Assuming that (1) the Universe underwent a postinflationary accelerated expansion phase driven by a fluid with equation of state <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>P</mi><mo>=</mo><mi>w</mi><mi>ρ</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>−</mo><mn>1</mn><mo>&lt;</mo><mi>w</mi><mo>&lt;</mo><mo>−</mo><mn>1</mn><mo>/</mo><mn>3</mn></math>, that (2) the cosmic horizon in an accelerating, quasi–de Sitter Universe has a temperature inversely proportional to the proper size of the horizon, and that (3) we are static observers, we calculate the frozen-in density of a stable particle of mass <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>m</mi></math> produced by the cosmic horizon that does not undergo any number-changing processes in the late Universe. We find that, as a function of the equation of state and the temperature when radiation domination starts and the quasi–de Sitter phase ends, the mass of the dark matter producing the observed cosmological abundance via this mechanism ranges from 10 keV up to close to the Planck scale.

United States

Stefano Profumo

Dark matter from quasi–de Sitter horizons

It is well known that the area of the de Sitter cosmological horizon is related to the entropy of the bulk spacetime. Recent work has however shown that the horizon encodes more information about the bulk spacetime than just the entropy. In this work, we show that the horizon contains all of the gauge invariant (diffeomorphism and U(1)) information about (static albeit unstable) configurations of charged and rotating objects placed deep inside the de Sitter spacetime. We study highly symmetric objects, such as dipoles and cubes, built of objects with electric charge and angular momentum at their vertices. We show how these configurations affect the geometry of the cosmological horizon and imprint detailed information about the objects in the bulk onto the cosmological horizon.

Willy Fischler

Hare Krishna

Sarah Racz

There is more to the de Sitter horizon than just the area

We propose a new formula for the entropy of a dynamical cosmological event horizon, which is valid to leading order for perturbations of a stationary asymptotically de Sitter spacetime. By introducing a nontrivial correction term, we generalize Gibbons and Hawking’s first law of event horizons to non-stationary eras. We also develop the non-stationary physical process first law between two arbitrary horizon cross-sections for the cosmological event horizon.

China

Jinan Zhao

The entropy of dynamical de Sitter horizons

I demonstrate that soft graviton modes in de Sitter spacetimes are the Goldstone modes of the spontaneously broken asymptotic symmetry group of de Sitter space. I then show that any local measurement, including the effects of the environment, will collapse the symmetric state onto the broken state in the large volume limit. In any discussion involving observers, de Sitter spacetimes are, therefore, best described globally by the broken phase, while local observers, in the small volume limit, can not discriminate between different degenerate global vacuum states and are therefore best described by the symmetric state. As a consequence, a small Hubbled-sized local region initially in the symmetric state will, after a time-scale corresponding to the Page time of de Sitter space, have expanded to a large region in the broken state. This illuminates the physical nature of soft graviton modes in de Sitter spacetimes.

Denmark

Martin S. Sloth

Soft gravitons as Goldstone modes of spontaneously broken asymptotic symmetries in de Sitter spacetimes

We study the causal structure of Schwarzschild-de Sitter (SdS), including shock wave perturbations, in $\textit{D >}$ 3 using reflected null ray trajectories, either through the interior black hole or the exterior de Sitter region. Specifically, we compute the quasinormal mode frequencies in the eikonal, high-frequency, limit, by identifying the ‘critical time’, for arbitrary values of the black hole mass. We emphasize the important role of the static sphere proper time normalization and related boundary conditions. The computed critical times indicate the presence of singularities in the late-time, large mass, scalar field correlator in SdS, which should be resolved by introducing complex geodesics consistent with interior black hole and exterior de Sitter effective thermofield double states. In addition we relate the critical time to a diverging holographic complexity observable and compute the ‘switchback’ delay by adding a pair of shock wave perturbations for arbitrary values of the mass of the black hole.

