arXiv subjects

Shinya Kanemura

Publications and source records attributed to Shinya Kanemura.

At least 73 records · Page 4Linked to original sources

arXiv2021

Testing aligned CP-violating Higgs sector at future lepton colliders

We discuss the testability of CP-violating phases at future lepton colliders for the scenario which satisfies electric dipole moment data by destructive interferences among several phases. We consider the general but aligned two Higgs doublet model which has the CP-violating phases in the Higgs potential and the Yukawa interaction. The Yukawa interaction terms are aligned to avoid flavor changing neutral currents at tree level. The Higgs potential is also aligned such that the coupling constants of the lightest Higgs boson with the mass of 125 GeV to the Standard Model (SM) particles are the same as those of the SM at tree level. We investigate the azimuthal angle distribution of the hadronic decay of tau leptons arising from production and decay of the extra Higgs bosons, which contains information of the CP-violating phases. From the signal and background simulation, we find that the scenario with finite CP-violating phases can be distinguished from CP conserving one at future lepton colliders like the International Linear Collider.

hep-ph↗

arXiv2020

New scenario for aligned Higgs couplings originated from the twisted custodial symmetry at high energies

We investigate a new scenario of the two Higgs doublet model, where the current experimental data for the electroweak rho parameter and those for the Higgs boson couplings can be simultaneously explained. In this scenario, the two Higgs doublet model is supposed to be a low energy effective theory up to a high energy scale $Λ$, above which a fundamental theory should appear. It is assumed that the Higgs potential respects a global symmetry at $Λ$ (the twisted custodial symmetry), which is to be given as a consequence of the global symmetry structure of the fundamental theory above $Λ$. By the analysis using one-loop renormalization group equations, the above experimental data can be explained in a natural way even when the masses of the extra Higgs bosons are near the electroweak scale. We also discuss the predictions on the mass spectrum of the additional Higgs bosons and also those on coupling constants of the standard-model-like Higgs boson, which make it possible to test this scenario at current and future collider experiments.

hep-ph↗

arXiv2020

Two-loop corrections to the Higgs trilinear coupling in models with extended scalar sectors

The Higgs trilinear coupling provides a unique opportunity to study the structure of the Higgs sector and probe indirect signs of BSM Physics -- even if new states are somehow hidden. In models with extended Higgs sectors, large deviations in the Higgs trilinear coupling can appear at one loop because of non-decoupling effects in the radiative corrections involving the additional scalar states. It is then natural to ask how two-loop corrections modify this result, and whether new large corrections can appear again. We present new results on the dominant two-loop corrections to the Higgs trilinear coupling in several models with extended scalar sectors. We illustrate the analytical expressions with numerical examples and show that, while they remain smaller than their one-loop counterparts and do not modify significantly the non-decoupling effects observed at one loop, the two-loop corrections are not entirely negligible -- a typical size being 10-20% of the one-loop corrections.

hep-ph↗

arXiv2020

Alternative dark matter phenomenology in a general $U(1)_X$ extension of the Standard Model

The existence of the neutrino mass and flavor mixing have been experimentally verified. These phenomena strongly motivate to extend the Standard Model (SM). Amongst many possibilities, a simple and interesting extension of the SM can be investigated using a general U$(1)_X$ extension of the SM gauge group. Demanding the cancellation of the gauge and mixed gauge gravity anomalies, three right handed neutrinos are introduced in this model where the U$(1)_X$ charge assignment becomes a linear combination of U$(1)_{\rm{B-L}}$ and U$(1)_Y$ hyper-charges. After the U$(1)_X$ breaking, an additional neutral gauge boson, $Z^\prime$ is evolved and the neutrino mass is generated by the seesaw mechanism. In such a model we investigate the properties of a Dark Matter (DM) candidate which is a massive weakly interacting particle and Dirac type in nature. The stability of the DM is protected by its U$(1)_X$ charge. Using the current bounds on the search results of $Z^\prime$ at the Large Hadron Collider (LHC) and the dark matter relic abundance we find a phenomenologically viable parameter space of our scenario.

hep-ph↗

arXiv2020

Two-loop analysis of classically scale-invariant models with extended Higgs sectors

