arXiv subjects

N. Nakazawa

Publications and source records attributed to N. Nakazawa.

8 recordsLinked to original sources

arXiv2014

Full $\mathcal{O}(α)$ electroweak radiative corrections to $e^+e^- \rightarrow e^+e^- γ$ at the ILC with GRACE-Loop

By using the GRACE-Loop system, we calculate the full $\mathcal{O}(α)$ electroweak radiative corrections to the process $e^+e^- \rightarrow e^+e^- γ$, which is important for future investigations at the International Linear Collider (ILC). With the GRACE-Loop system, the calculations are checked numerically by three consistency tests: ultraviolet finiteness, infrared finiteness, and gauge-parameter independence. The results show good numerical stability when quadruple precision is used. In the phenomenological results, we find that the electroweak corrections to the total cross section range from $\sim -4\%$ to $\sim -21\%$ when $\sqrt{s}$ varies from $250$ GeV to $1$ TeV. The corrections also significantly affect the differential cross sections, which are a function of the invariant masses and angles and the final-particle energies. Such corrections will play an important role for the high-precision program at the ILC.

hep-ph↗

arXiv2014

Full $\mathcal{O}(α)$ electroweak radiative corrections to $t \bar{t} γ$ and $e^-e^+γ$ productions at ILC with GRACE-Loop

The full $\mathcal{O}(α)$ electroweak radiative corrections to $t \bar{t} γ$ and $e^-e^+γ$ productions at the International Linear Collider (ILC) are presented in this paper. The computation is performed with the help of GRACE-Loop system. In the physical results, we discuss on the cross section, electroweak corrections, and the top quark forward-backward asymmetry ($A_{FB}$) which are the function of the center-of-mass energy.

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↗

arXiv1999

Implementation of the Non-Linear Gauge into GRACE

A general non-linear gauge condition is implemented into GRACE, an automated system for the calculation of physical processes in high-energy physics. This new gauge-fixing is used as a very efficient means to check the results of large scale evaluation in the standard model computed automatically. We report on some systematic test-runs which have been performed for one-loop two-to-two processes to show the validity of the gauge check.

hep-ph↗

arXiv1997

Automatic Calculation of Complete $O(α)$ Corrections to $e^+e^- \to W^+μ\barν_μ$

Using the automatic system GRACE-LOOP, the full $O(α)$ electroweak corrections has been calculated for the process $e^+e^- \to W^+μ\barν_μ$. The total correction to the cross section is found to be typically -6.4% at $\sqrt{s}=190$ GeV with $10^\circ$ cut on the muon angle from the beam, including the correction from the hard photon emission. It is observed that the correction is rather sensitive to the physical parameters. With the same conditions the correction corresponding to the real W-boson pair is -4.1% and hence the deviation is not negligible.

hep-ph↗

arXiv1995

Lattice Quantum Gravity from Stochastic 3-Geometries

I propose the Langevin equation for 3-geometries in the Ashtekar's formalism to describe 4D Euclidean quantum gravity, in the sense that the corresponding Fokker-Planck hamiltonian recovers the hamiltonian in 4D quantum gravity exactly. The stochastic time corresponds to the Euclidean time in the gauge, N=1 and $N^i=0$. In this approach, the time evolution in 4D quantum gravity is understood as a stochastic process where the quantum fluctuation of ` ` triad \rq\rq is characterized by the curvature at the one unit time step before. The lattice regularization of 4D quantum gravity is presented in this context.

gr-qc↗

arXiv1995

Stochastic Quantization of Matrix Models and Field Theory of Non-Orientable Strings

In quantizing gravity based on stochastic quantization method, the stochastic time plays a role of the proper time. We study 2D and 4D Euclidean quantum gravity in this context. By applying stochastic quantization method to real symmetric matrix models, it is shown that the stochastic process defined by the Langevin equation in loop space describes the time evolution of the non-orientable loops which defines non-orientable 2D surfaces. The corresponding Fokker-Planck hamiltonian deduces a non-orientable string field theory at the continuum limit. The strategy, which we have learned in the example of 2D quantum gravity, is applied to 4D case. Especially, the Langevin equation for the stochastic process of 3-geometries is proposed to describe the (Euclidean) time evolution in 4D quantum gravity with Ashtekar's canonical variables. We present it in both lattice regularized version and the naive continuum limit.

hep-th↗

arXiv1995

On Field Theories of Loops

We apply stochastic quantization method to matrix models for the second quantization of loops in both discretized and continuum levels. The fictitious time evolution described by the Langevin equation is interpreted as the time evolution in a field theory of loops. The corresponding Fokker-Planck hamiltonian defines a non-critical string field theory. We study both orientable and non-orientable interactions of loops in terms of matrix models and take the continuum limit for one-matrix case. As a consequence, we show the equivalence of stochastic quantization of matrix models in loop space to the transfer-matrix formalism in dynamical triangulation of random surfaces. We also clarifies the origin of Virasoro algebra in this context.

hep-th↗