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Abstract Analytic continuation from (3, 1) signature Minkowski to (2, 2) signature Klein space has emerged as a useful tool for the understanding of scattering amplitudes and flat space holography. Under this continuation, past and future null infinity merge into a single boundary ( ) which is the product of a null line with a (1, 1) signature torus. The Minkowskian -matrix continues to a Kleinian -vector which in turn may be represented by a Poincaré-invariant vacuum state in the Hilbert space built on . contains all information about in a novel, repackaged form. We give an explicit construction of in a Lorentz/conformal basis for a free massless scalar. separates into two halves which are the asymptotic null boundaries of the regions timelike and spacelike separated from the origin. is shown to be a maximally entangled state in the product of the Hilbert spaces.more » « lessFree, publicly-accessible full text available April 17, 2026
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We present a discrete basis of solutions of the massless Klein-Gordon equation in 3 + 1 Minkowski space which transform as 𝔰𝔩(2, ℂ) Lorentz/conformal primaries and descendants, and whose elements all have integer conformal dimension. We show that the basis is complete in the sense that the Wightman function can be expressed as a quadratic sum over the basis elements.more » « less
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We construct two-dimensional quantum states associated to four-dimensional linearized rotating self-dual black holes in (2, 2) signature Klein space. The states are comprised of global conformal primaries circulating on the celestial torus, the Kleinian analog of the celestial sphere. By introducing a generalized tower of Goldstone operators we identify the states as coherent exponentiations carrying an infinite tower of w1+∞charges or soft hair. We relate our results to recent approaches to black hole scattering, including a connection to Wilson lines,$$ \mathcal{S} $$ -matrix results, and celestial holography in curved backgrounds.more » « less
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A<sc>bstract</sc> Symmetry algebras deriving from towers of soft theorems can be deformed by a short list of higher-dimension Wilsonian corrections to the effective action. We study the simplest of these deformations in gauge theory arising from a massless complex scalar coupled toF2. The soft gauge symmetry ‘s-algebra’, compactly realized as a higher-spin current algebra acting on the celestial sphere, is deformed and enlarged to an associative algebra containing soft scalar generators. This deformed soft algebra is found to be non-abelian even in abelian gauge theory. A two-parameter family of central extensions of thes-subalgebra are generated by shifting and decoupling the scalar generators. It is shown that these central extensions can also be generated by expanding around a certain non-trivial but Lorentz invariant shockwave type background for the scalar field.more » « less
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A bstract The bulk-to-boundary dictionary for 4D celestial holography is given a new entry defining 2D boundary states living on oriented circles on the celestial sphere. The states are constructed using the 2D CFT state-operator correspondence from operator insertions corresponding to either incoming or outgoing particles which cross the celestial sphere inside the circle. The BPZ construction is applied to give an inner product on such states whose associated bulk adjoints are shown to involve a shadow transform. Scattering amplitudes are then given by BPZ inner products between states living on the same circle but with opposite orientations. 2D boundary states are found to encode the same information as their 4D bulk counterparts, but organized in a radically different manner.more » « less
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Coyle, Laura E; Perrin, Marshall D; Matsuura, Shuji (Ed.)
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The event horizon telescope (EHT) is expected to soon produce polarimetric images of the supermassive black hole at the centre of the neighbouring galaxy M87. There are indications that this black hole is rapidly spinning. General relativity predicts that such a high-spin black hole has an emergent conformal symmetry near its event horizon. In this paper, we use this symmetry to analytically predict the polarized near-horizon emissions to be seen at the EHT and find a distinctive pattern of whorls aligned with the spin.more » « less
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null (Ed.)The operator product expansion (OPE) on the celestial sphere of conformal primary gluons and gravitons is studied. Asymptotic symmetries imply recursion relations between products of operators whose conformal weights differ by half-integers. It is shown, for tree-level Einstein-Yang-Mills theory, that these recursion relations are so constraining that they completely fix the leading celestial OPE coefficients in terms of the Euler beta function. The poles in the beta functions are associated with conformally soft currents.more » « less
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