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The QCD Equation of State in Small Systems

by W. A. Horowitz, Alexander Rothkopf

This is not the latest submitted version.

Submission summary

As Contributors: William Horowitz
Arxiv Link: (pdf)
Date submitted: 2021-09-14 08:37
Submitted by: Horowitz, William
Submitted to: SciPost Physics Proceedings
Proceedings issue: 50th International Symposium on Multiparticle Dynamics (ISMD2021)
Academic field: Physics
  • High-Energy Physics - Theory
  • High-Energy Physics - Phenomenology
  • Nuclear Physics - Theory
Approaches: Theoretical, Phenomenological


We present first results on just such finite system size corrections to the equation of state, trace anomaly, and speed of sound for two model systems: 1) free, massless scalar theory and 2) quenched QCD with periodic boundary conditions (PBC). We further present work-in-progress results for quenched QCD with Dirichlet boundary conditions.

Current status:
Has been resubmitted

Submission & Refereeing History

Resubmission 2109.01422v2 on 2 March 2022

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Submission 2109.01422v1 on 14 September 2021

Reports on this Submission

Anonymous Report 1 on 2022-2-16 (Invited Report)


The structure in terms of a mix of analytic toy model and results from more realistic lattice calculations, with physical comparisons of the two is very nice, and mostly accessible.


The abstract seems to start mid-paragraph! Some initial context appears to have been accidentally trimmed.

In section 2, should the "phenomenologically relevant T ∼ 400 MeV" be phenomenologically *irrelevant*, since the volume is large and the finite-size effects small? This seems to be the case for the "plates" picture, but not the others, which fit the ~10% effect in the text. This part could do with some expansion to explain the relevance of the plates/tube/box labels, and the logic being used to argue T and TxL values in A+A and p+p systems: to a non-specialist like myself, this bit is interesting but opaque.

It would be good to give more physics context to the trace-anomaly discussion and conclusion: what effect can this reduced coupling / increased speed of sound be expected to have on e.g. flow observables?


A well-written contribution. I would just request a few improvements to the text (cf. the "weaknesses" field) to make it more comprehensible by non-specialists who can't follow the implicit logic or significance in some of the arguments made.

Requested changes

See three issues raised in "weaknesses"

  • validity: high
  • significance: high
  • originality: high
  • clarity: good
  • formatting: excellent
  • grammar: excellent

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