233 research outputs found
Shaken, but not stirred - Potts model coupled to quantum gravity
We investigate the critical behaviour of both matter and geometry of the
three-state Potts model coupled to two-dimensional Lorentzian quantum gravity
in the framework of causal dynamical triangulations. Contrary to what general
arguments of the effects of disorder suggest, we find strong numerical evidence
that the critical exponents of the matter are not changed under the influence
of quantum fluctuations in the geometry, compared to their values on fixed,
regular lattices. This lends further support to previous findings that quantum
gravity models based on causal dynamical triangulations are in many ways better
behaved than their Euclidean counterparts.Comment: 19 pages, 9 figure
L^p boundedness of the wave operator for the one dimensional Schroedinger operator
Given a one dimensional perturbed Schroedinger operator H=-(d/dx)^2+V(x) we
consider the associated wave operators W_+, W_- defined as the strong L^2
limits as s-> \pm\infty of the operators e^{isH} e^{-isH_0} We prove that the
wave operators are bounded operators on L^p for all 1<p<\infty, provided
(1+|x|)^2 V(x) is integrable, or else (1+|x|)V(x) is integrable and 0 is not a
resonance. For p=\infty we obtain an estimate in terms of the Hilbert
transform. Some applications to dispersive estimates for equations with
variable rough coefficients are given.Comment: 26 page
List Of Angiosperm Species In An Atlantic Forest Fragment Reveals Collection Gaps In Espírito Santo State, Brazil
This study presents a list of angiosperm species in an Atlantic Forest fragment in the southern portion of Espírito Santo state, Brazil, a region that represents a collection gap within the Atlantic Forest. The studied site is a relatively small fragment of 144 ha located within a conservation unit, the Mata das Flores State Park. The site belongs to a conservation priority area for the Atlantic Forest in Espírito Santo, and is under strong anthropic pressure. Of the 239 species listed here, 21 are new records for the state, eight are endemic, and 20 figure either in the country’s or the state’s Red Lists of endangered species. Rubiaceae and Piperaceae were the families with the highest number of species. We show that small fragments that were never inventoried before can reveal a relatively large number of threatened species and that collection gaps need to be filled in order to refine our understanding about conservation priorities within the Atlantic Forest Biome. © 2016 Check List and Authors.12111
Zero Modes and the Atiyah-Singer Index in Noncommutative Instantons
We study the bosonic and fermionic zero modes in noncommutative instanton
backgrounds based on the ADHM construction. In k instanton background in U(N)
gauge theory, we show how to explicitly construct 4Nk (2Nk) bosonic (fermionic)
zero modes in the adjoint representation and 2k (k) bosonic (fermionic) zero
modes in the fundamental representation from the ADHM construction. The number
of fermionic zero modes is also shown to be exactly equal to the Atiyah-Singer
index of the Dirac operator in the noncommutative instanton background. We
point out that (super)conformal zero modes in non-BPS instantons are affected
by the noncommutativity. The role of Lorentz symmetry breaking by the
noncommutativity is also briefly discussed to figure out the structure of U(1)
instantons.Comment: v3: 24 pages, Latex, corrected typos, references added, to appear in
Phys. Rev.
The Spin-Dependent Structure Functions of Nuclei in the Meson-Nucleon Theory
A theoretical approach to the investigation of spin-dependent structure
functions in deep inelastic scattering of polarized leptons off polarized
nuclei, based on the effective meson-nucleon theory and operator product
expansion method, is proposed and applied to deuteron and . The explicit
forms of the moments of the deuteron and spin-dependent structure
functions are found and numerical estimates of the influence of nuclear
structure effects are presented.Comment: 42 pages revtex, 7 postscript figures available from above e-mail
upon request. Perugia preprint DFUPG 92/9
Photon-pair generation in photonic crystal fibre with a 1.5 GHz modelocked VECSEL
Four-wave mixing (FWM) in optical fibre is a leading technique for generating
high-quality photon pairs. We report the generation of photon pairs by
spontaneous FWM in photonic crystal fibre pumped by a 1.5 GHz repetition-rate
vertical-external-cavity surface-emitting laser (VECSEL). The photon pairs
exhibit high count rates and a coincidence-to-accidental ratio of over 80. The
VECSEL's high repetition-rate, high average power, tunability, and small
footprint make this an attractive source for quantum key distribution and
photonic quantum-state engineering.Comment: 17 Pages, 5 Figure
Production of Sigma{\pm}pi?pK+ in p+p reactions at 3.5 GeV beam energy
We study the production of Sigma^+-pi^+-pK^+ particle quartets in p+p
reactions at 3.5 GeV kinetic beam energy. The data were taken with the HADES
experiment at GSI. This report evaluates the contribution of resonances like
Lambda(1405$, Sigma(1385)^0, Lambda(1520), Delta(1232), N^* and K^*0 to the
Sigma^+- pi^-+ p K+ final state. The resulting simulation model is compared to
the experimental data in several angular distributions and it shows itself as
suitable to evaluate the acceptance corrections properly.Comment: 15 pages, 5 figure
Origin of the low-mass electron pair excess in light nucleus-nucleus collisions
We report measurements of electron pair production in elementary p+p and d+p
reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the
electron pairs were reconstructed for n+p reactions by detecting the proton
spectator from the deuteron breakup. We find that the yield of electron pairs
with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger
in n+p reactions as compared to p+p. A comparison to model calculations
demonstrates that the production mechanism is not sufficiently described yet.
The electron pair spectra measured in C+C reactions are compatible with a
superposition of elementary n+p and p+p collisions, leaving little room for
additional electron pair sources in such light collision systems.Comment: 11 pages, 2 figures, \usepackage{epsfig
Study of dielectron production in C+C collisions at 1 AGeV
The emission of e+e- pairs from C+C collisions at an incident energy of 1 GeV
per nucleon has been investigated. The measured production probabilities,
spanning from the pi0-Dalitz to the rho/omega! invariant-mass region, display a
strong excess above the cocktail of standard hadronic sources. The
bombarding-energy dependence of this excess is found to scale like pion
production, rather than like eta production. The data are in good agreement
with results obtained in the former DLS experiment.Comment: submitted to Physics Letters
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
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