353 research outputs found
Duality in the Quantum Hall Effect - the Role of Electron Spin
At low temperatures the phase diagram for the quantum Hall effect has a
powerful symmetry arising from the Law of Corresponding States. This symmetry
gives rise to an infinite order discrete group which is a generalisation of
Kramers-Wannier duality for the two dimensional Ising model. The duality group,
which is a subgroup of the modular group, is analysed and it is argued that
there is a quantitative difference between a situation in which the spin
splitting of electron energy levels is comparable to the cyclotron energy and
one in which the spin splitting is much less than the cyclotron energy. In the
former case the group of symmetries is larger than in the latter case. These
duality symmetries are used to constrain the scaling functions of the theory
and, under an assumption of complex meromorphicity, a unique functional form is
obtained for the crossover of the conductivities between Hall states as a
function of the external magnetic field. This analytic form is shown to give
good agreement with experimental data.
The analysis requires a consideration of the way in which longitudinal
resistivities are extracted from the experimentally measured longitudinal
resistances and a novel method is proposed for determining the correct
normalisation for the former.Comment: 22 pages, 8 figures, typeset in LaTe
TIME-SYMMETRIC INITIAL DATA SETS IN 4--D DILATON GRAVITY
I study the time--symmetric initial--data problem in theories with a massless
scalar field (dilaton), free or coupled to a Maxwell field in the stringy way,
finding different initial--data sets describing an arbitrary number of black
holes with arbitrary masses, charges and asymptotic value of the dilaton. The
presence of the scalar field gives rise to a number of interesting effects. The
mass and charges of a single black hole are different in its two asymptotically
flat regions across the Einstein--Rosen bridge. The same happens to the value
of the dilaton at infinity. This forbids the identification of these asymptotic
regions in order to build (Misner) wormholes in the most naive way. Using
different techniques, I find regular initial data for stringy wormholes. The
price payed is the existence singularities in the dilaton field. The presence
of a single--valued scalar seems to constrain strongly the allowed topologies
of the initial space--like surface. Other kinds of scalar fields (taking values
on a circle or being defined up to an additive constant) are also briefly
considered.Comment: latex file, 38 pages
New and Interesting Fungi. 1
This study introduces two new families, one new genus, 22 new species, 10 new combinations, four epitypes, and 16 interesting new host and / or geographical records. Cylindriaceae (based on Cylindrium elongatum) is introduced as new family, with three new combinations.Xyladictyochaetaceae (based on Xyladictyochaetalusitanica) is introduced to accommodate Xyladictyochaeta. Pseudoanungitea gen. nov. (based on P.syzygii)is described on stems of Vaccinium myrtillus(Germany). New species include: Exophiala eucalypticola on Eucalyptus obliqua leaf litter, Phyllosticta hakeicola on leaves of Hakea sp.,Setophaeosphaeriacitricola on leaves of Citrus australasica, and Sirastachyscyperacearum on leaves of Cyperaceae(Australia); Polyscytalum chilense on leaves of Eucalyptus urophylla (Chile); Pseudoanungitea vaccinii on Vaccinium myrtillus (Germany); Teichospora quercus on branch tissue of Quercus sp. (France); Fusiconidiumlycopodiellae on stems of Lycopodiella inundata,Monochaetiajunipericola on twig of Juniperus communis,Myrmecridiumsorbicola on branch tissues of Sorbus aucuparia, Parathyridariaphiladelphi on twigs of Philadelphus coronarius, and Wettsteininaphiladelphi on twigs of Philadelphus coronarius (Germany); Zygosporium pseudogibbum on leaves of Eucalyptus pellita (Malaysia); Pseudoanungiteavariabilis on dead wood (Spain); Alfaria acaciae on leaves of Acacia propinqua, Dictyochaeta mimusopis on leaves of Mimusops caffra,and Pseudocercosporabreonadiae on leaves of Breonadia microcephala (South Africa); Colletotrichumkniphofiae on leaves of Kniphofia uvaria,Subplenodomusiridicola on Iris sp., and Trochila viburnicola on twig cankers on Viburnum sp. (UK); Polyscytalum neofecundissimum on Quercus robur leaf litter, and Roussoellaeuonymi on fallen branches of Euonymus europaeus (Ukraine). New combinations include: Cylindrium algarvense on leaves of Eucalyptus sp. (Portugal), Cylindrium purgamentum on leaf litter (USA), Cylindrium syzygii on leaves of Syzygium sp. (Australia), Microdochium musae on leaves of Musa sp. (Malaysia), Polyscytalum eucalyptigenum on Eucalyptus grandis × pellita (Malaysia), P. eucalyptorum on leaves of Eucalyptus (Australia), P. grevilleae on leaves of Grevillea (Australia), P. nullicananum on leaves of Eucalyptus (Australia), Pseudoanungiteasyzygii on Syzygium cordatum leaf litter (South