Fermion Production in Strong Magnetic Field and its Astrophysical Implications

We calculate the effective potential of a strong magnetic field induced by fermions with anomalous magnetic moments which couple to the electromagnetic field in the form of the Pauli interaction. For a uniform magnetic field, we find the explicit form of the effective potential. It is found that the non-vanishing imaginary part develops for a magnetic field stronger than a critical field and has a quartic form which is quite different from the exponential form of the Schwinger process. We also consider a linear magnetic field configuration as an example of inhomogeneous magnetic fields. We find that the imaginary part of the effective potential is nonzero even below the critical field and shows an exponentially decreasing behavior with respect to the inverse of the magnetic field gradient, which is the non-perturbative characteristics analogous to the Schwinger process. These results imply the instability of the strong magnetic field to produce fermion pairs as a purely magnetic effect. The possible applications to the astrophysical phenomena with strong magnetic field are also discussed.Comment: 13 pages, 3 figure

Universality classes and crossover behaviors in non-Abelian directed sandpiles

We study universality classes and crossover behaviors in non-Abelian directed sandpile models, in terms of the metastable pattern analysis. The non-Abelian property induces spatially correlated metastable patterns, characterized by the algebraic decay of the grain density along the propagation direction of an avalanche. Crossover scaling behaviors are observed in the grain density due to the interplay between the toppling randomness and the parity of the threshold value. In the presence of such crossovers, we show that the broadness of the grain distribution plays a crucial role in resolving the ambiguity of the universality class. Finally, we claim that the metastable pattern analysis is important as much as the conventional analysis of avalanche dynamics.Comment: 10 pages, 7 figures, 1 table; published in PRE as the full paper of PRL v101, 218001 (2008

Continuity of the Explosive Percolation Transition

The explosive percolation problem on the complete graph is investigated via extensive numerical simulations. We obtain the cluster-size distribution at the moment when the cluster size heterogeneity becomes maximum. The distribution is found to be well described by the power-law form with the decay exponent $\tau = 2.06(2)$, followed by a hump. We then use the finite-size scaling method to make all the distributions at various system sizes up to $N=2^{37}$ collapse perfectly onto a scaling curve characterized solely by the single exponent $\tau$. We also observe that the instant of that collapse converges to a well-defined percolation threshold from below as $N\rightarrow\infty$. Based on these observations, we show that the explosive percolation transition in the model should be continuous, contrary to the widely-spread belief of its discontinuity.Comment: Some corrections during the revie

Korean to English Translation Using Synchronous TAGs

It is often argued that accurate machine translation requires reference to contextual knowledge for the correct treatment of linguistic phenomena such as dropped arguments and accurate lexical selection. One of the historical arguments in favor of the interlingua approach has been that, since it revolves around a deep semantic representation, it is better able to handle the types of linguistic phenomena that are seen as requiring a knowledge-based approach. In this paper we present an alternative approach, exemplified by a prototype system for machine translation of English and Korean which is implemented in Synchronous TAGs. This approach is essentially transfer based, and uses semantic feature unification for accurate lexical selection of polysemous verbs. The same semantic features, when combined with a discourse model which stores previously mentioned entities, can also be used for the recovery of topicalized arguments. In this paper we concentrate on the translation of Korean to English.Comment: ps file. 8 page

Josephson-vortex-flow terahertz emission in layered high-TcT_c superconducting single crystals

We report on the successful terahertz emission (0.6$\sim$1 THz) that is continuous and tunable in its frequency and power, by driving Josephson vortices in resonance with the collective standing Josephson plasma modes excited in stacked Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ intrinsic Josephson junctions. Shapiro-step detection was employed to confirm the terahertz-wave emission. Our results provide a strong feasibility of developing long-sought solid-state terahertz-wave emission devices

Eleven-dimensional massless superparticles and matrix theory spin-orbit couplings revisited

The classical probe dynamics of the eleven-dimensional massless superparticles in the background geometry produced by N source M-momenta is investigated in the framework of N-sector DLCQ supergravity. We expand the probe action up to the two fermion terms and find that the fermionic contributions are the spin-orbit couplings, which precisely agree with the matrix theory calculations. We comment on the lack of non-perturbative corrections in the one-loop matrix quantum mechanics effective action and its compatibility with the supergravity analysis.Comment: 11 pages, Latex, no figure