17,044 research outputs found
Leptoquark explanation of HERA anomaly in the context of gauge unification
We examine the consequences of leptoquark explanation of HERA anomaly in the
context of R parity conserving supersymmetric gauge unified theory with the
gauge unification scale at GeV. We pointed out the difficulty of
constructing a grandunified theory. However gauge unification is still possible
at GeV when additional multiplets are introduced. We determine
the mass spectrum of these additional fields (fermions and scalars) in gauge
mediated and supergravity scenarios. Unique signatures and mass bounds are
discussed.Comment: 19 pages(Latex), 1 PS Figur
Electron-Electron Interactions on the Edge States of Graphene: A Many Body Configuration Interaction Study
We have studied zigzag and armchair graphene nano ribbons (GNRs), described
by the Hubbard Hamiltonian using quantum many body configuration interaction
methods. Due to finite termination, we find that the bipartite nature of the
graphene lattice gets destroyed at the edges making the ground state of the
zigzag GNRs a high spin state, whereas the ground state of the armchair GNRs
remains a singlet. Our calculations of charge and spin densities suggest that,
although the electron density prefers to accumulate on the edges, instead of
spin polarization, the up and down spins prefer to mix throughout the GNR
lattice. While the many body charge gap results in insulating behavior for both
kinds of GNRs, the conduction upon application of electric field is still
possible through the edge channels because of their high electron density.
Analysis of optical states suggest differences in quantum efficiency of
luminescence for zigzag and armchair GNRs, which can be probed by simple
experiments.Comment: 5 pages, 4 figure
Generating Cosmological Gaussian Random Fields
We present a generic algorithm for generating Gaussian random initial
conditions for cosmological simulations on periodic rectangular lattices. We
show that imposing periodic boundary conditions on the real-space correlator
and choosing initial conditions by convolving a white noise random field
results in a significantly smaller error than the traditional procedure of
using the power spectrum. This convolution picture produces exact correlation
functions out to separations of L/2, where L is the box size, which is the
maximum theoretically allowed. This method also produces tophat sphere
fluctuations which are exact at radii . It is equivalent to
windowing the power spectrum with the simulation volume before discretizing,
thus bypassing sparse sampling problems. The mean density perturbation in the
volume is no longer constrained to be zero, allowing one to assemble a large
simulation using a series of smaller ones. This is especially important for
simulations of Lyman- systems where small boxes with steep power
spectra are routinely used.
We also present an extension of this procedure which generates exact initial
conditions for hierarchical grids at negligible cost.Comment: 12 pages incl 3 figures, accepted in ApJ Letter
Horava-Lifshitz modifications of the Casimir effect
We study the modifications induced by spacetime anisotropy on the Casimir
effect in the case of two parallel plates. Nonperturbative and perturbative
regimes are analyzed. In the first case the Casimir force either vanishes or it
reverses its direction which, in any case, makes the proposal untenable. On the
other hand, the perturbative model enables us to incorporate appropriately the
effects of spacetime anisotropy.Comment: 6 pages, revtex
Phase transitions in periodically driven macroscopic systems
We study the large-time behavior of a class of periodically driven
macroscopic systems. We find, for a certain range of the parameters of either
the system or the driving fields, the time-averaged asymptotic behavior
effectively is that of certain other equilibrium systems. We then illustrate
with a few examples how the conventional knowledge of the equilibrium systems
can be made use in choosing the driving fields to engineer new phases and to
induce new phase transitions.Comment: LaTex, 8 page
- …