the Higgs sector with fifteen composite superfields, some of which are $Z_2$-odd. When the confinement scale is of the order of ten TeV, electroweak phase transition can be sufficiently of first order, which is required for successful electroweak baryogenesis. The lightest $Z_2$-odd particle can be a new candidate for dark matter, in addition to the lightest $R$-parity odd particle. Neutrino masses and mixings can be explained by the quantum effects of $Z_2$-odd fields via the one-loop and three-loop diagrams. We find a benchmark scenario of the model, where all the constraints from the current neutrino, dark matter, lepton flavour violation and LHC data are satisfied. Predictions of the model are shortly discussed.

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arXiv2014

Higgs Physics as a Proble of New Physics

The discovery of the Higgs boson at the LHC has opened the door to clarify the mechanism of electroweak symmetry breaking and the origin of masses of particles. The Higgs sector in the SM is the simplest but has no theoretical principle, so that there is a possibility of non-minimal Higgs sectors. While the standard model is not contradict with the current data at the LHC within the error, most of extended Higgs sectors can also reproduce the data. An extended Higgs sector often appears in a new physics model beyond the standard model, so that we can determine new physics from the Higgs sector. In this talk, we discuss various aspects of extended Higgs sectors, in particular its phenomenological properties and testability at future experiments at the International Linear Collider.

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arXiv2014

Radiative corrections to the Yukawa coupling constants in two Higgs doublet models

We calculate one-loop corrected Yukawa coupling constants $hf\bar{f}$ for the standard model like Higgs boson $h$ in two Higgs doublet models. We focus on the models with the softly-broken $Z_2$ symmetry, which is imposed to avoid the flavor changing neutral current. Under the $Z_2$ symmetry, there are four types of Yukawa interactions. We find that one-loop contributions from extra Higgs bosons modify the $hf\bar{f}$ couplings to be maximally about $5\%$ under the constraint from perturbative unitarity and vacuum stability. Our results show that the pattern of tree-level deviations by the mixing effect in each type of Yukawa couplings from the SM predictions does not change even including radiative corrections. Moreover, when the gauge couplings $hVV$ ($V=W,Z$) are found to be slightly (with a percent level) differ from the SM predictions, the $hf\bar{f}$ couplings also deviate but more largely. Therefore, in such a case, not only can we determine the type of Yukawa couplings but also we can obtain information on the extra Higgs bosons by comparing the predictions with precisely measured $hf\bar{f}$ and $hVV$ couplings at future electron-positron colliders.

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arXiv2014

Higgs as a Probe of Supersymmetric Grand Unification with the Hosotani Mechanism

The supersymmetric grand unified theory where the SU(5) gauge symmetry is broken by the Hosotani mechanism predicts the existence of adjoint chiral superfields whose masses are at the supersymmetry breaking scale. The Higgs sector is extended with the SU(2)_L triplet with hypercharge zero and neutral singlet chiral multiplets from that in the minimal supersymmetric standard model. Since the triplet and singlet chiral multiplets originate from a higher-dimensional vector multiplet, this model is highly predictive. Properties of the particles in the Higgs sector are characteristic and can be different from those in the Standard Model and other models. We evaluate deviations in coupling constants of the standard model-like Higgs boson and the mass spectrum of the additional Higgs bosons. We find that our model is discriminative from the others by precision measurements of these coupling constants and masses of the additional Higgs bosons. This model can be a good example of grand unification that is testable at future collider experiments such as the luminosity up-graded Large Hadron Collider and future electron-positron colliders.

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arXiv2013

Loop Suppression of Dirac Neutrino Mass in the Neutrinophilic Two Higgs Doublet Model

We extend the scalar sector of the neutrinophilic two Higgs doublet model, where small masses of Dirac neutrinos are obtained via a small vacuum expectation value v_nu of the neutrinophilic SU(2)_L-doublet scalar field which has a Yukawa interaction with only right-handed neutrinos. A global U(1)_X symmetry is used for the neutrinophilic nature of the second SU(2)_L-doublet scalar field and also for eliminating Majorana mass terms of neutrinos. By virtue of an appropriate assignment of the U(1)_X-charges to new particles, our model has an unbroken Z_2 symmetry, under which the lightest Z_2-odd scalar boson can be a dark matter candidate. In our model, v_nu is generated by the one-loop diagram to which Z_2-odd particles contribute. We briefly discuss a possible signature of our model at the LHC.

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arXiv2013

A UV complete model for radiative seesaw and electroweak baryogenesis based on the SUSY gauge theory

In a class of supersymmetric gauge theories with asymptotic freedom, the low energy effective theory below the confinement scale is described by the composite superfields of the fundamental representation fields. Based on the supersymmetric gauge theory with N_c=2 and N_f=3 with an additional unbroken Z_2 symmetry, we propose a new model where neutrino masses, dark matter, and baryon asymmetry of the Universe can be simultaneously explained by physics below the confinement scale. This is an example for the ultraviolet complete supersymmetric extension of so-called radiative seesaw scenarios with first-order phase transition required for successful electroweak baryogenesis. We show that there are benchmark points where all the neutrino data, the lepton flavor violation data, and the LHC data are satisfied. We also briefly discuss Higgs phenomenology in this model.

