50,347 research outputs found
Quantum canonical ensemble and correlation femtoscopy at fixed multiplicities
Identical particle correlations at fixed multiplicity are considered by means
of quantum canonical ensemble of finite systems. We calculate one-particle
momentum spectra and two-particle Bose-Einstein correlation functions in the
ideal gas by using a recurrence relation for the partition function. Within
such a model we investigate the validity of the thermal Wick's theorem and its
applicability for decomposition of the two-particle distribution function. The
dependence of the Bose-Einstein correlation parameters on the average momentum
of the particle pair is also investigated. Specifically, we present the
analytical formulas that allow one to estimate the effect of suppressing the
correlation functions in a finite canonical system. The results can be used for
the femtoscopy analysis of the A+A and p+p collisions with selected (fixed)
multiplicity.Comment: 20 pages, 1 figur
An Exact Fluctuating 1/2-BPS Configuration
This work explores the role of thermodynamic fluctuations in the two
parameter giant and superstar configurations characterized by an ensemble of
arbitrary liquid droplets or irregular shaped fuzzballs. Our analysis
illustrates that the chemical and state-space geometric descriptions exhibit an
intriguing set of exact pair correction functions and the global correlation
lengths. The first principle of statistical mechanics shows that the possible
canonical fluctuations may precisely be ascertained without any approximation.
Interestingly, our intrinsic geometric study exemplifies that there exist exact
fluctuating 1/2-BPS statistical configurations which involve an ensemble of
microstates describing the liquid droplets or fuzzballs. The Gaussian
fluctuations over an equilibrium chemical and state-space configurations
accomplish a well-defined, non-degenerate, curved and regular intrinsic
Riemannian manifolds for all physically admissible domains of black hole
parameters. An explicit computation demonstrates that the underlying chemical
correlations involve ordinary summations, whilst the state-space correlations
may simply be depicted by standard polygamma functions. Our construction
ascribes definite stability character to the canonical energy fluctuations and
to the counting entropy associated with an arbitrary choice of excited boxes
from an ensemble of ample boxes constituting a variety of Young tableaux.Comment: Minor changes, added references, 30 pages, 4 figures, PACS numbers:
04.70.-s: Physics of black holes; 04.70.-Bw: Classical black holes; 04.50.Gh
Higher-dimensional black holes, black strings, and related objects; 04.60.Cf
Gravitational aspects of string theory, accepted for publication in JHE
Nonlinear forced change and nonergodicity: The case of ENSO-Indian monsoon and global precipitation teleconnections
We study the forced response of the teleconnection between the El
Nino-Southern Oscillation (ENSO) and global precipitation in general and the
Indian summer monsoon (IM) in particular in the Max Planck Institute Grand
Ensemble. The forced response of the teleconnection is defined as the
time-dependence of a correlation coefficient evaluated over the ensemble. The
ensemble-wise variability is taken either wrt. spatial averages or dominant
spatial modes in the sense of Maximal Covariance Analysis or Canonical
Correlation Analysis or EOF analysis. We find that the strengthening of the
ENSO-IM teleconnection is robustly or consistently featured in view of all four
teleconnection representations, whether sea surface temperature (SST) or sea
level pressure (SLP) is used to characterise ENSO, and both in the historical
period and under the RCP8.5 forcing scenario. The main contributor to this
strengthening in terms of a linear regression model is the regression
coefficient, which can outcompete even a declining ENSO variability in view of
using the SLP. We also find that the forced change of the teleconnection is
typically nonlinear by (1) formally rejecting the hypothesis that ergodicity
holds, i.e., that expected values of temporal correlation coefficients with
respect to the ensemble equal the ensemble-wise correlation coefficient itself,
and also showing that (2) the trivial contributions of the forced changes of
e.g. the mean SST and/or precipitation to temporal correlations are
insignificant here. We also provide, in terms of the test statistics, global
maps of the degree of nonlinearity/nonergodicity of the forced change of the
teleconnection between local precipitation and ENSO
