Searcharxiv⌕ Search

arXiv subjects

Franco Ferrari

Publications and source records attributed to Franco Ferrari.

At least 55 records · Page 3Linked to original sources
arXiv2006

Cosmic ray recipes

Cosmic rays represent one of the most fascinating research themes in modern astronomy and physics. After almost a century since their discovery, a huge amount of scientific literature has been written on this topic and it is not always easy to extract from it the necessary information for somebody who approaches the subject for the first time. This has been the main motivation for preparing this article, which is a concise and self-contained review for whoever is interested in studying cosmic rays. The priority has been given here to well established facts, which are not at risk to get obsolete in a few years due to the fast progress of the research in this field. Also many data are presented, which are useful to characterize the doses of ionizing radiation delivered to organisms living on the Earth due to cosmic rays. The technical terms which are often encountered in the scientific literature are explained in a separate appendix.

astro-ph↗
arXiv2005

Directed Polymers with Constrained Winding Angle

In this article we study from a non-perturbative point of view the entanglement of two directed polymers subjected to repulsive interactions given by a Dirac $δ-$function potential. An exact formula of the so-called second moment of the winding angle is derived. This result is used to provide a thorough analysis of entanglement phenomena in the classical system of two polymers subjected to repulsive interactions and related problems. No approximation is made in treating the constraint on the winding angle and the repulsive forces. In particular, we investigate how repulsive forces influence the entanglement degree of the two-polymer system. In the limit of ideal polymers, in which the interactions are switched off, we show that our results are in agreement with those of previous works.

cond-mat.soft↗
arXiv2004

Topologically Linked Polymers are Anyon Systems

We consider the statistical mechanics of a system of topologically linked polymers, such as for instance a dense solution of polymer rings. If the possible topological states of the system are distinguished using the Gauss linking number as a topological invariant, the partition function of an ensemble of N closed polymers coincides with the 2N point function of a field theory containing a set of N complex replica fields and Abelian Chern-Simons fields. Thanks to this mapping to field theories, some quantitative predictions on the behavior of topologically entangled polymers have been obtained by exploiting perturbative techniques. In order to go beyond perturbation theory, a connection between polymers and anyons is established here. It is shown in this way that the topological forces which maintain two polymers in a given topological configuration have both attractive and repulsive components. When these opposite components reach a sort of equilibrium, the system finds itself in a self-dual point similar to that which, in the Landau-Ginzburg model for superconductors, corresponds to the transition from type I to type II superconductivity. The significance of self-duality in polymer physics is illustrated considering the example of the so-called $4-plat$ configurations, which are of interest in the biochemistry of DNA processes like replication, transcription and recombination. The case of static vortex solutions of the Euler-Lagrange equations is discussed.

cond-mat.stat-mech↗
arXiv2003

On Abelian Multi-Chern-Simons Field Theories

In this paper a class of multi-Chern-Simons field theories which is relevant to the statistical mechanics of polymer systems is investigated. Motivated by the problems which one encounters in the treatment of these theories, a general procedure is presented to eliminate the Chern-Simons fields from their action. In this way it has been possible to derive an expression of the partition function of topologically linked polymers which depends explicitly on the topological numbers and does not have intractable nonlocal terms as it happened in previous approaches. The new formulation of multi-Chern-Simons field theories is then used to remove and clarify some inconsistencies and ambiguities which apparently affect field theoretical models of topologically linked polymers. Finally, the limit of disentangled polymers is discussed.

hep-th↗
arXiv2002

Chern-Simons Field Theories with Non-semisimple Gauge Group of Symmetry

Subject of this work is a class of Chern-Simons field theories with non-semisimple gauge group, which may well be considered as the most straightforward generalization of an Abelian Chern-Simons field theory. As a matter of fact these theories, which are characterized by a non-semisimple group of gauge symmetry, have cubic interactions like those of non-abelian Chern-Simons field theories, but are free from radiative corrections. Moreover, at the tree level in the perturbative expansion,there are only two connected tree diagrams, corresponding to the propagator and to the three vertex originating from the cubic interaction terms. For such theories it is derived here a set of BRST invariant observables, which lead to metric independent amplitudes. The vacuum expectation values of these observables can be computed exactly. From their expressions it is possible to isolate the Gauss linking number and an invariant of the Milnor type, which describes the topological relations among three or more closed curves.