Canada

Mir Faruk

Netherlands

Facundo Rost

Jan Schaar

Quasinormal modes and the switchback effect in Schwarzschild-de Sitter

Radiative capture cross section strongly depends on the electromagnetic de-excitation probability, hence on the so-called photon strength function (PSF) and nuclear level density (NLD). Microscopic models for both PSF and NLD have been developed for the past decades but remain affected by fundamental assumptions, like the independent particle approximation for NLD and the assumption that the de-excitation PSF is equal to the photoabsorption PSF. The present study goes beyond the existing models by providing a common framework based on QRPA estimates of nuclear excitations that are used to derive NLD by coupling QRPA bosons as well as the de-excitation PSF by calculating all possible transition probabilities between QRPA states. The present framework is found to reproduce experimental data related to both NLD and PSF accurately, provided QRPA excitation energies are globally reduced by an energy-dependent shift. More specifically, the resulting NLDs, also extended to odd- <italic>A</italic> and odd-odd nuclei, are shown to be in good agreement with experimental s-wave resonance spacings and the photoabsorption PSF with photodata.

Belgium

S. Goriely

France

S. Péru

S. Hilaire

QRPA prediction of the nuclear level densities and de-excitation photon strength functions

We develop a formalism for computing the scattering amplitudes in maximally symmetric de Sitter spacetime with compact spatial dimensions. We describe quantum states by using the representation theory of de Sitter symmetry group and link the Hilbert space to “inertial” geodesic observers. The positive and negative “energy” wavefunctions are uniquely determined by the requirement that in observer's neighborhood, short wavelengths propagate as plane waves with positive and negative frequencies, respectively; they define a unique “Euclidean” (a.k.a. Bunch-Davies) de Sitter invariant vacuum, common to all inertial observers. By following the same steps as in Minkowski spacetime, we show that the scattering amplitudes are given by a generalized Dyson's formula. Compared to the flat case, they describe the scattering of wavepackets with the frequency spectrum determined by geometry. The frequency spread shrinks as the masses and/or momenta become larger than the curvature scale. Asymptotically, de Sitter amplitudes agree with the amplitudes evaluated in Minkowski spacetime.

Poland

Tomasz R. Taylor

United Kingdom

Bin Zhu

Scattering of quantum particles in global de Sitter spacetime I: The formalism

In this study, the methodology proposed by Goon and Penco for investigating the universality of thermodynamic relations with corrections in de Sitter black holes is extended. A universal thermodynamic extremality relation, considering the spacetime mass $\textit{M}$ with various state parameters, proposed by Goon and Penco is investigated in higher-dimensional spacetime. The established universal conclusions are not impacted by the convergence of energy from the coexistence region of two horizons to the point $\textit{N}$ or $\textit{C}$. Furthermore, by incorporating the shift of the angular momentum into our analysis, a more universal relation is derived, specifically applicable to rotating configurations. Notably, a novel conjecture is formulated that establishes a universal relationship framework connecting shifted thermodynamic quantities across arbitrary black hole backgrounds. These findings are expected to offer profound insights into the fundamental principles of quantum gravity.

Hai-Long Zhen

Yu-Bo Ma

Universality on the thermodynamic relation with corrections in higher-dimensional de Sitter black holes

We start with the consideration of the loop effects for light fields with nonzero mass in the expanding Poincaré patch of de Sitter spacetime. We derive the Dyson-Schwinger equation, which sums up the leading infrared (growing with time) loop corrections in certain limit for small initial perturbations above the Bunch-Davies state. The solution of this equation shows the destiny of the initial state at the future infinity. Then we discuss the case of the contracting Poincaré patch and global de Sitter spacetime and briefly the case of different initial conditions in the expanding Poincaré patch.

Russia

E.T. Akhmedov

V.I. Lapushkin

D.I. Sadekov

Light fields in various patches of de Sitter spacetime

We show how certain types of magnetic asymptotically anti–de Sitter Euclidean wormholes can catalyze the onset of inflation. These wormholes can be embedded as saddle point solutions of general relativity coupled to the Standard Model, the inflaton being identified with the Higgs particle. Our scenario is based on the assumption that the quantum effective potential for the Higgs turns negative at a certain high energy window, in line with current measured values for the Higgs and top quark masses. Within our proposal, we can estimate various parameters and physical quantities of interest, in consistency with current observational bounds.