arXiv subjects

Masaaki Kuroda

Publications and source records attributed to Masaaki Kuroda.

12 recordsLinked to original sources

arXiv2018

One-loop effects of MSSM particles in e^-e^+ \to Zh and e^-e^+ \to ν\barνh at the ILC

The 1-loop effects of the MSSM at the ILC are investigated through numerical analysis. We studied the higgs production processes $e^-e^+\rightarrow Zh$ and $e^-e^+\rightarrow ν\barνh$ at the ILC. It is found that the magnitude of the MSSM contribution through the 1-loop effects is sizable enough to be detected. In the study, three sets of the MSSM parameters are proposed, which are consistent with the observed higgs mass, the muon $g$-$2$, the dark matter abundance and the decay branching ratios of $B$ mesons. In the $e^-e^+\rightarrow Zh$ process, the 1-loop effects of the MSSM are visible and the distinction of the parameter sets is partially possible. For the study of $e^-e^+\rightarrow ν\barνh$, we used the equivalent $\it W$-boson approximation in the evaluation of the 1-loop cross section. While the 1-loop effect of the MSSM is visible, the distinction of the parameter sets might not be possible in this process under the value of realistic luminosity at the ILC.

hep-ph↗

arXiv2017

One loop effects of natural SUSY in third generation fermion production at the ILC

Within the framework of the Minimal Supersymmetric Standard Model, we investigate the 1-loop effects of supersymmetric particles on the third-generation fermion-pair production at the ILC. Three sets of the SUSY parameters are proposed which are consistent with the observed Higgs mass, the muon g-2, the Dark Matter abundance and the decay branching ratio of B meson. We discuss on the possibility of discovering the signals consistent with SUSY as well as of experimentally distinguishing the proposed sets of SUSY parameters.

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arXiv2016

Color Dipole Picture of Deep Inelastic Scattering, Revisited

Based upon the color-dipole picture, we provide closed analytic expressions for the longitudinal and the transverse photoabsorption cross sections at low values of the Bjorken variable of x<0.1. We compare with the experimental data for the longitudinal-to-transverse ratio of the (virtual) photoabsorption cross section and with our previous fit to the experimental data for the total photoabsorption cross section. Scaling in terms of the low-x scaling variable eta(W^2,Q^2) is analyzed in terms of the reduced cross section of deep inelastic scattering.

hep-ph↗

arXiv2013

On Ultrahigh-energy Neutrino Scattering

We predict the neutrino-nucleon cross section at ultrahigh energies relevant in connection with the search for high-energy cosmic neutrinos. Our investigation, employing the color-dipole picture, among other things allows us to quantitatively determine which fraction of the ultrahigh-energy neutrino-nucleon cross section stems from the saturation versus the color-transparency region. We disagree with various results in the literature that predict a strong suppression of the neutrino-nucleon cross section at neutrino energies above $E \cong 10^9 GeV$. Suppression in the sense of a diminished increase of the neutrino-nucleon cross section with energy only starts to occur at neutrino energies beyond $E \cong 10^{14} GeV$.

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arXiv2011

The Color Dipole Picture of low-x DIS: Model-Independent and Model-Dependent Results

We present a detailed examination of the color-dipole picture (CDP) of low-$x$ deep inelastic scattering. We discriminate model-independent results, not depending on a specific parameterization of the dipole cross section, from model-dependent ones. The model-independent results include the ratio of the longitudinal to the transverse photoabsorption cross section at large $Q^2$, or equivalently the ratio of the longitudinal to the unpolarized proton structure function, $F_L (x,Q^2)=0.27 F_2 (x, Q^2)$, as well as the low-$x$ scaling behavior of the total photoabsorption cross section $σ_{γ^*p} (W^2, Q^2)=σ_{γ^*p} (η(W^2, Q^2))$ as $\log (1 / η(W^2, Q^2))$ for $η(W^2, Q^2) <1$, and as $1/η(W^2, Q^2)$ for $η(W^2, Q^2) \gg 1$. Here, $η(W^2, Q^2)$ denotes the low-$x$ scaling variable, $η(W^2, Q^2)=(Q^2 + m^2_0) / Λ^2_{sat} (W^2)$ with $Λ^2_{sat} (W^2)$ being the saturation scale. The model-independent analysis also implies $\lim\limits_{W^2\rightarrow\infty, Q^2 {\rm fixed}} σ_{γ^*p} (W^2, Q^2) / σ_{γp} (W^2) \rightarrow 1$ at any $Q^2$ for asymptotically large energy, $W$. Consistency with pQCD evolution determines the underlying gluon distribution and the numerical value of $C_2 = 0.29$ in the expression for the saturation scale, $Λ^2 (W^2) \sim (W^2)^{C_2}$. In the model-dependent analysis, by restricting the mass of the actively contributing $q \bar q$ fluctuations by an energy-dependent upper bound, we extend the validity of the color-dipole picture to $x \cong Q^2 / W^2 \le 0.1$. The theoretical results agree with the world data on DIS for $0.036 {\rm GeV}^2 \le Q^2 \le 316 {\rm GeV}^2$.

