2,373 research outputs found
Small eigenvalues of the SU(3) Dirac operator on the lattice and in Random Matrix Theory
We have calculated complete spectra of the staggered Dirac operator on the
lattice in quenched SU(3) gauge theory for \beta = 5.4 and various lattice
sizes. The microscopic spectral density, the distribution of the smallest
eigenvalue, and the two-point spectral correlation function are analyzed. We
find the expected agreement of the lattice data with universal predictions of
the chiral unitary ensemble of random matrix theory up to a certain energy
scale, the Thouless energy. The deviations from the universal predictions are
determined using the disconnected scalar susceptibility. We find that the
Thouless energy scales with the lattice size as expected from theoretical
arguments making use of the Gell-Mann--Oakes--Renner relation.Comment: REVTeX, 5 pages, 4 figure
Spectrum of the SU(3) Dirac operator on the lattice: Transition from random matrix theory to chiral perturbation theory
We calculate complete spectra of the Kogut-Susskind Dirac operator on the
lattice in quenched SU(3) gauge theory for various values of coupling constant
and lattice size. From these spectra we compute the connected and disconnected
scalar susceptibilities and find agreement with chiral random matrix theory up
to a certain energy scale, the Thouless energy. The dependence of this scale on
the lattice volume is analyzed. In the case of the connected susceptibility
this dependence is anomalous, and we explain the reason for this. We present a
model of chiral perturbation theory that is capable of describing the data
beyond the Thouless energy and that has a common range of applicability with
chiral random matrix theory.Comment: 8 pages, RevTeX, 15 .eps figure
Electron energy loss and induced photon emission in photonic crystals
The interaction of a fast electron with a photonic crystal is investigated by
solving the Maxwell equations exactly for the external field provided by the
electron in the presence of the crystal. The energy loss is obtained from the
retarding force exerted on the electron by the induced electric field. The
features of the energy loss spectra are shown to be related to the photonic
band structure of the crystal. Two different regimes are discussed: for small
lattice constants relative to the wavelength of the associated electron
excitations , an effective medium theory can be used to describe the
material; however, for the photonic band structure plays an
important role. Special attention is paid to the frequency gap regions in the
latter case.Comment: 12 pages, 7 figure
Variations in water use by a mature mangrove of Avicennia germinans, French Guiana
In the tropical intertidal zones, little is known on water uptake by mangroves. Transpiration rates are generally measured at leaf level, but few studies exist on water use at tree or stand levels. The objective of this study was to measure sap flow in trees of different sizes to appreciate the range of variation in water use that may exist in a site dominated by 80% mature Avicennia germinans. The results showed that from the dry to the wet season the mean water use increased from 3.2 to 5.3 dm3 d−1 in small trees (DBH ∼ 13 cm), from 11.5 to 30.8 dm3 d−1 in medium trees (∼24 cm) and from 40.8 to 64.1 dm3 d−1 in large ones (∼45 cm). Sapwood remained active up to a depth of 8 cm with radial variations within the stem. Weak correlations were obtained with VPD and net radiation. This study confirmed that transpiration was larger under low levels of salinity. Water use at stand level (∼1900 living stems ha−1) was estimated to be in the range of 5.8 to 11.8 m3 ha−1 d−1 according to the season
Anomalous Effects of "Guest" Charges Immersed in Electrolyte: Exact 2D Results
We study physical situations when one or two "guest" arbitrarily-charged
particles are immersed in the bulk of a classical electrolyte modelled by a
Coulomb gas of positive/negative unit point-like charges, the whole system
being in thermal equilibrium. The models are treated as two-dimensional with
logarithmic pairwise interactions among charged constituents; the
(dimensionless) inverse temperature is considered to be smaller than 2
in order to ensure the stability of the electrolyte against the collapse of
positive-negative pairs of charges. Based on recent progress in the integrable
(1+1)-dimensional sine-Gordon theory, exact formulas are derived for the
chemical potential of one guest charge and for the asymptotic large-distance
behavior of the effective interaction between two guest charges. The exact
results imply, under certain circumstances, anomalous effects such as an
