arXiv subjects

Tsuneo Uematsu

Publications and source records attributed to Tsuneo Uematsu.

At least 19 recordsLinked to original sources

arXiv2021

Timelike Transition Form Factor for CP-odd Higgs Boson Production

We investigate the production of CP-odd Higgs boson $A^0$ associated with a real $γ$ in $e^+e^-$ collisions. Because of the properties of $A^0$ coupling to the other fields, the main contribution comes from the top-quark triangle loop diagrams. We obtain the timelike transition form factor which describes the production amplitude of $A^0$ in the $e^+e^-$ collisions. This timelike transition form factor is related to the spacelike transition form factor relevant for the $A^0$ production in $e^-γ$ collisions. It turns out that the possible extra contributions from chargino-sneutrino and neutralino-selectron box diagrams do not give sizable effects.

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arXiv2018

PHOTON-2017 conference proceedings

This document collects the proceedings of the PHOTON 2017 conference ("International Conference on the Structure and the Interactions of the Photon", including the 22th "International Workshop on Photon-Photon Collisions", and the "International Workshop on High Energy Photon Colliders") held at CERN (Geneva) in May 2017. The latest experimental and theoretical developments on the topics of the PHOTON conference series are covered: (i) $γ\,γ$ processes in e$^+$e$^-$, proton-proton (pp) and nucleus-nucleus (AA) collisions at current and future colliders, (ii) $γ$-hadron interactions in e$^\pm$p, pp, and AA collisions, (iii) final-state photon production (including Standard Model studies and searches beyond it) in pp and AA collisions, and (iv) high-energy $γ$-ray astrophysics. These proceedings are dedicated to the memory of Maria Krawczyk.

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arXiv2018

CP-odd Higgs Boson Production in $eγ$ Collisions

We investigate the CP-odd Higgs boson production via two-photon processes in $eγ$ collisions. The CP-odd Higgs boson, which we denote as $A^0$, is expected to appear in the Two-Higgs Doublet Models (2HDM) as a minimal extension of Higgs sector for which the Minimal Supersymmetric Standard Model (MSSM) is a special case. The scattering amplitude for $eγ\rightarrow eA^0$ is evaluated at the electroweak one-loop level. The dominant contribution comes only from top-quark loops when $A^0$ boson is rather light and $\tanβ$ is not large. There are no contributions from the $W$-boson and $Z$-boson loops nor from the scalar top-quark (stop) loops. The differential cross section for the $A^0$ production is analysed.

hep-ph↗

arXiv2014

Higgs production in $e$ and real $γ$ collision

We investigate the Standard Model Higgs boson production in $e^-γ$ collision. The electroweak one-loop contributions to the scattering amplitude for $e^-γ\rightarrow e^-H$ are calculated and expressed in analytical form. We analyze the cross section for the Higgs production in $e^-γ$ collision for each combination of polarizations of the initial electron and photon beams. The feasibility of observing the Higgs boson in $e^-+γ\rightarrow e^-+b+{\overline b}$ channel is examined.

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arXiv2013

Higgs Production in Two-Photon Process and Transition Form Factor

The Higgs production in the two-photon fusion process is investigated where one of the photons is off-shell while the other one is on-shell. This process is realized in either electron-positron collision or electron-photon collision where the scattered electron or positron is detected (single tagging) and described by the transition form factor. We calculate the contributions to the transition form factor of the Higgs boson coming from top-quark loops and W-boson loops. We then study the $Q^2$ dependence of each contribution to the total transition form factor and also of the differential cross section for the Higgs production.

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arXiv2012

Photon structure functions with heavy particle mass effects

In the framework of the perturbative QCD we investigate heavy particle mass effects on the unpolarized and polarized photon structure functions, $F_2^γ$ and $g_1^γ$, respectively. We present our basic formalism to treat heavy particle mass effects to NLO in perturbative QCD. We also study heavy quark effects on the QCD sum rule for the first moment of $g_1^γ$, which is related to axial anomaly. The photon structure function in supersymmetric QCD is also briefly discussed.

