11,554 research outputs found
Moving Five-Branes in Low-Energy Heterotic M-Theory
We construct cosmological solutions of four-dimensional effective heterotic
M-theory with a moving five-brane and evolving dilaton and T modulus. It is
shown that the five-brane generates a transition between two asymptotic
rolling-radii solutions. Moreover, the five-brane motion always drives the
solutions towards strong coupling asymptotically. We present an explicit
example of a negative-time branch solution which ends in a brane collision
accompanied by a small-instanton transition. The five-dimensional origin of
some of our solutions is also discussed.Comment: 16 pages, Latex, 3 eps figure
Persistent accelerations disentangle Lagrangian turbulence
Particles in turbulence frequently encounter extreme accelerations between
extended periods of quiescence. The occurrence of extreme events is closely
related to the intermittent spatial distribution of intense flow structures
such as vorticity filaments. This mixed history of flow conditions leads to
very complex particle statistics with a pronounced scale dependence, which
presents one of the major challenges on the way to a non-equilibrium
statistical mechanics of turbulence. Here, we introduce the notion of
persistent Lagrangian acceleration, quantified by the squared particle
acceleration coarse-grained over a viscous time scale. Conditioning Lagrangian
particle data from simulations on this coarse-grained acceleration, we find
remarkably simple, close-to-Gaussian statistics for a range of Reynolds
numbers. This opens the possibility to decompose the complex particle
statistics into much simpler sub-ensembles. Based on this observation, we
develop a comprehensive theoretical framework for Lagrangian single-particle
statistics that captures the acceleration, velocity increments as well as
single-particle dispersion
D7-Brane Chaotic Inflation
We analyze string-theoretic large-field inflation in the regime of
spontaneously-broken supergravity with conventional moduli stabilization by
fluxes and non-perturbative effects. The main ingredient is a shift-symmetric
Kahler potential, supplemented by flux-induced shift symmetry breaking in the
superpotential. The central technical observation is that all these features
are present for D7-brane position moduli in Type IIB orientifolds, allowing for
a realization of the axion monodromy proposal in a controlled string theory
compactification. On the one hand, in the large complex structure regime the
D7-brane position moduli inherit a shift symmetry from their mirror-dual Type
IIA Wilson lines. On the other hand, the Type IIB flux superpotential
generically breaks this shift symmetry and allows, by appealing to the large
flux discretuum, to tune the relevant coefficients to be small. The
shift-symmetric direction in D7-brane moduli space can then play the role of
the inflaton: While the D7-brane circles a certain trajectory on the Calabi-Yau
many times, the corresponding F-term energy density grows only very slowly,
thanks to the above-mentioned tuning of the flux. Thus, the large-field
inflationary trajectory can be realized in a regime where Kahler, complex
structure and other brane moduli are stabilized in a conventional manner, as we
demonstrate using the example of the Large Volume Scenario.Comment: 8 pages, 2 figures; v2: references adde
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