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Publications of the Research Institute for Mathematical Sciences

Temperature as Order Parameter of Broken Scale Invariance

Izumi Ojima

Published Sep 30, 2004• 20 citations
Publisher

Abstract

In algebraic quantum field theory the (inverse) temperature is shown to be a macroscopic order parameter to parametrize mutually disjoint thermal sectors arising from the broken scale invariance under renormalization-group transformations. This is accomplished in a mathematical formalism for the consistent treatment of explicitly broken symmetries such as broken scale invariance, on the basis of a clearcut criterion for the symmetry breakdown in a unified scheme for sectors proposed recently by the author.

DOI
10.2977/prims/1145475491

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Cambridge University Press eBooks•Feb 28, 2013•0 citations
In algebraic quantum field theory the (inverse) temperature is shown to be a macroscopic order parameter to parametrize mutually disjoint thermal sectors arising from the broken scale invariance under renormalization-group transformations. This is accomplished in a mathematical formalism for the consistent treatment of explicitly broken symmetries such as broken scale invariance, on the basis of a clearcut criterion for the symmetry breakdown in a unified scheme for sectors proposed recently by the author.
In algebraic quantum field theory the (inverse) temperature is shown to be a macroscopic \textit{order parameter} to parametrize mutually disjoint thermal \textit{sectors} arising from the \textit{broken scale invariance} under renormalization-group transformations. This is accomplished in a mathematical formalism for the consistent treatment of \textit{explicitly broken symmetries} such as broken scale invariance, on the basis of a clear-cut criterion for the symmetry breakdown in a unified scheme for sectors proposed recently by the author.
In algebraic quantum field theory the (inverse) temperature is shown to be a macroscopic order parameter to parametrize mutually dis- joint thermal sectors arising from the broken scale invariance under renormalization-group transformations.This is accomplished in a mathematical formalism for the consistent treatment of explicitly broken symmetries such as broken scale invari- ance, on the basis of a clear-cut criterion for the symmetry breakdown in a unified scheme for sectors proposed recently by the author.
A unified scheme for treating generalized superselection sectors is proposed on the basis of the notion of selection criteria to characterize states of relevance to each specific domain in quantum physics, ranging from the relativistic quantum fields in the vacuum situations with unbroken and spontaneously broken internal symmetries, through equilibrium and non-equilibrium states to some basic aspects in measurement processes. This is achieved by the help of c → q and q → c channels: the former determines the states to be selected and to be parameterized by the order parameters, and the latter provides the physical interpretations of selected states in terms of order parameters. This formulation extends the traditional range of applicability of the Doplicher-Roberts construction method for recovering the field algebra and the gauge group (of the first kind) from the data of group invariant observables to the situations with spontaneous symmetry breakdown: in use of the machinery proposed, the physical and mathematical meaning of basic structural ingredients associated with the spontaneously broken symmetry are re-examined, such as the degenerate vacua parameterized by the variables belonging to the relevant homogeneous space, the Goldstone modes and condensates, etc. The geometrical meaning of the space of order parameters is naturally understood in relation with the adjunction as the classifying space of a sector structure. As further examples of applications, some basic notions arising in the mathematical framework of quantum theory are reformulated and examined in connection with control theory.
A unified scheme for treating generalized superselection sectors is proposed on the basis of the notion of selection criteria to characterize states of relevance to each specific domain in quantum physics, ranging from the relativistic quantum fields in the vacuum situations with unbroken and spontaneously broken internal symmetries, through equi- librium and non-equilibrium states (see [1] for details).This is achieved by the help of carrowqcarrow qcarrowq and qarrowcqarrow cqarrowc channels, the former of which determines the states to be selected and to be parametrized by the order parameters defined as the spectrum of the centre constituting the su- perselection sectors, and the latter of which provides, as classifying maps, the physical interpretations of selected states in terms of order parameters.
A unified scheme for treating generalized superselection sectors is proposed on the basis of the notion of selection criteria to characterize states of relevance to each specific domain in quantum physics, ranging from the relativistic quantum fields in the vacuum situations with unbroken and spontaneously broken internal symmetries, through equilibrium and non-equilibrium states to the some basic aspects in measurement processes. This is achieved by the help of \textit{c} →\to→ \textit{q} and \textit{q} →\to→ \textit{c} channels, the former of which determines the states to be selected and to be parametrized by the order parameters defined as the spectrum of the centre constituting the superselection sectors, and the latter of which provides, as classifying maps, the physical interpretations of selected states in terms of order parameters. This formulation extends the traditional range of applicability of the Doplicher-Roberts construction method for recovering the field algebra and the gauge group (of the first kind) from the data of group invariant observables to the situations with spontaneous symmetry breakdown, as will be reported in a succeeding paper.
Classical and quantum criticality In most cases the phases of quantum field theories, in particular those of interest in condensed matter physics, can be described in terms of the behavior of local observables, such as order parameters or currents that transform properly under the symmetries of the theory. Quantum and thermal phase transitions are characterized by the behavior of these observables as a function of temperature and of the coupling constants of the theory. The phase transitions themselves, quantum or thermal, are classified into universality classes, which are represented by the critical exponents which specify the scaling laws of the expectation values of the observables. Historically, the development of this approach to critical behavior goes back to the Landau theory of critical behavior. It acquired its most complete form with the development of the renormalization group (RG) in the late 1960s and early 1970s. It is the centerpiece of Wilson’s approach to quantum field theory, in which all local quantum field theories are defined by the scaling regime of a physical system near a continuous phase transition. From this point of view there is no fundamental difference between classical (or thermal) phase transitions, which are described by the theory of classical critical behavior, and quantum phase transitions. For example, the expectation value of a local order parameter M as the thermal phase transition is approached from below behaves as M ~ (Tc − T) β . Here T c is the critical temperature and β is a critical exponent that depends on the universality class of the thermal phase transition and on the dimensionality of space. While quantum mechanics can play a key role in the existence of the ordered phase, e.g. superfluidity and superconductivity are macroscopic manifestations of essentially quantum-mechanical phenomena, the thermal transition itself is governed entirely by classical statistical mechanics, and quantum mechanics plays a role in setting the value of non-universal quantities such as the critical temperature, etc. On the other hand, in the case of a quantum phase transition, the order parameter M has a similar scaling behavior as a function of the coupling constant, M~(gc−g)β˜, where g is the coupling constant, g c is the critical coupling constant, and β˜ is a critical exponent that depends on the universality class of the quantum phase transition. Here we assume that M has a non-vanishing expectation value only for g < g c .