Syuhei Iguro

Motivated by an anomaly in R(D(⁎))=BR(B¯→D(⁎)τ−ν¯)/BR(B¯→D(⁎)l−ν¯) reported by BaBar, Belle and LHCb, we study R(D(⁎)) in a general two Higgs doublet model (2HDM). Although it has been suggested that it is difficult for the 2HDM to explain the current world average for R(D(⁎)), it would be important to clarify how large deviations from the standard model predictions for R(D(⁎)) are possible in the 2HDM. We investigate possible corrections to R(D(⁎)) in the 2HDM by taking into account various fla

A bstract In this paper, we study the extended Standard Model (SM) with an extra Higgs doublet and right-handed neutrinos. If the symmetry to distinguish the two Higgs doublets is not assigned, flavor changing neutral currents (FCNCs) involving the scalars are predicted even at the tree level. We investigate the constraints on the FCNCs at the one-loop level, and especially study the semileptonic B meson decays, e.g. B → D (∗) τ ν and B → K (∗) ll processes, where the SM predictions are more tha

Abstract We investigate the current LHC bounds on New Physics (NP) that contributes to $${\bar{B}} \rightarrow {D^{(*)}}l{\bar{\nu }}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>D</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow/> <mml:mo>∗</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:msup> <mml:mi>l</mml:mi> <mml:mover> <m

There are discrepancies between the experimental results and the Standard Model predictions, in the lepton flavor universality of the semileptonic $B$ decays: $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\ell}\ensuremath{\nu}$. As the new physics interpretations, new charged vector and charged scalar fields, that dominantly couple to the second and third generations, have been widely discussed. In this paper, we study the signals of the new particles at the LHC, and test the interpretations vi

Recently, the standard model predictions for the $B$-meson hadronic decays, ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{(*)+}{K}^{\ensuremath{-}}$ and ${\overline{B}}_{s}^{0}\ensuremath{\rightarrow}{D}_{s}^{(*)+}{\ensuremath{\pi}}^{\ensuremath{-}}$, have been updated based on the QCD factorization approach. This improvement sheds light on a novel puzzle in the $B$-meson hadronic decays: there are mild but universal tensions between data and the predicted branching ratios. Assuming the higher

In this paper, we show an explicit way to realize a TeV-scale vector leptoquark from the Pati-Salam (PS) unification with extra vectorlike families. The leptoquark mass is constrained to be heavier than PeV-scale by the measurement of a flavor violating kaon decay, $K_L \to \mu e$, in conventional models. This strong constraint can be avoided by introducing vectorlike families consistently with the quark and lepton masses and CKM and PMNS matrices. The other flavor violating processes are also s

Recently, several new experimental results of the test of lepton flavor universality (LFU) in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>B</a:mi><a:mo stretchy="false">→</a:mo><a:msup><a:mi>D</a:mi><a:mrow><a:mo stretchy="false">(</a:mo><a:mo>*</a:mo><a:mo stretchy="false">)</a:mo></a:mrow></a:msup></a:math> semileptonic decays were announced: the first result of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:msub><f:mi>R</f:mi><f:mi>D</

Thanks to the recent careful revisit of the theoretical prediction of the ${B}_{c}$ meson lifetime, the conservative upper bound on the branching ratio (BR) of $\ensuremath{\tau}\ensuremath{\nu}$ mode is found to be $\ensuremath{\simeq}63%$ due to the large charm quark mass uncertainty. Although it is well known that a charged Higgs (${H}^{\ensuremath{-}}$) interpretation of the ${R}_{{D}^{(*)}}$ anomaly is excluded by the previously proposed bounds, $\mathrm{BR}({B}_{c}\ensuremath{\rightarrow}\

We consider a general two Higgs doublet model which can simultaneously solve discrepancies in neutral $B$ meson decay ($b\ensuremath{\rightarrow}s\ensuremath{\ell}\overline{\ensuremath{\ell}}$ distribution) and charged $B$ meson decay ($b\ensuremath{\rightarrow}c\ensuremath{\tau}\overline{\ensuremath{\nu}}$) with a charged Higgs. The model contains two additional neutral scalars at the same mass scale and predicts distinctive signals at the LHC. Based on the recent same-sign top search by the AT

We investigate the di-Higgs production at the Large Hadron Collider in the two-Higgs doublet model (2HDM). In particular, we study the production of an extra neutral Higgs boson $\ensuremath{\phi}$ in association with the Standard Model (SM) Higgs boson $h$ in the Higgs alignment limit. We analyze two scenarios where the additional Higgs $\ensuremath{\phi}$ is in a $CP$-even or -odd state with a large top-Yukawa interaction. The leading contribution of this production comes from the top-quark lo

A bstract We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10 GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below $$ \mathcal{O}(10)\textrm{GeV} $$ <mml:math xmlns

A bstract In this paper, we discuss the multi-Higgs doublet models, that could be effectively induced by the extended Standard Model (SM). In particular, we focus on the phenomenology in the supersymmetric model with left-right (LR) symmetry, where the down-type and the up-type Yukawa couplings are unified and the Yukawa coupling matrices are expected to be hermitian. In this model, several Higgs doublets are introduced to realize the realistic fermion mass matrices, and the heavy Higgs doublets

Recently, the LHCb collaboration announced a preliminary result of the test of lepton flavor universality (LFU) in $B\to D^{(\ast)}$ semi-leptonic decays: $R_{D}^{\rm LHCb2022} = 0.441 \pm 0.089$ and $R_{D^{\ast}}^{\rm LHCb2022} = 0.281 \pm 0.030$ based on the LHC Run 1 data. This is the first result of $R_{D}$ for the LHCb experiment, and its precision is comparable to the other $B$-factory data. Interestingly, those data prefer the violation of the LFU again. A new world average of the data fr

A bstract We study lepton flavor violation (LFV) induced by one-loop box diagrams in Pati-Salam (PS) unification with vector-like families. The vector leptoquark (LQ) associated with the PS gauge symmetry breaking generally causes various LFV processes such as K L → μe and μ → e conversion at the tree-level, thereby driving its mass scale to be higher than PeV scale. The vector-like families are introduced to suppress such tree-level LFV processes, allowing the LQ to have TeV scale mass. In this

Magnetic monopoles have a long history of theoretical predictions and experimental searches, carrying direct implications for fundamental concepts such as electric charge quantization. We analyze in detail for the first time magnetic monopole production from collisions of cosmic rays bombarding the atmosphere. This source of monopoles is independent of cosmology, has been active throughout Earth's history, and supplies an irreducible monopole flux for all terrestrial experiments. Using results f