We present the first explicit calculation of leading two-loop corrections to the Higgs trilinear coupling $λ_{hhh}$ in models with classical scale invariance (CSI), using the effective-potential approximation. Furthermore, we also study -- for the first time at two loops -- the relation that appears between the masses of all states in CSI theories, due to the requirement of reproducing correctly the 125-GeV Higgs-boson mass. In addition to obtaining analytic results for general CSI models, we consider two particular examples of Beyond-the-Standard-Model theories with extended Higgs sectors, namely an $N$-scalar model (endowed with a global $O(N)$ symmetry) and a CSI version of the Two-Higgs-Doublet Model, and we perform detailed numerical studies of these scenarios. While at one loop the value of the Higgs trilinear coupling is identical in all CSI models, and deviates by approximately $82\%$ from the (one-loop) SM prediction, we find that the inclusion of two-loop corrections lifts this universality and allows distinguishing different BSM scenarios with CSI. Taking into account constraints from perturbative unitarity and the relation among masses, we find for both types of scenarios we consider that at two loops $λ_{hhh}$ deviates from its SM prediction by $100\pm10\%$ -- i.e. a quite significant further deviation with respect to the one-loop result of $\sim 82\%$.

hep-ph↗

arXiv2020

Probing extended Higgs sectors by the synergy between direct searches at the LHC and precision tests at future lepton colliders

We discuss a possibility that the parameter space of the two Higgs doublet model is significantly narrowed down by considering the synergy between direct searches for additional Higgs bosons at the LHC and its luminosity upgraded operation and precision measurements of the Higgs boson properties at future electron-positron colliders such as the International Linear Collider. We show that, in the case where the coupling constants of the discovered Higgs boson are slightly different from the predicted values in the standard model, most of the parameter space is explored by the direct searches of extra Higgs bosons, in particular for the decays of the extra Higgs bosons into the discovered Higgs boson, and also by the theoretical arguments such as perturbative unitarity and vacuum stability. This can be done because there appears an upper limit on the mass of the extra Higgs bosons as long as the deviation exists in the Higgs boson coupling. We also show that in the alignment limit where all the Higgs boson couplings take the standard model like values most of the parameter space cannot be excluded because most of the Higgs to Higgs decays are suppressed and also there is no upper limit on the masses from the theoretical arguments.

hep-ph↗

arXiv2020

H-COUP Version 2: a program for one-loop corrected Higgs boson decays in non-minimal Higgs sectors

We present the concept of H-COUP_ver 2, which evaluates the decay rates (including higher order corrections) for the Higgs boson with a mass of 125 GeV in various extended Higgs models. In the previous version (H-COUP_1.0), only a full set of the Higgs boson vertices are evaluated at one-loop level in a gauge invariant manner in these models. H-COUP_ver 2 contains all the functions of H-COUP_1.0. After shortly introducing these extended Higgs models and discussing their theoretical and experimental constraints, we summarize formulae for the renormalized vertices and the decay rates. We then explain how to install and run H-COUP_ver 2 with some numerical examples.

hep-ph↗

arXiv2020

Probing charged lepton number violation via $\ell^\pm \ell^{\prime \pm} W^\mp W^\mp$

We study impacts of dimension-five lepton-number violating operators associated with two same-sign weak bosons, $\ell^\pm \ell^{\prime \pm} W^\mp W^\mp$, on current and future experiments for neutrino oscillation, lepton-number violating rare processes and high-energy collider experiments. These operators can contain important information on the origin of tiny neutrino masses, which is independent of that from the so-called Weinberg operator. We examine constraints on the coefficients of the operators by the neutrino oscillation data. Upper bounds on the coefficients are also investigated by using the data for processes of lepton number violation such as neutrinoless double beta decays and $μ^-$-$e^+$ conversion. These operators can also be directly tested by searching for lepton-number violating dilepton production via the same-sign W boson fusion process at high-energy hadron colliders like the Large Hadron Collider. We find that these operators can be considerably probed by these current and future experiments.

hep-ph↗

arXiv2020

Current status of space gravitational wave antenna DECIGO and B-DECIGO

Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is the future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could be produced during the inflationary period right after the birth of the universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in the heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry-Perot Michelson interferometers with an arm length of 1,000 km. Three clusters of DECIGO will be placed far from each other, and the fourth cluster will be placed in the same position as one of the three clusters to obtain the correlation signals for the detection of the primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder of DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand the multi-messenger astronomy.

