Kento Asai

It is well known that the differences between the lepton numbers can be gauged with the standard model matter content. Such extended gauge theories, dubbed as the gauged $\mathrm{U}(1{)}_{{L}_{\ensuremath{\alpha}}\ensuremath{-}{L}_{\ensuremath{\beta}}}$ models, have been widely discussed so far as potential candidates for physics beyond the Standard Model. In this work, we study the minimal versions of these gauge theories, where three right-handed neutrinos as well as a single $\mathrm{U}(1{)}_

Abstract We study the minimal extensions of the Standard Model by a linear combination of U(1) $$_{L_e-L_\mu }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow/><mml:mrow><mml:msub><mml:mi>L</mml:mi><mml:mi>e</mml:mi></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>L</mml:mi><mml:mi>μ</mml:mi></mml:msub></mml:mrow></mml:msub></mml:math> , U(1) $$_{L_\mu -L_\tau }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow/><mml:mrow><mml:msub><mml:m

A bstract We study a simple Dirac fermion dark matter model in $$ \mathrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>U</mml:mi><mml:msub><mml:mfenced><mml:mn>1</mml:mn></mml:mfenced><mml:mrow><mml:msub><mml:mi>L</mml:mi><mml:mi>μ</mml:mi></mml:msub><mml:mo>−</mml:mo><mml:msub><mml:mi>L</mml:mi><mml:mi>τ</mml:mi></mml:msub></mml:mrow></mml:msub></mml:math> theory. The new light gauge boson X plays important roles in both dark matter physics

The origin of neutrino mass is a big unsolved problem of the Standard Model (SM) that motivate us to consider beyond the SM (BSM) scenarios where SM-singlet right-handed neutrinos (RHNs) are introduced to explain the origin of the light neutrino masses through the seesaw mechanism. There is a variety of ways which could lead us to this goal, and one of them is a general U(1) extension of the SM. In this scenario, three SM-singlet RHNs are introduced to cancel the gauge and mixed gauge gravity an

We study the prospects of searching for leptophilic gauge bosons (LGBs) at the beam dump experiment using e± beams of International e+e− Linear Collider (ILC). We consider LGBs in association of U(1)e−μ, U(1)e−τ, and U(1)μ−τ gauge symmetries, which are assumed to be light and long-lived. Utilizing the energetic electron and positron beams of the ILC, we show that the ILC beam dump experiment can cover the parameter regions which have not been explored before. We also discuss the possibility of d

We discuss the prospects of probing the ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ gauge boson at the MUonE experiment. The ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ gauge boson ${Z}^{\ensuremath{'}}$ with a mass of $\ensuremath{\lesssim}200\text{ }\text{ }\mathrm{MeV}$, which can explain the discrepancy between the measured value of the muon $g\ensuremath{-}2$ and the value calculated in the Standard Model, can be produced at the MUonE experiment through t

A bstract FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we focus on dark photon associating with an additional U(1) gauge symmetry, and also a scalar boson breaking this U(1) gauge symmetry. We study the sensitivity to the dark photon originated from U(1)-breaking scalar decays. We find that a sizable number of dark photon signatures can be expected in wider parameter space than previous studies.

Motivated by the observation that tiny neutrino mass cannot be explained within the framework of the Standard Model, we consider extra gauge extended scenarios in which tiny neutrino masses are generated through the seesaw mechanism. These scenarios are equipped with a beyond the Standard Model neutral gauge boson called <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msup><a:mi>Z</a:mi><a:mo>′</a:mo></a:msup></a:math> in the general <c:math xmlns:c="http://www.w3.org/19

We study a renormalizable scalar singlet dark matter model based on ${Z}_{4}$ lepton flavor symmetry. A $\ensuremath{\mu}\ensuremath{\tau}$-philic scalar doublet is introduced as a mediator which connects dark matter and standard model particles. The observed relic abundance of the dark matter is easily maintained while satisfying the current severe constraints on the dark matter from various experiments and observations thanks to the flavor off-diagonal interactions of scalar mediators. We furt

A bstract Light dark matter particles may be produced in electron and positron beam dumps of the International Linear Collider (ILC). We propose an experimental setup to search for such events, the Beam-Dump eXperiment at the ILC (ILC-BDX). The setup consists of a muon shield placed behind the beam dump, followed by a multi-layer tracker and an electromagnetic calorimeter. The calorimeter can detect electron recoils due to elastic scattering of dark matter particles produced in the dump, while t

Motivated by the observation of tiny neutrino mass can not be explained within the framework of Standard Model (SM), we consider extra gauge extended scenarios in which tiny neutrino masses are generated through seesaw mechanism. These scenarios are equipped with beyond the standard model (BSM) neutral gauge boson called $Z^\prime$ in the general $U(1)_X$ symmetry which is a linear combination of $U(1)_Y$ and $U(1)_{B-L}$. In this case, left and right handed fermions interact differently with th

Abstract In this paper, we analyze parameter regions that can alleviate the Hubble tension in the U(1)$_{L_\mu - L_\tau }$ model with broken lepton number U(1)$_L$ symmetry. As new particles, this model has a U(1)$_{L_\mu - L_\tau }$ gauge boson $Z^{\prime }$ and a Majoron $\phi$, which can affect the early universe and the effective number of neutrino species $N_\textrm{eff}$. If $Z^{\prime }$ and $\phi$ simultaneously exist in the early universe, $Z^{\prime }\,$–$\, \phi$ direct reaction proce

A bstract We investigate the twelve-dimensional gauge-Higgs unification models with an eight- dimensional coset space as the extra space. For each model, we apply the coset space dimensional reduction procedure and examine the particle contents of the resulting four-dimensional theory. All combinations of inputs to the procedure are exhaustively analyzed under several assumptions. As a result, some twelve-dimensional SO(18) gauge theories lead to models of the SO(10) × U(1) grand unified theory

A bstract Models based on a $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>U</mml:mi> <mml:msub> <mml:mfenced> <mml:mn>1</mml:mn> </mml:mfenced> <mml:mrow> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>μ</mml:mi> </mml:msub> <mml:mo>−</mml:mo> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>τ</mml:mi> </mml:msub> </mml:mrow> </mml:msub> </mml:math> gauge symmetry can explain the discrepancy between the measured value and theoretical prediction of the

We discuss the prospects of probing the $L_μ- L_τ$ gauge boson at the MUonE experiment. The $L_μ- L_τ$ gauge boson $Z^\prime$ with a mass of $\lesssim 200$ MeV, which can explain the discrepancy between the measured value of the muon $g-2$ and the value calculated in the Standard Model, can be produced at the MUonE experiment through the process $μe \to μe Z^\prime$. The $Z^\prime$ in the final state decays into a pair of neutrinos, and therefore we cannot observe the decay of $Z^\prime$ directl