
<!DOCTYPE article
  PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Publishing DTD v1.3 20210610//EN" "JATS-journalpublishing1-3.dtd">
<article dtd-version="1.3" article-type="research-article" xml:lang="en"><front xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:c="http://ns.iop.org/namespaces/content" xmlns:date="http://ns.iop.org/namespaces/functions/date" xmlns:m="http://ns.iop.org/namespaces/meta" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><journal-meta><journal-id journal-id-type="publisher-id">jstat</journal-id><journal-title-group><journal-title>Journal of Statistical Mechanics: Theory and Experiment</journal-title><abbrev-journal-title abbrev-type="IOP">JSTAT</abbrev-journal-title><abbrev-journal-title abbrev-type="publisher">J. Stat. Mech.</abbrev-journal-title></journal-title-group><issn pub-type="epub">1742-5468</issn><publisher><publisher-name>IOP Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="publisher-id">jstatadd0a2</article-id><article-id pub-id-type="doi">10.1088/1742-5468/add0a2</article-id><article-id pub-id-type="manuscript">add0a2</article-id><article-id pub-id-type="other">JSTAT_011P_0125</article-id><article-categories><subj-group subj-group-type="display-article-type"><subject>Paper</subject></subj-group><subj-group subj-group-type="section"><subject>Paper section: Classical statistical mechanics, equilibrium and non-equilibrium</subject></subj-group></article-categories><title-group><article-title>Geometric theory of (extended) time-reversal symmetries in stochastic processes: II. Field theory</article-title></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name name-style="western"><surname>O’Byrne</surname><given-names>J</given-names></name><xref ref-type="aff" rid="jstatadd0a2af1">1</xref><xref ref-type="aff" rid="jstatadd0a2af2">2</xref><xref ref-type="fn" rid="jstatadd0a2fn1"><sup>*</sup></xref><email>jeremy.obyrne@sorbonne-universite.fr</email></contrib><contrib contrib-type="author"><name name-style="western"><surname>Cates</surname><given-names>M E</given-names></name><xref ref-type="aff" rid="jstatadd0a2af1">1</xref></contrib><aff id="jstatadd0a2af1">
<label>1</label><institution>DAMTP, Centre for Mathematical Sciences, University of Cambridge</institution>, Wilberforce Road, Cambridge CB3 0WA, <country>United Kingdom</country></aff><aff id="jstatadd0a2af2">
<label>2</label>Laboratoire Jean Perrin, <institution>Sorbonne Université</institution>, 4 Place Jussieu, Paris 75005, <country>France</country></aff></contrib-group><author-notes><fn id="jstatadd0a2fn1"><label>*</label><p>Author to whom any correspondence should be addressed.</p></fn></author-notes><pub-date iso-8601-date="2025-05-01" pub-type="ppub"><day>01</day><month>05</month><year>2025</year></pub-date><pub-date iso-8601-date="2025-05-19" pub-type="epub"><day>19</day><month>05</month><year>2025</year></pub-date><pub-date iso-8601-date="2025-05-18" pub-type="open-access"><day>18</day><month>05</month><year>2025</year></pub-date><volume>2025</volume><issue>5</issue><elocation-id content-type="artnum">053204</elocation-id><supplementary-material content-type="colour-figures" orientation="portrait" position="float"/><history><date date-type="received"><day>15</day><month>01</month><year>2025</year></date><date date-type="rev-recd"><day>09</day><month>04</month><year>2025</year></date><date date-type="accepted"><day>12</day><month>04</month><year>2025</year></date><date date-type="oa-requested"><day>25</day><month>04</month><year>2025</year></date></history><permissions><copyright-statement>© 2025 The Author(s). Published on behalf of SISSA Medialab srl by IOP Publishing Ltd</copyright-statement><copyright-year>2025</copyright-year><license license-type="cc-by" xlink:href="https://creativecommons.org/licenses/by/4.0/"><license-p>
<graphic content-type="print" orientation="portrait" position="float" xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstatadd0a2license.eps"/>
<graphic content-type="online" orientation="portrait" position="float" xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstatadd0a2license.gif"/>
Original content from this work may be used under the terms of the <ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 license</ext-link>. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.