gr-qc↗

arXiv2020

Radiative generation of neutrino masses in a 3-3-1 type model

A new model for tiny neutrino masses is proposed in the gauge theory of $SU(3)_C \otimes SU(3)_L \otimes U(1)_X$, where neutrino masses are generated via the quantum effect of new particles. In this model, the fermion content is taken to be minimal to realize the gauge anomaly cancellation, while the scalar sector is extended from the minimal 3-3-1 model to have an additional $SU(3)_L$ triplet field. After $SU(3)_L\otimes U(1)_X$ is broken into $SU(2)_L\otimes U(1)_Y$, the "Zee model" like diagrams are naturally induced, which contain sufficient lepton flavor violating interactions to reproduce current neutrino oscillation data. Furthermore, the remnant $Z_2$ symmetry appears after the electroweak symmetry breaking, which guarantees the stability of dark matter. It is confirmed that this model can satisfy current dark matter data. As an important prediction to test this model, productions and decays of doubly-charged scalar bosons at collider experiments are discussed in successful benchmark scenarios.

hep-ph↗

arXiv2020

Aligned CP-violating Higgs sector canceling the electric dipole moment

We discuss the effect of CP violation in the aligned scenario of the general two-Higgs-doublet model, in which the Higgs potential and the Yukawa interaction provide additional CP-violating phases. An alignment is imposed to the Yukawa interaction in order to avoid dangerous flavor changing neutral currents. The Higgs potential is also aligned such that the coupling constants of the lightest Higgs boson, which is identified as the discovered Higgs boson with the mass of 125 GeV, are the same as those of the standard model. In general, CP-violating phases originated by the Yukawa interaction and the Higgs potential are strongly constrained by the current data for the electric dipole moment (EDM). It is found that in our scenario contributions from the two sources of CP violation can be destructive and consequently their total contribution can satisfy the EDM results, even when each CP-violating phase is large. Such a large CP-violating phase can be tested at collider experiments by looking at the angular distributions of particles generated by the decays of the additional Higgs bosons.

hep-ph↗

arXiv2020

Leading two-loop corrections to the Higgs boson self-couplings in models with extended scalar sectors

We compute the dominant two-loop corrections to the Higgs trilinear coupling $λ_{hhh}$ and to the Higgs quartic coupling $λ_{hhhh}$ in models with extended Higgs sectors, using the effective-potential approximation. We provide in this paper all necessary details about our calculations, and present general $\overline{\text{MS}}$ expressions for derivatives of the integrals appearing in the effective potential at two loops. We also consider three particular Beyond-the-Standard-Model (BSM) scenarios -- namely a typical scenario of an Inert Doublet Model (IDM), and scenarios of a Two-Higgs-Doublet Model (2HDM) and of a Higgs Singlet Model (HSM) without scalar mixing -- and we include all the necessary finite counterterms to obtain (in addition to $\overline{\text{MS}}$ results) on-shell scheme expressions for the corrections to the Higgs self-couplings. With these analytic results, we investigate the possible magnitude of two-loop BSM contributions to the Higgs self-couplings and the fate of the non-decoupling effects that are known to appear at one loop. We find that, at least as long as pertubative unitarity conditions are fulfilled, the size of two-loop corrections remains well below that of one-loop corrections. Typically, two-loop contributions to $λ_{hhh}$ amount to approximately 20% of those at one loop, implying that the non-decoupling effects observed at one loop are not significantly modified, but also meaning that higher-order corrections need to be taken into account for the future perspective of precise measurements of the Higgs trilinear coupling.

hep-ph↗

arXiv2020

Two-loop corrections to the Higgs trilinear coupling in models with extended scalar sectors

The Higgs trilinear coupling $λ_{hhh}$ is of great importance to understand the structure of the Higgs sector and allows searching for indirect signs of Beyond-the-Standard-Model (BSM) physics, even if new states are somehow hidden. In particular, in models with extended Higgs sectors, it is known that non-decouplings effects in BSM-scalar contributions at one loop can cause $λ_{hhh}$ to deviate significantly from its SM prediction, raising the question of what happens at two loops. We review here our calculation of the leading two-loop corrections to $λ_{hhh}$ in an aligned scenario of a Two-Higgs-Doublet Model. We find their typical size to be 10-20% of the one-loop corrections, meaning that they do not modify significantly the one-loop non-decoupling effects, but are not entirely negligible either.

