12,517 research outputs found
Berry phases for composite fermions: effective magnetic field and fractional statistics
The quantum Hall superfluid is presently the only viable candidate for a
realization of quasiparticles with fractional Berry phase statistics. For a
simple vortex excitation, relevant for a subset of fractional Hall states
considered by Laughlin, non-trivial Berry phase statistics were demonstrated
many years ago by Arovas, Schrieffer, and Wilczek. The quasiparticles are in
general more complicated, described accurately in terms of excited composite
fermions. We use the method developed by Kjonsberg, Myrheim and Leinaas to
compute the Berry phase for a single composite-fermion quasiparticle, and find
that it agrees with the effective magnetic field concept for composite
fermions. We then evaluate the "fractional statistics", related to the change
in the Berry phase for a closed loop caused by the insertion of another
composite-fermion quasiparticle in the interior. Our results support the
general validity of fractional statistics in the quantum Hall superfluid, while
also giving a quantitative account of corrections to it when the quasiparticle
wave functions overlap. Many caveats, both practical and conceptual, are
mentioned that will be relevant to an experimental measurement of the
fractional statistics. A short report on some parts of this article has
appeared previously.Comment: 14 pages, 9 figure
Phenomenology of the General NMSSM with Gauge Mediated Supersymmetry Breaking
We investigate various classes of Gauge Mediated Supersymmetry Breaking
models and show that the Next-to-Minimal Supersymmetric Standard Model can
solve the mu-problem in a phenomenologically acceptable way. These models
include scenarios with singlet tadpole terms, which are phenomenologically
viable, e.g., in the presence of a small Yukawa coupling <~ 10^{-5}. Scenarios
with suppressed trilinear A-terms at the messenger scale lead naturally to
light CP-odd scalars, which play the r\^ole of pseudo R-axions. A wide range of
parameters of such models satisfies LEP constraints, with CP-even Higgs scalars
below 114 GeV decaying dominantly into a pair of CP-odd scalars.Comment: 24 pages, 6 figures, typos corrected, reference adde
Multiplicative processes and power laws
[Takayasu et al., Phys. Rev.Lett. 79, 966 (1997)] revisited the question of
stochastic processes with multiplicative noise, which have been studied in
several different contexts over the past decades. We focus on the regime, found
for a generic set of control parameters, in which stochastic processes with
multiplicative noise produce intermittency of a special kind, characterized by
a power law probability density distribution. We briefly explain the physical
mechanism leading to a power law pdf and provide a list of references for these
results dating back from a quarter of century. We explain how the formulation
in terms of the characteristic function developed by Takayasu et al. can be
extended to exponents , which explains the ``reason of the lucky
coincidence''. The multidimensional generalization of (\ref{eq1}) and the
available results are briefly summarized. The discovery of stretched
exponential tails in the presence of the cut-off introduced in \cite{Taka} is
explained theoretically. We end by briefly listing applications.Comment: Extended version (7 pages). Phys. Rev. E (to appear April 1998
Dialogue Concerning Two Views on Quantum Coherence: Factist and Fictionist
A controversy that has arisen many times over in disparate contexts is
whether quantum coherences between eigenstates of certain quantities are fact
or fiction. We present a pedagogical introduction to the debate in the form of
a hypothetical dialogue between proponents from each of the two camps: a
factist and a fictionist. A resolution of the debate can be achieved, we argue,
by recognizing that quantum states do not only contain information about the
intrinsic properties of a system but about its extrinsic properties as well,
that is, about its relation to other systems external to it. Specifically, the
coherent quantum state of the factist is the appropriate description of the
relation of the system to one reference frame, while the incoherent quantum
state of the fictionist is the appropriate description of the relation of the
system to another, uncorrelated, reference frame. The two views, we conclude,
are alternative but equally valid paradigms of description.Comment: 14 pages, Contribution to the Int. J. of Quant. Info. issue dedicated
to the memory of Asher Peres; v2 updated summary and critique of prior
literatur
Fractal Spectrum of a Quasi_periodically Driven Spin System
We numerically perform a spectral analysis of a quasi-periodically driven
spin 1/2 system, the spectrum of which is Singular Continuous. We compute
fractal dimensions of spectral measures and discuss their connections with the
time behaviour of various dynamical quantities, such as the moments of the
distribution of the wave packet. Our data suggest a close similarity between
