arXiv subjects

Nikos Kalogeropoulos

Publications and source records attributed to Nikos Kalogeropoulos.

At least 19 recordsLinked to original sources

arXiv2016

Moduli of curve families and (quasi-)conformality of power-law entropies

We present aspects of the moduli of curve families on a metric measure space which may prove useful in calculating, or in providing bounds to, non-additive entropies having a power-law functional form. We use as paradigmatic cases the calculations of the moduli of curve families for a cylinder and for an annulus in $\mathbb{R}^n$. The underlying motivation for these studies is that the definitions and some properties of the modulus of a curve family resembles those of the Tsallis entropy, when the latter is seen from a micro-canonical viewpoint. We comment on the origin of the conjectured invariance of the Tsallis entropy under Möbius transformations of the non-extensive (entropic) parameter. Needing techniques applicable to both locallly Euclidean and fractal classes of spaces, we examine the behavior of the Tsallis functional, via the modulus, under quasi-conformal maps. We comment on properties of such maps and their possible significance for the dynamical foundations of power-law entropies.

cond-mat.stat-mech↗

arXiv2016

Non-additive entropies in ... gravity ?

We present aspects of entropic functionals relatively recently introduced in Physics which are non-additive, in the conventional sense of the word, some of which have a power-law functional form. We use as an example among them, and to be concrete in this work the "Tsallis entropy", which has, arguably, the simplest functional form. We present some of its properties and speculate about its potential uses in semi-Classical and Quantum Gravity.

gr-qc↗

arXiv2015

Entropies from coarse-graining: convex polytopes vs. ellipsoids

We examine the Boltzmann/Gibbs/Shannon $\mathcal{S}_{BGS}$ and the non-additive Havrda-Charvát / Daróczy/Cressie-Read/Tsallis \ $\mathcal{S}_q$ \ and the Kaniadakis $κ$-entropy \ $\mathcal{S}_κ$ \ from the viewpoint of coarse-graining, symplectic capacities and convexity. We argue that the functional form of such entropies can be ascribed to a discordance in phase-space coarse-graining between two generally different approaches: the Euclidean/Riemannian metric one that reflects independence and picks cubes as the fundamental cells and the symplectic/canonical one that picks spheres/ellipsoids for this role. Our discussion is motivated by and confined to the behaviour of Hamiltonian systems of many degrees of freedom. We see that Dvoretzky's theorem provides asymptotic estimates for the minimal dimension beyond which these two approaches are close to each other. We state and speculate about the role that dualities may play in this viewpoint.

cond-mat.stat-mech↗

arXiv2015

Ricci curvature, isoperimetry and a non-additive entropy

Searching for the dynamical foundations of the Havrda-Charvát/Daróczy/Cressie-Read/Tsallis non-additive entropy, we come across a covariant quantity called, alternatively, a generalized Ricci curvature, an $N$-Ricci curvature or a Bakry-Émery-Ricci curvature in the configuration/phase space of a system. We explore some of the implications of this tensor and its associated curvature and present a connection with the non-additive entropy under investigation. We present an isoperimetric interpretation of the non-extensive parameter and comment on further features of the system that can be probed through this tensor.

cond-mat.stat-mech↗

arXiv2014

Groups, non-additive entropy and phase transitions

We investigate the possibility of discrete groups furnishing a kinematic framework for systems whose thermodynamic behaviour may be given by non-additive entropies. Relying on the well-known result of the growth rate of balls of nilpotent groups, we see that maintaining extensivity of the entropy of a nilpotent group requires using a non-Boltzmann/Gibbs/Shannon (BGS) entropic form. We use the Tsallis entropy as an indicative alternative. Using basic results from hyperbolic and random groups, we investigate the genericity and possible range of applicability of the BGS entropy in this context. We propose a sufficient condition for phase transitions, in the context of (multi-) parameter families of non-additive entropies.

cond-mat.stat-mech↗

arXiv2014

Extensive limit of a non-extensive entanglement entropy

An important calculation has been that of the (von Neumann) entanglement entropy of the ground state of 1-dimensional lattice models at criticality and of their massive perturbations. This entropy turned out to be, generally, non-extensive. It was noticed, by contrast, that the Tsallis entropy of such systems can be extensive for a particular value of the non-extensive parameter. This value was expressed as function of the central charge of the underlying conformal field theory. We provide an answer to the question on why for central charge approaching infinity, extensivity of the von Neumann entropy of the ground state is restored.

cond-mat.stat-mech↗

arXiv2014

Long-range interactions, doubling measures and Tsallis entropy

We present a path toward determining the statistical origin of the thermodynamic limit for systems with long-range interactions. We assume throughout that the systems under consideration have thermodynamic properties given by the Tsallis entropy. We rely on the composition property of the Tsallis entropy for determining effective metrics and measures on their configuration/phase spaces. We point out the significance of Muckenhoupt weights, of doubling measures and of doubling measure-induced metric deformations of the metric. We comment on the volume deformations induced by the Tsallis entropy composition and on the significance of functional spaces for these constructions.

cond-mat.stat-mech↗

arXiv2014

Almost additive entropy

We explore consequences of a hyperbolic metric induced by the composition property of the Harvda-Charvat/Daróczy/Cressie-Read/Tsallis entropy. We address the special case of systems described by small deviations of the non-extensive parameter \ $q\approx 1$ \ from the "ordinary" additive case which is described by the Boltzmann/Gibbs/Shannon entropy. By applying the Gromov/Ruh theorem for almost flat manifolds, we show that such systems have a power-law rate of expansion of their configuration/phase space volume. We explore the possible physical significance of some geometric and topological results of this approach.

cond-mat.stat-mech↗

arXiv2013

Nilpotence and the generalized uncertainty principle(s)

We point out that some of the proposed generalized/modified uncertainty principles originate from solvable, or nilpotent at appropriate limits, "deformations" of Lie algebras. We briefly comment on formal aspects related to the well-posedness of one of these algebras. We point out a potential relation of such algebras with Classical Mechanics in the spirit of the symplectic non-squeezing theorem. We also point out their relation to a hierarchy of generalized measure theories emerging in a covariant formalism of quantum gravity.

gr-qc↗

arXiv2013

Asymptotic cones and quantum gravity

Asymptotic cones are structures that encode how a metric space appears when seen from far away. We discuss their meaning and potential significance for quantum gravity.

gr-qc↗

arXiv2013

Tsallis entropy and hyperbolicity

Some preliminary evidence suggests the conjecture that the collective behaviour of systems having long-range interactions may be described more effectively by the Tsallis rather than by the Boltzmann/Gibbs/Shannon entropy. To this end, we examine consequences of the biggest difference between these two entropies: their composition properties. We rely on a metric formalism that establishes the "hyperbolic" nature of Tsallis entropy and explore some of its consequences for the underlying systems. We present some recent and some forthcoming results of our work

cond-mat.stat-mech↗

arXiv2013

Vanishing largest Lyapunov exponent and Tsallis entropy

We present a geometric argument that explains why some systems having vanishing largest Lyapunov exponent have underlying dynamics aspects of which can be effectively described by the Tsallis entropy. We rely on a comparison of the generalised additivity of the Tsallis entropy versus the ordinary additivity of the BGS entropy. We translate this comparison in metric terms by using an effective hyperbolic metric on the configuration/phase space for the Tsallis entropy versus the Euclidean one in the case of the BGS entropy. Solving the Jacobi equation for such hyperbolic metrics effectively sets the largest Lyapunov exponent computed with respect to the corresponding Euclidean metric to zero. This conclusion is in agreement with all currently known results about systems that have a simple asymptotic behaviour and are described by the Tsallis entropy.

cond-mat.stat-mech↗

arXiv2013

Tsallis entropy composition and the Heisenberg group

We present an embedding of the Tsallis entropy into the 3-dimensional Heisenberg group, in order to understand the meaning of generalized independence as encoded in the Tsallis entropy composition property. We infer that the Tsallis entropy composition induces fractal properties on the underlying Euclidean space. Using a theorem of Milnor/Wolf/Tits/Gromov, we justify why the underlying configuration/phase space of systems described by the Tsallis entropy has polynomial growth for both discrete and Riemannian cases. We provide a geometric framework that elucidates Abe's formula for the Tsallis entropy, in terms the Pansu derivative of a map between sub-Riemannian spaces.

math-ph↗

arXiv2012

Weak Chaos from Tsallis Entropy

We present a geometric, model-independent, argument that aims to explain why the Tsallis entropy describes systems exhibiting "weak chaos", namely systems whose underlying dynamics has vanishing largest Lyapunov exponent. Our argument relies on properties of a deformation map of the reals induced by the Tsallis entropy, and its conclusion agrees with all currently known results.

math-ph↗

arXiv2012

Generalized diffusion and asymptotics induced by Tsallis entropy

We formulate and solve the diffusion equation over a previously studied field $\mathcal{R}$, whose construction was motivated by the Tsallis entropy composition property. We compare this solution with the solutions of the diffusion and of the porous medium equations. We comment on the asymptotics of such solutions for large values of their spatial and temporal variables. We present conclusions for the generalised operations inspired by the Tsallis entropy composition and their relations to hyperbolicity.

cond-mat.stat-mech↗

arXiv2012

Nilpotence in Physics: the case of Tsallis entropy

In an attempt to understand the Tsallis entropy composition property, we construct an embedding of the reals into the set of $3\times 3$ upper triangular matrices with real entries. We explore consequences of this embedding and of the geometry of the ambient $3\times 3$ Heisenberg group. This approach establishes the polynomial growth of the volume of phase space of systems described by the Tsallis entropy and provides a general framework for understanding Abe's formula in terms of the Pansu derivative between Riemannian spaces.

math-ph↗

arXiv2012

Escort distributions and Tsallis entropy

We present an argument justifying the origin of the escort distributions used in calculations involving the Tsallis entropy. We rely on an induced hyperbolic Riemannian metric reflecting the generalized composition property of the Tsallis entropy. The mapping of the corresponding Riemannian measure on the space of thermodynamic variables gives the specific form of the escort distributions and provides a geometric interpretation of the non-extensive parameter. In addition, we explain the polynomial rate of increase of the sample space volume for systems described by the Tsallis entropy, thus extending the previously reached conclusions for discrete systems to the case of systems whose evolution is described by flows on Riemannian manifolds.

cond-mat.stat-mech↗

arXiv2012

Tsallis entropy induced metrics and CAT(k) spaces

Generalizing the group structure of the Euclidean space, we construct a Riemannian metric on the deformed set \ $\mathbb{R}^n_q$ \ induced by the Tsallis entropy composition property. We show that the Tsallis entropy is a "hyperbolic analogue" of the "Euclidean" Boltzmann/Gibbs/Shannon entropy and find a geometric interpretation for the nonextensive parameter $q$. We provide a geometric explanation of the uniqueness of the Tsallis entropy as reflected through its composition property, which is provided by the Abe and the Santos axioms. For two, or more, interacting systems described by the Tsallis entropy, having different values of $q$, we argue why a suitable extension of this construction is provided by the Cartan/Alexandrov/Toponogov metric spaces with a uniform negative curvature upper bound.

math-ph↗