2,687 research outputs found
Towards Microscopic Understanding of the Phonon Bottleneck
The problem of the phonon bottleneck in the relaxation of two-level systems
(spins) to a narrow group of resonant phonons via emission-absorption processes
is investigated from the first principles. It is shown that the kinetic
approach based on the Pauli master equation is invalid because of the narrow
distribution of the phonons exchanging their energy with the spins. This
results in a long-memory effect that can be best taken into account by
introducing an additional dynamical variable corresponding to the nondiagonal
matrix elements responsible for spin-phonon correlation. The resulting system
of dynamical equations describes the phonon-bottleneck plateau in the spin
excitation, as well as a gap in the spin-phonon spectrum for any finite
concentration of spins. On the other hand, it does not accurately render the
lineshape of emitted phonons and still needs improving.Comment: 13 Phys. Rev. pages, 5 figure captions (7 figures
On Simulating Liouvillian Flow From Quantum Mechanics Via Wigner Functions
The interconnection between quantum mechanics and probabilistic classical
mechanics for a free relativistic particle is derived in terms of Wigner
functions (WF) for both Dirac and Klein-Gordon (K-G) equations. Construction of
WF is achieved by first defining a bilocal 4-current and then taking its
Fourier transform w.r.t. the relative 4-coordinate. The K-G and Proca cases
also lend themselves to a closely parallel treatment provided the Kemmer-
Duffin beta-matrix formalism is employed for the former. Calculation of WF is
carried out in a Lorentz-covariant fashion by standard `trace' techniques. The
results are compared with a recent derivation due to Bosanac.Comment: 9 pages, Latex; email: [email protected]
Vacuum polarization induced by a uniformly accelerated charge
We consider a point charge fixed in the Rindler coordinates which describe a
uniformly accelerated frame. We determine an integral expression of the induced
charge density due to the vacuum polarization at the first order in the fine
structure constant. In the case where the acceleration is weak, we give
explicitly the induced electrostatic potential.Comment: 13 pages, latex, no figures, to appear in Int. J. Theor. Phys
Lukewarm black holes in quadratic gravity
Perturbative solutions to the fourth-order gravity describing
spherically-symmetric, static and electrically charged black hole in an
asymptotically de Sitter universe is constructed and discussed. Special
emphasis is put on the lukewarm configurations, in which the temperature of the
event horizon equals the temperature of the cosmological horizon
Classical and quantum scattering by a Coulomb potential
For relativistic energies the small angle classical cross section for
scattering on a Coulomb potential agrees with the first Born approximation for
quantum cross section for scalar particle only in the leading term. The
disagreement in other terms can be avoided if the sum of all corrections to the
first Born approximation for large enough Coulomb charge contain the classical
terms which are independent of that charge. A small part of the difference in
classical and quantum cross sections may be attributed to the fact that the
relativistic quantum particle can rush through the field without interaction.
We expect that smaller impact parameters and spin facilitate this affect.Comment: 5pages, no figure
Density perturbations in general modified gravitational theories
We derive the equations of linear cosmological perturbations for the general
Lagrangian density , where is a Ricci scalar,
is a scalar field, and is a field kinetic energy. We
take into account a nonlinear self-interaction term recently studied in
the context of "Galileon" cosmology, which keeps the field equations at second
order. Taking into account a scalar-field mass explicitly, the equations of
matter density perturbations and gravitational potentials are obtained under a
quasi-static approximation on sub-horizon scales. We also derive conditions for
the avoidance of ghosts and Laplacian instabilities associated with propagation
speeds. Our analysis includes most of modified gravity models of dark energy
proposed in literature and thus it is convenient to test the viability of such
models from both theoretical and observational points of view.Comment: 17 pages, no figure
Strong Orientation Effects in Ionization of H by Short, Intense, High-Frequency Light Sources
We present three dimensional time-dependent calculations of ionization of
arbitrarily spatially oriented H by attosecond, intense, high-frequency
laser fields. The ionization probability shows a strong dependence on both the
internuclear distance and the relative orientation between the laser field and
the internuclear axis.Comment: 4 pages, 4 figure
The Post-Newtonian Limit of f(R)-gravity in the Harmonic Gauge
A general analytic procedure is developed for the post-Newtonian limit of
-gravity with metric approach in the Jordan frame by using the harmonic
gauge condition. In a pure perturbative framework and by using the Green
function method a general scheme of solutions up to order is shown.
Considering the Taylor expansion of a generic function it is possible to
parameterize the solutions by derivatives of . At Newtonian order,
, all more important topics about the Gauss and Birkhoff theorem are
discussed. The corrections to "standard" gravitational potential
(-component of metric tensor) generated by an extended uniform mass
ball-like source are calculated up to order. The corrections, Yukawa
and oscillating-like, are found inside and outside the mass distribution. At
last when the limit is considered the -gravity converges
in General Relativity at level of Lagrangian, field equations and their
solutions.Comment: 16 pages, 10 figure
A Test of CPT Symmetry in K^0 vs \bar{K}^0 to \pi^+\pi^-\pi^0 Decays
I show that the CP-violating asymmetry in K^0 vs \bar{K}^0 \to
\pi^+\pi^-\pi^0 decays differs from that in K_L \to \pi^+\pi^-, K_L \to
\pi^0\pi^0 or the semileptonic K_L transitions, if there exists CPT violation
in K^0-\bar{K}^0 mixing. A delicate measurement of this difference at a super
flavor factory (e.g., the \phi factory) will provide us with a robust test of
CPT symmetry in the neutral kaon system.Comment: 4 pages, 1 figure. To appear in the Proceedings of the International
PHIPSI09 Workshop, October 2009, Beijing, Chin
Double-valuedness of the electron wave function and rotational zero-point motion of electrons in rings
I propose that the phase of an electron's wave function changes by when
the electron goes around a loop maintaining phase coherence. Equivalently, that
the minimum orbital angular momentum of an electron in a ring is
rather than zero as generally assumed, hence that the electron in a ring has
azimuthal zero point motion. This proposal provides a physical explanation for
the origin of electronic `quantum pressure', it implies that a spin current
exists in the ground state of aromatic ring molecules, and it suggests an
explanation for the ubiquitousness of persistent currents observed in
mesoscopic rings
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