hep-th↗
arXiv2001

On A Bosonization Approach To Disordered Systems

In [1] a new bosonization procedure has been illustrated, which allows to express a fermionic gaussian system in terms of commuting variables at the price of introducing an extra dimension. The Fermi-Bose duality principle established in this way has many potential applications also outside the context of gauge field theories in which it has been developed. In this work we present an application to the problem of averaging the correlation functions with respect to random potentials in disordered systems and similar problems.

cond-mat.dis-nn↗
arXiv2001

A Topological Field Theory With a Finite Number of Connected Feynman Diagrams

A new topological field theory is constructed, which is characterized by cubic interactions similar to those of non-abelian Chern-Simons field theories, but still retains the simplicity of the abelian case. The perturbative expansion of this theory contains in fact only two connected Feynman diagrams, the propagator and a three vertex. Apart from the Gauss linking number, the Wilson loop amplitudes generate a further topological invariant, whose physical and mathematical meaning is investigated.

math-ph↗
arXiv2000

Generalized Weierstrass Kernels on the Intersection of Two Complex Hypersurfaces

On plane algebraic curves the so-called Weierstrass kernel plays the same role of the Cauchy kernel on the complex plane. A straightforward prescription to construct the Weierstrass kernel is known since one century. How can it be extended to the case of more general curves obtained from the intersection of hypersurfaces in a $n$ dimensional complex space? This problem is solved in this work in the case $n=3$. As an application, the correlation functions of bosonic string theories are constructed on a canonical curve of genus four.

math.AG↗
arXiv1999

Bosonic Field Propagators on Algebraic Curves

In this paper we investigate massless scalar field theory on non-degenerate algebraic curves. The propagator is written in terms of the parameters appearing in the polynomial defining the curve. This provides an alternative to the language of theta functions. The main result is a derivation of the third kind differential normalized in such a way that its periods around the homology cycles are purely imaginary. All the physical correlation functions of the scalar fields can be expressed in terms of this object. This paper contains a detailed analysis of the techniques necessary to study field theories on algebraic curves. A simple expression of the scalar field propagator is found in a particular case in which the algebraic curves have $Z_n$ internal symmetry and one of the fields is located at a branch point.

hep-th↗
arXiv1999

Field Theories of Topological Random Walks

In this work we derive certain topological theories of transverse vector fields whose amplitudes reproduce topological invariants involving the interactions among the trajectories of three and four random walks. This result is applied to the construction of a field theoretical model which describes the statistical mechanics of an arbitrary number of topologically linked polymers in the context of the analytical approach of Edwards. With respect to previous attempts, our approach is very general, as it can treat a system involving an arbitrary number of polymers and the topological states are not only specified by the Gauss linking number, but also by higher order topological invariants.

hep-th↗
arXiv1998

Topological Entanglement of Polymers and Chern-Simons Field Theory

In recent times some interesting field theoretical descriptions of the statistical mechanics of entangling polymers have been proposed by various authors. In these approaches, a single test polymer fluctuating in a background of static polymers or in a lattice of obstacles is considered. The extension to the case in which the configurations of two or more polymers become non-static is not straightforward unless their trajectories are severely constrained. In this paper we present another approach, based on Chern--Simons field theory, which is able to describe the topological entanglements of two fluctuating polymers in terms of gauge fields and second quantized replica fields.

