90,626 research outputs found
Gaussian Effective Potential and the Coleman's normal-ordering Prescription : the Functional Integral Formalism
For a class of system, the potential of whose Bosonic Hamiltonian has a
Fourier representation in the sense of tempered distributions, we calculate the
Gaussian effective potential within the framework of functional integral
formalism. We show that the Coleman's normal-ordering prescription can be
formally generalized to the functional integral formalism.Comment: 6 pages, revtex; With derivation details and an example added. To
appear in J. Phys.
Antilinear spectral symmetry and the vortex zero-modes in topological insulators and graphene
We construct the general extension of the four-dimensional Jackiw-Rossi-Dirac
Hamiltonian that preserves the antilinear reflection symmetry between the
positive and negative energy eigenstates. Among other systems, the resulting
Hamiltonian describes the s-wave superconducting vortex at the surface of the
topological insulator, at a finite chemical potential, and in the presence of
both Zeeman and orbital couplings to the external magnetic field. Here we find
that the bound zero-mode exists only when the Zeeman term is below a critical
value. Other physical realizations pertaining to graphene are considered, and
some novel zero-energy wave functions are analytically computed.Comment: 6 revtex pages; typos corrected, published versio
GRB afterglows: deep Newtonian phase and its application
Gamma-ray burst afterglows have been observed for months or even years in a
few cases. It deserves noting that at such late stages, the remnants should
have entered the deep Newtonian phase, during which the majority of
shock-accelerated electrons will no longer be highly relativistic. To calculate
the afterglows, we must assume that the electrons obey a power-law distribution
according to their kinetic energy, not simply the Lorentz factor.Comment: Poster at the 4th workshop "Gamma-Ray Bursts in the Afterglow Era"
(Rome, 2004), accepted for publication in the proceedings. 4 pages, with 3
figures inserte
Beaming effects in GRBs and orphan afterglows
The overall dynamical evolution and radiation mechanism of -ray burst
jets are briefly introduced. Various interesting topics concerning beaming in
-ray bursts are discussed, including jet structures, orphan afterglows
and cylindrical jets. The possible connection between -ray bursts and
neutron star kicks is also addressed.Comment: 10 Pages, 4 figures, to appear in a special issue of ApSS. Oral
report presented at "The Multiwavelength Approach to Unidentified Gamma-Ray
Sources" (Hong Kong, June 1 - 4, 2004; Conference organizers: K.S. Cheng and
G.E. Romero
Cluster dynamical mean field theory of quantum phases on a honeycomb lattice
We have studied the ground state of the half-filled Hubbard model on a
honeycomb lattice by performing the cluster dynamical mean field theory
calculations with exact diagonalization on the cluster-impurity solver. Through
using elaborate numerical analytic continuation, we identify the existence of a
`spin liquid' from the on-site interaction U=0 to (between and
) with a smooth crossover correspondingly from the charge fluctuation
dominating phase into the charge correlation dominating phase. The
semi-metallic state exits only at U=0. We further find that the magnetic phase
transition at from the `spin liquid' to the N\'{e}el antiferromagnetic
Mott insulating phase is a first-order quantum phase transition. We also show
that the charge fluctuation plays a substantial role on keeping the `spin
liquid' phase against the emergence of a magnetic order.Comment: 5 pages and 8 figure
Beaming Effects in Gamma-Ray Bursts
Based on a refined generic dynamical model, we investigate afterglows from
jetted gamma-ray burst (GRB) remnants numerically. In the relativistic phase,
the light curve break could marginally be seen. However, an obvious break does
exist at the transition from the relativistic phase to the non-relativistic
phase, which typically occurs at time 10 to 30 days. It is very interesting
that the break is affected by many parameters, especially by the electron
energy fraction (xi_e), and the magnetic energy fraction (xi_B^2). Implication
of orphan afterglow surveys on GRB beaming is investigated. The possible
existence of a kind of cylindrical jets is also discussed.Comment: Minor changes; 10 pages, with 9 eps figures embedded. Talk given at
the Sixth Pacific Rim Conference on Stellar Astrophysics (Xi'an, China, July
11-17, 2002). A slightly revised version will appear in the proceeding
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