697 research outputs found
Path Integral Bosonization of Massive GNO Fermions
We show the quantum equivalence between certain symmetric space sine-Gordon
models and the massive free fermions. In the massless limit, these fermions
reduce to the free fermions introduced by Goddard, Nahm and Olive (GNO) in
association with symmetric spaces . A path integral formulation is given
in terms of the Wess-Zumino-Witten action where the field variable takes
value in the orthogonal, unitary, and symplectic representations of the group
in the basis of the symmetric space. We show that, for example, such a path
integral bosonization is possible when the symmetric spaces are or . We also address the
relation between massive GNO fermions and the nonabelian solitons, and explain
the restriction imposed on the fermion mass matrix due to the integrability of
the bosonic model.Comment: 11 page
Landau Damping of Spin Waves in Trapped Boltzmann Gases
A semiclassical method is used to study Landau damping of transverse
pseudo-spin waves in harmonically trapped ultracold gases in the collisionless
Boltzmann limit. In this approach, the time evolution of a spin is calculated
numerically as it travels in a classical orbit through a spatially dependent
mean field. This method reproduces the Landau damping results for spin-waves in
unbounded systems obtained with a dielectric formalism. In trapped systems, the
simulations indicate that Landau damping occurs for a given spin-wave mode
because of resonant phase space trajectories in which spins are "kicked out" of
the mode (in spin space). A perturbative analysis of the resonant and nearly
resonant trajectories gives the Landau damping rate, which is calculated for
the dipole and quadrupole modes as a function of the interaction strength. The
results are compared to a numerical solution of the kinetic equation by Nikuni
et al.Comment: 6 pages, 2 figure
Bioseedling: a chain approach to the production of healthier seeds and seedlings of Lamb’s lettuce Valerianella locusta
The project BIOSEEDLING “Robust planting material from seeds to young plants - an implementation oriented chain approach” aims to find improved production procedures for vegetable seedlings of lamb’s lettuce. First, the production of lamb’s lettuce seeds of a professional seed producer was analyzed and the effect of harvest time and seed size on the germination and disease rate in the seeds was studied.
Then, using seeds naturally infected by Peronospora valerianellae and Acidovorax valerianellae, several seed disinfection methods were compared: aerated steam, hot water, sodium hypochlorite, ethanol, Calcium hydroxide, and compost pellet. After testing methods for the identification of the seed pathogens and the quantification of the infection, an assessment on how the different treatments reduce the pathogens and whether they alter the seeds germination capacity was made. In a third step, substrates suppressive of the soil borne pathogens Rhizoctonia solanii and Pythium ultimum were developed and several plant protection agents were tested against Peronospora valerianellae. Furthermore, the effect of night interruption on the sporulation of lamb’s lettuce downy mildew (Peronospora valerianellae) using periods of lighting in the red and blue regions was tested. The aim is to combine the best methods resulting from all the experiments cited above in a future experiment and compare them to the standard methods in an on-farm experiment
Asymptotics for the Fredholm Determinant of the Sine Kernel on a Union of Intervals
In the bulk scaling limit of the Gaussian Unitary Ensemble of Hermitian
matrices the probability that an interval of length contains no eigenvalues
is the Fredholm determinant of the sine kernel over
this interval. A formal asymptotic expansion for the determinant as tends
to infinity was obtained by Dyson. In this paper we replace a single interval
of length by where is a union of intervals and present a proof
of the asymptotics up to second order. The logarithmic derivative with respect
to of the determinant equals a constant (expressible in terms of
hyperelliptic integrals) times , plus a bounded oscillatory function of
(zero of , periodic if , and in general expressible in terms of the
solution of a Jacobi inversion problem), plus . Also determined are the
asymptotics of the trace of the resolvent operator, which is the ratio in the
same model of the probability that the set contains exactly one eigenvalue to
the probability that it contains none. The proofs use ideas from orthogonal
polynomial theory.Comment: 24 page
Carbon antisite clusters in SiC: a possible pathway to the D_{II} center
The photoluminescence center D_{II} is a persistent intrinsic defect which is
common in all SiC polytypes. Its fingerprints are the characteristic phonon
replicas in luminescence spectra. We perform ab-initio calculations of
vibrational spectra for various defect complexes and find that carbon antisite
clusters exhibit vibrational modes in the frequency range of the D_{II}
spectrum. The clusters possess very high binding energies which guarantee their
thermal stability--a known feature of the D_{II} center. The di-carbon antisite
(C_{2})_{Si} (two carbon atoms sharing a silicon site) is an important building
block of these clusters.Comment: RevTeX 4, 6 pages, 3 figures Changes in version 2: Section headings,
footnote included in text, vibrational data now given for neutral
split-interstitial, extended discussion of the [(C_2)_Si]_2 defect incl.