Africa), and Setophaeosphaeriasidae on leaves of Sida sp. (Brazil). New records include: Sphaerellopsis paraphysata on leaves of Phragmites sp., Vermiculariopsiella dichapetali on leaves of Melaleuca sp. and Eucalyptus regnans, and Xyladictyochaetalusitanica on leaf litter of Eucalyptus sp. (Australia); Camarosporidiella mackenziei on twigs of Caragana sp. (Finland); Cyclothyriella rubronotata on twigs of Ailanthus altissima, Rhinocladiella quercus on Sorbus aucuparia branches (Germany); Cytospora viticola on stems of Vitis vinifera (Hungary); Echinocatena arthrinioides on leaves of Acacia crassicarpa (Malaysia); Varicosporellopsis aquatilis from garden soil (Netherlands); Pestalotiopsis hollandica on needles of Cupressus sempervirens (Spain), Pseudocamarosporiumafricanum on twigs of Erica sp. (South Africa), Pseudocamarosporium brabeji on branch of Platanus sp. (Switzerland); Neocucurbitaria cava on leaves of Quercus ilex (UK); Chaetosphaeriamyriocarpaon decaying wood of Carpinus betulus,Haplograhium delicatum on decaying Carpinus betulus wood (Ukraine). Epitypes are designated for: Elsinoë mimosae on leaves of Mimosa diplotricha (Brazil), Neohendersonia kickxii on Fagus sylvatica twig bark (Italy), Caliciopsis maxima on fronds of Niphidium crassifolium (Brazil), Dictyochaeta septata on leaves of Eucalyptus grandis ×urophylla (Chile), and Microdochium musae on leaves of Musa sp. (Malaysia)
Role of beam polarization in the determination of and couplings from
We evaluate the constraints on anomalous trilinear gauge-boson couplings that
can be obtained from the study of electron-positron annihilation into pairs
at a facility with either the electron beam longitudinally polarized or both
electron and positron beams transversely polarized. The energy ranges
considered in the analysis are the ones relevant to the next-linear collider
and to LEP~200. We discuss the possibilities of a model independent analysis of
the general conserving anomalous effective Lagrangian, as well as its
restriction to some specific models with reduced number of independent
couplings. The combination of observables with initial and final state
polarizations allows to separately constrain the different couplings and to
improve the corresponding numerical bounds.Comment: 24 pages, LaTeX, 9 figures (available on request from the authors
Sensitivity of the IceCube Detector to Astrophysical Sources of High Energy Muon Neutrinos
We present the results of a Monte-Carlo study of the sensitivity of the
planned IceCube detector to predicted fluxes of muon neutrinos at TeV to PeV
energies. A complete simulation of the detector and data analysis is used to
study the detector's capability to search for muon neutrinos from sources such
as active galaxies and gamma-ray bursts. We study the effective area and the
angular resolution of the detector as a function of muon energy and angle of
incidence. We present detailed calculations of the sensitivity of the detector
to both diffuse and pointlike neutrino emissions, including an assessment of
the sensitivity to neutrinos detected in coincidence with gamma-ray burst
observations. After three years of datataking, IceCube will have been able to
detect a point source flux of E^2*dN/dE = 7*10^-9 cm^-2s^-1GeV at a 5-sigma
significance, or, in the absence of a signal, place a 90% c.l. limit at a level
E^2*dN/dE = 2*10^-9 cm^-2s^-1GeV. A diffuse E-2 flux would be detectable at a
minimum strength of E^2*dN/dE = 1*10^-8 cm^-2s^-1sr^-1GeV. A gamma-ray burst
model following the formulation of Waxman and Bahcall would result in a 5-sigma
effect after the observation of 200 bursts in coincidence with satellite
observations of the gamma-rays.Comment: 33 pages, 13 figures, 6 table
On the selection of AGN neutrino source candidates for a source stacking analysis with neutrino telescopes
The sensitivity of a search for sources of TeV neutrinos can be improved by
grouping potential sources together into generic classes in a procedure that is
known as source stacking. In this paper, we define catalogs of Active Galactic
Nuclei (AGN) and use them to perform a source stacking analysis. The grouping
of AGN into classes is done in two steps: first, AGN classes are defined, then,
sources to be stacked are selected assuming that a potential neutrino flux is
linearly correlated with the photon luminosity in a certain energy band (radio,
IR, optical, keV, GeV, TeV). Lacking any secure detailed knowledge on neutrino
production in AGN, this correlation is motivated by hadronic AGN models, as
briefly reviewed in this paper.
The source stacking search for neutrinos from generic AGN classes is
illustrated using the data collected by the AMANDA-II high energy neutrino
detector during the year 2000. No significant excess for any of the suggested
groups was found.Comment: 43 pages, 12 figures, accepted by Astroparticle Physic
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
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