Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: $T{\overline T}$ deformations and the width of fundamental particles   We provide a simple geometric meaning for deformations of so-called
$T{\overline T}$ type in relativistic and non-relativistic systems.
Deformations by the cross products of energy and momentum currents in
integrable quantum field theories are known to modify the thermodynamic Bethe
ansatz equations by a "CDD factor". In turn, CDD factors may be interpreted as
additional, fixed shifts incurred in scattering processes: a finite width added
to the fundamental particles (or, if negative, to the free space between them).
We suggest that this physical effect is a universal way of understanding
$T{\overline T}$ deformations, both in classical and quantum systems. We first
show this in non-relativistic systems, with particle conservation and
translation invariance, using the deformation formed out of the densities and
currents of particles and momentum. This holds at the level of the equations of
motion, and for any interaction potential, integrable or not. We then argue,
and show by similar techniques in free relativistic particle systems, that
$T\overline T$ deformations of relativistic systems produce the equivalent
phenomenon, accounting for length contractions. We also show that, in both the
relativistic and non-relativistic cases, the width of particles is equivalent
to a state-dependent change of metric, where the distance function discounts
the particles' widths, or counts the additional free space. This generalises
and explains the known field-dependent coordinate change describing $T\overline
T$ deformations. The results connect such deformations with generalised
hydrodynamics, where the relations between scattering shifts, widths of
particles and state-dependent changes of metric have been established.

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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga