http://hdl.handle.net/10016/5855 2013-05-21T17:16:53Z 2013-05-21T17:16:53Z Sánchez, Raúl Newman, David E. Leboeuf, J.-N. Carreras, Benjamín A. Decyk, V. K. http://hdl.handle.net/10016/9109 2010-08-03T22:20:42Z 2009-04-30T22:00:00Z

Title: On the nature of radial transport across sheared zonal flows in electrostatic ion-temperature-gradient gyrokinetic tokamak plasma turbulence Author(s): Sánchez, Raúl; Newman, David E.; Leboeuf, J.-N.; Carreras, Benjamín A.; Decyk, V. K. Abstract: It is argued that the usual understanding of the suppression of radial turbulent transport across a sheared zonal flow based on a reduction in effective transport coefficients is, by itself, incomplete. By means of toroidal gyrokinetic simulations of electrostatic, ion-temperature-gradient turbulence, it is found instead that the character of the radial transport is altered fundamentally by the presence of a sheared zonal flow, changing from diffusive to anticorrelated and subdiffusive. Furthermore, if the flows are self-consistently driven by the turbulence via the Reynolds stresses (in contrast to being induced externally), radial transport becomes non-Gaussian as well. These results warrant a reevaluation of the traditional description of radial transport across sheared flows in tokamaks via effective transport coefficients, suggesting that such description is oversimplified and poorly captures the underlying dynamics, which may in turn compromise its predictive capabilities. Description: 11 pages, 12 figures.-- PACS nrs.: 52.35.Ra, 52.55.Fa, 05.40.Fb.

2009-04-30T22:00:00Z Akofor, Earnest Balachandran, Aiyalan P. http://hdl.handle.net/10016/6936 2010-02-19T09:08:29Z 2009-07-31T22:00:00Z

Title: Finite temperature field theory on the Moyal plane Author(s): Akofor, Earnest; Balachandran, Aiyalan P. Abstract: In this paper, we initiate the study of finite temperature quantum field theories on the Moyal plane. Such theories violate causality which influences the properties of these theories. In particular, causality influences the fluctuation-dissipation theorem: as we show, a disturbance in a space-time region M1 creates a response in a space-time region M2 spacelike with respect to M1 (M1×M2). The relativistic Kubo formula with and without noncommutativity is discussed in detail, and the modified properties of relaxation time and the dependence of mean square fluctuations on time are derived. In particular, the Sinha-Sorkin result [Phys. Rev. B 45, 8123 (1992)] on the logarithmic time dependence of the mean square fluctuations is discussed in our context. We derive an exact formula for the noncommutative susceptibility in terms of the susceptibility for the corresponding commutative case. It shows that noncommutative corrections in the four-momentum space have remarkable periodicity properties as a function of the four-momentum k. They have direction dependence as well and vanish for certain directions of the spatial momentum. These are striking observable signals for noncommutativity. The Lehmann representation is also generalized to any value of the noncommutativity parameter θ(μν) and finite temperatures. Description: 10 pages, no figures.-- PACS nr.: 11.10.Wx.-- ArXiv pre-print available at: http://arxiv.org/abs/0907.0905v1.pdf

2009-07-31T22:00:00Z Balachandran, Aiyalan P. Govindarajan, Thupil R. Vaidya, Sachindeo http://hdl.handle.net/10016/6934 2010-02-18T16:40:27Z 2009-05-14T22:00:00Z

Title: Spontaneous symmetry breaking in twisted noncommutative quantum theories Author(s): Balachandran, Aiyalan P.; Govindarajan, Thupil R.; Vaidya, Sachindeo Abstract: We analyze aspects of symmetry breaking for Moyal spacetimes within a quantization scheme which preserves the twisted Poincaré symmetry. Towards this purpose, we develop the Lehmann-Symanzik-Zimmermann (LSZ) approach for Moyal spacetimes. The latter gives a formula for scattering amplitudes on these spacetimes which can be obtained from the corresponding ones on the commutative spacetime. This formula applies in the presence of spontaneous breakdown of symmetries as well. We also derive Goldstone’s theorem on Moyal spacetime. The formalism developed here can be directly applied to the twisted standard model. Description: 9 pages, no figures.-- PACS nrs.: 11.10.Nx, 11.30.Cp.-- ArXiv pre-print available at: http://arxiv.org/abs/0901.1712v4.pdf

2009-05-14T22:00:00Z Condon, Marissa Deaño, Alfredo Iserles, Arieh http://hdl.handle.net/10016/6645 2013-01-22T00:15:58Z 2009-12-31T23:00:00Z

Title: On second-order differential equations with highly oscillatory forcing terms Author(s): Condon, Marissa; Deaño, Alfredo; Iserles, Arieh Abstract: We present a method to compute efficiently solutions of systems of ordinary differential equations (ODEs) that possess highly oscillatory forcing terms. This approach is based on asymptotic expansions in inverse powers of the oscillatory parameter, and features two fundamental advantages with respect to standard numerical ODE solvers: first, the construction of the numerical solution is more efficient when the system is highly oscillatory, and, second, the cost of the computation is essentially independent of the oscillatory parameter. Numerical examples are provided, featuring the Van der Pol and Duffing oscillators and motivated by problems in electronic engineering.

2009-12-31T23:00:00Z