arXiv subjects

Simeon Hellerman

Publications and source records attributed to Simeon Hellerman.

At least 19 recordsLinked to original sources

arXiv2025

Resurgence Analysis of the Nambu-Jona-Lasinio model at large charge

We study the fixed point of the three-dimensional NJL model in a double-scaling limit where both the charge $Q$ and the number of fermion flavors $N$ become large with a fixed ratio $q=Q/(2N)$. While a similar analysis has been performed for the bosonic O(N) model, fermionic models pose new challenges. In this work, we systematically explore the CFT spectrum in both the large and small $q$ limits beyond the first few orders, and perform a resurgence analysis. Through this approach, we identify the exponential corrections that relate the convergent small-$q$ expansion to the asymptotic large-$q$ behavior. Our results are suggestive of a geometric interpretation of these results in terms of the worldline of particles moving along the geodesics on the cylinder.

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arXiv2023

The unitary Fermi gas at large charge and large N

We study the unitary Fermi gas in a harmonic trapping potential starting from a microscopic theory in the limit of large charge and large number of fermion flavors N. In this regime, we present an algorithmic procedure for extracting data from perturbation theory, order-by-order, without the need for other assumptions. We perform a gradient expansion in the interior of the particle cloud, sufficiently far from the cloud edge where the particle density drops rapidly to zero. In this latter region we present the first microscopic computation characterizing the contribution of the edge terms. The microscopic theory reproduces the predictions of the superfluid EFT, including the action, the form of the gap equation, and the energy of the system in a harmonic trap (which maps, via the non-relativistic state-operator correspondence, to the scaling dimension of the lowest operator of charge Q). We additionally give the Wilsonian coefficients at leading order in N up to NNLO in the large-charge expansion.

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arXiv2023

Integrability of Large-Charge Sectors in Generic 2D EFTs

It is shown that integrability is an accidental property of generic two-dimensional $O(2)$-symmetric asymptotically-free theories in the regime where the charge density is much larger than the dynamical scale. We show this by constructing an infinite tower of higher-spin conserved currents in the most generic effective Lagrangian at large chemical potential to all orders in perturbative expansion in the renormalization-group invariant coupling constant.

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arXiv2022

Fermionic CFTs at large charge and large N

We study the large-charge sector of large-N fermionic CFTs in three dimensions. Depending on the model and the nature of the fixed charge, we find two types of descriptions: in terms of a superfluid or a Fermi sphere. We explicitly compute the conformal dimensions of the lowest operator of fixed charge and in the superfluid case verify the EFT predictions for the phonon spectrum.

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arXiv2022

Nonrelativistic CFTs at Large Charge: Casimir Energy and Logarithmic Enhancements

The unitary Fermi gas, by virtue of its description as a nonrelativistic conformal field theory, has proven an interesting system by which the quantum properties of CFT can be held to experimental verification. Here, we examine the structure of conformal dimensions of charge-Q operators in nonrelativistic CFT, in the large-Q regime, from the non-linear sigma model perspective. We discuss in detail the renormalization of edge divergences using dimensional regularization, elucidating the presence of $\log(Q)$ terms in the large-charge expansion. Finally we use dimensional regularization to compute the universal one-loop $Q^0 \log(Q)$ contribution to the ground-state energy in $d = 3$ spatial dimensions, with the result $\left.Δ(Q)\right|_{Q^0} = \frac{1}{3\sqrt{3}} \log(Q) + \text{const.}$

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arXiv2021

On the exponentially small corrections to ${\cal N} = 2$ superconformal correlators at large R-charge

