353 research outputs found
Local conserved charges in principal chiral models
Local conserved charges in principal chiral models in 1+1 dimensions are
investigated. There is a classically conserved local charge for each totally
symmetric invariant tensor of the underlying group. These local charges are
shown to be in involution with the non-local Yangian charges. The Poisson
bracket algebra of the local charges is then studied. For each classical
algebra, an infinite set of local charges with spins equal to the exponents
modulo the Coxeter number is constructed, and it is shown that these commute
with one another. Brief comments are made on the evidence for, and implications
of, survival of these charges in the quantum theory.Comment: 36 pages, LaTeX; v2: minor correction
Conserved charges and supersymmetry in principal chiral and WZW models
Conserved and commuting charges are investigated in both bosonic and
supersymmetric classical chiral models, with and without Wess-Zumino terms. In
the bosonic theories, there are conserved currents based on symmetric invariant
tensors of the underlying algebra, and the construction of infinitely many
commuting charges, with spins equal to the exponents of the algebra modulo its
Coxeter number, can be carried out irrespective of the coefficient of the
Wess-Zumino term. In the supersymmetric models, a different pattern of
conserved quantities emerges, based on antisymmetric invariant tensors. The
current algebra is much more complicated than in the bosonic case, and it is
analysed in some detail. Two families of commuting charges can be constructed,
each with finitely many members whose spins are exactly the exponents of the
algebra (with no repetition modulo the Coxeter number). The conserved
quantities in the bosonic and supersymmetric theories are only indirectly
related, except for the special case of the WZW model and its supersymmetric
extension.Comment: LaTeX; 49 pages; v2: minor changes and additions to text and ref
Gapless Spin-Fluid Ground State in a Random Quantum Heisenberg Magnet
We examine the spin- quantum Heisenberg magnet with Gaussian-random,
infinite-range exchange interactions. The quantum-disordered phase is accessed
by generalizing to symmetry and studying the large limit. For large
the ground state is a spin-glass, while quantum fluctuations produce a
spin-fluid state for small . The spin-fluid phase is found to be generically
gapless - the average, zero temperature, local dynamic spin-susceptibility
obeys \bar{\chi} (\omega ) \sim \log(1/|\omega|) + i (\pi/2) \mbox{sgn}
(\omega) at low frequencies. This form is identical to the phenomenological
`marginal' spectrum proposed by Varma {\em et. al.\/} for the doped cuprates.Comment: 13 pages, REVTEX, 2 figures available by request from
[email protected]
Exact multilocal renormalization on the effective action : application to the random sine Gordon model statics and non-equilibrium dynamics
We extend the exact multilocal renormalization group (RG) method to study the
flow of the effective action functional. This important physical quantity
satisfies an exact RG equation which is then expanded in multilocal components.
Integrating the nonlocal parts yields a closed exact RG equation for the local
part, to a given order in the local part. The method is illustrated on the O(N)
model by straightforwardly recovering the exponent and scaling
functions. Then it is applied to study the glass phase of the Cardy-Ostlund,
random phase sine Gordon model near the glass transition temperature. The
static correlations and equilibrium dynamical exponent are recovered and
several new results are obtained. The equilibrium two-point scaling functions
are obtained. The nonequilibrium, finite momentum, two-time response and
correlations are computed. They are shown to exhibit scaling forms,
characterized by novel exponents , as well as
universal scaling functions that we compute. The fluctuation dissipation ratio
is found to be non trivial and of the form . Analogies and
differences with pure critical models are discussed.Comment: 33 pages, RevTe
Dynamic structure factor of the Ising model with purely relaxational dynamics
We compute the dynamic structure factor for the Ising model with a purely
relaxational dynamics (model A). We perform a perturbative calculation in the
expansion, at two loops in the high-temperature phase and at one
loop in the temperature magnetic-field plane, and a Monte Carlo simulation in
the high-temperature phase. We find that the dynamic structure factor is very
well approximated by its mean-field Gaussian form up to moderately large values
of the frequency and momentum . In the region we can investigate,
, , where is the correlation
length and the zero-momentum autocorrelation time, deviations are at
most of a few percent.Comment: 21 pages, 3 figure
25.1 High Efficiency Monolithic Perovskite Silicon Tandem Solar Cell with a High Bandgap Perovskite Absorber
Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 amp; 8201;eV in planar p i n tandem configuration. A methylammonium free FA0.75Cs0.25Pb I0.8Br0.2 3 perovskite with high Cs content is investigated for improved stability. A 10 molarity increase to 1.1 amp; 8201;m of the perovskite precursor solution results in amp; 8776;75 amp; 8201;nm thicker absorber layers and 0.7 amp; 8201;mA amp; 8201;cm amp; 8722;2 higher short circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80 and up to 25.1 certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3 absolute over 5 amp; 8201;months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30 tandem efficiency in the near futur
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
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
Rapid Communication
Observation of Orbitally Excited B_s Mesons
We report the first observation of two narrow resonances consistent with
states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar
collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the
Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed
as B^+ \to J/\psi K^+, J/\psi \to \mu^+ \mu^- or B^+ \to \bar{D}^0 \pi^+,
\bar{D}^0 \to K^+ \pi^-. We deduce the masses of the two states to be m(B_{s1})
= 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.Comment: Version accepted and published by Phys. Rev. Let
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