the information dimension of the spectrum and the exponent ruling the algebraic
growth of the 'entropic width' of wavepackets.Comment: 17 pages, RevTex, 5 figs. available on request from
[email protected]
Science with the Keck Interferometer ASTRA Program
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide
phase referencing and astrometric observations at the Keck Interferometer,
leading to enhanced sensitivity and the ability to monitor orbits at an
accuracy level of 30-100 microarcseconds. Here we discuss recent scientific
results from ASTRA, and describe new scientific programs that will begin in
2010-2011. We begin with results from the "self phase referencing" (SPR) mode
of ASTRA, which uses continuum light to correct atmospheric phase variations
and produce a phase-stabilized channel for spectroscopy. We have observed a
number of protoplanetary disks using SPR and a grism providing a spectral
dispersion of ~2000. In our data we spatially resolve emission from dust as
well as gas. Hydrogen line emission is spectrally resolved, allowing
differential phase measurements across the emission line that constrain the
relative centroids of different velocity components at the 10 microarcsecond
level. In the upcoming year, we will begin dual-field phase referencing (DFPR)
measurements of the Galactic Center and a number of exoplanet systems. These
observations will, in part, serve as precursors to astrometric monitoring of
stellar orbits in the Galactic Center and stellar wobbles of exoplanet host
stars. We describe the design of several scientific investigations capitalizing
on the upcoming phase-referencing and astrometric capabilities of ASTRA.Comment: Published in the proceedings of the SPIE 2010 conference on "Optical
and Infrared Interferometry II
Higgs Mass from D-Terms: a Litmus Test
We explore supersymmetric theories in which the Higgs mass is boosted by the
non-decoupling D-terms of an extended gauge symmetry, defined here to
be a general linear combination of hypercharge, baryon number, and lepton
number. Crucially, the gauge coupling, , is bounded from below to
accommodate the Higgs mass, while the quarks and leptons are required by gauge
invariance to carry non-zero charge under . This induces an irreducible
rate, BR, for relevant to
existing and future resonance searches, and gives rise to higher dimension
operators that are stringently constrained by precision electroweak
measurements. Combined, these bounds define a maximally allowed region in the
space of observables, (BR, ), outside of which is excluded by
naturalness and experimental limits. If natural supersymmetry utilizes
non-decoupling D-terms, then the associated boson can only be observed
within this window, providing a model independent `litmus test' for this broad
class of scenarios at the LHC. Comparing limits, we find that current LHC
results only exclude regions in parameter space which were already disfavored
by precision electroweak data.Comment: 7 pages, 9 figure
Purity-bounded uncertainty relations in multidimensional space -- generalized purity
Uncertainty relations for mixed quantum states (precisely, purity-bounded
position-momentum relations, developed by Bastiaans and then by Man'ko and
Dodonov) are studied in general multi-dimensional case. An expression for
family of mixed states at the lower bound of uncertainty relation is obtained.
It is shown, that in case of entropy-bounded uncertainty relations, lower-bound
state is thermal, and a transition from one-dimensional problem to
multi-dimensional one is trivial. Results of numerical calculation of the
relation lower bound for different types of generalized purity are presented.
Analytical expressions for general purity-bounded relations for highly mixed
states are obtained.Comment: 12 pages, 2 figures. draft version, to appear in J. Phys. A Partially
based on a poster "Multidimensional uncertainty relations for states with
given generalized purity" presented on X Intl. Conf. on Quantum Optics'2004
(Minsk, Belarus, May 30 -- June 3, 2004) More actual report is to be
presented on ICSSUR-2005, Besan\c{c}on, France and on EQEC'05, Munich. V. 5:
amended article after referees' remark
Forecasting global ENSO-related climate anomalies
Long-range global climate forecasts have been made by use of a model for predicting a tropical Pacific sea surface temperature (SST) in tandem with an atmospheric general circulation model. The SST is predicted first at long lead times into the future. These ocean forecasts are then used to force the atmospheric model and so produce climate forecasts at lead times of the SST forecasts. Prediction of the wintertime 500 mb height, surface air temperature and precipitation for seven large climatic events of the 1970 to 1990s by this two-tiered technique agree well in general with observations over many regions of the globe. The levels of agreement are high enough in some regions to have practical utility. -Author
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