effective attraction (repulsion) between like-charged (oppositely-charged)
guest particles and the charge inversion in the electrolyte vicinity of a
highly-charged guest particle. The adequacy of the concept of renormalized
charge is confirmed in the whole stability region of inverse temperatures and
the related saturation phenomenon is revised.Comment: 21 pages, 1 figur
Possible Gauge Theoretic Origin for Quark-Lepton Complementarity
Similarity between the weak interaction properties of quarks and leptons has
led to suggestions that the origin of lepton mixing angles may be related to
those of quarks. In this paper, we present a gauge model based on group that leads to a new form for the quark
lepton complementarity which predicts the solar neutrino mixing angle in terms
of the Cabibbo angle for the case of inverted mass hierarchy for neutrinos. We
also indicate how these ideas can be implemented in an inspired
trinification model, which is more
closely allied to string theory by the AdS/CFT correspondence.Comment: 9 pages, latex, no figures; presentation improved; results unchanged;
minor typos correcte
Backward diode composed of a metallic and semiconducting nanotube
The conditions necessary for a nanotube junction connecting a metallic and
semiconducting nanotube to rectify the current are theoretically investigated.
A tight binding model is used for the analysis, which includes the Hartree-Fock
approximation and the Green's function method.
It is found that the junction has a behavior similar to the backward diode if
the gate electrode is located nearby and the Fermi level of the semiconducting
tube is near the gap.
Such a junction would be advantageous since the required length for the
rectification could be reduced.Comment: 4 pages, RevTeX, uses epsf.st
Probing neutrino properties with charged scalar lepton decays
Supersymmetry with bilinear R-parity violation provides a predictive
framework for neutrino masses and mixings in agreement with current neutrino
oscillation data. The model leads to striking signals at future colliders
through the R-parity violating decays of the lightest supersymmetric particle.
Here we study charged scalar lepton decays and demonstrate that if the scalar
tau is the LSP (i) it will decay within the detector, despite the smallness of
the neutrino masses, (ii) the relative ratio of branching ratios Br({tilde
tau}_1 --> e sum nu_i)/ Br({tilde tau}_1 --> mu sum nu_i) is predicted from the
measured solar neutrino angle, and (iii) scalar muon and scalar electron decays
will allow to test the consistency of the model. Thus, bilinear R-parity
breaking SUSY will be testable at future colliders also in the case where the
LSP is not the neutralino.Comment: 24 pages, 8 ps figs Report-no.: IFIC/02-33 and ZU-TH 11/0
Can inflationary models of cosmic perturbations evade the secondary oscillation test?
We consider the consequences of an observed Cosmic Microwave Background (CMB)
temperature anisotropy spectrum containing no secondary oscillations. While
such a spectrum is generally considered to be a robust signature of active
structure formation, we show that such a spectrum {\em can} be produced by
(very unusual) inflationary models or other passive evolution models. However,
we show that for all these passive models the characteristic oscillations would
show up in other observable spectra. Our work shows that when CMB polarization
and matter power spectra are taken into account secondary oscillations are
indeed a signature of even these very exotic passive models. We construct a
measure of the observability of secondary oscillations in a given experiment,
and show that even with foregrounds both the MAP and \pk satellites should be
able to distinguish between models with and without oscillations. Thus we
conclude that inflationary and other passive models can {\em not} evade the
secondary oscillation test.Comment: Final version accepted for publication in PRD. Minor improvements
have been made to the discussion and new data has been included. The
conclusions are unchagne
Gravitino constraints on models of neutrino masses and leptogenesis
In the supersymmetric extensions of the standard model, neutrino masses and
leptogenesis requires existence of new particles. We point out that if these
particles with lepton number violating interactions have standard model gauge
interactions, then they may not be created after reheating because of the
gravitino problem. This will rule out all existing models of neutrino masses
and leptogenesis, except the one with right-handed singlet neutrinos.Comment: 12 pages latex file with one postscript figur
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