<p>We analyse a class of SYK models whose Hamiltonian is the sum of two SYK Hamiltonians with different numbers of fermions <i>q,</i> <InlineEquation ID="IEq1"> <EquationSource Format="MATHML"><math display="inline"> <mover accent="true"> <mi>q</mi> <mo stretchy="true">~</mo> </mover> </math></EquationSource> <EquationSource Format="TEX">\( \overset{\sim }{q} \)</EquationSource> </InlineEquation> in each interaction. We consider both Euclidean and Lorentzian probes of the quantum system in the large <i>N</i> limit. In the strong coupling phase, the entropy provides a diagnostic of the thermal renormalisation group flow. Under certain conditions, two parametrically separated regimes of near-conformal behaviour emerge. The first reproduces the standard linear-in-temperature scaling characteristic of the single SYK model. The system then flows to another near-fixed point whose entropy scaling depends on the ratio <InlineEquation ID="IEq2"> <EquationSource Format="MATHML"><math display="inline"> <mi>n</mi> <mo>=</mo> <mi>q</mi> <mo>/</mo> <mover accent="true"> <mi>q</mi> <mo stretchy="true">~</mo> </mover> </math></EquationSource> <EquationSource Format="TEX">\( n=q/\overset{\sim }{q} \)</EquationSource> </InlineEquation>. For <i>n &lt;</i> 3<i>/</i>2, the entropy exhibits anomalous, stronger-than-linear scaling in temperature. At <i>n</i> = 3<i>/</i>2, there is an additional logarithmic enhancement. Using conformal perturbation theory, we argue that in the infrared regime of the SYK model, there may exist disordered conformal operators with dimensions 1 <i>&lt;</i> ∆ ≤ 3<i>/</i>2. In Lorentzian signature, we study the out-of-time-ordered correlator and show that these deformed theories exhibit near-maximal chaos in both regimes (when they exist). We comment on the relation between the anomalous scalings found here and those observed in certain near-extremal black holes in two and higher dimensions.</p>

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Exploring the infrared landscape of the SYK model

  • Weam Abou Hamdan,
  • Damián A. Galante

摘要

We analyse a class of SYK models whose Hamiltonian is the sum of two SYK Hamiltonians with different numbers of fermions q, q ~ \( \overset{\sim }{q} \) in each interaction. We consider both Euclidean and Lorentzian probes of the quantum system in the large N limit. In the strong coupling phase, the entropy provides a diagnostic of the thermal renormalisation group flow. Under certain conditions, two parametrically separated regimes of near-conformal behaviour emerge. The first reproduces the standard linear-in-temperature scaling characteristic of the single SYK model. The system then flows to another near-fixed point whose entropy scaling depends on the ratio n = q / q ~ \( n=q/\overset{\sim }{q} \) . For n < 3/2, the entropy exhibits anomalous, stronger-than-linear scaling in temperature. At n = 3/2, there is an additional logarithmic enhancement. Using conformal perturbation theory, we argue that in the infrared regime of the SYK model, there may exist disordered conformal operators with dimensions 1 < ∆ ≤ 3/2. In Lorentzian signature, we study the out-of-time-ordered correlator and show that these deformed theories exhibit near-maximal chaos in both regimes (when they exist). We comment on the relation between the anomalous scalings found here and those observed in certain near-extremal black holes in two and higher dimensions.