3,077 research outputs found
Morita cohomology
We consider two categorifications of the cohomology of a topological space X
by taking coefficients in the category of differential graded categories. We
consider both derived global sections of a constant presheaf and singular
cohomology and find the resulting dg-categories are quasi-equivalent and
moreover quasi-equivalent to representations in perfect complexes of chains on
the loop space of X.Comment: 33 page
Coccinia intermedia
Nuclear and plastid sequences from two individuals of a suspected new species of Coccinia from West Africa were added to an available molecular phylogeny for the remaining 27 species of the genus. Phylogenetic analyses of these data indicate the new species' monophyletic status and closest relatives. Based on four fertile collections, we here describe and illustrate Coccinia intermedia Holstein. We also provide a key to the Coccinia species of West Africa and map their distributions
A Brief Introduction to Chiral Perturbation Theory
A brief introduction to the subject of chiral perturbation theory (pt)
is presented, including a discussion of effective field theory and applications
of pt in the arena of purely mesonic interactions as well as in the sector.Comment: 15 pages, talk given at TAPS detector workshop, Rez, Czech Republic,
Sept. 1999, to be published in Czech. J. Phy
Ground state overlap and quantum phase transitions
We present a characterization of quantum phase transitions in terms of the
the overlap function between two ground states obtained for two different
values of external parameters. On the examples of the Dicke and XY models, we
show that the regions of criticality of a system are marked by the extremal
points of the overlap and functions closely related to it. Further, we discuss
the connections between this approach and the Anderson orthogonality
catastrophe as well as with the dynamical study of the Loschmidt echo for
critical systems.Comment: 5 pages. Version to be published, title change
Electron-nuclear correlations for photo-induced dynamics in molecular dimers
Ultrafast photoinduced dynamics of electronic excitation in molecular dimers
is drastically affected by the dynamic reorganization of inter- and intra-
molecular nuclear configuration modeled by a quantized nuclear degree of
freedom [Cina et. al, J. Chem Phys. {118}, 46 (2003)]. The dynamics of the
electronic population and nuclear coherence is analyzed by solving the chain of
coupled differential equations for %mean coordinate, population inversion,
electron-vibrational correlation, etc. [Prezhdo, Pereverzev, J. Chem. Phys.
{113} 6557 (2000)]. Intriguing results are obtained in the approximation of a
small change of the nuclear equilibrium upon photoexcitation. In the limiting
case of resonance between the electronic energy gap and the frequency of the
nuclear mode these results are justified by comparison to the exactly solvable
Jaynes-Cummings model. It is found that the photoinduced processes in the model
dimer are arranged according to their time scales: (i) fast scale of nuclear
motion, (ii) intermediate scale of dynamical redistribution of electronic
population between excited states as well as growth and dynamics of
electron-nuclear correlation, (iii) slow scale of electronic population
approach to the quasi-equilibrium distribution, decay of electron-nuclear
correlation, and decrease of the amplitude of mean coordinate oscillation. The
latter processes are accompanied by a noticeable growth of the nuclear
coordinate dispersion associated with the overall nuclear wavepacket width. The
demonstrated quantum relaxation features of the photoinduced vibronic dynamics
in molecular dimers are obtained by a simple method, applicable to systems with
many degrees of freedom
Quantum phase transition in the multi-mode Dicke model
An investigation of the quantum phase transition in both discrete and
continuum field Dicke models is presented. A series of anticrossing features
following the criticality is revealed in the band of the field modes. Critical
exponents are calculated. We investigate the properties of a pairwise
entanglement measured by a concurrence and obtain analytical results in the
thermodynamic limit.Comment: 7 pages, 3 figure
Subleading corrections to parity-violating pion photoproduction
We compute the photon asymmetry Bγ for near threshold parity-violating (PV) pion photoproduction through subleading order. We show that subleading contributions involve a new combination of PV couplings not included in previous analyses of hadronic PV. We argue that existing constraints on the leading order contribution to Bγ—obtained from the PV γ-decay of 18F—suggest that the impact of the subleading contributions may be more significant than expected from naturalness arguments
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