1,396 research outputs found
Dynamical q-deformation in quantum theory and the stochastic limit
A model of particle interacting with quantum field is considered. The model
includes as particular cases the polaron model and non-relativistic quantum
electrodynamics. We show that the field operators obey q-commutation relations
with q depending on time. After the stochastic (or van Hove) limit, due to the
nonlinearity, the atomic and field degrees of freedom become entangled in the
sense that the field and the atomic variables no longer commute but give rise
to a new algebra with new commutation relations replacing the Boson ones. This
new algebra allows to give a simple proof of the fact that the non crossing
half-planar diagrams give the dominating contribution in a weak coupling regime
and to calculate explicitly the correlations associated to the new algebra. The
above results depend crucially on the fact that we do not introduce any dipole
or multipole approximation.Comment: Latex, 11 page
Dual variables for the SU(2) lattice gauge theory at finite temperature
We study the three-dimensional SU(2) lattice gauge theory at finite
temperature using an observable which is dual to the Wilson line. This
observable displays a behaviour which is the reverse of that seen for the
Wilson line. It is non-zero in the confined phase and becomes zero in the
deconfined phase. At large distances, it's correlation function falls off
exponentially in the deconfined phase and remains non-zero in the confined
phase. The dual variable is non-local and has a string attached to it which
creates a Z(2) interface in the system. It's correlation function measures the
string tension between oppositely oriented Z(2) domains. The construction of
this variable can also be made in the four-dimensional theory where it measures
the surface tension between oppositely oriented Z(2) domains.Comment: 13 pages, LaTeX, 4 figures are included in the latex fil
Anomalies without Massless Particles
Baryon and lepton number in the standard model are violated by anomalies,
even though the fermions are massive. This problem is studied in the context of
a two dimensional model. In a uniform background field, fermion production
arise from non-adiabatic behavior that compensates for the absence of massless
modes. On the other hand, for localized instanton-like configurations, there is
an adiabatic limit. In this case, the anomaly is produced by bound states which
travel across the mass gap. The sphaleron corresponds to a bound state at the
halfway point.Comment: (26 pages, 3 figures, uses harvmac and uufiles), UCSD/PTH 93-3
Renormalization of the Hamiltonian and a geometric interpretation of asymptotic freedom
Using a novel approach to renormalization in the Hamiltonian formalism, we
study the connection between asymptotic freedom and the renormalization group
flow of the configuration space metric. It is argued that in asymptotically
free theories the effective distance between configuration decreases as high
momentum modes are integrated out.Comment: 22 pages, LaTeX, no figures; final version accepted in Phys.Rev.D;
added reference and appendix with comment on solution of eq. (9) in the tex
2D Conformal Field Theories and Holography
It is known that the chiral part of any 2d conformal field theory defines a
3d topological quantum field theory: quantum states of this TQFT are the CFT
conformal blocks. The main aim of this paper is to show that a similar CFT/TQFT
relation exists also for the full CFT. The 3d topological theory that arises is
a certain ``square'' of the chiral TQFT. Such topological theories were studied
by Turaev and Viro; they are related to 3d gravity. We establish an
operator/state correspondence in which operators in the chiral TQFT correspond
to states in the Turaev-Viro theory. We use this correspondence to interpret
CFT correlation functions as particular quantum states of the Turaev-Viro
theory. We compute the components of these states in the basis in the
Turaev-Viro Hilbert space given by colored 3-valent graphs. The formula we
obtain is a generalization of the Verlinde formula. The later is obtained from
our expression for a zero colored graph. Our results give an interesting
``holographic'' perspective on conformal field theories in 2 dimensions.Comment: 29+1 pages, many figure
The Secret to Successful User Communities: An Analysis of Computer Associates’ User Groups
This paper provides the first large scale study that examines the impact of both individual- and group-specific factors on the benefits users obtain from their user communities. By empirically analysing 924 survey responses from individuals in 161 Computer Associates' user groups, this paper aims to identify the determinants of successful user communities. To measure success, the amount of time individual members save through having access to their user networks is used. As firms can significantly profit from successful user communities, this study proposes four key implications of the empirical results for the management of user communities
Hidden Non-Abelian Gauge Symmetries in Doped Planar Antiferromagnets
We investigate the possibility of hidden non-Abelian Local Phase symmetries
in large-U doped planar Hubbard antiferromagnets, believed to simulate the
physics of two-dimensional (magnetic) superconductors. We present a spin-charge
separation ansatz, appropriate to incorporate holon spin flip, which allows for
such a hidden local gauge symmetry to emerge in the effective action. The group
is of the form , where SU(2) is a local
non-Abelian group associated with the spin degrees of freedom, U_E(1) is that
of ordinary electromagnetism, associated with the electric charge of the holes,
and U_S(1) is a `statistical' Abelian gauge group pertaining to the fractional
statistics of holes on the spatial plane. In a certain regime of the parameters
of the model, namely strong U_S(1) and weak SU(2), there is the possibility of
dynamical formation of a holon condensate. This leads to a dynamical breaking
of . The resulting Abelian effective theory is closely related
to an earlier model proposed as the continuum limit of large-spin planar doped
antiferromagnets, which lead to an unconventional scenario for two-dimensional
parity-invariant superconductivity.Comment: 32 pages LATEX, one figure. (More details given in the passage from
the Hubbard model to the long wavelength lattice gauge theory; one figure
added; no changes in the conclusions.
