1,325 research outputs found
Turbulence and turbulent pattern formation in a minimal model for active fluids
Active matter systems display a fascinating range of dynamical states,
including stationary patterns and turbulent phases. While the former can be
tackled with methods from the field of pattern formation, the spatio-temporal
disorder of the active turbulence phase calls for a statistical description.
Borrowing techniques from turbulence theory, we here establish a quantitative
description of correlation functions and spectra of a minimal continuum model
for active turbulence. Further exploring the parameter space, we also report on
a surprising type of turbulence-driven pattern formation far beyond linear
onset: the emergence of a dynamic hexagonal vortex lattice state after an
extended turbulent transient, which can only be explained taking into account
turbulent energy transfer across scales.Comment: Supplemental videos available at https://youtu.be/gbf6cRho03w
https://youtu.be/n0qUUhAUJFQ https://youtu.be/LGmamkM012
Gravitational Correction to Running of Gauge Couplings
We calculate the contribution of graviton exchange to the running of gauge
couplings at lowest non-trivial order in perturbation theory. Including this
contribution in a theory that features coupling constant unification does not
upset this unification, but rather shifts the unification scale. When
extrapolated formally, the gravitational correction renders all gauge couplings
asymptotically free.Comment: 4 pages, 2 figures; v2: Clarified awkward sentences and notations.
Corrected typos. Added references and discussion thereof in introduction.
Minor copy editting changes to agree with version to be published in Physical
Review Letter
Higher-Dimensional QCD without the Strong CP Problem
QCD in a five-dimensional sliced bulk with chiral extra-quarks on the
boundaries is generically free from the strong CP problem. Accidental axial
symmetry is naturally present except for suppressed breaking interactions,
which plays a role of the Peccei-Quinn symmetry to make the strong CP phase
sufficiently small.Comment: 7 pages, late
Gravity: A New Holographic Perspective
A general paradigm for describing classical (and semiclassical) gravity is
presented. This approach brings to the centre-stage a holographic relationship
between the bulk and surface terms in a general class of action functionals and
provides a deeper insight into several aspects of classical gravity which have
no explanation in the conventional approach. After highlighting a series of
unresolved issues in the conventional approach to gravity, I show that (i)
principle of equivalence, (ii) general covariance and (iii)a reasonable
condition on the variation of the action functional, suggest a generic
Lagrangian for semiclassical gravity of the form with
. The expansion of in terms of the
derivatives of the metric tensor determines the structure of the theory
uniquely. The zeroth order term gives the Einstein-Hilbert action and the first
order correction is given by the Gauss-Bonnet action. Any such Lagrangian can
be decomposed into a surface and bulk terms which are related holographically.
The equations of motion can be obtained purely from a surface term in the
gravity sector. Hence the field equations are invariant under the
transformation and gravity does not
respond to the changes in the bulk vacuum energy density. The cosmological
constant arises as an integration constant in this approach. The implications
are discussed.Comment: Plenary talk at the International Conference on Einstein's Legacy in
the New Millennium, December 15 - 22, 2005, Puri, India; to appear in the
Proceedings to be published in IJMPD; 16 pages; no figure
The Unbearable Beingness of Light, Dressing and Undressing Photons in Black Hole Spacetimes
Gravitational tidal forces acting on the virtual e+ e- cloud surrounding a
photon endow spacetime with a non-trivial refractive index. This has remarkable
properties unique to gravitational theories including superluminal
low-frequency propagation, in apparent violation of causality, and
amplification of the renormalized photon field, in apparent violation of
unitarity. Using the geometry of null congruences and the Penrose limit, we
illustrate these phenomena and their resolution by tracing the history of a
photon as it falls into the near-singularity region of a black hole.Comment: 8 pages, Essay awarded third prize in the Gravity Research Foundation
essay competition 201
Introduction to {\it Quantum Matter}
This paper records my opening remarks at Nobel Symposium 148, on Graphene and
Quantum Matter, at Saltsj\"obaden, Sweden, in June 2010. After some broad
comments on the quantum theory of matter as a frontier of physics, and some
slightly more particular comments about re-quantization, I report on the
universal geometry that arises in a refined discussion of quantum-mechanical
level crossing.Comment: 12 pages, 1 table; Opening talk at at Nobel Symposium 148, on
Graphene and Quantum Matter, at Saltsj\"obaden, Sweden, in June 2010, to be
published in the Proceeedings (Physica Scripta). v. 2: Some garbling in
equation 1 correcte
Quantum Numbers of Textured Hall Effect Quasiparticles
We propose a class of variational wave functions with slow variation in spin
and charge density and simple vortex structure at infinity, which properly
generalize both the Laughlin quasiparticles and baby Skyrmions. We argue that
the spin of the corresponding quasiparticle has a fractional part related in a
universal fashion to the properties of the bulk state, and propose a direct
experimental test of this claim. We show that certain spin-singlet quantum Hall
states can be understood as arising from primary polarized states by Skyrmion
condensation.Comment: 13 pages, no figures, Phyzz
Theory for the single-point velocity statistics of fully developed turbulence
We investigate the single-point velocity probability density function (PDF)
in three-dimensional fully developed homogeneous isotropic turbulence within
the framework of PDF equations focussing on deviations from Gaussianity. A
joint analytical and numerical analysis shows that these deviations may be
quantified studying correlations of dynamical quantities like pressure
gradient, external forcing and energy dissipation with the velocity. A
stationary solution for the PDF equation in terms of these quantities is
presented, and the theory is validated with the help of direct numerical
simulations indicating sub-Gaussian tails of the PDF.Comment: 6 pages, 4 figures, corrected typo in eq. (4
Schr\"{o}dinger Fields on the Plane with non-Abelian Chern-Simons Interactions
Physical content of the nonrelativistic quantum field theory with non-Abelian
Chern-Simons interactions is clarified with the help of the equivalent first-
quantized description which we derive in any physical gauge.Comment: 12 pages, LaTex, SNUTP 94-1
Comments on ``Lattice Formulation of the Standard Model'' by Creutz. et. al
The main construction of the paper in the title [hep-lat/9612017] is
summarized using more standard particle physics language. Also, a flaw is
pointed out and several objections to the more general thoughts expressed by
Creutz et. al. are raised.Comment: 5 pages, plain Te
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