50,231 research outputs found
Discrete and finite Genral Relativity
We develop the General Theory of Relativity in a formalism with extended
causality that describes physical interaction through discrete, transversal and
localized pointlike fields. The homogeneous field equations are then solved for
a finite, singularity-free, point-like field that we associate to a ``classical
graviton". The standard Einstein's continuous formalism is retrieved by means
of an averaging process, and its continuous solutions are determined by the
chosen imposed symetry. The Schwarzschild metric is obtained by the imposition
of spherical symmetry on the averaged field.Comment: Modified conform the version to appear in Classical and Quantum
Gravit
Correlated electrons systems on the Apollonian network
Strongly correlated electrons on an Apollonian network are studied using the
Hubbard model. Ground-state and thermodynamic properties, including specific
heat, magnetic susceptibility, spin-spin correlation function, double occupancy
and one-electron transfer, are evaluated applying direct diagonalization and
quantum Monte Carlo. The results support several types of magnetic behavior. In
the strong-coupling limit, the quantum anisotropic spin 1/2 Heisenberg model is
used and the phase diagram is discussed using the renormalization group method.
For ferromagnetic coupling, we always observe the existence of long-range
order. For antiferromagnetic coupling, we find a paramagnetic phase for all
finite temperatures.Comment: 7 pages, 8 figure
Generalizing the Planck distribution
Along the lines of nonextensive statistical mechanics, based on the entropy
, and Beck-Cohen
superstatistics, we heuristically generalize Planck's statistical law for the
black-body radiation. The procedure is based on the discussion of the
differential equation (with ),
whose particular case leads to the celebrated law, as originally shown by
Planck himself in his October 1900 paper. Although the present generalization
is mathematically simple and elegant, we have unfortunately no physical
application of it at the present moment. It opens nevertheless the door to a
type of approach that might be of some interest in more complex, possibly
out-of-equilibrium, phenomena.Comment: 6 pages, including 2 figures. To appear in {\it Complexity,
Metastability and Nonextensivity}, Proc. 31st Workshop of the International
School of Solid State Physics (20-26 July 2004, Erice-Italy), eds. C. Beck,
A. Rapisarda and C. Tsallis (World Scientific, Singapore, 2005
Bare LO-Phonon Peak in THz-Emission Signals: a Dielectric-Function Analysis
We present a normal-mode analysis of coupled photocarrier-phonon dynamics in
Te. We consider a dielectric function which accounts for LO phonons and the
electron-hole gas within the Debye-Huckel model and RPA. Our main finding is
the existence of a bare LO phonon mode in the system even at high carrier
density. This oscillation is an unscreened L- mode arising from ineffective
screening at large wave vectors. This mode is consistent with the bare
LO-phonon peak in recent THz-emission spectra of Te.Comment: 3 pages, 1 figure, Special Issue: Proceedings of the 10th Brazilian
Workshop on Semiconductor Physics, Guaruja/SP, April/200
- …