Daisuke Kawai

Schwinger pair production rate in confining theories via holography

We study the Schwinger pair production in confining theories. The production rate in an external electric field E is numerically evaluated by using the holographic description. There exist two kinds of critical values of the electric field, i) E=E_c, above which there is no potential barrier and particles are freely generated, ii) E=E_s, below which the confining string tension dominates the electric field and the pair production does not occur. We argue the universal exponents associated with the critical behaviors.

Chaotic strings in a near Penrose limit of AdS 5 × T 1,1

A bstractWe study chaotic motions of a classical string in a near Penrose limit of AdS5 × T1,1. It is known that chaotic solutions appear on R ×T1,1, depending on initial conditions. It may be interesting to ask whether the chaos persists even in Penrose limits or not. In this paper, we show that sub-leading corrections in a Penrose limit provide an unstable separatrix, so that chaotic motions are generated as a consequence of collapsed KolmogorovArnold-Moser (KAM) tori. Our analysis is based on deriving a reduced system composed of two degrees of freedom by supposing a winding string ansatz. Then, we provide support for the existence of chaos by computing Poincaré sections. In comparison to the AdS5 ×T1,1 case, we argue that no chaos lives in a near Penrose limit of AdS5×S5, as expected from the classical integrability of the parent system.

A holographic description of the Schwinger effect in a confining gauge theory

This is a review of the recent progress on a holographic description of the Schwinger effect. In 2011, Semenoff and Zarembo proposed a scenario to study the Schwinger effect in the context of the AdS/CFT correspondence. The production rate of quark anti-quark pairs was computed in the Coulomb phase. In particular, it provided the critical value of external electric field, above which particles are freely created and the vacuum decays catastrophically. Then the potential analysis in the holographic approach was invented and it enabled us to study the Schwinger effect in the confining phase as well. A remarkable feature of the Schwinger effect in the confining phase is to exhibit another kind of the critical value, below which the pair production cannot occur and the vacuum of the system is non-perturbatively stable. The critical value is tantamount to the confining string tension. We computed the pair production rate numerically and introduced new exponents associated with the critical electric fields.

Chaos in the BMN matrix model

A bstractWe study classical chaotic motions in the Berenstein-Maldacena-Nastase (BMN) matrix model. For this purpose, it is convenient to focus upon a reduced system composed of two-coupled anharmonic oscillators by supposing an ansatz. We examine three ansätze: 1) two pulsating fuzzy spheres, 2) a single Coulomb-type potential, and 3) integrable fuzzy spheres. For the first two cases, we show the existence of chaos by computing Poincaré sections and a Lyapunov spectrum. The third case leads to an integrable system. As a result, the BMN matrix model is not integrable in the sense of Liouville, though there may be some integrable subsectors.

Digital History Meets Wikipedia: Analyzing Historical Persons in Wikipedia

Wikipedia is the result of a collaborative effort aiming to represent human knowledge and to make it accessible for everyone. As such it contains lots of contemporary as well as history-related information. This research looks into historical data available in Wikipedia to explore its various time-related characteristics. In particular, we study Wikipedia articles on historical persons. Our analysis sheds new light on the characteristics of information about historical persons in Wikipedia and quantifies user interest in such data. We use signals derived from the hyperlink structure of Wikipedia as well as from article view logs and we overlay them over temporal dimension to understand relations between time, link structure and article popularity. In the latter part of the paper, we also demonstrate different ways for estimating person importance based on the temporal aspects of the link structure.

ΛcN interaction from lattice QCD and its application to Λc hypernuclei

Abstract The interaction between Λ c and a nucleon (N) is investigated by employing the HAL QCD method in the ( 2 + 1 ) -flavor lattice QCD on a ( 2.9 fm ) 3 volume at m π ≃ 410 , 570 , 700 MeV. We study the central potential in S 0 1 channel as well as central and tensor potentials in S 1 3 − 3 D 1 channel, and find that the tensor potential for Λ c N is negligibly weak and central potentials in both S 0 1 and S 1 3 − 3 D 1 channels are almost identical with each other except at short distances. Phase shifts and scattering lengths calculated with these potentials show that the interaction of Λ c N system is attractive and has a similar strength in S 0 1 and S 1 3 channels at low energies (i.e. the kinetic energy less than about 40 MeV). While the attractions are not strong enough to form two-body bound states, our results lead to a possibility to form Λ c hypernuclei for sufficiently large atomic numbers (A). To demonstrate this, we derive a single-folding potential for Λ c hypernuclei from the Λ c -nucleon potential obtained in lattice QCD, and find that Λ c hypernuclei can exist for A ≥ 12 with the binding energies of a few MeV. We also estimate the Coulomb effect for the Λ c hypernuclei.

Parallelizing local search for CNF satisfiability using vectorization and PVM

The purpose of this paper is to speed up the local search algorithm for the CNF Satisfiability problem. Our basic strategy is to run some 105 independent search paths simultaneously using PVM on a vector supercomputer VPP800, which consists of 40 vector processors. Using the above parallelization and vectorization together with some improvement of data structure, we obtained 600-times speedup in terms of the number of flips the local search can make per second, compared to the original GSAT by Selman and Kautz. We ran our parallel GSAT for benchmark instances and compared the running time with those of existing SAT programs. We could observe an apparent benefit of parallelization: Especially, we were able to solve two instances that have never been solved before this paper. We also tested parallel local search for the SAT encoding of the class scheduling problem. Again we were able to get almost the best answer in reasonable time.

Parallelizing Local Search for CNF Satisfiability Using Vectorization and PVM

The purpose of this paper is to speed up the local search algorithm for the CNF Satisfiability problem. Our basic strategy is to run some 105 independent search paths simultaneously using PVM on a vector supercomputer VPP800, which consists of 40 vector processors. Usingthe above parallelization and vectorization together with some improvement of data structure, we obtained 600-times speedup in terms of the number of flips the local search can make per second compared to the original GSAT by Selman and Kautz. We run our parallel GSAT for benchmark instances and compared the runningtime with those of existingSA T programs. We could observe an apparent benefit of parallelization: Especially, we were able to solve two instances that have never been solved before this paper. We also tested parallel local search for the SAT encoding of the class scheduling problem. Again we were able to get almost the best answer in reasonable time.

Ι = 2ππ scattering phase shift from the HAL QCD method with the LapH smearing

Physical observables, such as the scattering phase shifts and the binding energies, calculated from the non-local HAL QCD potential do not depend on the sink operators used to define the potential. This is called the scheme independence of the HAL QCD method. In practical applications, the derivative expansion of the non-local potential is employed, so that physical observables may receive some scheme dependence at given order of the expansion. In this paper, we compare the

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