arXiv subjects

Syuhei Iguro

Publications and source records attributed to Syuhei Iguro.

At least 37 records · Page 2Linked to original sources

arXiv2024

Cosmology-Independent Constraints on Irreducible Magnetic Monopole Background

We present a novel mechanism for the irreducible production of magnetic monopoles from interactions of cosmic rays and interstellar medium (ISM). Resulting monopoles drain energy from galactic magnetic fields, disrupting their formation and sustainability. We generalize conventional Parker bounds to monopoles with extended energy spectrum and, considering cosmic ray ISM monopole production, set novel constraints from disruption of Milky Way Galactic magnetic fields and their seeds. Further, we set first constraints on disruption of galactic magnetic fields and their seeds of Andromeda galaxy, with results being competitive with distinct existing bounds. Unlike Parker limits of previous works that relied on cosmological monopoles, our constraints are independent of cosmological monopole production or their primordial abundance. Besides, we estimate new constraints on dipole magnetic moments generated from cosmic ray ISM interactions. We discuss implications for monopoles with generalized magnetic charges.

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arXiv2024

Global fit to the 2HDM with generic sources of flavour violation using \textsf{GAMBIT}

We perform a global statistical analysis of the two-Higgs-doublet model with generic sources of flavour violation using \textsf{GAMBIT}. This is particularly interesting in light of deviations from the Standard Model predictions observed in $b\to cτ\bar ν$ and $b\to s\ell^+\ell^-$ transitions as well as the indications for a charged Higgs with a mass of 130\,GeV in top quark decays. Including all relevant constraints from precision, flavour and collider observables, we find that it is possible to simultaneously explain both the charged and neutral current $B$ anomalies. We study the impact of using different values for the $W$ mass and the Standard Model prediction for $g-2$ of the muon and provide predictions for observables that can probe our model in the future such as lepton flavour violation searches at Belle II and Higgs coupling strength measurements at the high-luminosity LHC.

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arXiv2024

Global fit to $b \to cτν$ anomalies as of Spring 2024

Recently, several new experimental results of the test of lepton flavor universality (LFU) in $B\to D^{(\ast)}$ semi-leptonic decays were announced: the first result of $R_{D}$ from the LHCb Run 1 data, the first results of $R_{D}$ and $R_{D^\ast}$ from the LHCb Run 2 data, and the first result of $R_{D^\ast}$ from the Belle II collaboration. Including these new data, a global analysis still prefers the violation of the LFU between the tau and light leptons. A new world average of the data from the BaBar, LHCb, Belle, and Belle II collaborations is $R_{D} = 0.342 \pm 0.026$ and $R_{D^{\ast}} = 0.287 \pm 0.012$. Including this new data, we update a circumstance of the $b \to c τ\overlineν$ measurements and their implications for new physics (NP). Incorporating recent developments for the $B \to D^{(\ast)}$ form factors in the Standard Model (SM), we observe a $4.4 σ$ deviation from the SM prediction. Our updates also include; model-independent NP formulae for the related observables; and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different NP scenarios with the use of the precise measurements of the polarization observables in $B\to D^{(\ast)}τ\overlineν$ at the Belle II and the high-$p_{\rm T}$ flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in $Υ\to l^+ l^-$.

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arXiv2024

Electric Dipole Moments as Probes of $B$ Anomaly

The measurements of the lepton flavor universality (LFU) in $\mathcal{B}({\bar{B}} \to D^{(\ast)} l \barν)$ indicate a significant deviation from the standard model prediction at a 3-4$σ$ level, revealing a violation of the LFU ($R_{D^{(\ast)}}$ anomaly). It is known that the $R_{D^{(\ast)}}$ anomaly can be easily accommodated by an $SU(2)_L$-singlet vector leptoquark (LQ) coupled primarily to third-generation fermions, whose existence is further motivated by a partial gauge unification. In general, such a LQ naturally leads to additional $CP$-violating phases in the LQ interactions. In this paper, we point out that the current $R_{D^{(\ast)}}$ anomaly prefers the $CP$-violating interaction although $\mathcal{B}({\bar{B}} \to D^{(\ast)} l\barν)$ are $CP$-conserving observables. The $CP$-violating LQ predicts a substantial size of the bottom-quark electric dipole moment (EDM), the chromo-EDM, and also the tau-lepton EDM. Eventually at low energy, the nucleon and electron EDMs are radiatively induced. Therefore, we conclude that the $R_{D^{(\ast)}}$ anomaly with the $SU(2)_L$-singlet vector LQ provides unique predictions: neutron and proton EDMs with opposite signs and a magnitude of $\mathcal{O}(10^{-27})\,e$cm, and suppressed electron EDM. Furthermore, we show that a similar EDM pattern is predicted in an $SU(2)_L$-doublet scalar LQ scenario that can accommodate the $R_{D^{(\ast)}}$ anomaly as well. These EDM signals could serve as crucial indicators in future experiments.