In this note we consider Coulomb-branch chiral primary correlation functions in ${\cal N} = 2$ superconformal QCD with gauge group $SU(2)$, in the limit of large R-charge ${\cal J} = 2n$ for the chiral primary operators $[{\cal O}(x)]^ n$ with the inverse gauge coupling $τ$ held fixed. In previous work, these correlation functions were determined to all orders in $n$, up to unknown exponentially small corrections. In this paper we determine the first several orders of the asymptotic expansion of the exponentially small correction itself. To do this we use: the physical interpretation of the exponentially small correction as the virtual propagation of a massive BPS particle, to fix the leading term in the expansion; the supersymmetric recursion relations to derive differential equations for the coupling-dependence of the subleading terms; and the double-scaling limit, to fix undetermined coefficients in the solution of the differential equation. We calculate the expansion of the exponentially small term up to and including relative order $n^{-{5\over 2}}$. We also use the recursion relations to calculate the subleading large-${\cal J}$ corrections to the exponentially small correction in the double-scaling limit, up to and including relative order $n^{-5}$ at fixed double-scaled coupling $λ$. We compare the expansion to exact results from supersymmetric localization at the coupling $τ= {{25}\over π} i$, up to $n=150$. At values $n\sim 100-150$, we find the fixed-coupling and double-scaled large-R-charge expansions are accurate to within one part in $10^ 6$ and $10^ 8$, respectively, of the size of the exponentially small correction itself. Relative to the full correlator including the dominant EFT contribution, these estimates give results accuracte to one part in $10^{15}$ and $10^{17}$, respectively.

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arXiv2021

Large R-charge EFT correlators in N=2 SQCD

We consider large-R-charge Coulomb branch correlation functions in $\mathcal{N} = 2$ superconformal QCD in D=4 dimensions, with gauge group $SU(2)$ and $N_f = 4$ hypermultiplets in the fundamental representation. Using information from supersymmetric recursion relations, S-duality, and matching of EFT parameters with the double-scaling limit, we give an exact formula for the massless Coulomb branch EFT contribution to the correlation function two-point functions of the n.th power of the chiral ring generator, $G_{2n}^{\text{(EFT)}} = \frac{2^{4n}}{Z_{S^4}[τ]} Γ(2n + 5/2) e^{A[τ]n + B[τ]}$ with $A[τ]$ and $B[τ]$ given as explicit functions of the coupling constant $τ$ in closed form. We note the precise agreement of the EFT formula with supersymmetric localization even at low values of $n$, and discuss aspects of the post-EFT remainder contributed by the macroscopic virtual propagation of massive particles.

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arXiv2021

Quantum Information Theory of the Gravitational Anomaly

We show that the standard notion of entanglement is not defined for gravitationally anomalous two-dimensional theories because they do not admit a local tensor factorization of the Hilbert space into local Hilbert spaces. Qualitatively, the modular flow cannot act consistently and unitarily in a finite region, if there are different numbers of states with a given energy traveling in the two opposite directions. We make this precise by decomposing it into two observations: First, a two-dimensional CFT admits a consistent quantization on a space with boundary only if it is not anomalous. Second, a local tensor factorization always leads to a definition of consistent, unitary, energy-preserving boundary condition. As a corollary we establish a generalization of the Nielsen-Ninomiya theorem to all two-dimensional unitary local QFTs: No continuum quantum field theory in two dimensions can admit a lattice regulator unless its gravitational anomaly vanishes. We also show that the conclusion can be generalized to six dimensions by dimensional reduction on a four-manifold of nonvanishing signature. We advocate that these points be used to reinterpret the gravitational anomaly quantum-information-theoretically, as a fundamental obstruction to the localization of quantum information.

