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A Primer on Resurgent Transseries and Their Asymptotics (1802.10441v2)

Published 28 Feb 2018 in hep-th, hep-lat, hep-ph, math-ph, math.MP, and quant-ph

Abstract: The computation of observables in general interacting theories, be them quantum mechanical, field, gauge or string theories, is a non-trivial problem which in many cases can only be addressed by resorting to perturbative methods. In most physically interesting problems these perturbative expansions result in asymptotic series with zero radius of convergence. These asymptotic series then require the use of resurgence and transseries in order for the associated observables to become nonperturbatively well-defined. Resurgence encodes the complete large-order asymptotic behaviour of the coefficients from a perturbative expansion, generically in terms of (multi) instanton sectors and for each problem in terms of its Stokes constants. Some observables arise from linear problems, and have a finite number of instanton sectors and associated Stokes constants; some other observables arise from nonlinear problems, and have an infinite number of instanton sectors and Stokes constants. By means of two very explicit examples, and with emphasis on a pedagogical style of presentation, this work aims at serving as a primer on the aforementioned resurgent, large-order asymptotics of general perturbative expansions. This includes discussions of transseries, Stokes phenomena, generalized steepest-descent methods, Borel transforms, nonlinear resonance, and alien calculus. Furthermore, resurgent properties of transseries---usually described mathematically via alien calculus---are recast in equivalent physical languages: either a "statistical mechanical" language, as motions in chains and lattices; or a "conformal field theoretical" language, with underlying Virasoro-like algebraic structures.

Citations (211)

Summary

  • The paper introduces resurgent transseries that reconcile divergent perturbative expansions by incorporating nonperturbative effects via instanton sectors.
  • It employs Borel analysis and alien calculus to structure asymptotic behaviors and manage Stokes phenomena in complex quantum systems.
  • The work outlines computational techniques, including Borel-Padé approximants, that extend nonperturbative analysis in quantum field, gauge, and string theories.

Resurgent Transseries and Their Implications in Quantum Theories

The paper entitled "A Primer on Resurgent Transseries and Their Asymptotics" by Inês Aniceto, Gökçe Başar, and Ricardo Schiappa provides an extensive survey of resurgent transseries and their applications to problems in quantum, field, gauge, and string theories. These transseries play a critical role in defining observables in these contexts that are typically only accessible via perturbative methods, which often result in asymptotic series with no radius of convergence.

Overview of Resurgent Transseries

Resurgent transseries are a mathematical formalism that allows for the handling of asymptotic series by encoding nonperturbative information through structures known as transseries. This approach involves the decomposition of perturbative expansions into a series of terms represented by both analytic and non-analytic components—commonly referred to as "instanton sectors", each of which is associated with different exponentials that collectively capture the large order behavior of the series' coefficients.

Key Concepts

Theoretical advancements discussed in the paper include:

  • Stokes Phenomena: This phenomenon describes how different asymptotic expansions are valid in different sectors of the complex plane, whose transitions are encoded in Stokes automorphisms.
  • Borel Analysis: A pivotal technique in avoiding divergent behaviors of perturbative series, Borel transforms simplify these series using analytically continuable elements across singularities, facilitating their resummation.
  • Alien Calculus and Bridge Equations: These provide the formal structure for analyzing singularities of the Borel transform, allowing for the derivation of precise relationships in different sectors of the series.

Implications and Applications

In practical terms, understanding the structure of resurgent series offers valuable insights into nonperturbative effects in quantum theories. For instance, the decomposition of quantum mechanical path integrals into transseries components reveals deeper structures like renormalons and can influence the understanding of QFTs and nonperturbative physics.

Additional implications extend to:

  • Quantum Field Theories: Transseries offer a framework to explore phenomena such as instantons and renormalons which are radiative corrections beyond what convergent series can capture.
  • String Theory and Gauge Theories: The framework is applicable to the paper of large-N expansions and 't Hooft anomalies in string theoretic contexts, showcasing resurgence in the gauge-string duality.
  • Computational Methods: Through techniques like Borel-Padé approximants, resurgent transseries provide computational means to extrapolate beyond the limits of traditional perturbative expansions.

Future Directions

The paper speculates on further advancements, including:

  • Exploring multi-parameter transseries in interesting physical scenarios with multiple scales or couplings.
  • Investigating the role of modular transformations and symmetries in resurgence, linking to topological string theory and integrable models.
  • Delving deeper into Borel-Ecalle resummation techniques, particularly in complex and multinodal sectors which currently challenge computational approaches.

Conclusion

This work underscores the foundational role that resurgent transseries play in rendering meaningful and rigorous nonperturbative descriptions of quantum phenomena. The resurgence framework contributes to the unification of analytic and non-analytic information into coherent mathematical structures poised to advance our understanding of complex physical systems.

By framing these concepts within the algebra of resurgence, the paper provides a roadmap for both identifying the intricate linkages among different sectors of transseries and facilitating their computational realization across various fields of theoretical physics.

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