Lattice fusion rules and logarithmic operator product expansions

Abstract Applying an operator product expansion approach we update the Standard Model prediction of the Bc lifetime from over 20 years ago. The non-perturbative velocity expansion is carried out up to third order in the relative velocity of the heavy quarks. The scheme dependence is studied using three different mass schemes for the $$ \overline{b} $$ b ¯ and c quarks, resulting in three different values consistent with each other and with experiment. Special focus has been laid on renormalon cancellation in the computation. Uncertainties resulting from scale dependence, neglecting the strange quark mass, non-perturbative matrix elements and parametric uncertainties are discussed in detail. The resulting uncertainties are still rather large compared to the experimental ones, and therefore do not allow for clear-cut conclusions concerning New Physics effects in the Bc decay.

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Disentangling QCD and new physics in D → πℓ+ℓ−

Journal of High Energy Physics ◽

10.1007/jhep04(2021)158 ◽

2021 ◽

Vol 2021 (4) ◽

Author(s):

Aoife Bharucha ◽

Diogo Boito ◽

Cédric Méaux

Keyword(s):

Standard Model ◽

Branching Ratio ◽

Branching Ratios ◽

New Physics ◽

Operator Product ◽

Beyond The Standard Model ◽

Spectral Functions ◽

The Standard Model ◽

Model Independent ◽

Weak Annihilation

Abstract In this paper we consider the decay D+ → π+ℓ+ℓ−, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q2 and at high q2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e+e− → (hadrons) and τ → (hadrons) + ντ data as well as the branching ratios for the resonant decays D+ → π+R(R → ℓ+ℓ−), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q2. Focusing then on the observables FH and AFB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

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High-energy operator product expansion at sub-eikonal level

Journal of High Energy Physics ◽

10.1007/jhep06(2021)096 ◽

2021 ◽

Vol 2021 (6) ◽

Author(s):

Giovanni Antonio Chirilli

Keyword(s):

Operator Product Expansion ◽

Evolution Equations ◽

Energy Operator ◽

High Energy ◽

Structure Functions ◽

Distribution Functions ◽

Impact Factors ◽

Operator Product ◽

The Impact ◽

New Distribution

Abstract The high energy Operator Product Expansion for the product of two electromagnetic currents is extended to the sub-eikonal level in a rigorous way. I calculate the impact factors for polarized and unpolarized structure functions, define new distribution functions, and derive the evolution equations for unpolarized and polarized structure functions in the flavor singlet and non-singlet case.

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Conformal Regge theory at finite boost

Journal of High Energy Physics ◽

10.1007/jhep05(2021)059 ◽

2021 ◽

Vol 2021 (5) ◽

Author(s):

Simon Caron-Huot ◽

Joshua Sandor

Keyword(s):

Field Theory ◽

Operator Product Expansion ◽

Operator Product ◽

Exact Results ◽

Double Integral ◽

Regge Theory ◽

Conformal Field ◽

Regge Trajectories ◽

Continuous Spins ◽

Regge Limit

Abstract The Operator Product Expansion is a useful tool to represent correlation functions. In this note we extend Conformal Regge theory to provide an exact OPE representation of Lorenzian four-point correlators in conformal field theory, valid even away from Regge limit. The representation extends convergence of the OPE by rewriting it as a double integral over continuous spins and dimensions, and features a novel “Regge block”. We test the formula in the conformal fishnet theory, where exact results involving nontrivial Regge trajectories are available.

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On local and integrated stress-tensor commutators

Journal of High Energy Physics ◽

10.1007/jhep07(2021)148 ◽

2021 ◽

Vol 2021 (7) ◽

Author(s):

Mert Besken ◽

Jan de Boer ◽

Grégoire Mathys

Keyword(s):

