9,809 research outputs found
Binary Black Hole Coalescence in Semi-Analytic Puncture Evolution
Binary black-hole coalescence is treated semi-analytically by a novel
approach. Our prescription employs the conservative Skeleton Hamiltonian that
describes orbiting Brill-Lindquist wormholes (termed punctures in Numerical
Relativity) within a waveless truncation to the Einstein field equations [G.
Faye, P. Jaranowski and G. Sch\"afer, Phys. Rev. D {\bf 69}, 124029 (2004)]. We
incorporate, in a transparent Hamiltonian way and in Burke-Thorne gauge
structure, the effects of gravitational radiation reaction into the above
Skeleton dynamics with the help of 3.5PN accurate angular momentum flux for
compact binaries in quasi-circular orbits to obtain a Semi-Analytic Puncture
Evolution to model merging black-hole binaries. With the help of the TaylorT4
approximant at 3.5PN order, we perform a {\it first-order} comparison between
gravitational wave phase evolutions in Numerical Relativity and our approach
for equal-mass binary black holes. This comparison reveals that a modified
Skeletonian reactive dynamics that employs flexible parameters will be required
to prevent the dephasing between our scheme and Numerical Relativity, similar
to what is pursued in the Effective One Body approach. A rough estimate for the
gravitational waveform associated with the binary black-hole coalescence in our
approach is also provided.Comment: 16 pages, 5 figure
Mass Terms in Effective Theories of High Density Quark Matter
We study the structure of mass terms in the effective theory for
quasi-particles in QCD at high baryon density. To next-to-leading order in the
expansion we find two types of mass terms, chirality conserving
two-fermion operators and chirality violating four-fermion operators. In the
effective chiral theory for Goldstone modes in the color-flavor-locked (CFL)
phase the former terms correspond to effective chemical potentials, while the
latter lead to Lorentz invariant mass terms. We compute the masses of Goldstone
bosons in the CFL phase, confirming earlier results by Son and Stephanov as
well as Bedaque and Sch\"afer. We show that to leading order in the coupling
constant there is no anti-particle gap contribution to the mass of
Goldstone modes, and that our results are independent of the choice of gauge.Comment: 22 pages, 4 figure
Superdense Matter
We review recent work on the phase structure of QCD at very high baryon
density. We introduce the phenomenon of color superconductivity and discuss the
use of weak coupling methods. We study the phase structure as a function of the
number of flavors and their masses. We also introduce effective theories that
describe low energy excitations at high baryon density. Finally, we study the
possibility of kaon condensation at very large baryon density.Comment: 13 pages, talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; to appear
in the proceeding
Phases of QCD at High Baryon Density
We review recent work on the phase structure of QCD at very high baryon
density. We introduce the phenomenon of color superconductivity and discuss how
the quark masses and chemical potentials determine the structure of the
superfluid quark phase. We comment on the possibility of kaon condensation at
very high baryon density and study the competition between superfluid, density
wave, and chiral crystal phases at intermediate density.Comment: 15 pages. To appear in the proceedings of the ECT Workshop on Neutron
Star Interiors, Trento, Italy, June 200
Excitation Induced Dephasing in Semiconductor Quantum Dots
A quantum kinetic theory is used to compute excitation induced dephasing in
semiconductor quantum dots due to the Coulomb interaction with a continuum of
states, such as a quantum well or a wetting layer. It is shown that a frequency
dependent broadening together with nonlinear resonance shifts are needed for a
microscopic explanation of the excitation induced dephasing in such a system,
and that excitation induced dephasing for a quantum-dot excitonic resonance is
different from quantum-well and bulk excitons.Comment: 6 pages, 4 figures. Extensively revised text, two figures change
On Color Superconductivity in External Magnetic Field
We study color superconductivity in external magnetic field. We discuss the
reason why the mixing angles in color-flavor locked (CFL) and two-flavor
superconductivity (2SC) phases are different despite the fact that the CFL gap
goes to the 2SC gap for . Although flavor symmetry is
explicitly broken in external magnetic field, we show that all values of gaps
in their coset spaces of possible solutions in the CFL phase are equivalent in
external magnetic field.Comment: 12 pages, LaTe
On bare masses in time-symmetric initial-value solutions for two black holes
The Brill-Lindquist time-symmetric initial-value solution for two uncharged
black holes is rederived using the Hamiltonian constraint equation with Dirac
delta distributions as a source for the binary black-hole field. The bare
masses of the Brill-Lindquist black holes are introduced in a way which is
applied, after straightforward modification, to the Misner-Linquist binary
black-hole solution.Comment: LaTeX, 4 page
QCD at Finite Density and Color Superconductivity
Brief review of current status of the field.Comment: Invited talk at Lattice 99, Pisa, July 1999. 5 pages, 7 fig
Femtosecond Coherent Control of Spin with Light in (Ga,Mn)As ferromagnets
Using density matrix equations of motion, we predict a femtosecond collective
spin tilt triggered by nonlinear, near--ultraviolet (3eV), coherent
photoexcitation of (Ga,Mn)As ferromagnetic semiconductors with linearly
polarized light. This dynamics results from carrier coherences and nonthermal
populations excited in the \{111\} equivalent directions of the Brillouin zone
and triggers a subsequent uniform precession. We predict nonthermal
magnetization control by tuning the laser frequency and polarization direction.
Our mechanism explains recent ultrafast pump--probe experiments.Comment: 4 pages, 3 figures, published in Physical Review Letter
Debye screening and Meissner effect in a three-flavor color superconductor
I compute the gluon self-energy in a color superconductor with three flavors
of massless quarks, where condensation of Cooper pairs breaks the color and
flavor SU(3)_c x U(3)_V x U(3)_A symmetry of QCD to the diagonal subgroup
SU(3)_{c+V}. At zero temperature, all eight electric gluons obtain a Debye
screening mass, and all eight magnetic gluons a Meissner mass. The Debye as
well as the Meissner masses are found to be equal for the different gluon
colors. These masses determine the coefficients of the kinetic terms in the
effective theory for the low-energy degrees of freedom. Their values agree with
those obtained by Son and Stephanov.Comment: 10 pages, 1 figure (eps
- …