Fluctuation of the Top Location and Avalanches in the Formation Process of a Sandpile

We investigate the formation processes of a sandpile using numerical simulation. We find a new relation between the fluctuation of the motion of the top and the surface state of a sandpile. The top moves frequently as particles are fed one by one every time interval T. The time series of the top location has the power spectrum which obeys a power law, S(f)~f^{\alpha}, and its exponent \alpha depends on T and the system size w. The surface state is characterized by two time scales; the lifetime of an avalanche, T_{a}, and the time required to cause an avalanche, T_{s}. The surface state is fluid-like when T_{a}~T_{s}, and it is solid-like when T_{a}<<T_{s}. Our numerical results show that \alpha is a function of T_{s}/T_{a}.Comment: 15 pages, 13 figure

On the direct search for spin-dependent WIMP interactions

We examine the current directions in the search for spin-dependent dark matter. We discover that, with few exceptions, the search activity is concentrated towards constraints on the WIMP-neutron spin coupling, with significantly less impact in the WIMP-proton sector. We review the situation of those experiments with WIMP-proton spin sensitivity, toward identifying those capable of reestablishing the balance.Comment: 7 pages, 4 figure

Progress in QCD next-to-leading order calculations

I review progress related to the calculation of QCD jet cross sections at the NLO accuracy. After a short introduction into the theory of NLO calculations, I discuss two recent developments: the calculation of two- and three-jet leptoproduction at the NLO accuracy and the extension of the dipole subtraction method for computing NLO corrections for processes involving massive partons.Comment: 5 pages, 4 figures, LaTeX using JHEP3.cls, Invited talk at the International Europhysics Conference on High-Energy Physics (HEP 2001

Traffic Equations and Granular Convection

We investigate both numerically and analytically the convective instability of granular materials by two dimensional traffic equations. In the absence of vibrations the traffic equations assume two distinctive classes of fixed bed solutions with either a spatially uniform or nonuniform density profile. The former one exists only when the function V(\rho) that monitors the relaxation of grains assumes a cut off at the closed packed density, \rho_c, with V(\rho_c)=0, while the latter one exists for any form of V. Since there is little difference between the uniform and nonuniform solution deep inside the bed, the convective instability of the bulk may be studied by focusing on the stability of the uniform solution. In the presence of vibrations, we find that the uniform solution bifurcates into a bouncing solution, which then undergoes a supercritical bifurcation to the convective instability. We determine the onset of convection as a function of control parameters and confirm this picture by solving the traffic equations numerically, which reveals bouncing solutions, two convective rolls, and four convective rolls. Further, convective patterns change as the aspect ratio changes: in a vertically long container, the rolls move toward the surface, and in a horizontally long container, the rolls move toward the walls. We compare these results with those reported previously with a different continuum model by Hayakawa, Yue and Hong[Phys. Rev. Lett. 75,2328, 1995]. Finally, we also present a derivation of the traffic equations from Enskoq equation.Comment: 34 pages, 10 figure

Search for solar axions using Li-7

We describe a novel approach to the search for solar, near-monochromatic hadronic axions, the latter being suggested to be created in the solar core during M1 transitions between the first excited level of Li-7, at 478 keV, and the ground state. As a result of Doppler broadening, in principle these axions can be detected via resonant absorption by the same nuclide on the Earth. Excited nuclei of Li-7 are produced in the solar interior by Be-7 electron capture and thus the axions are accompanied by emission of Be-7 solar neutrinos of energy 384 keV. An experiment was made which has yielded an upper limit on hadronic axion mass of 32 keV at the 95% confidence level.Comment: revtex, 4 pages with 2 figures, title revised, minor changes, matches version to appear in Phys. Rev.

Conformal Symmetry and A New Gauge in the Matrix Model

We generalize the background gauge in the Matrix model to propose a new gauge which is useful for discussing the conformal symmetry. In this gauge, the special conformal transformation (SCT) as the isometry of the near-horizon geometry of the D-particle solution is directly reproduced with the correct coefficient as the quantum correction to the SCT in the Matrix model. We also present a general argument for the relation between the gauge choice and the field redefinition in the Matrix model.Comment: 17 pages, LaTeX, no figures; v2: Introduction modified, references added and typos corrected; v3: Introduction changed; v4: Eq.(12) corrected; v5: final version to appear in Phys. Rev.

Realization of Brane Descent Relations in Effective Theories

We examine Sen's descent relations among (non-)BPS D-branes by using low energy effective field theories of DpDpbar system. We find that the fluctuation around the kink solution reproduces the low energy matter content on a non-BPS D(p-1)-brane. The effective action for these fluctuation modes turns out to be a generalization of Minahan-Zwiebach model. In addition, it is shown that the fluctuations around the vortex solution consist of massless fields on a BPS D(p-2)-brane and they are subject to Dirac-Born-Infeld action. We find the universality that the above results do not refer to particular forms of the effective action.Comment: 24 pages, LaTeX, 1 eps figure; v2:minor correction

ADHM/Nahm Construction of Localized Solitons in Noncommutative Gauge Theories

We study the relationship between ADHM/Nahm construction and ``solution generating technique'' of BPS solitons in noncommutative gauge theories. ADHM/Nahm construction and ``solution generating technique'' are the most strong ways to construct exact BPS solitons. Localized solitons are the solitons which are generated by the ``solution generating technique.'' The shift operators which play crucial roles in ``solution generating technique'' naturally appear in ADHM/Nahm construction and we can construct various exact localized solitons including new solitons: localized periodic instantons (=localized calorons) and localized doubly-periodic instantons. Nahm construction also gives rise to BPS fluxons straightforwardly from the appropriate input Nahm data which is expected from the D-brane picture of BPS fluxons. We also show that the Fourier-transformed soliton of the localized caloron in the zero-period limit exactly coincides with the BPS fluxon.Comment: 30 pages, LaTeX, 3 figures; v3: minor changes, references added; v4: references added, version to appear in PR

Dimming Supernovae without Cosmic Acceleration

We present a simple model where photons propagating in extra-galactic magnetic fields can oscillate into very light axions. The oscillations may convert some of the photons departing a distant supernova into axions, making the supernova appear dimmer and hence more distant than it really is. Averaging over different configurations of the magnetic field we find that the dimming saturates at about 1/3 of the light from the supernovae at very large redshifts. This results in a luminosity-distance vs. redshift curve almost indistinguishable from that produced by the accelerating Universe, if the axion mass and coupling scale are m ~ 10^-16 eV, M ~ 4 10^11 GeV. This phenomenon may be an alternative to the accelerating Universe for explaining supernova observations.Comment: 11 pages, LaTex, 2 figures included. Comments on effects of refraction within galaxies and references adde

Electrical and thermoelectrical transport in Dirac fermions through a quantum dot

We investigate the conductance and thermopower of massless Dirac fermions through a quantum dot using a pseudogap Anderson model in the non-crossing approximation. When the Fermi level is at the Dirac point, the conductance has a cusp where the thermopower changes its sign. When the Fermi level is away from the Dirac point, the Kondo temperature illustrates a quantum impurity transition between an asymmetric strong coupling Kondo state and a localized moment state. The conductance shows a peak near this transition and reaches the unitary limit at low temperatures. The magnitude of the thermopower exceeds $k_B/e$, and the thermoelectric figure of merit exceeds unity.Comment: 5 pages, 4 figure