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M. Kuroda

Publications and source records attributed to M. Kuroda.

At least 19 recordsLinked to original sources
arXiv2024

Photoabsorption cross section in the low-$x$ and low-$Q^2$ domain, and DGLAP evolution

The behavior of the gluon distribution of the proton in the low-$x$, low-$Q^2$ domain of deep inelastic electron-proton scattering (DIS) is being investigated. By considering two-gluon exchange as the dominant interaction in the low-$x$, low-$Q^2$ domain, we imply the well-known result of scaling of the photoabsorption cross section in terms of the scaling variable $\eta(W^2,Q^2)$. From this, we derive a reliable result for the gluon distribution at the leading order of the perturbative QCD improved parton model, based on evolution from a starting scale of $Q_0^2\cong 2$ GeV$^2$. The validity of evolution, when considering its quantitative modification at low-$Q^2$ without any alteration at larger values of $Q^2$, leads to a quantitative improvement in the extraction of the gluon distribution based on evolution from a starting scale of $Q^2$ conventionally chosen as $Q^2= Q_0^2\cong 2$ GeV$^2$.

hep-ph↗
arXiv2022

The Proton Gluon Distribution from the Color Dipole Picture

Employing the representation of the experimental data on deep inelastic electron-proton scattering (DIS) in the color-dipole picture (CDP), we determine the gluon distribution of the proton at small Bjorken $x$. At sufficiently large momentum transfer, $Q^2$, the extracted gluon distribution fulfills the standard evolution equation for the proton structure function. For low values of $Q^2$, e.g. for $Q^2 = 1.9 {\rm GeV}^2$, the evolution equation for the proton structure function is violated. The standard procedure of adopting a low-$Q^2$ starting scale for the extraction of the gluon density is questionable and requires further investigations.

hep-ph↗
arXiv2019

Spin structure and spin Hall magnetoresistance of epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO$_3$

We report a combined study of imaging the antiferromagnetic (AFM) spin structure and measuring the spin Hall magnetoresistance (SMR) in epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO$_3$. X-ray magnetic linear dichroism photoemission electron microscopy measurements reveal that the AFM spins of the SmFeO$_3$(110) align in the plane of the film. Angularly dependent magnetoresistance measurements show that SmFeO$_3$/Ta bilayers exhibit a positive SMR, in contrast to the negative SMR expected in previously studied collinear AFMs. The SMR amplitude increases linearly with increasing external magnetic field at higher magnetic field, suggesting that field-induced canting of the AFM spins plays an important role. In contrast, around the coercive field, no detectable SMR signal is observed, indicating that SMR of AFM and canting magnetization components cancel out. Below 50~K, the SMR amplitude increases sizably by a factor of two as compared to room temperature, which likely correlates with the long-range ordering of the Sm ions. Our results show that the SMR is a sensitive technique for non-equilibrium spin system of non-collinear AFM systems.

cond-mat.mtrl-sci↗
arXiv2017

Color Dipole picture at Low-x DIS: The Mass Range of Active Photon Fluctuations

We investigate the mass range of the quark-antiquark fluctuations of the photon that are active in producing the total photoabsorption cross section in the color dipole picture, emphasizing the notion of color transparency and saturation. We consider the implications of measurements at future extensions of the available electron-proton-scattering energy.

hep-ph↗
arXiv2017

One loop effects of natural SUSY in indirect searches for SUSY particles at the ILC

We have found the possible region of parameters of the minimal supersymmetric standard model (MSSM) within the bounds from the experimental results of the Higgs mass, the rare decay mode of $b$-quark, the muon $g-2$, the dark matter abundance, and the direct searches for the lighter stop (i.e., one of the supersymmetric partners of top quark) at the LHC. We present numerical results of calculations for the one loop effects of supersymmetric particles in the processes of $τ^+ τ^-$, $b \overline{b}$, $t \overline{t}$, and $Z h$ production at the ILC by using benchmark points within the possible region of the MSSM parameters.

hep-ph↗
arXiv2012

Pair-production and Three-body Decay of the Lighter Stop at the ILC in One-loop Order in the MSSM

We have been developing a program package called GRACE/SUSY-loop which automatically calculates the MSSM amplitudes in one-loop order. We present numerical results of calculations for pair-production and three-body decay of the lighter stop ($\widetilde{t}_1$) at the International Linear Collider (ILC) using GRACE/SUSY-loop. Since the distributions of missing transverse energy (MET) depend on mass spectrum of SUSY particles, we consider two scenarios on three-body decay of $\widetilde{t}_1$. In these scenarios, both QCD and EW corrections have positive sign for decay widths and cross sections.

hep-ph↗
arXiv2010

Present Status of GRACE/SUSY-loop

GRACE/SUSY-loop is a program package for the automatic calculation of the MSSM amplitudes in one-loop order. We present features of GRACE/SUSY-loop, processes calculated using GRACE/SUSY-loop and an extension of the non-linear gauge formalism applied to GRACE/SUSY-loop.

hep-ph↗
arXiv2010

Systematic study of 1-loop correction on sparticle decay widths using GRACE/SUSY-loop

The 1-loop corrected decay widths of sparticles (charginos, neutralinos, gluino and sfermions) in the framework of the MSSM are calculated systematically using GRACE/SUSY-loop, which is the program package for the automatic calculation of the MSSM amplitudes in the 1-loop order. We present the renormalization scheme used in our system and show some numerical results of decay widths of sfermions and gluino using the SPS1a' parameter set and other SUSY parameter sets.

