11,733 research outputs found
A general approach to the sign problem - the factorization method with multiple observables
The sign problem is a notorious problem, which occurs in Monte Carlo
simulations of a system with the partition function whose integrand is not real
positive. The basic idea of the factorization method applied on such a system
is to control some observables in order to determine and sample efficiently the
region of configuration space which gives important contribution to the
partition function. We argue that it is crucial to choose appropriately the set
of the observables to be controlled in order for the method to work
successfully in a general system. This is demonstrated by an explicit example,
in which it turns out to be necessary to control more than one observables.
Extrapolation to large system size is possible due to the nice scaling
properties of the factorized functions, and known results obtained by an
analytic method are shown to be consistently reproduced.Comment: 6 pages, 3 figures, (v2) references added (v3) Sections IV, V and VI
improved, final version accepted by PR
A Study of the Complex Action Problem in a Simple Model for Dynamical Compactification in Superstring Theory Using the Factorization Method
The IIB matrix model proposes a mechanism for dynamically generating four
dimensional space--time in string theory by spontaneous breaking of the ten
dimensional rotational symmetry . Calculations using the
Gaussian expansion method (GEM) lend support to this conjecture. We study a
simple invariant matrix model using Monte Carlo simulations
and we confirm that its rotational symmetry breaks down, showing that lower
dimensional configurations dominate the path integral. The model has a strong
complex action problem and the calculations were made possible by the use of
the factorization method on the density of states of properly
normalized eigenvalues of the space--time moment of inertia
tensor. We study scaling properties of the factorized terms of and
we find them in agreement with simple scaling arguments. These can be used in
the finite size scaling extrapolation and in the study of the region of
configuration space obscured by the large fluctuations of the phase. The
computed values of are in reasonable agreement with GEM
calculations and a numerical method for comparing the free energy of the
corresponding ansatze is proposed and tested.Comment: 7 pages, 4 figures, Talk presented at the XXVIII International
Symposium on Lattice Field Theory, Lattice2010, Villasimius, Italy, June 201
The Area Law in Matrix Models for Large N QCD Strings
We study the question whether matrix models obtained in the zero volume limit
of 4d Yang-Mills theories can describe large N QCD strings. The matrix model we
use is a variant of the Eguchi-Kawai model in terms of Hermitian matrices, but
without any twists or quenching. This model was originally proposed as a toy
model of the IIB matrix model. In contrast to common expectations, we do
observe the area law for Wilson loops in a significant range of scale of the
loop area. Numerical simulations show that this range is stable as N increases
up to 768, which strongly suggests that it persists in the large N limit. Hence
the equivalence to QCD strings may hold for length scales inside a finite
regime.Comment: 12 pages, 4 figure
Production of 92Nb, 92Mo, and 146Sm in the gamma-process in SNIa
The knowledge of the production of extinct radioactivities like 92Nb and
146Sm by photodisintegration processes in ccSN and SNIa models is essential for
interpreting abundances in meteoritic material and for Galactic Chemical
Evolution (GCE). The 92Mo/92Nb and 146Sm/144Sm ratios provide constraints for
GCE and production sites. We present results for SNIa with emphasis on nuclear
uncertainties.Comment: 6 pages, 4 figures, Proceedings of the 13th Symposium on Nuclei in
the Cosmos (NIC XIII), July 2014, Debrecen, Hungar
The Factorization Method for Simulating Systems With a Complex Action
We propose a method for Monte Carlo simulations of systems with a complex
action. The method has the advantages of being in principle applicable to any
such system and provides a solution to the overlap problem. We apply it in
random matrix theory of finite density QCD where we compare with analytic
results. In this model we find non--commutativity of the limits and
which could be of relevance in QCD at finite density.Comment: Talk by K.N.A. at Confinement 2003, Tokyo, July 2003, 5 pages, 4
figures, ws-procs9x6.cl
Monte Carlo Studies of the Dimensionally Reduced 4d SU(N) Super Yang-Mills Theory
We simulate a supersymmetric matrix model obtained from dimensional reduction
of 4d SU(N) super Yang-Mills theory. The model is well defined for finite N and
it is found that the large N limit obtained by keeping g^2 N fixed gives rise
to well defined operators which represent string amplitudes. The space-time
structure which arises dynamically from the eigenvalues of the bosonic matrices
is discussed, as well as the effect of supersymmetry on the dynamical
properties of the model. Eguchi-Kawai equivalence of this model to ordinary
gauge theory does hold within a finite range of scale. We report on new
simulations of the bosonic model for N up to 768 that confirm this property,
which comes as a surprise since no quenching or twist is introduced.Comment: 6 pages, 7 figures, Talk presented by K.N.A. at the HEP 2000 Annual
Workshop of the Hellenic Society for the Study of High Energy Physics at the
University of Ioannina. References added, minor correction
Large N Dynamics of Dimensionally Reduced 4D SU(N) Super Yang-Mills Theory
We perform Monte Carlo simulations of a supersymmetric matrix model, which is
obtained by dimensional reduction of 4D SU(N) super Yang-Mills theory. The
model can be considered as a four-dimensional counterpart of the IIB matrix
model. We extract the space-time structure represented by the eigenvalues of
bosonic matrices. In particular we compare the large N behavior of the
space-time extent with the result obtained from a low energy effective theory.
We measure various Wilson loop correlators which represent string amplitudes
and we observe a nontrivial universal scaling in N. We also observe that the
Eguchi-Kawai equivalence to ordinary gauge theory does hold at least within a
finite range of scale. Comparison with the results for the bosonic case
clarifies the role of supersymmetry in the large N dynamics. It does affect the
multi-point correlators qualitatively, but the Eguchi-Kawai equivalence is
observed even in the bosonic case.Comment: 35 pages, 17 figure
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