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arXiv2020

Droplet-Edge Operators in Nonrelativistic Conformal Field Theories

We consider the large-charge expansion of the charged ground state of a Schrodinger-invariant, nonrelativistic conformal field theory in a harmonic trap, in general dimension d. In the existing literature, the energy in the trap has been computed to next-to-leading order (NLO) at large charge Q, which comes from the classical contribution of two higher-derivative terms in the effective field theory. In this note, we explain the structure of operators localized at the edge of the droplet, where the density drops to zero. We list all operators contributing to the ground-state energy with nonnegative powers of Q in the large-Q expansion. As a test, we use dimensional regularization to reproduce the calculation of the NLO ground state energy by Kravec and Pal , and we recover the same universal coefficient for the logarithmic term as in that work. We refine the derivation by presenting a systematic operator analysis of the possible edge counterterms, showing that different choices of cutoff procedures must yield the same renormalized result up to an enumerable list of Wilson coefficients for conformally invariant local counterterms at the droplet edge. We also demonstrate the existence of a previously unnoticed edge contribution to the ground-state operator dimension of order Q^{{2\over 3} - {1\over d}} in d spatial dimensions. Finally, we show there is no bulk or edge counterterm scaling as Q^0 in two spatial dimensions, which establishes the universality of the order Q^0 term in large-Q expansion of the lowest charged operator dimension in d=2.

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arXiv2020

S-duality and correlation functions at large R-charge

We study the ratio of pairs of adjacent correlators of Coulomb-branch operators in $SU(2)$ $\mathcal{N}=2$ SQCD with four flavors within the framework of the Large Quantum Number Expansion. Capitalizing on the order-by-order S-duality invariance of the large-R-charge expansion we compute ab initio the dependence of the leading large-$\mathcal{J}$ behavior on the marginal coupling $τ$ and we find excellent agreement with numerical estimates from localization.

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arXiv2019

On the CFT Operator Spectrum at Large Global Charge

We calculate the anomalous dimensions of operators with large global charge $J$ in certain strongly coupled conformal field theories in three dimensions, such as the O(2) model and the supersymmetric fixed point with a single chiral superfield and a $W = Φ^3$ superpotential. Working in a $1/J$ expansion, we find that the large-$J$ sector of both examples is controlled by a conformally invariant effective Lagrangian for a Goldstone boson of the global symmetry. For both these theories, we find that the lowest state with charge $J$ is always a scalar operator whose dimension $Δ_J$ satisfies the sum rule $ J^2 Δ_J - \left( \tfrac{J^2}{2} + \tfrac{J}{4} + \tfrac{3}{16} \right) Δ_{J-1} - \left( \tfrac{J^2}{2} - \tfrac{J}{4} + \tfrac{3}{16} \right) Δ_{J+1} = 0.035147 $ up to corrections that vanish at large $J$. The spectrum of low-lying excited states is also calculable explcitly: For example, the second-lowest primary operator has spin two and dimension $Δ\ll J + \sqrt{3}$. In the supersymmetric case, the dimensions of all half-integer-spin operators lie above the dimensions of the integer-spin operators by a gap of order $J^{1/2}$. The propagation speeds of the Goldstone waves and heavy fermions are $\frac{1}{\sqrt{2}}$ and $\pm \frac{1}{2}$ times the speed of light, respectively. These values, including the negative one, are necessary for the consistent realization of the superconformal symmetry at large $J$.

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arXiv2019

Universal correlation functions in rank 1 SCFTs

Carrying to higher precision the large-$\mathcal{J}$ expansion of Hellerman and Maeda, we calculate to all orders in $1/\mathcal{J}$ the power-law corrections to the two-point functions $\mathcal{Y}_n \equiv |x - y|^{2nΔ_{\mathcal{O}}} \langle {\mathcal{O}}_n(x) \bar{\mathcal{O}}_n(y) \rangle$ for generators $\mathcal{O}$ of Coulomb branch chiral rings in four-dimensional $\mathcal{N} =2$ superconformal field theories. We show these correlators have the universal large-$n$ expansion \[ \log(\mathcal{Y}_n) \simeq \mathcal{J} \mathbf{A} + \mathbf{B} + \log(Γ( \mathcal{J} + α+ 1)) , \] where $\mathcal{J} \equiv 2 n Δ_{\mathcal{O}}$ is the total $R$-charge of $\mathcal{O}_n$, the $\mathbf{A}$ and $\mathbf{B}$ are theory-dependent coefficients, $α$ is the coefficient of the Wess-Zumino term for the Weyl $a$-anomaly, and the $\simeq$ denotes equality up to terms exponentially small in $\mathcal{J}$. Our methods combine the structure of the Coulomb-branch effective field theory (EFT) with the supersymmetric recursion relations. However, our results constrain the power-law corrections to all orders, even for non-Lagrangian theories to which the recursion relations do not apply. For the case of $\mathcal{N} = 2$ SQCD, we also comment on the nature of the exponentially small corrections, which can be calculated to high precision in the double-scaling limit recently discussed by Bourget et al. We show the exponentially small correction is consistent with the interpretation of the EFT breaking down due to the propagation of massive BPS particles over distances of order of the infrared scale $|x - y|$.