hep-ph↗
arXiv2005

Complete Lagrangian of MSSM

A brief derivation of the lagrangian of the minimal supersymmetric theory is given and the complete expression of the lagrangian in terms of mass eigenstates is presented.

hep-ph↗
arXiv2004

Automatic one-loop calculation of MSSM processes with GRACE

We have developed the system for the automatic computation of cross-sections, {\tt GRACE/SUSY}, including the one-loop calculations for processes of the minimal supersymmetric extension of the the standard model. For an application, we investigate the process $e^+ e^- \to Z^0 h^0$ .

hep-ph↗
arXiv2003

Deep inelastic scattering and "elastic" diffraction

We examine the total cross section of virtual photons on protons, $σ_{γ^* p}(W^2,Q^2)$, at low $x \cong Q^2/W^2 \ll 1$ and its connection with ``elastic'' diffractive production $γ^*_{T,L}p \to X^{J=1}_{T,L} p$ in the two-gluon exchange dynamics for the virtual forward Compton scattering amplitude. Solely based on the generic structure of two-gluon exchange, we establish that the cross section is described by the (imaginary part of the) amplitude for forward scattering of $q \bar q$ vector states, $(q \bar q)^{J=1}_{T,L} p \to (q \bar q)^ {J=1}_{T,L} p$. The generalized vector dominance/color dipole picture (GVD/CDP) is accordingly established to only rest on the two-gluon-exchange generic structure. This is explicitly seen by the sum rules that allow one to directly relate the total cross section to the cross section for elastic diffractive forward production, $γ^*_{T,L} p\to (q \bar q)^{J=1}_{T,L} p$, of vector states.

hep-ph↗
arXiv2002

Diffractive production and the total cross section in deep inelastic scattering

We explore the consequences for diffractive production, gamma* p --> X p, in deep inelastic scattering at low values of x\sim Q^2/W^2 <<1 that follow from our recent representation of the total photoabsorption cross section, sigma_{gamma* p}, in the generalized vector dominance/ color dipole picture(GVD/CDP) that is based on the generic structure of the two-gluon-exchange from QCD. Sum rules are derived that relate the transverse and the longitudinal (virtual) photoabsorption cross section to diffractive forward production of q q-bar states that carry photon quantum numbers ("elastic diffraction"). Agreement with experiment in the W^2 and Q^2 dependence is found for M_X^2/Q^2<<1, where M_X is the mass of the produced system X. An additional component ("inelastic diffraction"), not actively contributing to the forward Compton amplitude, is needed for diffractive production at high values of M_X. Our previous theoretical representation of the total photoabsorption cross section sigma_{gamma* p}=sigma_{gamma* p}(eta), in terms of the scaling variable eta=(Q^2+m_0^2)/Lambda^2(W^2) is extended to include the entire kinematic domain, x=<0.1 and all Q^2 with Q^2>=0, where scaling in eta holds experimentally.

hep-ph↗
arXiv2002

Diffraction and sigma_{gamma* p}

The empirical scaling law, wherein the total photoabsorption cross section depends on the single variable eta=(Q^2+m_0^2)/Lambda^2(W^2), provides empirical evidence for saturation in the sense of sigma_{gamma* p}(W^2,Q^2)/sigma_{gamma p}(W^2) --> 1 for W^2 --> infinity at fixed Q^2. The total photoabsorption cross section is related to elastic diffraction in terms of a sum rule. The excess of diffractive production over the elastic component is due to inelastic diffraction that contains the production of hadronic states of higher spins. Motivated by the diffractive mass spectrum, the generalized vector dominance/color dipole picture (GVD/CDP) is extended to successfully describe the DIS data in the full region of x=<0.1, all Q^2>=0, where the diffractive two-gluon-exchange mechanism dominates.

hep-ph↗
arXiv2000

Automatic Computation of Cross Sections in HEP

For the study of reactions in High Energy Physics (HEP) automatic computation systems have been developed and are widely used nowadays. GRACE is one of such systems and it has achieved much success in analyzing experimental data. Since we deal with the cross section whose value can be given by calculating hundreds of Feynman diagrams, we manage the large scale calculation, so that effective symbolic manipulation, the treat of singularity in the numerical integration are required. The talk will describe the software design of GRACE system and computational techniques in the GRACE.

hep-ph↗
arXiv2000

Four-Fermion Production in Electron-Positron Collisions

This report summarises the results of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the calculation of four-fermion processes in electron-positron collisions at LEP-2 centre-of-mass energies are presented, concentrating on predictions for four main reactions: W-pair production, visible photons in four-fermion events, single-W production and Z-pair production. Based on a comparison of results derived within different approaches, theoretical uncertainties on these predictions are established.

hep-ph↗
arXiv2000

Summary of the SUSY Working Group of the 1999 Les Houches Workshop

The results obtained by the Working Group on Supersymmetry at the 1999 Les Houches Workshop on Collider Physics are summarized. Separate chapters treat "general" supersymmetry, R-parity violation, gauge mediated supersymmetry breaking, and anomaly mediated supersymmetry breaking.

hep-ph↗
arXiv1999

High-Energy Cross Section for e^+e^- to W^+ W^- to 4 fermions + gamma

A recently suggested high-energy Born-form representation of the one-loop helicity amplitudes for e^+e^- to W^+W^- is supplemented by including W^+- decay and hard-photon radiation. Results for the differential and the total cross section for e^+e^- to W^+W^- to 4 fermions + gamma are given for the high-energy region of sqrt(s) > 500 GeV.

hep-ph↗