Anomalous size-dependence of interfacial profiles between coexisting phases of polymer mixtures in thin film geometry: A Monte-Carlo simulation
The interfacial profile between coexisting phases of a binary mixture (A,B)
in a thin film of thickness D and lateral linear dimensions L depends
sensitively on both linear dimensions and on the nature of boundary conditions
and statistical ensembles applied. These phenomena generic for systems in
confined geometry are demonstrated by Monte-Carlo simulations of the bond
fluctuation model of symmetric polymer mixtures. Both the canonical and
semi-grand-canonical ensemble are studied. In the canonical ensemble, the
interfacial width w increases (from small values which are of the same order as
the intrinsic profile) like sqrt{D}, before a crossover to a saturation value
w_max (w_max^2 proportional to ln L) sets in. In the semi-grand-canonical
ensemble, however, one finds the same widths (w proportional to sqrt{D}) as in
the canonical ensemble for not too large L, while for large L the interfacial
profile is smeared out over a finite fraction of the film thickness (w
proportional to D for D -> infinity). We discuss the implications of these
findings for the interpretation of both simulations and experiments.Comment: 42 pages, including 15 PS figures, to appear in JC
Finite-size scaling properties of random transverse-field Ising chains : Comparison between canonical and microcanonical ensembles for the disorder
The Random Transverse Field Ising Chain is the simplest disordered model
presenting a quantum phase transition at T=0. We compare analytically its
finite-size scaling properties in two different ensembles for the disorder (i)
the canonical ensemble, where the disorder variables are independent (ii) the
microcanonical ensemble, where there exists a global constraint on the disorder
variables. The observables under study are the surface magnetization, the
correlation of the two surface magnetizations, the gap and the end-to-end
spin-spin correlation for a chain of length . At criticality, each
observable decays typically as in both ensembles, but the
probability distributions of the rescaled variable are different in the two
ensembles, in particular in their asymptotic behaviors. As a consequence, the
dependence in of averaged observables differ in the two ensembles. For
instance, the correlation decays algebraically as 1/L in the canonical
ensemble, but sub-exponentially as in the microcanonical
ensemble. Off criticality, probability distributions of rescaled variables are
governed by the critical exponent in both ensembles, but the following
observables are governed by the exponent in the microcanonical
ensemble, instead of the exponent in the canonical ensemble (a) in the
disordered phase : the averaged surface magnetization, the averaged correlation
of the two surface magnetizations and the averaged end-to-end spin-spin
correlation (b) in the ordered phase : the averaged gap. In conclusion, the
measure of the rare events that dominate various averaged observables can be
very sensitive to the microcanonical constraint.Comment: 24 page
Density functional theory in the canonical ensemble I General formalism
Density functional theory stems from the Hohenberg-Kohn-Sham-Mermin (HKSM)
theorem in the grand canonical ensemble (GCE). However, as recent work shows,
although its extension to the canonical ensemble (CE) is not straightforward,
work in nanopore systems could certainly benefit from a mesoscopic DFT in the
CE. The stumbling block is the fixed constraint which is responsible for
the failure in proving the interchangeability of density profiles and external
potentials as independent variables. Here we prove that, if in the CE the
correlation functions are stripped off of their asymptotic behaviour (which is
not in the form of a properly irreducible -body function), the HKSM theorem
can be extended to the CE. In proving that, we generate a new {\it hierarchy}
of -modified distribution and correlation functions which have the same
formal structure that the more conventional ones have (but with the proper
irreducible -body behaviour) and show that, if they are employed, either a
modified external field or the density profiles can indistinctly be used as
independent variables. We also write down the -modified free energy
functional and prove that the thermodynamic potential is minimized by the
equilibrium values of the new hierarchy.Comment: 17 pages, IOP style, submitted to J. Phys. Condens. Matte
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