arXiv subjects

Sidan A

Publications and source records attributed to Sidan A.

7 recordsLinked to original sources

arXiv2026

Matrix Multiverses Meet Multiple Mythologies

We present a model in which asymptotically de Sitter universes of various types, and de Sitter (dS) radii $R_n$, live in the interiors of black holes in a maximally entropic flat $p = \rho$ Friedmann-Robertson-Walker universe. These dS universes clearly have many quantum states. We argue that they decay and equilibrate with the maximal entropy universe on time scales of order $\alpha_n R_n {\rm ln} (R_n /\delta_n)$, where $\alpha_n$ are model-dependent dimensionless constants and $\delta_n$ are the initial distances between the shell, satisfying the Israel junction conditions, and the dS horizon. These are time-scales as viewed by a detector following a trajectory far from the would-be cosmological horizon. These times are all exponentially shorter than dS recurrence times, which have no meaning in this model. It is impossible for a detector inside one of the dS universes to determine whether it is actually part of such a structure. This model could be used as the basis for claiming that certain constants of nature or cosmological initial conditions were chosen to have mathematically unnatural values because other values could not lead to any form of intelligent life.

hep-th↗

arXiv2026

Can Primordial Black Holes Be Seeds for Early Galaxies in Models Satisfying the Covariant Entropy Bound?

We argue that cosmological models obeying the Covariant Entropy Bound (CEB) mathematically favor states with no localized excitations or one large black hole containing all the energy in a constrained initial state. In order to get a long radiation-dominated era, one must postulate that at a very early time, most horizon volumes of the universe contained tiny black holes that decayed into radiation. A previous work by two of the authors showed that such a scenario could fit the data on the Cosmic Microwave Background (CMB). In order to account for dark matter, we also postulate some random black holes of at least horizon size at that time. A reasonable distribution of such primordial black holes can account for all of dark matter as well as the early galaxies seen by the James Webb Space Telescope. Some of the dark matter may also be in Planck-scale remnants of the decaying black holes. We describe our model both in terms of approximate solutions to General Relativity and a speculative quantum gravity model whose hydrodynamics matches the flat $p = \pm \rho$ FRW model that saturates the CEB.

hep-ph↗

arXiv2026

JT de Sitter Gravity as a Model of Coleman-de Luccia Tunneling

We interpret the Euclidean solution of JT de Sitter gravity as the Coleman-de Luccia instanton for the decay of the low-entropy horizon of its static patch solution into either a Big Crunch or an infinite-entropy Lorentzian de Sitter cosmology. As in previous work by one of the authors, the Big Crunch is interpreted as bounding the entropy of the static state. The principle of detailed balance then guarantees it will transition back to a higher entropy causal diamond in the expanding cosmology. We then construct a family of explicit quantum mechanical models and appropriate metastable states, with transition probabilities well approximated by the semi-classical calculations in JT de Sitter gravity.

hep-th↗

arXiv2026

Diamonds in the Bulk and Large-$N$ Scaling in AdS/CFT

Quantum Field Theory introduced us to the notion that a causal diamond in space-time corresponded to a subsystem of a quantum mechanical system defined on the global space-time. Work by Jacobson, Fischler and Susskind, and particularly Bousso suggested that, in the quantum theory of gravity, this subsystem should have a density matrix of finite entropy. These authors formalized older intuitive arguments based on black hole physics. Although mathematically, Type II von Neumann algebras admit finite entropy density matrices, the black hole arguments suggest that the number of physical states in these subsystems is finite. The conjecture that de Sitter (dS) space has a finite number of physical states was first made by Fischler and one of the present authors. Leutheusser and Liu showed that, in the $N = \infty$ limit, causal diamonds with finite area in AdS radius units had Type $III_1$ von Neumann sub-algebras of the full operator algebra. They claimed that this was true for finite values of the UV cutoff, and that the algebra was the algebra of bulk local fields in the diamond. We will argue that the second part of this conjecture is incorrect and that the bulk field algebra emerges only in a double scaled limit, where the boundary UV cutoff is taken to infinity as $N$ is taken to infinity. There is never a bulk field theory description that resolves distances smaller than the AdS radius.

hep-th↗

arXiv2025

The holographic space-time model of inflation and its predictions for the CMB primordial spectra

In 1998 Carlip and Solodukhin independently conjectured the equality between fluctuations in the modular Hamiltonian of black holes and its expectation value. Banks and Zurek's 2021 work generalized this observation to any causal diamonds. We use this observation to calculate the precise normalization of primordial scalar and tensor power spectra in the Holographic Space-time (HST) model of inflation. In previous work Banks and Fischler outlined the general calculation of inflationary power spectra in this model, which we review here. Its conceptual basis is radically different from field theoretic inflation and it has no Transplanckian problems, but its predictions for power spectra will be shown to fit extant data equally well, and the tensor-to-scalar ratio agrees with experimental observations.

hep-th↗

arXiv2024

Fixed lines in four fermion models in two dimensions

Motivated by conjectures about near-horizon dynamics in quantum gravity, we search for lines of perturbatively accessible fixed points emanating from models of $N$ free fermions. Through two loops we find a new class of models, apart from the well-known Abelian Thirring models. Further study is needed to see whether these can lead to true conformal manifolds, or perhaps a new class of large N fixed points.

hep-th↗

arXiv2024

Quantum theory of three-dimensional de Sitter space

We sketch the construction of a quantum model of 3 dimensional de Sitter space, based on the Covariant Entropy Principle and the observation that semi-classical physics suggests the possibility of a consistent theory of a finite number of unstable massive particles with purely gravitational interactions. Our model is holographic, finite, unitary, causal, plausibly exhibits fast scrambling, and qualitatively reproduces features of semi-classical de Sitter physics. In an appendix we outline some calculations that might lead to further tests of the model.

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