arXiv subjects

Beatrix Mühlmann

Publications and source records attributed to Beatrix Mühlmann.

25 records · Page 2Linked to original sources

arXiv2023

Finite Features of Quantum De Sitter Space

We consider degrees of freedom for a quantum de Sitter spacetime. The problem is studied from both a Lorentzian and a Euclidean perspective. From a Lorentzian perspective, we compute dynamical properties of the static patch de Sitter horizon. These are compared to dynamical features of black holes. We point out differences suggestive of non-standard thermal behaviour for the de Sitter horizon. We establish that geometries interpolating between an asymptotically AdS$_2 \times S^2$ space and a dS$_4$ interior are compatible with the null energy condition, albeit with a non-standard decreasing radial size of $S^2$. The putative holographic dual of an asymptotic AdS$_2$ spacetime is comprised of a finite number of degrees of freedom. From a Euclidean perspective we consider the gravitational path integral for fields over compact manifolds. In two-dimensions, we review Polchinski's BRST localisation of Liouville theory and propose a supersymmetric extension of timelike Liouville theory which exhibits supersymmetric localisation. We speculate that localisation of the Euclidean gravitational path integral is a reflection of a finite number of degrees of freedom in a quantum de Sitter universe.

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arXiv2022

The two-sphere partition function from timelike Liouville theory at three-loop order

While the Euclidean two-dimensional gravitational path integral is in general highly fluctuating, it admits a semiclassical two-sphere saddle if coupled to a matter CFT with large and positive central charge. In Weyl gauge this gravity theory is known as timelike Liouville theory, and is conjectured to be a non-unitary two-dimensional CFT. We explore the semiclassical limit of timelike Liouville theory by calculating the two-sphere partition function from the perspective of the path integral to three-loop order, extending the work in 2106.01665. We also compare our result to the conjectured all-loop sphere partition function obtained from the DOZZ formula. Since the two-sphere is the geometry of Euclidean two-dimensional de Sitter space our discussion is tied to the conjecture of Gibbons-Hawking, according to which the dS entropy is encoded in the Euclidean gravitational path integral over compact manifolds.

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arXiv2021

The semiclassical gravitational path integral and random matrices

We study the genus expansion on compact Riemann surfaces of the gravitational path integral $\mathcal{Z}^{(m)}_{\text{grav}}$ in two spacetime dimensions with cosmological constant $Λ>0$ coupled to one of the non-unitary minimal models $\mathcal{M}_{2m-1,2}$. In the semiclassical limit, corresponding to large $m$, $\mathcal{Z}^{(m)}_{\text{grav}}$ admits a Euclidean saddle for genus $h\geq 2$. Upon fixing the area of the metric, the path integral admits a round two-sphere saddle for $h=0$. We show that the OPE coefficients for the minimal weight operators of $\mathcal{M}_{2m-1,2}$ grow exponentially in $m$ at large $m$. Employing the sewing formula, we use these OPE coefficients to obtain the large $m$ limit of the partition function of $\mathcal{M}_{2m-1,2}$ for genus $h\ge 2$. Combining these results we arrive at a semiclassical expression for $\mathcal{Z}^{(m)}_{\text{grav}}$. Conjecturally, $\mathcal{Z}^{(m)}_{\text{grav}}$ admits a completion in terms of an integral over large random Hermitian matrices, known as a multicritical matrix integral. This matrix integral is built from an even polynomial potential of order $2m$. We obtain explicit expressions for the large $m$ genus expansion of multicritical matrix integrals in the double scaling limit. We compute invariant quantities involving contributions at different genera, both from a matrix as well as a gravity perspective, and establish a link between the two pictures. Inspired by the proposal of Gibbons and Hawking relating the de Sitter entropy to a gravitational path integral, our setup paves a possible path toward a microscopic picture of a two-dimensional de Sitter universe.

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arXiv2021

The two-sphere partition function in two-dimensional quantum gravity at fixed area

We discuss two-dimensional quantum gravity coupled to conformal matter and fixed area in a semiclassical large and negative matter central charge limit. In this setup the gravity theory -- otherwise highly fluctuating -- admits a round two-sphere saddle. We discuss the two-sphere partition function up to two-loop order from the path integral perspective. This amounts to studying Feynman diagrams incorporating the fixed area constraint on the round two-sphere. In particular we find that all ultraviolet divergences cancel to this order. We compare our results with the two-sphere partition function obtained from the DOZZ formula.

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arXiv2021

Matrix integrals $\&$ finite holography

We explore the conjectured duality between a class of large $N$ matrix integrals, known as multicritical matrix integrals (MMI), and the series $(2m-1,2)$ of non-unitary minimal models on a fluctuating background. We match the critical exponents of the leading order planar expansion of MMI, to those of the continuum theory on an $S^2$ topology. From the MMI perspective this is done both through a multi-vertex diagrammatic expansion, thereby revealing novel combinatorial expressions, as well as through a systematic saddle point evaluation of the matrix integral as a function of its parameters. From the continuum point of view the corresponding critical exponents are obtained upon computing the partition function in the presence of a given conformal primary. Further to this, we elaborate on a Hilbert space of the continuum theory, and the putative finiteness thereof, on both an $S^2$ and a $T^2$ topology using BRST cohomology considerations. Matrix integrals support this finiteness.

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arXiv2021

Notes on Matrix Models

In these notes we explore a variety of models comprising a large number of constituents. An emphasis is placed on integrals over large Hermitian matrices, as well as quantum mechanical models whose degrees of freedom are organised in a matrix-like fashion. We discuss the relation of matrix models to two-dimensional quantum gravity coupled to conformal matter. We provide a brief overview of a variety of more general quantum mechanical matrix models and their putative worldsheet interpretation, as well as other recent developments on large $N$ systems. We end with a discussion of open questions and future directions.

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arXiv2020

Gravitational Anomalies in nAdS$_2$/nCFT$_1$

We revisit the holographic description of the near horizon geometry of the BTZ black hole in AdS$_3$ gravity, with a gravitational Chern-Simons term included. After a dimensional reduction of the three dimensional theory, we use the framework of nAdS$_2$/nCFT$_1$ to describe the near horizon physics. This setup allows us to contrast the role of the gravitational and conformal anomaly inherited from AdS$_3$/CFT$_2$ in the symmetry breaking mechanism of nAdS$_2$/nCFT$_1$. Our results display how boundary conditions in the 3D spacetime, combined with the gravitational anomaly, affect the holographic description of the near horizon of the black hole relative to the physics near the AdS$_3$ boundary.

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