32,477 research outputs found
The Singularity in Generic Gravitational Collapse Is Spacelike, Local, and Oscillatory
A longstanding conjecture by Belinskii, Khalatnikov, and Lifshitz that the
singularity in generic gravitational collapse is spacelike, local, and
oscillatory is explored analytically and numerically in spatially inhomogeneous
cosmological spacetimes. With a convenient choice of variables, it can be seen
analytically how nonlinear terms in Einstein's equations control the approach
to the singularity and cause oscillatory behavior. The analytic picture
requires the drastic assumption that each spatial point evolves toward the
singularity as an independent spatially homogeneous universe. In every case,
detailed numerical simulations of the full Einstein evolution equations support
this assumption.Comment: 7 pages includes 4 figures. Uses Revtex and psfig. Received
"honorable mention" in 1998 Gravity Research Foundation essay contest.
Submitted to Mod. Phys. Lett.
Evidence for an oscillatory singularity in generic U(1) symmetric cosmologies on
A longstanding conjecture by Belinskii, Lifshitz, and Khalatnikov that the
singularity in generic gravitational collapse is locally oscillatory is tested
numerically in vacuum, U(1) symmetric cosmological spacetimes on . If the velocity term dominated (VTD) solution to Einstein's equations is
substituted into the Hamiltonian for the full Einstein evolution equations, one
term is found to grow exponentially. This generates a prediction that
oscillatory behavior involving this term and another (which the VTD solution
causes to decay exponentially) should be observed in the approach to the
singularity. Numerical simulations strongly support this prediction.Comment: 15 pages, Revtex, includes 12 figures, psfig. High resolution
versions of figures 7, 8, 9, and 11 may be obtained from anonymous ftp to
ftp://vela.acs.oakland.edu/pub/berger/u1genfig
Exclusive electroproduction of lepton pairs as a probe of nucleon structure
We suggest the measurement of exclusive electroproduction of lepton pairs as
a tool to study inter-parton correlations in the nucleon via generalized parton
distributions in the kinematical region where this process is light-cone
dominated. We demonstrate how the single beam-spin asymmetry allows to perform
such kind of analysis and give a number of predictions for several experimental
setups. We comment on other observables which allow for a clean separation of
different species of generalized parton distributions.Comment: 4 pages RevTeX4, 6 figures, typo fixe
Hunting Local Mixmaster Dynamics in Spatially Inhomogeneous Cosmologies
Heuristic arguments and numerical simulations support the Belinskii et al
(BKL) claim that the approach to the singularity in generic gravitational
collapse is characterized by local Mixmaster dynamics (LMD). Here, one way to
identify LMD in collapsing spatially inhomogeneous cosmologies is explored. By
writing the metric of one spacetime in the standard variables of another,
signatures for LMD may be found. Such signatures for the dynamics of spatially
homogeneous Mixmaster models in the variables of U(1)-symmetric cosmologies are
reviewed. Similar constructions for U(1)-symmetric spacetimes in terms of the
dynamics of generic -symmetric spacetime are presented.Comment: 17 pages, 5 figures. Contribution to CQG Special Issue "A Spacetime
Safari: Essays in Honour of Vincent Moncrief
Dynamical electroweak symmetry breaking with superheavy quarks and 2+1 composite Higgs model
Recently, a new class of models describing the quark mass hierarchy has been
introduced. In this class, while the t quark plays a minor role in electroweak
symmetry breaking (EWSB), it is crucial in providing the quark mass hierarchy.
In this paper, we analyze the dynamics of a particular model in this class, in
which the b' and t' quarks of the fourth family are mostly responsible for
dynamical EWSB. The low energy effective theory in this model is derived. It
has a clear signature, a 2 + 1 structure of composite Higgs doublets: two
nearly degenerate \Phi_{b'} and \Phi_{t'}, and a heavier top-Higgs resonance
\Phi_t \sim \bar{t}_{R}(t,b)_L. The properties of these composites are
described in detail, and it is shown that the model satisfies the electroweak
precision data constraints. The signatures of these composites at the Large
Hadron Collider are briefly discussed.Comment: 17 pages, 3 figures; v.2: references and clarifications added: PRD
versio
A Modified Version of the Waxman Algorithm
The iterative algorithm recently proposed by Waxman for solving eigenvalue
problems, which relies on the method of moments, has been modified to improve
its convergence considerably without sacrificing its benefits or elegance. The
suggested modification is based on methods to calculate low-lying eigenpairs of
large bounded hermitian operators or matrices
Quantum transport in weakly coupled superlattices at low temperature
We report on the study of the electrical current flowing in weakly coupled
superlattice (SL) structures under an applied electric field at very low
temperature, i.e. in the tunneling regime. This low temperature transport is
characterized by an extremely low tunneling probability between adjacent wells.
Experimentally, I(V) curves at low temperature display a striking feature, i.e
a plateau or null differential conductance. A theoretical model based on the
evaluation of scattering rates is developed in order to understand this
behaviour, exploring the different scattering mechanisms in AlGaAs alloys. The
dominant interaction in usual experimental conditions such as ours is found to
be the electron-ionized donors scattering. The existence of the plateau in the
I(V) characteristics is physically explained by a competition between the
electric field localization of the Wannier-Stark electron states in the weakly
coupled quantum wells and the electric field assisted tunneling between
adjacent wells. The influence of the doping concentration and profile as well
as the presence of impurities inside the barrier are discussed
Anomalously enhanced photoemission from the Dirac point and symmetry of the self-energy variations for the surface states in Bi2Se3
Accurate analysis of the photoemission intensity from the surface states of
Bi2Se3 reveals two unusual features: spectral line asymmetry and anomalously
enhanced photoemission from the Dirac point. The former indicates a certain
symmetry of a scattering process, which results in strongly k\omega-dependent
contribution to the imaginary part of the self-energy that changes sign while
crossing both the dispersion curves and the energy of the Dirac point. The
latter is hard to describe by one particle spectral function while a final
state interference seems to be plausible explanation
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