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arXiv2010

Slepton NLG (Non-Linear Gauge) in GRACE/SUSY-loop

We have been developing a program package called GRACE/SUSY-loop which is for the automatic calculations of the MSSM amplitudes in one-loop order. The non-linear gauge (NLG) fixing conditions play the crucial role in the calculations in one-loop order which contain a large number of Feynman diagrams. We present the recent progress in GRACE/SUSY-loop which is obtained by extending the non-linear gauge formalism to the slepton sector.

hep-ph↗

arXiv2008

The Color Dipole Picture and the ratio of R(W, Q) = sigma L/sigma T

The transverse size of q q-bar fluctuations of the longitudinal photon is reduced relative to the transverse size of q q-bar fluctuations of the transverse photon. This implies R(W2, Q2) = 0.375 or, equivalently, FL/F2 = 0.27 at x<<0.1 and Q2 sufficiently large, while R(W2, Q2) = 0.5, if this effect is not taken into account. Forthcoming experimental data from HERA will allow to test this prediction.

hep-ph↗

arXiv2005

The Energy Dependence of the Saturation Scale

At low $x \cong Q^2/W^2 << 1$, in deep inelastic scattering, the photon fluctuates into a $q \bar q$ vector state that interacts via two gluons with the proton. The energy dependence is determined by the saturation scale, in our approach given by $Λ^2_{sat} (W^2) \sim (W^2)^{C_2}$. Imposing DGLAP evolution, we find $C_2^{theory} = 0.27$ in agreement with the model-independent analysis of the HERA data. Different values of the exponent $C_2$ are correlated with different ratios of the longitudinal to transverse structure function. This stresses the need for experiments to separate longitudinal and transverse contributions in deep inelastic scattering.

hep-ph↗

arXiv2005

The energy dependence of the saturation scale in DIS at low x

Consistency of the previously suggested color-dipole representation of deep-inelastic scattering (DIS_) and vector-meson production at low x with DGLAP evolution allows one to predict the exponent of the W^2 dependence of the saturation scale Lambda_sat^2(W^2) ~ (W^2)^C-2. One finds C_2^theory = 0.27 in agreement with the model-independent analysis of the experimental data from HERA on deep-inelastic electron scattering.

hep-ph↗

arXiv2004

The total virtual photoabsorption cross section, deeply virtual Compton scattering and vector-meson production

Based on the two-gluon-exchange dynamical mechanism for deeply inelastic scattering at low x ~= Q^2/W^2 <<1, we stress the intimate connection between the total virtual photoabsorption cross section, deeply virtual Compton scattering and vector-meson electroproduction. A simple expression for the cross section for deeply virtual Compton scattering is derived. Parameter-free predictions are obtained for deeply-virtual Compton forward scattering and vector-meson forward production, once the parameters in the total virtual photoabsorption cross section are determined in a fit to the experimental data on deeply inelastic scattering. Our predictions are compared with the experimental data from HERA.

hep-ph↗

arXiv2001

On e+e- --> W+W- --> 4f(+gamma) at LEP2

The results on e+e- --> W+W- --> 4f(+gamma) obtained by different groups are compared with each other. Differences in the results for the total cross section of up to about 0.6% are traced back to different ways of implementing the double-pole approximation.

hep-ph↗

arXiv2000

Born-form approximation and full one-loop results for e^+e^- --> W^+W^- --> 4 fermions (+γ)

We review the results on representing the differential cross section for W-pair produciton, including W decay and hard-photon bremsstrahlung, in terms of a Born-form approximation of fairly simple analytic form. The result of the Born-form approximation are compared with full-one-loop results. The emphasis is on the energy range of future $e^+e^-$ (or $μ^+μ^-$) colliders.

hep-ph↗