hep-ph↗

arXiv2019

Full next-to-leading-order calculations of Higgs boson decay rates in models with non-minimal scalar sectors

We present a complete set of decay rates of the Higgs boson with the mass of 125 GeV at the full next-to-leading order in a variety of extended Higgs models; i.e., a model with an additional real singlet scalar field, four types of two Higgs doublet models and the inert doublet model. All the one-loop contributions due to QCD and electroweak interactions as well as scalar interactions are taken into account, and the calculations are systematically performed. Branching ratios for all the decay modes are evaluated in these models, and patterns of deviations in each decay mode from the standard model predictions are comprehensively analyzed. We show how these models with extended Higgs sectors can be distinguished by using our calculation of the branching ratios and future precision measurements of the Higgs boson decays.

hep-ph↗

arXiv2019

Tests of the Standard Model at the International Linear Collider

We present an overview of the capabilities that the International Linear Collider (ILC) offers for precision measurements that probe the Standard Model. First, we discuss the improvements that the ILC will make in precision electroweak observables, both from W boson production and radiative return to the Z at 250 GeV in the center of mass and from a dedicated GigaZ stage of running at the Z pole. We then present new results on precision measurements of fermion pair production, including the production of b and t quarks. We update the ILC projections for the determination of Higgs boson couplings through a Standard Model Effective Field Theory fit taking into account the new information on precision electroweak constraints. Finally, we review the capabilities of the ILC to measure the Higgs boson self-coupling.

hep-ex↗

arXiv2019

On two-loop corrections to the Higgs trilinear coupling in models with extended scalar sectors

We investigate the possible size of two-loop radiative corrections to the Higgs trilinear coupling $λ_{hhh}$ in two types of models with extended Higgs sectors, namely in a Two-Higgs-Doublet Model (2HDM) and in the Inert Doublet Model (IDM). We calculate the leading contributions at two loops arising from the additional (heavy) scalars and the top quark of these theories in the effective-potential approximation. We include all necessary conversion shifts in order to obtain expressions both in the $\overline{\text{MS}}$ and on-shell renormalisation schemes, and in particular, we devise a consistent "on-shell" prescription for the soft-breaking mass of the 2HDM at the two-loop level. We illustrate our analytical results with numerical studies of simple aligned scenarios and show that the two-loop corrections to $λ_{hhh}$ remain smaller than their one-loop counterparts, with a typical size being 10-20% of the one-loop corrections, at least while perturbative unitarity conditions are fulfilled. As a consequence, the existence of a large deviation of the Higgs trilinear coupling from the prediction in the Standard Model, which has been discussed in the literature at one loop, is not altered significantly.

hep-ph↗

arXiv2019

Exploring the global symmetry structure of the Higgs potential via same-sign pair production of charged Higgs bosons

We propose a novel process where singly charged Higgs bosons are produced in a same-sign pair via vector boson fusion at hadron colliders in two Higgs doublet models. The process directly relates to the global symmetry structure of the Higgs potential. The produced charged Higgs bosons predominantly decay into a tau lepton and the neutrino or into a pair of top and bottom quarks, depending on the type of Yukawa interactions. We evaluate the signal and the background for the both cases at the CERN Large Hadron Collider and future higher-energy hadron colliders. We find that the process can be feasible and useful to explore the nature of the Higgs potential.

hep-ph↗

arXiv2019

New model for radiatively generated Dirac neutrino masses and lepton flavor violating decays of the Higgs boson

We propose a new mechanism to explain neutrino masses with lepton number conservation, in which the Dirac neutrino masses are generated at the two-loop level involving a dark matter candidate. In this model, branching ratios of lepton flavor violating decays of the Higgs boson can be much larger than those of lepton flavor violating decays of charged leptons. If lepton flavor violating decays of the Higgs boson are observed at future collider experiments without detecting lepton flavor violating decays of charged leptons, most of the models previously proposed for tiny neutrino masses are excluded while our model can still survive. We show that the model can be viable under constraints from current data for neutrino experiments, searches for lepton flavor violating decays of charged leptons and dark matter experiments.

hep-ph↗