hep-th↗
arXiv1997

Chern-Simons Field Theories in the Coulomb Gauge

In this talk some recent results in the quantization of Chern-Simons field theories in the Coulomb gauge will be presented. In the first part, the consistency of the Chern-Simons field theories in this gauge is proven using the Dirac's canonical formalism for constrained systems. Despite the presence of non-trivial self-interactions in the gauge fixed functional, it will be shown that the commutation relations between the fields are trivial at any perturbative order in the absence of couplings with matter fields. If these couplings are present, instead, the commutation relations become rather involved, but it is still possible to study their main properties and to show that they vanish at the tree level. In the second part of the talk the perturbative aspects of Chern-Simons field theories in the Coulomb gauge will be analysed. In particular, it will be shown by explicit computations and in a regularization independent way that there are no radiative contributions to the $n-$point correlation functions. Finally the Feynman rules in the Coulomb gauge will be derived on a three dimensional manifold with a spatial section given by a closed and orientable Riemann surface.

hep-th↗
arXiv1997

Operator Formalism for Bosonic Beta-Gamma Fields on General Algebraic Curves

An operator formalism for bosonic $β-γ$ systems on arbitrary algebraic curves is introduced. The classical degrees of freedom are identified and their commutation relations are postulated. The explicit realization of the algebra formed by the fields is given in a Hilbert space equipped with a bilinear form. The construction is based on the "gaussian" representation for $β-γ$ systems on the complex sphere [Alvarez-Gaum\' e et al, Nucl. Phys. B 311 (1988) 333]. Detailed computations are provided for the two and four points correlation functions.

hep-th↗
arXiv1997

Monodromy Properties of the Energy Momentum Tensor on General Algebraic Curves

A new approach to analyze the properties of the energy-momentum tensor $T(z)$ of conformal field theories on generic Riemann surfaces (RS) is proposed. $T(z)$ is decomposed into $N$ components with different monodromy properties, where $N$ is the number of branches in the realization of RS as branch covering over the complex sphere. This decomposition gives rise to new infinite dimensional Lie algebra which can be viewed as a generalization of Virasoro algebra containing information about the global properties of the underlying RS. In the simplest case of hyperelliptic curves the structure of the algebra is calculated in two ways and its central extension is explicitly given. The algebra possess an interesting symmetry with a clear interpretation in the framework of the radial quantization of CFT's with multivalued fields on the complex sphere.

hep-th↗
arXiv1997

Perturbative Analysis of Chern-Simons Field Theory in the Coulomb Gauge

In this paper we analyse the perturbative aspects of Chern-Simons field theories in the Coulomb gauge. We show that in the perturbative expansion of the Green functions there are neither ultraviolet not infrared divergences. Moreover, all the radiative corrections are zero at any loop order. Some problems connected with the Coulomb gauge fixing, like the appearance of spurious singularities in the computation of the Feynman diagrams, are discussed and solved. The regularization used here for the spurious singularities can be easily applied also to the Yang-Mills case, which is affected by similar divergences.

hep-th↗
arXiv1996

Topologically Nontrivial Sectors of the Maxwell Field Theory on Algebraic Curves

In this paper the Maxwell field theory is considered on the $Z_n$ symmetric algebraic curves. As a first result, a large family of nondegenerate metrics is derived for general curves. This allows to treat many differential equations arising in quantum mechanics and field theory on Riemann surfaces as differential equations on the complex sphere. The examples of the scalar fields and of an electron immersed in a constant magnetic field will be briefly investigated. Finally, the case of the Maxwell equations on curves with $Z_n$ group of automorphisms is studied in details. These curves are particularly important because they cover the entire moduli space spanned by the Riemann surfaces of genus $g\le 2$. The solutions of these equations corresponding to nontrivial values of the first Chern class are explicitly constructed.

hep-th↗
arXiv1996

Dirac Quantization of the Chern-Simons Field Theory in the Coulomb Gauge

In this letter the Chern-Simons field theories are studied in the Coulomb gauge using the Dirac's canonical formalism for constrained systems. As a strategy, we first work out the constraints and then quantize, replacing the Dirac brackets with quantum commutators. We find that the Chern-Simons field theories become two dimensional models with no propagation along the time direction. Moreover, we prove that, despite of the presence of non-trivial self-interactions in the gauge fixed functional, the commutation relations between the fields are trivial at any order in perturbation theory in the absence of couplings with matter fields. If these couplings are present, instead, the commutation relations become rather involved, but it is still possible to study their main properties and to show that they vanish at the tree level.

hep-th↗