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arXiv2012

Photon Structure Function in Supersymmetric QCD Revisited

We investigate the virtual photon structure function in the supersymmetric QCD (SQCD), where we have squarks and gluinos in addition to the quarks and gluons. Taking into account the heavy particle mass effects to the leading order in QCD and SQCD we evaluate the photon structure function and numerically study its behavior for the QCD and SQCD cases.

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arXiv2011

Squark Contributions to Photon Structure Functions and Positivity Constraints

Photon structure functions in supersymmetric QCD are investigated in terms of the parton model where squark contributions are evaluated. We calculate the eight virtual photon structure functions by taking the discontinuity of the squark massive one-loop diagrams of the photon-photon forward amplitude. The model-independent positivity constraints derived from the Cauchy-Schwarz inequalities are satisfied by the squark parton model calculation and actually the two equality relations hold for the squark contribution. We also show that our polarized photon structure function $g_1^γ$ for the real photon leads to the vanishing 1st moment sum rule, and the constraint $|g_1^γ|\leq F_1^γ$ is satisfied by the real photon. We also discuss a squark signature in the structure function $W_{TT}^τ$.

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arXiv2010

Resummation of large logarithms in the heavy quark effects on the parton distributions inside the virtual photon

We discuss the resummation of the large logarithmic terms appearing in the heavy quark effects on parton distribution functions inside the virtual photon. We incorporate heavy quark mass effects by changing the initial condition of the leading-order DGLAP evolution equation. In a certain kinematical limit, we recover the logarithmic terms of the next-to-leading order heavy quark effects obtained in the previous work. This method enables us to resum the large logarithmic terms due to heavy quark mass effects on the parton distributions in the virtual photon. We numerically calculate parton distributions using the formulae derived in this work, and discuss the property of the resummed heavy quark effects.

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arXiv2010

Heavy quark effects on parton distribution functions in the unpolarized virtual photon up to the next-to-leading order in QCD

We investigate the heavy quark mass effects on the parton distribution functions in the unpolarized virtual photon up to the next-to-leading order in QCD. Our formalism is based on the QCD-improved parton model described by the DGLAP evolution equation as well as on the operator product expansion supplemented by the mass-independent renormalization group method. We evaluate the various components of the parton distributions inside the virtual photon with the massive quark effects, which are included through the initial condition for the heavy quark distributions, or equivalently from the matrix element of the heavy quark operators. We discuss some features of our results for the heavy quark effects and their factorization-scheme dependence.

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arXiv2009

Parton distributions in the virtual photon target up to NNLO in QCD

Parton distributions in the virtual photon target are investigated in perturbative QCD up to the next-to-next-to-leading order (NNLO). In the case $Λ^2 \ll P^2 \ll Q^2$, where $-Q^2$ ($-P^2$) is the mass squared of the probe (target) photon, parton distributions can be predicted completely up to the NNLO, but they are factorisation-scheme-dependent. We analyse parton distributions in two different factorisation schemes, namely $\bar{\rm MS}$ and ${\rm DIS}_γ$ schemes, and discuss their scheme dependence. We show that the factorisation-scheme dependence is characterised by the large-$x$ behaviours of quark distributions. Gluon distribution is predicted to be very small in absolute value except in the small-$x$ region.

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arXiv2008

Heavy Quark Effects in the Virtual Photon Structure Functions

We investigate the heavy quark mass effects in the virtual photon structure functions $F_{2}^γ(x, Q^2, P^2)$ and $F_{L}^γ(x, Q^2, P^2)$ in the framework of the mass-independent renormalization group equation (RGE). We study a formalism in which the heavy quark mass effects are treated based on parton picture as well as on the operator product expansion (OPE), and perform the numerical evaluation of $F_{\rm eff}^γ(x, Q^2, P^2)$ to the next-leading order (NLO) in QCD.