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arXiv2013

Reconstruction of Inert Doublet Scalars at the International Linear Collider

We study collider signatures for extra scalar bosons in the inert doublet model at the international linear collider (ILC). The inert doublet model is a simple extension of the standard model by introducing an additional isospin-doublet scalar field which is odd under an unbroken Z_2 symmetry. The model predicts four kinds of Z_2-odd scalar bosons, and the lightest of them becomes stable and a candidate of the dark matter as long as it is electrically neutral. Taking into account the constraints from various theoretical and phenomenological conditions, we perform a simulation study for the distinctive signatures of the extra scalars over the standard-model background contributions at the ILC with the center-of-mass energy of sqrt{s} = 250 GeV and 500 GeV. We further discuss observables for determination of the mass of the scalars. We find that the parameter regions which cannot be detected at the large hadron collider can be probed at the ILC.

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arXiv2013

First constraint on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenario at the LHC

When the doubly-charged Higgs bosons $H^{\pm\pm}$ mainly decay into the same-sign dilepton, a lower bound on the mass is around 400 GeV by the current LHC data. On the other hand, no such bound has been reported by using the data at LEP and at the LHC for the case where the same-sign diboson decay $H^{\pm\pm}\to W^{\pm(*)} W^{\pm(*)}$ is dominant. We study limits on the mass for such a case by using the current experimental data. From the precise measurement of the total width of the Z boson at the LEP experiment, the mass below 43 GeV is excluded with the 95% C.L. It turns out that the results from four charged lepton searches at LEP do not provide any significant constraint. We show that a new lower bound is obtained in the diboson decay scenario at the LHC with the collision energy to be 7 TeV and the integrated luminosity to be 4.7 fb$^{-1}$. By using the data of the same-sign dilepton events, the lower limit is found to be 60 GeV at the 95% C.L. By the extrapolation of the data to 20 fb$^{-1}$ with the same collision energy, the lower limit is evaluated to be 85 GeV.

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arXiv2013

Probing exotic Higgs sectors from the precise measurement of Higgs boson couplings

We study coupling constants of the standard model like Higgs boson with the gauge bosons $hZZ$ and $hWW$ and fermions $hf\bar{f}$ in the general Higgs sector which contains higher isospin representations with arbitrary hypercharge. In Higgs sectors with exotic Higgs representations, the $hZZ$ and $hWW$ coupling constants can be larger than those in the standard model. We calculate deviations in the Higgs boson couplings from standard model values in the model with a real or complex triplet field, the Georgi-Machacek model and the model with a septet scalar field. We also study deviations in the event rates of $h\to ZZ^*$, $h\to WW^*$, $h\to γγ$, $h\to b\bar{b}$ and $h\to ττ$ channels.

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arXiv2013

The International Linear Collider Technical Design Report - Volume 2: Physics

The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. It is shown that no significant technical issues remain to be solved. Once a site is selected and the necessary site-dependent engineering is carried out, construction can begin immediately. The TDR also gives baseline documentation for two high-performance detectors that can share the ILC luminosity by being moved into and out of the beam line in a "push-pull" configuration. These detectors, ILD and SiD, are described in detail. They form the basis for a world-class experimental programme that promises to increase significantly our understanding of the fundamental processes that govern the evolution of the Universe.

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arXiv2013

Determination of tan(beta) from the Higgs boson decay at linear colliders

In the two Higgs doublet model, $\tanβ$ is an important parameter, which is defined as the ratio of the vacuum expectation values of the doublets. We study how accurately $\tanβ$ can be determined at linear colliders via the precision measurement of the decay branching fraction of the standard model (SM) like Higgs boson. Since the effective coupling constants of the Higgs boson with the weak gauge bosons are expected to be measured accurately, the branching ratios can be precisely determined. Consequently, $\tanβ$ can be determined with a certain amount of accuracy. Comparing the method to those using direct production of the additional Higgs bosons, we find that, depending on the type of Yukawa interactions, the precision measurement of the decay of the SM-like Higgs boson can be the best way to determine $\tanβ$, when the deviations in the coupling constants with the gauge boson from the SM prediction are observed at linear colliders.

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arXiv2013

Higgs inflation in a radiative seesaw model

We investigate a simple model to explain inflation, neutrino masses and dark matter simultaneously. This is based on the so-called radiative seesaw model proposed by Ma in order to explain neutrino masses and dark matter by introducing a $Z_2$-odd isospin doublet scalar field and $Z_2$-odd right-handed neutrinos. We study the possibility that the Higgs boson as well as neutral components of the $Z_2$-odd scalar doublet field can satisfy conditions from slow-roll inflation and vacuum stability up to the inflation scale. We find that a part of parameter regions where these scalar fields can play a role of an inflaton is compatible with the current data from neutrino experiments and those of the dark matter abundance as well as the direct search results. A phenomenological consequence of this scenario results in a specific mass spectrum of scalar bosons, which can be tested at the LHC, the International Linear Collider and the Compact Linear Collider.

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