12,415 research outputs found
Biosatellite attitude stabilization and control system
Design and operation of attitude stabilization and control system for Biosatellit
The role of initial conditions in the ageing of the long-range spherical model
The kinetics of the long-range spherical model evolving from various initial
states is studied. In particular, the large-time auto-correlation and -response
functions are obtained, for classes of long-range correlated initial states,
and for magnetized initial states. The ageing exponents can depend on certain
qualitative features of initial states. We explicitly find the conditions for
the system to cross over from ageing classes that depend on initial conditions
to those that do not.Comment: 15 pages; corrected some typo
Field-theory results for three-dimensional transitions with complex symmetries
We discuss several examples of three-dimensional critical phenomena that can
be described by Landau-Ginzburg-Wilson theories. We present an
overview of field-theoretical results obtained from the analysis of high-order
perturbative series in the frameworks of the and of the
fixed-dimension d=3 expansions. In particular, we discuss the stability of the
O(N)-symmetric fixed point in a generic N-component theory, the critical
behaviors of randomly dilute Ising-like systems and frustrated spin systems
with noncollinear order, the multicritical behavior arising from the
competition of two distinct types of ordering with symmetry O() and
O() respectively.Comment: 9 pages, Talk at the Conference TH2002, Paris, July 200
Dynamic crossover in the global persistence at criticality
We investigate the global persistence properties of critical systems relaxing
from an initial state with non-vanishing value of the order parameter (e.g.,
the magnetization in the Ising model). The persistence probability of the
global order parameter displays two consecutive regimes in which it decays
algebraically in time with two distinct universal exponents. The associated
crossover is controlled by the initial value m_0 of the order parameter and the
typical time at which it occurs diverges as m_0 vanishes. Monte-Carlo
simulations of the two-dimensional Ising model with Glauber dynamics display
clearly this crossover. The measured exponent of the ultimate algebraic decay
is in rather good agreement with our theoretical predictions for the Ising
universality class.Comment: 5 pages, 2 figure
An exact solution for the KPZ equation with flat initial conditions
We provide the first exact calculation of the height distribution at
arbitrary time of the continuum KPZ growth equation in one dimension with
flat initial conditions. We use the mapping onto a directed polymer (DP) with
one end fixed, one free, and the Bethe Ansatz for the replicated attractive
boson model. We obtain the generating function of the moments of the DP
partition sum as a Fredholm Pfaffian. Our formula, valid for all times,
exhibits convergence of the free energy (i.e. KPZ height) distribution to the
GOE Tracy Widom distribution at large time.Comment: 4 pages, no figur
Time evolution of 1D gapless models from a domain-wall initial state: SLE continued?
We study the time evolution of quantum one-dimensional gapless systems
evolving from initial states with a domain-wall. We generalize the
path-integral imaginary time approach that together with boundary conformal
field theory allows to derive the time and space dependence of general
correlation functions. The latter are explicitly obtained for the Ising
universality class, and the typical behavior of one- and two-point functions is
derived for the general case. Possible connections with the stochastic Loewner
evolution are discussed and explicit results for one-point time dependent
averages are obtained for generic \kappa for boundary conditions corresponding
to SLE. We use this set of results to predict the time evolution of the
entanglement entropy and obtain the universal constant shift due to the
presence of a domain wall in the initial state.Comment: 27 pages, 10 figure
Bethe Ansatz approach to quench dynamics in the Richardson model
By instantaneously changing a global parameter in an extended quantum system,
an initially equilibrated state will afterwards undergo a complex
non-equilibrium unitary evolution whose description is extremely challenging. A
non-perturbative method giving a controlled error in the long time limit
remained highly desirable to understand general features of the quench induced
quantum dynamics. In this paper we show how integrability (via the algebraic
Bethe ansatz) gives one numerical access, in a nearly exact manner, to the
dynamics resulting from a global interaction quench of an ensemble of fermions
with pairing interactions (Richardson's model). This possibility is deeply
linked to the specific structure of this particular integrable model which
gives simple expressions for the scalar product of eigenstates of two different
Hamiltonians. We show how, despite the fact that a sudden quench can create
excitations at any frequency, a drastic truncation of the Hilbert space can be
carried out therefore allowing access to large systems. The small truncation
error which results does not change with time and consequently the method
grants access to a controlled description of the long time behavior which is a
hard to reach limit with other numerical approaches.Comment: Proceedings of the CRM (Montreal) workshop on Integrable Quantum
Systems and Solvable Statistical Mechanics Model
Entanglement entropy of random quantum critical points in one dimension
For quantum critical spin chains without disorder, it is known that the
entanglement of a segment of N>>1 spins with the remainder is logarithmic in N
with a prefactor fixed by the central charge of the associated conformal field
theory. We show that for a class of strongly random quantum spin chains, the
same logarithmic scaling holds for mean entanglement at criticality and defines
a critical entropy equivalent to central charge in the pure case. This
effective central charge is obtained for Heisenberg, XX, and quantum Ising
chains using an analytic real-space renormalization group approach believed to
be asymptotically exact. For these random chains, the effective universal
central charge is characteristic of a universality class and is consistent with
a c-theorem.Comment: 4 pages, 3 figure
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