arXiv subjects

Takahiro Waki

Publications and source records attributed to Takahiro Waki.

7 recordsLinked to original sources

arXiv2026

Bridging dS/CFT and Celestial Holography via Ward-Takahashi Identities

In 2507.17558, we provide a map from a scalar theory on $(D+2)$-dimensional Minkowski spacetime to a scalar theory with a continuous mass spectrum on $(D+1)$-dimensional de Sitter spacetime, and propose a link between celestial amplitudes and cosmological correlators (the cosmological-celestial dictionary). We extend the construction to fields with spin 1 and 2, and find that massless spin fields map to spin fields with continuous mass spectra. In this construction, we identify the de Sitter counterparts of the Nambu-Goldstone modes associated with the asymptotic symmetries in Minkowski spacetime. For $U(1)$ gauge theories, the counterpart is restricted to the massless sector within the continuous Proca spectrum, while for linearized gravity supertranslations are encoded in the partially massless sector and superrotations in the strictly massless sector. Using the identification, we reveal that the associated Ward-Takahashi identities of the cosmological correlators reproduce the conformally soft photon and graviton theorems via the cosmological-celestial dictionary. In particular, the celestial stress tensor is derived from the asymptotic limit of gravitons in de Sitter spacetime.

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arXiv2025

Celestial Holography meets dS/CFT

We provide a concrete link between celestial amplitudes and cosmological correlators. We first construct a map from quantum field theories (QFTs) in $(D+2)$-dimensional Euclidean space to theories on the $(D+1)$-dimensional sphere, through a Weyl rescaling and a Fourier transformation. An analytic continuation extends this map to a relation between QFTs in Minkowski spacetime $\text{M}_{D+2}$ and in de Sitter spacetime $\text{dS}_{D+1}$ with the Bunch-Davies vacuum. Combining this relation with celestial holography, we show that the extrapolated operators in de Sitter space can be represented by operators on the celestial sphere $S^{D}$. Our framework offers a systematic route to transfer computational techniques and physical insights between celestial holography and the dS/CFT correspondence.

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arXiv2025

Flat Space Holography via AdS/BCFT

In this paper, we study a new class of AdS/BCFT setups, where the world-volumes of end-of-the-world branes (EOW branes) are given by flat spaces, to explore flat space holography from an AdS bulk. We show that they provide gravity duals of CFTs in the presence of null boundaries. Our holographic calculations lead to many new predictions on entanglement entropy, correlation functions and partition functions for CFTs with null boundaries. By considering a bulk region between two EOW branes, we present an AdS/BCFT explanation that the flat space gravity is dual to a Carrollian CFT (CCFT), including the swing surface calculation of entanglement entropy.

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arXiv2024

Celestial CFT from $H_3^+$-WZW Model

Recently, there has been a growing interest in celestial holography, which is holography in asymptotically flat spacetimes. This holographic duality exhibits numerous mysterious and fruitful features, particularly on the dual CFT side. In this paper, we present the candidate of dual CFT for Minkowski spacetime extracted from $SL(2,\mathbb{C})/SU(2)\cong H^+_3$ Wess-Zumino-Witten (WZW) model, the simplest non-compact CFT. We demonstrate that it reproduces the well-known principal series and correlation functions dual to the bulk scattering amplitudes.

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arXiv2023

Celestial two-point functions and rectified dictionary

A naive celestial dictionary causes massless two-point functions to take the delta-function forms in the celestial conformal field theory (CCFT). We rectify the dictionary, involving the shadow transformation so that the two-point functions follow the standard power-law. In this new definition, we can smoothly take the massless limit of the massive dictionary. We also compute a three-point function using the new dictionary and discuss the OPE in CCFT.

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arXiv2023

Soft hair, dressed coordinates and information loss paradox

Understanding the dynamics of soft hair might shine some light on the information loss paradox. In this paper, we introduce a new coordinate system, dressed coordinates, in order to analyze the quantum states of Hawking radiation as a first step toward understanding the connection between soft hair and the information paradox. Dressed coordinates can be introduced by an operator-dependent coordinate transformation that makes the soft hair degrees of freedom apparently disappear from the metric. We show that some results of previous studies, such as the angle-dependent Hawking temperature and the soft graviton theorem, can be easily reproduced using these dressed coordinates. Finally, we discuss future possible applications of dressed coordinates toward understanding the information loss paradox.

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arXiv2022

Wedge Holography in Flat Space and Celestial Holography

In this paper, we study codimension two holography in flat spacetimes, based on the idea of the wedge holography. We propose that a region in a $d+1$ dimensional flat spacetime surrounded by two end of the world-branes, which are given by $d$ dimensional hyperbolic spaces, is dual to a conformal field theory (CFT) on a $d-1$ dimensional sphere. Similarly, we also propose that a $d+1$ dimensional region in the flat spacetime bounded by two $d$ dimensional de Sitter spaces is holographically dual to a CFT on a $d-1$ dimensional sphere. Our calculations of the partition function, holographic entanglement entropy and two point functions, support these duality relations and imply that such CFTs are non-unitary. Finally, we glue these two dualities along null surfaces to realize a codimension two holography for a full Minkowski spacetime and discuss a possible connection to the celestial holography.

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