Stress Tensor ◽

Free Field ◽

Virasoro Algebra ◽

Light Sheet ◽

Operator Product ◽

Local Form ◽

Two Dimensional ◽

Conformal Embedding ◽

General Aspects ◽

The Right

Abstract We discuss some general aspects of commutators of local operators in Lorentzian CFTs, which can be obtained from a suitable analytic continuation of the Euclidean operator product expansion (OPE). Commutators only make sense as distributions, and care has to be taken to extract the right distribution from the OPE. We provide explicit computations in two and four-dimensional CFTs, focusing mainly on commutators of components of the stress-tensor. We rederive several familiar results, such as the canonical commutation relations of free field theory, the local form of the Poincaré algebra, and the Virasoro algebra of two-dimensional CFT. We then consider commutators of light-ray operators built from the stress-tensor. Using simplifying features of the light sheet limit in four-dimensional CFT we provide a direct computation of the BMS algebra formed by a specific set of light-ray operators in theories with no light scalar conformal primaries. In four-dimensional CFT we define a new infinite set of light-ray operators constructed from the stress-tensor, which all have well-defined matrix elements. These are a direct generalization of the two-dimensional Virasoro light-ray operators that are obtained from a conformal embedding of Minkowski space in the Lorentzian cylinder. They obey Hermiticity conditions similar to their two-dimensional analogues, and also share the property that a semi-infinite subset annihilates the vacuum.

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Aspects of quantum information in finite density field theory

Journal of High Energy Physics ◽

10.1007/jhep03(2021)079 ◽

2021 ◽

Vol 2021 (3) ◽

Author(s):

Lucas Daguerre ◽

Raimel Medina ◽

Mario Solís ◽

Gonzalo Torroba

Keyword(s):

Field Theory ◽

Quantum Information ◽

Mutual Information ◽

Fermi Surface ◽

Relative Entropy ◽

Chemical Potential ◽

Operator Product ◽

Dirac Fermions ◽

Long Distance ◽

Finite Density

Abstract We study different aspects of quantum field theory at finite density using methods from quantum information theory. For simplicity we focus on massive Dirac fermions with nonzero chemical potential, and work in 1 + 1 space-time dimensions. Using the entanglement entropy on an interval, we construct an entropic c-function that is finite. Unlike what happens in Lorentz-invariant theories, this c-function exhibits a strong violation of monotonicity; it also encodes the creation of long-range entanglement from the Fermi surface. Motivated by previous works on lattice models, we next calculate numerically the Renyi entropies and find Friedel-type oscillations; these are understood in terms of a defect operator product expansion. Furthermore, we consider the mutual information as a measure of correlation functions between different regions. Using a long-distance expansion previously developed by Cardy, we argue that the mutual information detects Fermi surface correlations already at leading order in the expansion. We also analyze the relative entropy and its Renyi generalizations in order to distinguish states with different charge and/or mass. In particular, we show that states in different superselection sectors give rise to a super-extensive behavior in the relative entropy. Finally, we discuss possible extensions to interacting theories, and argue for the relevance of some of these measures for probing non-Fermi liquids.

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Monodromy defects in free field theories

Journal of High Energy Physics ◽

10.1007/jhep08(2021)013 ◽

2021 ◽

Vol 2021 (8) ◽

Author(s):

Lorenzo Bianchi ◽

Adam Chalabi ◽

Vladimír Procházka ◽

Brandon Robinson ◽

Jacopo Sisti

Keyword(s):

Entanglement Entropy ◽

Free Field ◽

Operator Product ◽

Dirac Fermions ◽

Maxwell Theory ◽

Conformal Field ◽

Defect Operator ◽

Crucial Information ◽

The One ◽

Group Flow

Abstract We study co-dimension two monodromy defects in theories of conformally coupled scalars and free Dirac fermions in arbitrary d dimensions. We characterise this family of conformal defects by computing the one-point functions of the stress-tensor and conserved current for Abelian flavour symmetries as well as two-point functions of the displacement operator. In the case of d = 4, the normalisation of these correlation functions are related to defect Weyl anomaly coefficients, and thus provide crucial information about the defect conformal field theory. We provide explicit checks on the values of the defect central charges by calculating the universal part of the defect contribution to entanglement entropy, and further, we use our results to extract the universal part of the vacuum Rényi entropy. Moreover, we leverage the non-supersymmetric free field results to compute a novel defect Weyl anomaly coefficient in a d = 4 theory of free $$ \mathcal{N} $$ N = 2 hypermultiplets. Including singular modes in the defect operator product expansion of fundamental fields, we identify notable relevant deformations in the singular defect theories and show that they trigger a renormalisation group flow towards an IR fixed point with the most regular defect OPE. We also study Gukov-Witten defects in free d = 4 Maxwell theory and show that their central charges vanish.

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