arXiv subjects

Keisuke Fujii

Publications and source records attributed to Keisuke Fujii.

At least 325 records · Page 18Linked to original sources

arXiv2010

Fault-Tolerant Topological One-Way Quantum Computation with Probabilistic Two-Qubit Gates

We propose a scalable way to construct a 3D cluster state for fault-tolerant topological one-way computation (TOWC) even if the entangling two-qubit gates succeed with a small probability. It is shown that fault-tolerant TOWC can be performed with the success probability of the two-qubit gate such as 0.5 (0.1) provided that the conditional error probability of the two-qubit gate is less than 0.040% (0.016%). Furthermore, the resource usage is considerably suppressed compared to the conventional fault-tolerant schemes with probabilistic two-qubit gates.

quant-ph↗

arXiv2010

Extra dimensions and Seesaw Neutrinos at the International Linear Collider

We study the capability of the international linear collider (ILC) to probe extra dimensions via the seesaw mechanism. In the scenario we study, heavy Kaluza-Klein neutrinos generate tiny neutrino masses and, at the same time, have sizable couplings to the standard-model particles. Consequently, a Kaluza-Klein tower of heavy neutrinos (N) can be produced and studied at the ILC through the process: e+e- -> vN followed by N -> Wl decay. We show that the single lepton plus two-jets final states with large missing energy from this signal process will provide a good opportunity to measure the masses and cross sections of Kaluza-Klein neutrinos up to the third level. Furthermore, the neutrino oscillation parameters can be extracted from the flavor dependence of the lowest-mode signals, which give us information about the origin of low-energy neutrino masses.

hep-ph↗

arXiv2010

Anti-Zeno Effect for Quantum Transport in Disordered Systems

We demonstrate that repeated measurements in disordered systems can induce quantum anti-Zeno effect under certain condition to enhance quantum transport. The enhancement of energy transfer is really exhibited with a simple model under repeated measurements. The optimal measurement interval for the anti-Zeno effect and the maximal efficiency of energy transfer are specified in terms of the relevant physical parameters. Since the environment acts as frequent measurements on the system, the decoherence-induced energy transfer, which has been discussed recently for photosynthetic complexes, may be interpreted in terms of the anti-Zeno effect. We further find an interesting phenomenon, where local decoherence or repeated measurements may even promote entanglement generation between the non-local sites.

quant-ph↗

arXiv2010

Proceedings of the ILC Physics Working Group Meeting at KEK in the period from May 2007 to June 2009

The ILC physics working group is a mixture of experimentalists and theorists mainly working in Japan. It has its origin in the previous LC physics study group and has been reformed with the initiative of a JSPS Creative Scientific Research project: "Research and Development of a Novel Detector System for the International Linear Collider". The working group is, however, formally independent of the JSPS project and is open to everybody who is interested in ILC physics. The primary task of the working group is to reexamine the ILC physics in the context of the expected LHC outcome and to further strengthen the physics case for the ILC project. The topics covered in the working group activities range from key measurements such as those of the Higgs self-coupling and the top Yukawa coupling to uncover the secrets of the electroweak symmetry breaking to various new physics scenarios like supersymmetry, large extra dimensions, and other models of terascale physics. The working group has held ten General Meetings in the period of May 2007 to June 2009 to discuss the topics mentioned above. This report ummarizes the progress made in this period and sets a milestone for future developments in ILC physics.

hep-ph↗

arXiv2010

A study of top-quark Yukawa coupling measurement in e+e- -> t tbar H at sqrt(s) = 500 GeV

We report on the feasibility of measuring the top Yukawa coupling in the process: $e^+e^-\to t\bar{t}H$. This measurement is crucial to test the mass generation mechanism for matter particles. Since the cross section for this process attains its maximum around $\sqrt{s}=700 $GeV, most of the past studies were done assuming this energy region. It has been pointed out, however, that the QCD threshold correction enhances the cross section significantly and might enable its measurement at $\sqrt{s}=500 $GeV, which will be accessible already in the first phase of the ILC project. We have implemented this threshold enhancement into our $t\bar{t}H$ event generator and carried out Monte Carlo simulations. Our results show that $t\bar{t}H$ events can be observed with a significance of $4.1\,σ$ with no beam polarization and $5.4 σ$ with the $e^-$ and $e^+$ beam polarization combination: $(-0.8,+0.3)$.

hep-ex↗

arXiv2010

Study of Higgs Self-coupling at ILC

In this Analysis we investigated the possibility of the measurement of Higgs self-coupling at ILC through the process $e^++e^-\rightarrow ZHH$ using fast simulation data. So far two combinations of decay modes: $Z\rightarrow q \bar q,H\rightarrow b\bar b, H\rightarrow WW^*$ and $Z\rightarrow l \bar l, H\rightarrow b\bar b, H\rightarrow b\bar b$ were studied. Our preliminary results show that it is very challenging to suppress the huge standard model backgrounds effectively.

hep-ex↗

arXiv2010

Feasibility study of Higgs pair creation in gamma gamma collider

We studied a feasibility of measuring Higgs boson pair production in a Photon Linear Collider. The optimum energy of gamma gamma collision was estimated with a realistic luminosity distribution. We also discussed simulation study for detecting the signal against W boson pair backgrounds.

hep-ph↗

arXiv2010

Observing the Coupling between Dark Matter and Higgs Boson at the ILC

One of the main purposes on physics at the International Linear Collider (ILC) is to study the property of dark matter such as its mass, spin, and interactions between the dark matter and particles in the standard model. Among those, the interaction between dark matter and higgs boson is important, because, if the dark matter is a weakly interacting massive particle, the existence of the dark matter is expected to relate to physics of electroweak symmetry breaking. In addition, the interaction plays an important role at direct detection experiments of dark matter. In this report, we discuss how accurately the coupling constant of the interaction can be measured at the ILC with the center of mass energy less than 500 GeV.