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arXiv2024

Determining Weak-Mixing Angle at $μ$TRISTAN

$μ$TRISTAN is a realistic high energy lepton collider based on the existing technology aiming at indirect and direct search for the physics beyond the standard model (SM). We propose a measurement to determine one of the most prominent parameters of the SM, weak mixing angle to test the SM and probe the new physics effect in Møller-like scattering with a wide range of interaction scales. We show that this experiment not only can determine the weak mixing angle with percent to milli-level accuracy but also scan over a wide range of interaction scales that have never been archived in a single experiment elsewhere.

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arXiv2024

Global fit to $b \to cτν$ anomalies 2022 mid-autumn

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 from the BaBar, Belle, and LHCb collaborations is $R_{D} = 0.358 \pm 0.027$ and $R_{D^{\ast}} = 0.285 \pm 0.013$. Including this new data, we update a circumstance of the $b \to c τ\overlineν$ measurements and their implications for new physics. Incorporating recent developments for the $B \to D^{(\ast)}$ form factors in the Standard Model (SM), we observe a $4.1 σ$ deviation from the SM predictions. Our updates also include; model-independent new physics (NP) formulae for the related observables; and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different new physics scenarios with the use of the precise measurements of the polarization observables in $B\to D^{(\ast)}τ\overlineν$ at the Belle II and the high-$p_{\rm T}$ flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in $Υ\to l^+ l^-$.

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arXiv2024

Prospects for $B_c^+$ and $B^+\to τ^+ ν_τ$ at FCC-ee

The prospects are presented for precise measurements of the branching ratios of the purely leptonic $B_c^+ \to τ^+ ν_τ$ and $B^+ \to τ^+ ν_τ$ decays at the Future Circular Collider (FCC). This work is focused on the hadronic $τ^{+} \to π^+ π^+ π^- \barν_τ$ decay in both $B_c^+ \to τ^+ ν_τ$ and $B^+ \to τ^+ ν_τ$ processes. Events are selected with two Boosted Decision Tree algorithms to optimise the separation between the two signal processes as well as the generic hadronic $Z$ decay backgrounds. The range of the expected precision for both signals are evaluated in different scenarios of non-ideal background modelling. This paper demonstrates, for the first time, that the $B^+ \to τ^+ ν_τ$ decay can be well separated from both $B_c^+ \to τ^+ ν_τ$ and generic $Z\to b\bar{b}$ processes in the FCC-ee collision environment and proposes the corresponding branching ratio measurement as a novel way to determine the CKM matrix element $|V_{ub}|$. The theoretical impacts of both $B^+ \to τ^+ ν_τ$ and $B_c^+ \to τ^+ ν_τ$ measurements on New Physics cases are discussed for interpretations in the generic Two-Higgs-doublet model and leptoquark models.

hep-ex↗

arXiv2023

A closer look at isodoublet vector leptoquark solution to $R_{D^{(*)}}$ anomaly

We discuss a model with a SU$(2)_L$ doublet vector leptoquark (LQ), motivated by the recent experimental results relating to the lepton universality of $\overline{B} \to D^{(*)} τ\overlineν_τ$. We find that scalar operators predicted by the LQ are favored to explain the deviations, taking into account the recent LHCb result. We investigate the extensive phenomenology of the model and conclude that $B_s\toτ\overlineτ$, $B\to Kτ\overlineτ$, $B_u\to τ\overline ν_τ$ and high-$p_T$ di-$τ$ lepton signatures at the LHC will probe the interesting parameter region in the near future.

