7,808 research outputs found
Hadron Polarizabilities and Form Factors
This is the summary of the working group on Hadron Polarizabilities and Form
Factors of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997.Comment: 21 pages LaTeX2e, uses epsf, 9 fig
Nature of singularities in gravitational collapse
We discuss several aspects of cosmic censorship hypothesis. There is evidence
both in favor and against the hypothesis. On one hand one can prove that cosmic
censorship holds in several special cases and on the other hand there is a
number of special solutions of Einstein equations in which it is violated. One
way to resolve cosmic censorship problem is to test it observationally. We
point out to several possibilities of such tests using present and future
instruments.Comment: 11 pages, PTPTeX, references added, typos corrected, submitted to
Proceedings of the Yukawa-Kyoto International Seminar 9
QCD and the Structure of the Nucleon in Electron Scattering
The internal structure of the nucleon is discussed within the context of QCD.
Recent progress in understanding the distribution of flavor and spin in the
nucleon is reviewed, and prospects for extending our knowledge of nucleon
structure in electron scattering experiments at modern facilities such as
Jefferson Lab are outlined.Comment: 52 pages, 11 figures, lectures presented at the 1999 Hampton
University Graduate Studies (HUGS) summer school, Jefferson La
Nucleon Structure and Parity-Violating Electron Scattering
We review the area of strange quark contributions to nucleon structure. In
particular, we focus on current models of strange quark vector currents in the
nucleon and the associated parity-violating elastic electron scattering
experiments from which vector- and axial-vector currents are extractedComment: 40 pages including 7 figures; review article to be published in Int.
J. Mod. Phys.
Summary of the Heavy Flavor Working Group
During the last year many important results have been achieved in heavy
flavour physics: New measurements of charm and beauty production have been
performed at HERA and the Tevatron. A wealth of new spectroscopy data with
several new, unexpected states in the charmonium and the D_s systems has been
collected and b to d gamma transitions have been established. The oscillation
frequency in the B_s Bbar_s is now measured, and mixing in the D0 D0bar system
has been observed. Theoretical progress in the areas of open heavy flavour
production, quarkonium production and decays, and multiquark spectroscopy has
been presented at this workshop.Comment: 17 pages, 3 figures, to appear in the Proceedings of the XV
International Workshop on Deep-Inelastic Scattering and Related Subjectes,
DIS 2007, April 16--20, 2007, Munich, German
Condensation of Excitons in Cu2O at Ultracold Temperatures: Experiment and Theory
We present experiments on the luminescence of excitons confined in a
potential trap at milli-Kelvin bath temperatures under cw-excitation. They
reveal several distinct features like a kink in the dependence of the total
integrated luminescence intensity on excitation laser power and a bimodal
distribution of the spatially resolved luminescence. Furthermore, we discuss
the present state of the theoretical description of Bose-Einstein condensation
of excitons with respect to signatures of a condensate in the luminescence. The
comparison of the experimental data with theoretical results with respect to
the spatially resolved as well as the integrated luminescence intensity shows
the necessity of taking into account a Bose-Einstein condensed excitonic phase
in order to understand the behaviour of the trapped excitons.Comment: 41 pages, 23 figure
The Standard Model of Particle Physics
Particle physics has evolved a coherent model that characterizes forces and
particles at the most elementary level. This Standard Model, built from many
theoretical and experimental studies, is in excellent accord with almost all
current data. However, there are many hints that it is but an approximation to
a yet more fundamental theory. We trace the development of the Standard Model
and indicate the reasons for believing that it is incomplete.Comment: 25 pages, 17 figures; accepted for publication in Rev. Mod. Physics
(APS centenary issue
Universal spatial correlations in the anisotropic Kondo screening cloud: analytical insights and numerically exact results from a coherent state expansion
We analyze the spatial correlations in the spin density of an electron gas in
the vicinity of a Kondo impurity. Our analysis extends to the spin-anisotropic
regime, which was not investigated in the literature. We use an original and
numerically exact method, based on a systematic coherent-state expansion of the
ground state of the underlying spin-boson Hamiltonian, which we apply to the
computation of observables that are specific to the fermionic Kondo model. We
also present an important technical improvement to the method, that obviates
the need to discretize modes of the Fermi sea, and allows one to tackle the
problem in the thermodynamic limit. One can thus obtain excellent spatial
resolution over arbitrary length scales, for a relatively low computational
cost, a feature that gives the method an advantage over popular techniques such
as NRG and DMRG. We find that the anisotropic Kondo model shows rich universal
scaling behavior in the spatial structure of the entanglement cloud. First,
SU(2) spin-symmetry is dynamically restored in a finite domain in parameter
space in vicinity of the isotropic line, as expected from poor man's scaling.
We are also able to obtain in closed analytical form a set of different, yet
universal, scaling curves for strong exchange asymmetry, which are parametrized
by the longitudinal exchange coupling. Deep inside the cloud, i.e. for
distances smaller than the Kondo length, the correlation between the electron
spin density and the impurity spin oscillates between ferromagnetic and
antiferromagnetic values at the scale of the Fermi wavelength, an effect that
is drastically enhanced at strongly anisotropic couplings. Our results also
provide further numerical checks and alternative analytical approximations for
the recently computed Kondo overlaps [PRL 114, 080601 (2015)].Comment: 27 pages + 2 pages of Supplementary materials. The manuscript was
largely extended in V2, and contains now a comparison to the Toulouse limit,
and well as a detailed study of the restoration of SU(2) symmetry. The
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