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arXiv2008

NNLO QCD analysis of the virtual photon structure functions

The next-to-next-to-leading order (NNLO) QCD analysis is performed for the virtual photon structure functions which can be measured in the double-tag events in two-photon processes in $e^+e^-$ collisions. We investigate the perturbative QCD evaluation of $F_2^γ(x,Q^2,P^2)$ to NNLO and $F_L^γ(x,Q^2,P^2)$ to NLO with and without taking into account the target mass effects, which are relevant for the large $x$ region. We also carry out the phenomenological analysis for the experimentally accessible effective structure function $F_{\rm eff}^γ=F_2^γ+(3/2)F_L^γ$.

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arXiv2008

Virtual Photon Structure Functions to NNLO in QCD

The unpolarized virtual photon structure functions $F_2^γ(x,Q^2,P^2)$ and $F_L^γ(x,Q^2,P^2)$ are investigated in perturbative QCD for the kinematical region $Λ^2 \ll P^2 \ll Q^2$, where $-Q^2(-P^2)$ is the mass squared of the probe (target) photon and $Λ$ is the QCD scale parameter. In the framework of operator product expansion supplemented by the renormalization group method, the definite predictions are derived for the moments of $F_2^γ(x,Q^2,P^2)$ up to the next-to-next-to-leading order (the order $αα_s$) and for the moments of $F_L^γ(x,Q^2,P^2)$ up to the next-to-leading order (the order $αα_s$)

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arXiv2008

Target Mass Corrections for the Virtual Photon Structure Functions to the Next-to-next-to-leading Order in QCD

We investigate target mass effects in the unpolarized virtual photon structure functions $F_2^γ(x,Q^2,P^2)$ and $F_L^γ(x,Q^2,P^2)$ in perturbative QCD for the kinematical region $Λ^2 \ll P^2 \ll Q^2$, where $-Q^2(-P^2)$ is the mass squared of the probe (target) photon and $Λ$ is the QCD scale parameter. We obtain the Nachtmann moments for the structure functions and then, by inverting the moments, we get the expressions in closed form for $F_2^γ(x,Q^2,P^2)$ up to the next-to-next-to-leading order and for $F_L^γ(x,Q^2,P^2)$ up to the next-to-leading order, both of which include the target mass corrections. Numerical analysis exhibits that target mass effects appear at large $x$ and become sizable near $x_{\rm max}(=1/(1+\frac{P^2}{Q^2}))$, the maximal value of $x$, as the ratio $P^2/Q^2$ increases.

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arXiv2004

Mass effects in the polarized virtual photon structure

We discuss target mass effects in the polarized virtual photon structure functions $g_1^γ(x,Q^2,P^2)$, $g_2^γ(x,Q^2,P^2)$ for the kinematic region $Λ^2\ll P^2 \ll Q^2$, where $-Q^2 (-P^2)$ is the mass squared of the probe (target) photon. We obtain the expressions for the structure functions in closed form by inverting the Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis shows that target mass effects appear at large $x$ and become sizable near the maximal value of $x$, as the ratio $P^2/Q^2$ increases. Target mass effects for the QCD sum rules of $g_1^γ$ and $g_2^γ$ are also investigated.

hep-ph↗

arXiv2003

Target Mass Effects in Polarized Virtual Photon Structure Functions

We study target mass effects in the polarized virtual photon structure functions $g_1^γ(x,Q^2,P^2)$, $g_2^γ(x,Q^2,P^2)$ in the kinematic region $Λ^2\ll P^2 \ll Q^2$, where $-Q^2 (-P^2)$ is the mass squared of the probe (target) photon. We obtain the expressions for $g_1^γ(x,Q^2,P^2)$ and $g_2^γ(x,Q^2,P^2)$ in closed form by inverting the Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis shows that target mass effects appear at large $x$ and become sizable near $x_{\rm max}(=1/(1+\frac{P^2}{Q^2}))$, the maximal value of $x$, as the ratio $P^2/Q^2$ increases. Target mass effects for the sum rules of $g_1^γ$ and $g_2^γ$ are also discussed.

hep-ph↗

arXiv2002

Virtual Photon Structure Functions

We discuss the perturbatively calculable virtual photon structure functions. First we present the framework for analyzing the structure functions of the virtual photon and derive a first moment of $g_1^γ$ of the virtual photon. We then investigate the three positivity constraints satisfied by the eight structure functions of the virtual photon.

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