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arXiv2018

Observables in Inhomogeneous Ground States at Large Global Charge

As a sequel to previous work, we extend the study of the ground state configuration of the $D=3$, Wilson-Fisher conformal $O(4)$ model. In this work, we prove that for generic ratios of two charge densities, $ρ_1/ρ_2$, the ground-state configuration is inhomogeneous and that the inhomogeneity expresses itself towards longer spatial periods. This is the direct extension of the similar statements we previously made for $ρ_1/ρ_2\ll 1$. We also compute, at fixed set of charges, $ρ_1,\, ρ_2$, the ground state energy and the two-point function(s) associated with this inhomogeneous configuration on the torus. The ground state energy was found to scale $(ρ_1+ρ_2)^{3/2}$, as dictated by dimensional analysis and similarly to the case of the $O(2)$ model. Unlike the case of the $O(2)$ model, the ground also strongly violates cluster decomposition in the large-volume, fixed-density limit, with a two-point function that is negative definite at antipodal points of the torus at leading order at large charge.

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arXiv2017

On the Large $R$-charge Expansion in ${\mathcal N} = 2$ Superconformal Field Theories

In this note we study two point functions of Coulomb branch chiral ring elements with large $R$-charge, in quantum field theories with ${\mathcal N} = 2$ superconformal symmetry in four spacetime dimensions. Focusing on the case of one-dimensional Coulomb branch, we use the effective-field-theoretic methods of arXiv:1706.05743, to estimate the two-point function $${\mathcal Y}_n \equiv |x-y|^{2nΔ_{\mathcal O}}\left<({\mathcal O}(x))^n(\bar{\mathcal O}(y))^n\right>$$ in the limit where the operator insertion On has large total $R$-charge ${\mathcal J} = nΔ_{\mathcal O}$. We show that ${\mathcal Y}_n$ has a nontrivial but universal asymptotic expansion at large ${\mathcal J}$, of the form $${\mathcal Y}_n = {\mathcal J}! \left(\frac{\left| {\mathbf N}_{\mathcal O}\right|}{2π}\right)^{2{\mathcal J}}{\mathcal J}^α{\tilde{\mathcal Y}}_n$$ where ${\mathcal Y}_n$ approaches a constant as $n\to\infty$, and ${\mathbf N}_{\mathcal O}$ is an $n$-independent constant describing on the normalization of the operator relative to the effective Abelian gauge coupling. The exponent $α$ is a positive number proportional to the difference between the $a$-anomaly coefficient of the underlying CFT and that of the effective theory of the Coulomb branch. For Lagrangian SCFT, we check our predictions against exact results from supersymmetric localization of Baggio et. al. and Gerchkovitz et. al., and find precise agreement for the logarithm ${\mathcal B}_n = \log{\mathcal Y}_n$, up to and including order $\log{\mathcal J}$. We also give predictions for the growth of two-point functions in all rank-one SCFT in the classification of Argyres et. al. In this way, we show the large-$R$-charge expansion serves as a bridge from the world of unbroken superconformal symmetry, OPE data, and bootstraps, to the world of the low-energy dynamics of the moduli space of vacua.

