Enzo Marinari

Simulated tempering: A New Monte Carlo Scheme

We propose a new global optimization method (Simulated Tempering) for simulating effectively a system with a rough free-energy landscape (i.e., many coexisting states) at finite nonzero temperature. This method is related to simulated annealing, but here the temperature becomes a dynamic variable, and the system is always kept at equilibrium. We analyse the method on the Random Field Ising Model, and we find a dramatic improvement over conventional Metropolis and cluster methods. We analyse and discuss the conditions under which the method has optimal performances.

Glueball masses and string tension in lattice QCD

We study glueball masses in lattice QCD. We present the first numerical determination of the mass of the lowest spin 2 state in the scaling region, and find that it is close to the lowest spin 0 state. We present very precise results for the string tension and for the spin 0 state, obtained by analyzing a large set of operators. We find that finite size effects are significant.

A new method for updating SU(N) matrices in computer simulations of gauge theories

Abstract We present a new method for updating SU( N ) matrices in lattice gauge theories simulations. The new method has been found for the case of SU(3) to be about three times more efficient than the Metropolis method.

A non-perturbative ambiguity free solution of a string model

Abstract We study the m = 3 multicritical string model at d = 0, and we find a solution free of singularities on the real axis. We discuss the consequences of such a finding on the behaviour of macroscopic loops.

The supersymmetric one-dimensional string

Abstract We consider a supersymmetric discretized string. The full string theory is defined as the sum over the triangulations of the surface, which is imbedded in the superspace. In the continuum limit such a string theory is described by an appropriate Wess-Zumino model. We present an explicit computation of the properties of the string in the ID case: we find that supersymmetry is spontaneously broken.

Complex zeros in the partition function of the four-dimensional SU(2) lattice gauge model

Abstract We build up the partition function of the SU(2) lattice gauge model by Monte Carlo method, and search for its zeros in the complex β-plane. They correspond (for a finite lattice) tosingularities in the specific heat. A zero is found in the region where previous results gave a peak in the specific heat.

On the p-adic five-point function

Abstract The Koba-Nielsen amplitude five-point dual function is computed integrating over the p-adic field. Contrary to what happens for the four-point function the infinite product of all the p-adic functions and the usual five-point functions is not a constant.

MicroRNAs as a Selective Channel of Communication between Competing RNAs: a Steady-State Theory

It has recently been suggested that the competition for a finite pool of microRNAs (miRNA) gives rise to effective interactions among their common targets (competing endogenous RNAs or ceRNAs) that could prove to be crucial for posttranscriptional regulation. We have studied a minimal model of posttranscriptional regulation where the emergence and the nature of such interactions can be characterized in detail at steady state. Sensitivity analysis shows that binding free energies and repression mechanisms are the key ingredients for the cross-talk between ceRNAs to arise. Interactions emerge in specific ranges of repression values, can be symmetrical (one ceRNA influences another and vice versa) or asymmetrical (one ceRNA influences another but not the reverse), and may be highly selective, while possibly limited by noise. In addition, we show that nontrivial correlations among ceRNAs can emerge in experimental readouts due to transcriptional fluctuations even in the absence of miRNA-mediated cross-talk.

Replica field theory for deterministic models. II. A non-random spin glass with glassy behaviour

We introduce and sNdy a model which admits a complex landscape without containing quenched disorder. Continuing our previous investigation we introduce a disordered model which allows us to reconstruct ail the main leaturcs of the originnl phase diagram. including a low-T spin-glass phase and a complex dynamical behaviour.

Replica Symmetry Breaking in Short-Range Spin Glasses: Theoretical Foundations and Numerical Evidences

We discuss replica symmetry breaking (RSB) in spin glasses. We update work in this area, from both the analytical and numerical points of view. We give particular attention to the difficulties stressed by Newman and Stein concerning the problem of constructing pure states in spin glass systems. We mainly discuss what happens in finite-dimensional, realistic spin glasses. Together with a detailed review of some of the most important features, facts, data, and phenomena, we present some new theoretical ideas and numerical results. We discuss among others the basic idea of the RSB theory, correlation functions, interfaces, overlaps, pure states, random field, and the dynamical approach. We present new numerical results for the behaviors of coupled replicas and about the numerical verification of sum rules, and we review some of the available numerical results that we consider of larger importance (for example, the determination of the phase transition point, the correlation functions, the window overlaps, and the dynamical behavior of the system).