figure Changes version 3: Correction of binding energy for 3rd and 4th carbon
atom at antisite; correction of typo
Indices for Superconformal Field Theories in 3,5 and 6 Dimensions
We present a trace formula for a Witten type Index for superconformal field
theories in d=3,5 and 6 dimensions, generalizing a similar recent construction
in d=4. We perform a detailed study of the decomposition of long
representations into sums of short representations at the unitarity bound to
demonstrate that our trace formula yields the most general index (i.e. quantity
that is guaranteed to be protected by superconformal symmetry alone) for the
corresponding superalgebras. Using the dual gravitational description, we
compute our index for the theory on the world volume of N M2 and M5 branes in
the large N limit. We also compute our index for recently constructed Chern
Simons theories in three dimensions in the large N limit, and find that, in
certain cases, this index undergoes a large N phase transition as a function of
chemical potentials.Comment: a small typo corrected, 46 page
Experimental Proposal for Achieving Superadditive Communication Capacities with a Binary Quantum Alphabet
We demonstrate superadditivity in the communication capacity of a binary
alphabet consisting of two nonorthogonal quantum states. For this scheme,
collective decoding is performed two transmissions at a time. This improves
upon the previous schemes of Sasaki et al. [Phys. Rev. A 58, 146 (1998)] where
superadditivity was not achieved until a decoding of three or more
transmissions at a time. This places superadditivity within the regime of a
near-term laboratory demonstration. We propose an experimental test based upon
an alphabet of low photon-number coherent states where the signal decoding is
done with atomic state measurements on a single atom in a high-finesse optical
cavity.Comment: 7 pages, 5 figure
Castaing Instability and Precessing Domains in Confined Alkali Gases
We explore analogy between two-component quantum alkali gases and
spin-polarized helium systems. Recent experiments in trapped gases are put into
the frame of the existing theory for Castaing instability in transverse channel
and formation of homogeneous precessing domains in spin-polarized systems.
Analogous effects have already been observed in spin-polarized and
mixtures systems. The threshold effect of the confining
potential on the instability is analyzed. New experimental possibilities for
observation of transverse instability in a trap are discussed.Comment: 6 RevTex pages, no figure
Magnetic Properties of Scalar Particles --The Scalar Aharonov-Casher Effect and Supersymmetry
The original topological Aharonov-Casher (AC) effect is due to the
interaction of the anomalous magnetic dipole moment (MDM) with certain
configurations of electric field. Naively one would not expect an AC effect for
a scalar particle for which no anomalous MDM can be defined in the usual sense.
In this letter we study the AC effect in supersymmetric systems. In this
framework there is the possibility of deducing the AC effect of a scalar
particle from the corresponding effect for a spinor particle. In 3+1 dimensions
such a connection is not possible because the anomalous MDM is zero if
supersymmetry is an exact symmetry. However, in 2+1 dimensions it is possible
to have an anomalous MDM even with exact supersymmetry.
Having demonstrated the relationship between the spinor and the scalar MDM,
we proceed to show that the scalar AC effect is uniquely defined. We then
compute the anomalous MDM at the one loop level, showing how the scalar form
arises in 2+1 dimensions from the coupling of the scalar to spinors. This model
shows how an AC effect for a scalar can be generated for non-supersymmetric
theories, and we construct such a model to illustrate the mechanism.Comment: RevTex 13 pages including one Figure. New Discussions adde
Topics in Chiral Perturbation Theory
I consider some selected topics in chiral perturbation theory (CHPT). For the
meson sector, emphasis is put on processes involving pions in the isospin zero
S-wave which require multi-loop calculations. The advantages and shortcomings
of heavy baryon CHPT are discussed. Some recent results on the structure of the
baryons are also presented.Comment: 30 pp, TeX, Review talk, Third Workshop on High Energy Particle
Physics (WHEPP III), Madras, India, January 1994. 7 figures available upon
request. CRN--94/0
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