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arXiv2017

Operator Dimensions from Moduli

We consider the operator spectrum of a three-dimensional ${\cal N} = 2$ superconformal field theory with moduli spaces of one complex dimension, such as the fixed point theory with three chiral superfields $X,Y,Z$ and a superpotential $W = XYZ$. By using the existence of an effective theory on each branch of moduli space, we calculate the anomalous dimensions of certain low-lying operators carrying large $R$-charge $J$. While the lowest primary operator is a BPS scalar primary, the second-lowest scalar primary is in a semi-short representation, with dimension exactly $J+1$, a fact that cannot be seen directly from the $XYZ$ Lagrangian. The third-lowest scalar primary lies in a long multiplet with dimension $J+2 - c_{-3} \, J^{-3} + O(J^{-4})$, where $c_{-3}$ is an unknown positive coefficient. The coefficient $c_{-3}$ is proportional to the leading superconformal interaction term in the effective theory on moduli space. The positivity of $c_{-3}$ does not follow from supersymmetry, but rather from unitarity of moduli scattering and the absence of superluminal signal propagation in the effective dynamics of the complex modulus. We also prove a general lemma, that scalar semi-short representations form a module over the chiral ring in a natural way, by ordinary multiplication of local operators. Combined with the existence of scalar semi-short states at large $J$, this proves the existence of scalar semi-short states at all values of $J$. Thus the combination of ${\cal N}=2$ superconformal symmetry with the large-$J$ expansion is more powerful than the sum of its parts.

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arXiv2017

A Note on Inhomogeneous Ground States at Large Global Charge

In this note we search for the ground state, in infinite volume, of the $D=3$ Wilson-Fisher conformal $O(4)$ model, at nonzero values of the two independent charge densities $ρ_{1,2}$. Using an effective theory valid on scales longer than the scale defined by the charge density, we show that the ground-state configuration is inhomogeneous for generic ratios $ρ_1 / ρ_2$. This result confirms, within the context of a well-defined effective theory, a recent no-go result of Alvarez-Gaume' et al. We also show that any spatially periodic ground state solutions have an energetic preference towards longer periods, within some range of $ρ_1 / ρ_2$ containing a neighborhood of zero. This suggests that the scale of variation of the ground state solution in finite volume will be the infrared scale, and that the use of the effective theory at large charge in finite volume is self-consistent.

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arXiv2017

On Vertex Operators in Effective String Theory

In this note we construct vertex operators in effective string theory using the simplified covariant formalism, i.e. by embedding it in the Polyakov formalism supplemented by an anomaly term, and fixing to conformal gauge. These vertex operators represent off-shell background fields rather than dynamical string states. We construct vertex operators for nontrivial scalar, electromagnetic, and gravitational backgrounds. As an application, we compute a scalar form factor of a long string with length $R$, where the Fourier momentum $q$ of the external scalar field satisfies $q^2 \ll 1/α^\prime$, and we find the expected logarithmic dependence on the size of the string.

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arXiv2016

Boundary Operators in Effective String Theory

Various universal features of relativistic rotating strings depend on the organization of allowed local operators on the worldsheet. In this paper, we study the set of Neumann boundary operators in effective string theory, which are relevant for the controlled study of open relativistic strings with freely moving endpoints. Relativistic open strings are thought to encode the dynamics of confined quark-antiquark pairs in gauge theories in the planar approximation. Neumann boundary operators can be organized by their behavior under scaling of the target space coordinates X, and the set of allowed X-scaling exponents is bounded above by +1/2 and unbounded below. Negative contributions to X-scalings come from powers of a single invariant, or "dressing" operator, which is bilinear in the embedding coordinates. In particular, we show that all Neumann boundary operators are dressed by quarter-integer powers of this invariant, and we demonstrate how this rule arises from various ways of regulating the short-distance singularities of the effective theory.

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