hep-ph↗

arXiv2010

Measurement of Higgs Anomalous Coupling with H->WW* at International Linear Collider

The measurement of the Higgs coupling to W bosons is an important program at the international linear collider (ILC) to search for the anomaly in the coupling to the gauge bosons. We study the sensitivity of ILC to the Higgs anomalous coupling to W bosons by using ZH->vvWW* events. In this article, we report the status of the study.

hep-ph↗

arXiv2010

Analysis of Little Higgs Model with T-parity at ILC

The Littlest Higgs Model with T-parity is one of the attractive candidates of physics beyond the Standard Model. One of the important predictions of the model is the existence of new heavy gauge bosons, where they acquire mass terms through the breaking of global symmetry necessarily imposed on the model. The determination of the masses are, hence, quite important to test the model. In this paper, the measurement accuracy of the heavy gauge bosons at the international linear collider (ILC) is reported.

hep-ph↗

arXiv2010

Feasibility study of the forward-backward asymmetry of the e+e- -> t tbar process in all-hadronic decay modes at sqrt(s) = 500 GeV with the ILD detector

We have studied the measurement accuracy of the forward-backward asymmetry of the $e^+e^- \rightarrow t\bar{t}$ process in the 6-jet mode at $\sqrt{s} = 500$ GeV with the ILD detector. In the analysis the vertex charges of b-jets were used to distinguish t from $\bar{t}$ in each event. The distribution of the cosine of the reconstructed polar angle of so identified t or $\bar{t}$ showed a clear forward-backward asymmetry. After the correction for charge misidentification the forward-backward asymmetry was determined to be $A^t_{FB} = 0.334 \pm 0.0079$ for 500 fb$^{-1}$ with the beam polarization combination of $P(e^+, e^-) = (+30\%, -80\%)$, demonstrating a very good statistical accuracy ($\sim 2\%$) even in the 6-jet mode.

hep-ex↗

arXiv2009

Cluster-based architecture for fault-tolerant quantum computation

We present a detailed description of an architecture for fault-tolerant quantum computation, which is based on the cluster model of encoded qubits. In this cluster-based architecture, concatenated computation is implemented in a quite different way from the usual circuit-based architecture where physical gates are recursively replaced by logical gates with error-correction gadgets. Instead, some relevant cluster states, say fundamental clusters, are recursively constructed through verification and postselection in advance for the higher-level one-way computation, which namely provides error-precorrection of gate operations. A suitable code such as the Steane seven-qubit code is adopted for transversal operations. This concatenated construction of verified fundamental clusters has a simple transversal structure of logical errors, and achieves a high noise threshold ~ 3 % for computation by using appropriate verification procedures. Since the postselection is localized within each fundamental cluster with the help of deterministic bare controlled-Z gates without verification, divergence of resources is restrained, which reconciles postselection with scalability.

quant-ph↗

arXiv2009

Measurement of Heavy Gauge Bosons in Little Higgs Model with T-parity at ILC

hep-ph↗

arXiv2009

Precision Measurements of the model parameters in the Littlest Higgs model with T-parity

We investigate a possibility of precision measurements for parameters of the Littlest Higgs model with T-parity at the International Linear Collider (ILC). The model predicts new gauge bosons which masses strongly depend on the vacuum expectation value that breaks a global symmetry of the model. Through Monte Carlo simulations of production processes of new gauge bosons, we show that these masses can be determined very accurately at the ILC for a representative parameter point of the model. From the simulation result, we also discuss the determination of other model parameters at the ILC.

hep-ph↗

arXiv2009

Precision Measurements of Little Higgs Parameters at the International Linear Collider

We investigate a possibility of precision measurements for parameters of the Littlest Higgs model with T-parity at the International Linear Collider (ILC). The model predicts new gauge bosons (AH, ZH, and WH), among which the heavy photon (AH) is a candidate for dark matter. The masses of these new gauge bosons strongly depend on the vacuum expectation value that breaks a global symmetry of the model. Through Monte Carlo simulations of the processes: e+ e- ->AH ZH and e+ e- -> WH+ WH-, we show how precisely the masses can be determined at the ILC for a representative parameter point of the model. We also discuss the determination of the Little Higgs parameters and its impact on the future measurement of the thermal abundance of the dark matter relics in our universe.

hep-ph↗

arXiv2009

Tau-pair Performance in ILD detectors

Tau-pair process has been analyzed in the ILD detector model as a benchmark process for LoI. Results of background rejection, forward-backward asymmetry and polarization measurements are obtained with full detector simulation. Impact of detector parameters for tau-pair analysis is also discussed in this paper.

hep-ex↗

arXiv2009

How accurately is the property of the Little Higgs Dark Matter determined at the ILC?

Little Higgs scenario provides us a new solution for the hierarchy problem of the Standard Model. The Littlest Higgs model with T-parity, which is one of models in the scenario, solves the dark matter problem in our universe. In this talk, we discuss how accurately the property of the dark matter is determined at linear collides. We also mention how precisely does the thermal abundance of the dark matter determined at the 500 GeV and 1 TeV collides, and compare the results with those at the LHC.

hep-ph↗

arXiv2009

Measurements of the model parameter in the littlest Higgs model with T-parity

In the Littlest Higgs model with T-parity, we study production processes of new gauge bosons at the international linear collider (ILC). Through Monte Carlo simulations of the production processes, we show that the heavy gauge boson masses can be determined very accurately at the ILC for a representative parameter point of the model. From the simulation result, we also discuss the determination of other model parameters at the ILC.

hep-ph↗