Patterns of photometric and chromospheric variation among Sun-like stars: A 20-year perspective
We examine patterns of variation of 32 primarily main sequence stars,
extending our previous 7-12 year time series to 13-20 years by combining b, y
data from Lowell Observatory with similar data from Fairborn Observatory.
Parallel chromospheric Ca II H and K emission data from the Mount Wilson
Observatory span the entire interval. The extended data strengthen the
relationship between chromospheric and photometric variation derived
previously. Twenty-seven stars are deemed variable. On a year-to-year timescale
young active stars become fainter when their Ca II emission increases while
older less active stars such as the Sun become brighter when their Ca II
emission increases. The Sun's total irradiance variation, scaled to the b and y
filter photometry, still appears to be somewhat smaller than stars in our
limited sample with similar mean chromospheric activity, but we now regard this
discrepancy as probably due mainly to our limited stellar sampl
Fitoconstituintes isolados da fração em diclorometano das cascas do tronco de Scutia buxifolia Reissek
Fracionamento cromatográfico da fração em diclorometano obtida do extrato etanólico das cascas do tronco de Scutia buxifolia Reissek (Rhamnaceae) conduziu ao isolamento de lupeol, β-sitosterol e estigmasterol. As estruturas foram identificadas através de técnicas espectroscópicas usuais, além da comparação com dados relatados na literatura. Os compostos isolados são relatados pela primeira vez para a espécie S. buxifolia.Fractionation of the dichloromethane soluble fraction from the ethanol extract of the stem bark of Scutia buxifolia Reissek (Rhamnaceae) led to the isolation of lupeol, β-sitosterol and stigmasterol. The structures of the isolates were elucidated by spectroscopic analysis and comparison with literature data. The isolated compounds are reported for the first time to the species S. buxifolia.Colegio de Farmacéuticos de la Provincia de Buenos Aire
Impurity scattering and transport of fractional Quantum Hall edge state
We study the effects of impurity scattering on the low energy edge state
dynamic s for a broad class of quantum Hall fluids at filling factor , for integer and even integer . When is positive all
of the edge modes are expected to move in the same direction, whereas for
negative one mode moves in a direction opposite to the other modes.
Using a chiral-Luttinger model to describe the edge channels, we show that for
an ideal edge when is negative, a non-quantized and non-universal Hall
conductance is predicted. The non-quantized conductance is associated with an
absence of equilibration between the edge channels. To explain the robust
experimental Hall quantization, it is thus necessary to incorporate impurity
scattering into the model, to allow for edge equilibration. A perturbative
analysis reveals that edge impurity scattering is relevant and will modify the
low energy edge dynamics. We describe a non-perturbative solution for the
random channel edge, which reveals the existence of a new
disorder-dominated phase, characterized by a stable zero temperature
renormalization group fixed point. The phase consists of a single propagating
charge mode, which gives a quantized Hall conductance, and neutral modes.
The neutral modes all propagate at the same speed, and manifest an exact SU(n)
symmetry. At finite temperatures the SU(n) symmetry is broken and the neutral
modes decay with a finite rate which varies as at low temperatures.
Various experimental predictions and implications which follow from the exact
solution are described in detail, focusing on tunneling experiments through
point contacts.Comment: 19 pages (two column), 5 post script figures appended, 3.0 REVTE
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