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arXiv2023

Current Status of the Muon g-2 Interpretations within Two-Higgs-Doublet Models

In this article, we review and update implications of the muon anomalous magnetic moment (muon $g-2$) anomaly for two-Higgs-doublet models (2HDMs), which are classified according to imposed symmetries and their resulting Yukawa sector. In the minimal setup, the muon $g-2$ anomaly can be accommodated by the type-X (lepto-philic) 2HDM, flavor-aligned 2HDM (FA2HDM), muon-specific 2HDM ($μ$2HDM), and $μτ$-flavor violating 2HDM. We summarize all relevant experimental constraints from high-energy collider experiments and flavor experiments, as well as the theoretical constraints from the perturbative unitarity and vacuum stability bounds, to these 2HDMs in light of the muon $g-2$ anomaly. We clarify the available parameter spaces of these 2HDMs and investigate how to probe the remaining parameter regions in future experiments. In particular, we find that, due to the updated $B_s\toμ^+ μ^-$ measurement, the remaining parameter region of the FA2HDM is almost equivalent to the one of the type-X 2HDM. Furthermore, based on collider simulations, we find that the type-X 2HDM is excluded and the $μ$2HDM scenario will be covered with the upcoming Run 3 data.

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arXiv2023

Asymmetric di-Higgs signals of the next-to-minimal 2HDM with a $U(1)$ symmetry

The two-Higgs-doublet model with a $U(1)_H$ gauge symmetry (N2HDM-$U(1)$) has several advantages compared to the ``standard'' $Z_2$ version (N2HDM-$Z_2$): It is purely based on gauge symmetries, involves only spontaneous symmetry breaking, and is more predictive because it contains one parameter less in the Higgs potential, which further ensures $CP$ conservation, i.e., avoiding the stringent bounds from electric dipole moments. After pointing out that a second, so far unknown version of the N2HDM-$U(1)$ exists, we examine the phenomenological consequences for the Large Hadron Collider (LHC) of the differences in the scalar potentials. In particular, we find that while the N2HDM-$Z_2$ predicts suppressed branching ratios for decays into different Higgs bosons for the case of the small scalar mixing (as suggested by Higgs coupling measurements), both versions of the N2HDM-$U(1)$ allow for sizable rates. This is particularly relevant in light of the CMS excess in resonant Higgs-pair production at around $650\,$GeV of a Standard Model Higgs boson subsequently decaying to photons and a new scalar with a mass of $\approx90\,$GeV subsequently decaying to bottom quarks (i.e., compatible with the CMS and ATLAS $γγ$ excesses at $95\,$GeV and $\approx 670\,$GeV). As we will show, this excess can be addressed within the N2HDM-$U(1)$ in case of a nonminimal Yukawa sector, predicting an interesting and unavoidable $Z+ b\bar b$ signal and motivating further asymmetric di-Higgs searches at the LHC.

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arXiv2023

Light mass window of inert doublet dark matter with lepton portal interaction

We study phenomenology of a light scalar dark matter (DM). In the model, there are an inert doublet scalar and a singlet Dirac fermion $ψ$, both charged under a global $Z_2$ symmetry. The mass of the lightest inert scalar $H$ can be lighter than 10 GeV by imposing appropriate relations between three scalar quartic couplings. The lightest $Z_2$ odd particle is stable and DM. In this paper, focusing on the parameter space where $H$ is lighter than $ψ$ and is DM, we discuss DM physics related to relic density, direct detection, indirect detection, collider searches and other cosmological observations. We clarify differences from the case where $ψ$ is instead DM, which has been focused on in the previous works.

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arXiv2023

Discriminating $B\to D^{*}\ellν$ form factors via polarization observables and asymmetries

Form factors are crucial theory input in order to extract $|V_{cb}|$ from $B \to D^{(*)}\ellν$ decays, to calculate the Standard Model prediction for ${\cal R}(D^{(*)})$ and to assess the impact of New Physics. In this context, the Dispersive Matrix approach, a first-principle calculation of the form factors, using no experimental data but rather only lattice QCD results as input, was recently applied to $B \to D^{(*)}\ellν$. It predicts (within the Standard Model) a much milder tension with the ${\cal R}(D^*)$ measurements than the other form factor approaches, while at the same time giving a value of $|V_{cb}|$ compatible with the inclusive value. However, this comes at the expense of creating tensions with differential $B\to D^*\ellν$ distributions (with light leptons). In this article, we explore the implications of using the Dispersive Matrix method form factors, in light of the recent Belle (II) measurements of the longitudinal polarization fraction of the $D^*$ in $B\to D^*\ellν$ with light leptons, $F_L^{\ell}$, and the forward-backward asymmetry, $A_{\rm FB}^{\ell}$. We find that the Dispersive Matrix approach predicts a Standard Model value of $F_L^{\ell}$ that is in significant tension with these measurements, while mild deviations in $A_{\rm FB}^{\ell}$ appear. Furthermore, $F_L^{\ell}$ is very insensitive to New Physics such that the latter cannot account for the tension between Dispersive Matrix predictions and its measurement. While this tension can be resolved by deforming the original Dispersive Matrix form factor shapes within a global fit, a tension in ${\cal R}(D^*)$ reemerges. As this tension is milder than for the other form factors, it can be explained by New Physics not only in the tau lepton channel but also in the light lepton modes.

