50,655 research outputs found
Mean-value identities as an opportunity for Monte Carlo error reduction
In the Monte Carlo simulation of both Lattice field-theories and of models of
Statistical Mechanics, identities verified by exact mean-values such as
Schwinger-Dyson equations, Guerra relations, Callen identities, etc., provide
well known and sensitive tests of thermalization bias as well as checks of
pseudo random number generators. We point out that they can be further
exploited as "control variates" to reduce statistical errors. The strategy is
general, very simple, and almost costless in CPU time. The method is
demonstrated in the two dimensional Ising model at criticality, where the CPU
gain factor lies between 2 and 4.Comment: 10 pages, 2 tables. References updated and typos correcte
Pairing Correlations in Finite Systems: From the weak to the strong fluctuations regime
The Particle Number Projected Generator Coordinate Method is formulated for
the pairing Hamiltonian in a detailed way in the projection after variation and
the variation after projection methods. The dependence of the wave functions on
the generator coordinate is analyzed performing numerical applications for the
most relevant collective coordinates. The calculations reproduce the exact
solution in the weak, crossover and strong pairing regimes. The physical
insight of the Ansatz and its numerical simplicity make this theory an
excellent tool to study pairing correlations in complex situations and/or
involved Hamiltonians.Comment: Submitted to EPJ
Strongly misaligned triple system in SR 24 revealed by ALMA
We report the detection of the 1.3 mm continuum and the molecular emission of the disks of the young triple system SR24 by analyzing ALMA (The Atacama Large Millimeter/Submillimter Array) subarcsecond archival observations. We estimate the mass of the disks (0.025 M ⊙ and 4 × 10‑5 M ⊕ for SR24S and SR24N, respectively) and the dynamical mass of the protostars (1.5 M ⊙ and 1.1 M ⊙). A kinematic model of the SR24S disk to fit its C18O (2-1) emission allows us to develop an observational method to determine the tilt of a rotating and accreting disk. We derive the size, inclination, position angle, and sense of rotation of each disk, finding that they are strongly misaligned (108^circ ) and possibly rotate in opposite directions as seen from Earth, in projection. We compare the ALMA observations with 12CO SMA archival observations, which are more sensitive to extended structures. We find three extended structures and estimate their masses: a molecular bridge joining the disks of the system, a molecular gas reservoir associated with SR24N, and a gas streamer associated with SR24S. Finally, we discuss the possible origin of the misaligned SR24 system, concluding that a closer inspection of the northern gas reservoir is needed to better understand it. Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Zapata, L. A.. Universidad Nacional Autónoma de México; MéxicoFil: Gabbasov, R.. Universidad Autónoma del Estado de Hidalgo; Méxic
Optimized Monte Carlo Method for glasses
A new Monte Carlo algorithm is introduced for the simulation of supercooled
liquids and glass formers, and tested in two model glasses. The algorithm is
shown to thermalize well below the Mode Coupling temperature and to outperform
other optimized Monte Carlo methods. Using the algorithm, we obtain finite size
effects in the specific heat. This effect points to the existence of a large
correlation length measurable in equal time correlation functions.Comment: Proceedings of "X International workshop on Disordered Systems" held
in Molveno (Italy), March 200
Finite size effects in the specific heat of glass-formers
We report clear finite size effects in the specific heat and in the
relaxation times of a model glass former at temperatures considerably smaller
than the Mode Coupling transition. A crucial ingredient to reach this result is
a new Monte Carlo algorithm which allows us to reduce the relaxation time by
two order of magnitudes. These effects signal the existence of a large
correlation length in static quantities.Comment: Proceeding of "3rd International Workshop on Complex Systems". Sendai
(Japan). To appear on AIP Conference serie
On the critical behavior of the specific heat in glass-formers
We show numeric evidence that, at low enough temperatures, the potential
energy density of a glass-forming liquid fluctuates over length scales much
larger than the interaction range. We focus on the behavior of translationally
invariant quantities. The growing correlation length is unveiled by studying
the Finite Size effects. In the thermodynamic limit, the specific heat and the
relaxation time diverge as a power law. Both features point towards the
existence of a critical point in the metastable supercooled liquid phase.Comment: Version to be published in Phys. Rev.
The Coulomb-Higgs transition of the three-parameter U(1)-Higgs model
We find a first order Coulomb--Higgs phase transition at moderately large
values of the coupling , and no evidence for a change of order at any
finite value of it.Comment: 3 pages, uuencoded compressed ps file. Contribution to Lattice '9
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