</license-p></license></permissions><self-uri content-type="pdf" xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstat_2025_5_053204.pdf?Expires=1748268402&amp;Signature=EszgsxFeDZqHPqHuRQ25AWn7aIb29R2edo1~8vcVA8d07tV9NcI7fxFMNq-oIxk-mi0K45PICV9ivqYHhqwZa8mH7Enej~6LvXMRJv5YYlhnHdBfGuwjQZ015YrUUE-8fqkpQHerm9jOmDuX5teUrj-B8SkyXBIw-1RrUzw~DG2L9silEK89Uwd-Ev8WlgpoJfVAvrlyM-M-Z39lZFF2lI6aEWmcRFYrijcs8h7GOd~kfCUW~4CHotvfW2Jhaa2-7Y27E3ppW0QufVZLDBaaRlUyFXOpzinPnHeG3f44MeXVoZpe9JIb3endBxx9vVkVMmvQT8VgCp0-PqmS0oOQYQ__&amp;Key-Pair-Id=KL1D8TIY3N7T8"/><abstract abstract-type="standard"><title>Abstract</title><p>In this article, we study the time-reversal properties of a generic Markovian stochastic field dynamics with Gaussian noise. We introduce a convenient functional geometric formalism that allows us to straightforwardly generalize known results from finite dimensional systems to the case of continuous fields. We give, at field level, full reversibility conditions for three notions of time-reversal defined in the first article of this two-part series, namely T-, MT-, and EMT-reversibility. When the noise correlator is invertible, these reversibility conditions do not make reference to any generically unknown function like the stationary probability, and can thus be verified systematically. Focusing on the simplest of these notions, where only the time variable is flipped upon time reversal, we show that time-reversal symmetry breaking is quantified by a single geometric object: the vorticity two-form, which is a two-form over the functional space <inline-formula><tex-math><?CDATA $\mathbb{F}$?></tex-math><mml:math overflow="scroll"><mml:mrow><mml:mrow><mml:mi mathvariant="double-struck">F</mml:mi></mml:mrow></mml:mrow></mml:math><inline-graphic xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstatadd0a2ieqn1.gif"/></inline-formula> to which the field belongs. Reversibility then amounts to the cancellation of this vorticity two-form. This condition applies at distributional level and can thus be difficult to use in practice. For fields that are defined on a spatial domain of dimension <italic toggle="yes">d</italic> = 1, we overcome this problem by building a basis of the space of two-forms <inline-formula><tex-math><?CDATA $\Omega^2(\mathbb{F})$?></tex-math><mml:math overflow="scroll"><mml:mrow><mml:msup><mml:mi mathvariant="normal">Ω</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mi mathvariant="double-struck">F</mml:mi></mml:mrow><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math><inline-graphic xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstatadd0a2ieqn2.gif"/></inline-formula>. Reversibility is then equivalent to the vanishing of the vorticity’s coordinates in this basis, a criterion that is readily applicable to concrete examples. Furthermore, we show that this basis provides a natural direct-sum decomposition of <inline-formula><tex-math><?CDATA $\Omega^2(\mathbb{F})$?></tex-math><mml:math overflow="scroll"><mml:mrow><mml:msup><mml:mi mathvariant="normal">Ω</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mi mathvariant="double-struck">F</mml:mi></mml:mrow><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math><inline-graphic xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstatadd0a2ieqn3.gif"/></inline-formula>, each subspace of which is associated with a distinctive kind of phenomenology. This decomposition enables a classification of celebrated out-of-equilibrium phenomena, ranging from non-reciprocal (chaser/chased) interactions to the flocking of active agents, dynamical reaction-diffusion patterns, and interface-growth dynamics. We then partially extend these results to dimensions <italic toggle="yes">d</italic> &gt; 1. Furthermore, we study several notions of entropy production and show, in particular, the entropy production rate to be a linear functional of the vorticity two-form, which implies that the factors in our decomposition of <inline-formula><tex-math><?CDATA $\Omega^2(\mathbb{F})$?></tex-math><mml:math overflow="scroll"><mml:mrow><mml:msup><mml:mi mathvariant="normal">Ω</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mi mathvariant="double-struck">F</mml:mi></mml:mrow><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math><inline-graphic xlink:href="https://content.cld.iop.org/journals/1742-5468/2025/5/053204/revision3/jstatadd0a2ieqn4.gif"/></inline-formula> can be interpreted as independent sources of entropy production. Finally, we discuss how extending our results to more general situations could provide a natural framework for the generic study of the notoriously diverse and surprising behavior of active systems at their boundaries. The geometric framework offered in this paper is illustrated throughout by reference to particular models that break time-reversal symmetry, such as Active Model B.</p></abstract><kwd-group kwd-group-type="author"><kwd>dynamical processes</kwd><kwd>exact results</kwd><kwd>fluctuating hydrodynamics</kwd><kwd>stochastic thermodynamics</kwd></kwd-group><counts><page-count count="95"/></counts><custom-meta-group><custom-meta><meta-name>crossmark</meta-name><meta-value>yes</meta-value></custom-meta></custom-meta-group></article-meta></front><back><ack xmlns=""><title>Acknowledgments</title><p>The authors thank Julien Tailleur for useful discussions and Balázs Németh for a careful reading of the manuscript and for greatly simplifying the argument that appears in appendix <xref ref-type="sec" rid="jstatadd0a2s8">D.1</xref>. This work was partially funded by the European Research Council under the Horizon 2020 Programme (ERC Grant Agreement No. 740269) and the Horizon Europe Programme (ERC Synergy Grant <italic toggle="yes">Shapincellfate</italic>).</p></ack></back></article>