6,668 research outputs found
Phase Diagram of the Dissipative Hofstadter Model
The dissipative quantum mechanics of a charged particle in a uniform magnetic
field and periodic potential has delocalization critical points which
correspond to backgrounds for the open string. We study the phase diagram of
this system (in the magnetic field/dissipation constant plane) and find a
fractal structure which, in the limit of zero dissipation, matches the fractal
energy level structure of the pure quantum mechanical version of this problem
(Hofstadter model).Comment: 23 page
Critical Theories of the Dissipative Hofstadter Model
It has recently been shown that the dissipative Hofstadter model (dissipative
quantum mechanics of an electron subject to uniform magnetic field and periodic
potential in two dimensions) exhibits critical behavior on a network of lines
in the dissipation/magnetic field plane. Apart from their obvious condensed
matter interest, the corresponding critical theories represent non-trivial
solutions of open string field theory, and a detailed account of their
properties would be interesting from several points of view. A subject of
particular interest is the dependence of physical quantities on the magnetic
field since it, much like , serves only to give relative
phases to different sectors of the partition sum. In this paper we report the
results of an initial investigation of the free energy, -point functions and
boundary state of this type of critical theory. Although our primary goal is
the study of the magnetic field dependence of these quantities, we will present
some new results which bear on the zero magnetic field case as well.Comment: 42 pages (25 reduced
Dynamics of Diblock Copolymers in Dilute Solutions
We consider the dynamics of freely translating and rotating diblock (A-B),
Gaussian copolymers, in dilute solutions. Using the multiple scattering
technique, we have computed the diffusion and the friction coefficients D_AB
and Zeta_AB, and the change Eta_AB in the viscosity of the solution as
functions of x = N_A/N and t = l_B/l_A, where N_A, N are the number of segments
of the A block and of the whole copolymer, respectively, and l_A, l_B are the
Kuhn lengths of the A and B blocks. Specific regimes that maximize the
efficiency of separation of copolymers with distinct "t" values, have been
identified.Comment: 20 pages Revtex, 7 eps figures, needs epsf.tex and amssymb.sty,
submitted to Macromolecule
The universality of the shift of the Chern-Simons parameter for a general class of BRS invariant regularizations
We consider a biparametric family of BRS invariant regularization methods of
SU(N) Chern-Simons theory (the parameters defining the family taking arbitrary
values in \RR^2) and show that the shift of the
Chern-Simons parameter occurs for arbitrary values of the family defining
parameters. This supports irrefutably the conjecture that the shift of is
universal for BRS invariant regulators.Comment: phyzzx, 7 pages (no figures
T-duality and Differential K-Theory
We give a precise formulation of T-duality for Ramond-Ramond fields. This
gives a canonical isomorphism between the "geometrically invariant" subgroups
of the twisted differential K-theory of certain principal torus bundles. Our
result combines topological T-duality with the Buscher rules found in physics.Comment: 23 pages, typos corrected, submitted to Comm.Math.Phy
One size fits all: equilibrating chemically different polymer liquids through universal long-wavelength description
Mesoscale behavior of polymers is frequently described by universal laws.
This physical property motivates us to propose a new modeling concept, grouping
polymers into classes with a common long-wavelength representation. In the same
class samples of different materials can be generated from this representation,
encoded in a single library system. We focus on homopolymer melts, grouped
according to the invariant degree of polymerization. They are described with a
bead-spring model, varying chain stiffness and density to mimic chemical
diversity. In a renormalization group-like fashion library samples provide a
universal blob-based description, hierarchically backmapped to create
configurations of other class-members. Thus large systems with
experimentally-relevant invariant degree of polymerizations (so far accessible
only on very coarse-grained level) can be microscopically described.
Equilibration is verified comparing conformations and melt structure with
smaller scale conventional simulations
On Supermultiplet Twisting and Spin-Statistics
Twisting of off-shell supermultiplets in models with 1+1-dimensional
spacetime has been discovered in 1984, and was shown to be a generic feature of
off-shell representations in worldline supersymmetry two decades later. It is
shown herein that in all supersymmetric models with spacetime of four or more
dimensions, this off-shell supermultiplet twisting, if non-trivial, necessarily
maps regular (non-ghost) supermultiplets to ghost supermultiplets. This feature
is shown to be ubiquitous in all fully off-shell supersymmetric models with
(BV/BRST-treated) constraints.Comment: Extended version, including a new section on manifestly off-shell and
supersymmetric BRST treatment of gauge symmetry; added reference
Apex Exponents for Polymer--Probe Interactions
We consider self-avoiding polymers attached to the tip of an impenetrable
probe. The scaling exponents and , characterizing the
number of configurations for the attachment of the polymer by one end, or at
its midpoint, vary continuously with the tip's angle. These apex exponents are
calculated analytically by -expansion, and numerically by simulations
in three dimensions. We find that when the polymer can move through the
attachment point, it typically slides to one end; the apex exponents quantify
the entropic barrier to threading the eye of the probe
Shift versus no-shift in local regularizations of Chern-Simons theory
We consider a family of local BRS-invariant higher covariant derivative
regularizations of Chern-Simons theory that do not shift the value of
the Chern-Simons parameter to k+\,{\rm sign}(k)\,\cv at one loop.Comment: phyzzx, 6 pages, FTUAM 94/8, NIKHEF-H 94/14 and UPRF 93/39
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