10,475 research outputs found
On Fractional Tempered Stable Motion
Fractional tempered stable motion (fTSm)} is defined and studied. FTSm has
the same covariance structure as fractional Brownian motion, while having tails
heavier than Gaussian but lighter than stable. Moreover, in short time it is
close to fractional stable L\'evy motion, while it is approximately fractional
Brownian motion in long time. A series representation of fTSm is derived and
used for simulation and to study some of its sample path properties.Comment: 25 pages, 6 figure
Asymptotically Vanishing Cosmological Constant in the Multiverse
We study the problem of the cosmological constant in the context of the
multiverse in Lorentzian spacetime, and show that the cosmological constant
will vanish in the future. This sort of argument was started from Coleman in
1989, and he argued that the Euclidean wormholes make the multiverse partition
a superposition of various values of the cosmological constant , which
has a sharp peak at . However, the implication of the Euclidean
analysis to our Lorentzian spacetime is unclear. With this motivation, we
analyze the quantum state of the multiverse in Lorentzian spacetime by the WKB
method, and calculate the density matrix of our universe by tracing out the
other universes. Our result predicts vanishing cosmological constant. While
Coleman obtained the enhancement at through the action itself, in
our Lorentzian analysis the similar enhancement arises from the front factor of
in the universe wave function, which is in the next leading order in
the WKB approximation.Comment: 17 pages, 7 figures; v2:minor correction
Jarzynski equality for the Jepsen gas
We illustrate the Jarzynski equality on the exactly solvable model of a
one-dimensional ideal gas in uniform expansion or compression. The analytical
results for the probability density of the work performed by the gas
are compared with the results of molecular dynamics simulations for a
two-dimensional dilute gas of hard spheres.Comment: 7 pages, 4 figures, submitted to Europhys. Let
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Neural Representations of Courtship Song in the Drosophila Brain
Acoustic communication in drosophilid flies is based on the production and perception of courtship songs, which facilitate mating. Despite decades of research on courtship songs and behavior in Drosophila, central auditory responses have remained uncharacterized. In this study, we report on intracellular recordings from central neurons that innervate the Drosophila antennal mechanosensory and motor center (AMMC), the first relay for auditory information in the fly brain. These neurons produce graded-potential (nonspiking) responses to sound; we compare recordings from AMMC neurons to extracellular recordings of the receptor neuron population [Johnston's organ neurons (JONs)]. We discover that, while steady-state response profiles for tonal and broadband stimuli are significantly transformed between the JON population in the antenna and AMMC neurons in the brain, transient responses to pulses present in natural stimuli (courtship song) are not. For pulse stimuli in particular, AMMC neurons simply low-pass filter the receptor population response, thus preserving low-frequency temporal features (such as the spacing of song pulses) for analysis by postsynaptic neurons. We also compare responses in two closely related Drosophila species, Drosophila melanogaster and Drosophila simulans, and find that pulse song responses are largely similar, despite differences in the spectral content of their songs. Our recordings inform how downstream circuits may read out behaviorally relevant information from central neurons in the AMMC
Renormalization of 3d quantum gravity from matrix models
Lorentzian simplicial quantum gravity is a non-perturbatively defined theory
of quantum gravity which predicts a positive cosmological constant. Since the
approach is based on a sum over space-time histories, it is perturbatively
non-renormalizable even in three dimensions. By mapping the three-dimensional
theory to a two-matrix model with ABAB interaction we show that both the
cosmological and the (perturbatively) non-renormalizable gravitational coupling
constant undergo additive renormalizations consistent with canonical
quantization.Comment: 14 pages, 3 figure
Large N reduction on coset spaces
As an extension of our previous work concerning the large N reduction on
group manifolds, we study the large N reduction on coset spaces. We show that
large N field theories on coset spaces are described by certain corresponding
matrix models. We also construct Chern-Simons-like theories on group manifolds
and coset spaces, and give their reduced models.Comment: 22 pages, typos correcte
Quantum Electrodynamics at Large Distances II: Nature of the Dominant Singularities
Accurate calculations of macroscopic and mesoscopic properties in quantum
electrodynamics require careful treatment of infrared divergences: standard
treatments introduce spurious large-distances effects. A method for computing
these properties was developed in a companion paper. That method depends upon a
result obtained here about the nature of the singularities that produce the
dominant large-distance behaviour. If all particles in a quantum field theory
have non-zero mass then the Landau-Nakanishi diagrams give strong conditions on
the singularities of the scattering functions. These conditions are severely
weakened in quantum electrodynamics by effects of points where photon momenta
vanish. A new kind of Landau-Nakanishi diagram is developed here. It is geared
specifically to the pole-decomposition functions that dominate the macroscopic
behaviour in quantum electrodynamics, and leads to strong results for these
functions at points where photon momenta vanish.Comment: 40 pages, 11 encapsulated postscript figures, latexed,
math_macros.tex can be found on Archive. full postscript available from
http://theorl.lbl.gov/www/theorgroup/papers/35972.p
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