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arXiv2023

Light lepton portal dark matter meets the LHC

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 ${\cal O}(10)$GeV and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run$\,$2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-$Z$ plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.

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arXiv2023

Collider probe of heavy additional Higgs bosons solving the muon $g-2$ and dark matter problems

We study the Large Hadron Collider (LHC) search potential of a $\mathbb{Z}_4$-based two Higgs doublet model which can simultaneously explain the muon $g-2$ anomaly and the observed dark matter. The neutral scalars in the second Higgs doublet couple to $μ$ and $τ$ and largely contribute to the muon anomalous magnetic moment through the one-loop diagram involving $τ$ and scalars. An additional singlet scalar which is charged under the discrete symmetry can be a dark matter candidate. An upper limit on the scalar mass originates from the unitarity constraint, and the $μτ$ flavor-violating nature of the scalars predicts non-standard signatures at the LHC. However, the previously proposed $μ^\pmμ^\pmτ^\mpτ^\mp$ signal via the electroweak heavy neutral scalar pair production at the LHC loses sensitivity for increasing scalar mass. We revisit this model and investigate the LHC prospects for the single production of the $μτ$ flavor-violating neutral scalar. It is shown that the single scalar process helps to extend the LHC reach to the 1$\,$TeV mass regime of the scenario. The search potential at the high energy LHC is also discussed.

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arXiv2023

Chasing the two-Higgs doublet model in the di-Higgs production

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 $ϕ$ in association with the Standard Model (SM) Higgs boson $h$ in the Higgs alignment limit. We analyze two scenarios where the additional Higgs $ϕ$ is CP-even or -odd state with a large top-Yukawa interaction. The leading contribution of this production comes from the top-quark loop-induced gluon-fusion channel $gg \to hϕ$. The measurement of the $hϕ$ production can probe the quartic couplings in the Higgs potential as well as the top-Yukawa couplings. Imposing both theoretical constraints (from the perturbative unitarity and the vacuum stability bounds) and experimental bounds (from the SM Higgs and flavor physics measurements) on the 2HDM parameter space, we calculate the production cross-section of $gg \to hϕ$. Furthermore, we scrutinize these processes in the parameter spaces where the CMS di-tau and di-photon excesses around 100$\,$GeV, and/or the muon $g-2$ anomaly can be accommodated.

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arXiv2023

Impact of $Λ_b\to Λ_cτν$ measurement on New Physics in $b\to c \, l ν$ transitions

Measurements of the branching ratios of $B \to D^{(*)}τ\barν/B \to D^{(*)}\ell\barν$ and $B_c\to J/ψ\, τ\barν/B_c\to J/ψ\, \ell\barν$ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio $Λ_b \toΛ_c τ\barν/Λ_b \toΛ_c \ell\barν$ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within $2σ$ or $1.5σ$, depending on the ${\cal R}(Λ_c)$ normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.

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arXiv2023

Coup de grace to the charged Higgs solution of $P_5^\prime$ and $R_{D^{(*)}}$ discrepancies

We consider a general two Higgs doublet model which can simultaneously solve discrepancies in neutral B meson decay ($b\to s\ell \overline \ell$ distribution) and charged B meson decay ($b\to cτ\overlineν$) 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 ATLAS collaboration, we found the constraint on the scalar mass spectrum. To probe the remaining mass window, we propose a novel $cg\to tτ\overlineτ$ process at the LHC.

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arXiv2022

The direct CP violation in a general two Higgs doublet model

In this paper, we study the CP violating processes in a general two-Higgs-doublet model (2HDM) with tree-level flavor changing neutral currents. In this model, sizable Yukawa couplings involving top and charm quarks are still allowed by the collider and flavor experiments, while the other couplings are strongly constrained experimentally. The sizable couplings, in general, have imaginary parts and could largely contribute to the CP violating observables concerned with the $B$ and $K$ mesons. In particular, the contribution may be so large that it affects the direct CP violating $K$ meson decay, where the discrepancy between the experimental result and the Standard Model prediction is reported. We discuss how well the anomaly is resolved in the 2HDM, based on study of the other flavor observables. We also propose the way to test our 2HDM at the LHC.

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