We compute the holographic entanglement entropy via the Ryu-Takayanagi prescription in the three-dimensional Friedmann-Lemaître-Robertson-Walker universe. We consider two types of holographic scenarios analogous to the static patch holography and half de Sitter holography, in which the holographic boundary is timelike and placed in the bulk. We find in general that strong subadditivity can be satisfied only in the former scenario, and, in addition, the holographic boundary must lie within the apparent horizon. Also, for the universe filled with an ideal fluid with constant equation of state $\textit{w}$ < –1, the condition is sharpened as that the holographic boundary must lie within the event horizon instead. These constraints provide necessary conditions for the dual quantum field theory to be standard and compatible with strong subadditivity.

Japan

Toshifumi Noumi

South Korea

Fumiya Sano

Yu-ki Suzuki

Holographic entanglement entropy in the FLRW universe

We elaborate on the effective field theory (EFT) construction for dissipative open systems coupled to dynamical gravity, in light of recent developments on the EFT of dissipative hydrodynamics (HydroEFT). Our construction is based on the Schwinger-Keldysh formalism and its symmetries as well as microscopic unitarity. A key aspect of dynamical gravity is that gravity couples to all degrees of freedom universally, hence the EFT has to take into account the energy-momentum tensor of the environment to which the energy escapes from the dissipative system of interest. We incorporate this effect by modeling the environment based on HydroEFT, assuming validity of the derivative expansion of the environment sector. For illustration, we apply our EFT recipe to a dissipative scalar field coupled to dynamical gravity that can be used, e.g., for dissipative inflation. In particular we quantify impacts of fluctuations in the environment sector on the scalar dynamics. We also apply the same framework to dissipative gravity, discussing dissipative gravitational waves and the generalized second law of black hole thermodynamics.

China

Pak Lau

Kanji Nishii

Gravitational EFT for dissipative open systems

We derive the cutoff length scale of the quadratic gravity in <math><mi>d</mi><mo>≥</mo><mn>5</mn></math> dimensional spacetime by demanding that the quantum focusing conjecture for the smeared quantum expansion holds at the classical level. The cutoff scale has a different dependence on the spacetime dimension depending on the sign of the coupling constant of the quadratic gravity. We also investigate a concrete example of the five-dimensional Schwarzschild spacetime and directly confirm that the quantum focusing conjecture holds when the quantum expansion is smeared over the scale larger than our cutoff scale.

Takamasa Kanai

Kengo Maeda

Daisuke Yoshida

Cutoff scale of quadratic gravity from quantum focusing conjecture

We investigate a gedanken experiment to destroy an extremally charged black hole by dropping a test particle, provided that there are multiple <math><mrow><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></mrow></math> gauge fields coupled with each other through higher derivative interactions. It is known that the Coulomb repulsion prevents a test particle that would break the extremal condition from falling into an extremal black hole and therefore the black hole cannot be destroyed. We extend this observation to include higher derivative corrections. Although the extremal condition is modified by the higher derivative interactions, we find that the repulsive force induced by the higher derivative couplings is responsible for preventing a test particle that would break the modified extremal condition to reach the event horizon. Thus, we confirm that the weak cosmic censorship conjecture holds for extremally charged black holes even in the presence of higher derivative corrections, as long as the test particle approximation is justified.

Keisuke Izumi

Gedanken experiments to destroy a black hole by a test particle: Multiply charged black hole with higher derivative corrections

The gravitational positivity bound gives quantitative “swampland” constraints on low-energy effective theories inside theories of quantum gravity. We give a comprehensive discussion of this bound for those interested in applications to phenomenological model building. We present a practical recipe for deriving the bound, and discuss subtleties relevant for realistic models. As an illustration, we study the positivity bound on the scattering of the massive gauge bosons in the Higgs/Stückelberg mechanism. Under certain assumptions on gravitational amplitudes at high energy, we obtain a lower bound <math><msub><mi>m</mi><mi>V</mi></msub><mo>≳</mo><msubsup><mi>Λ</mi><mi>UV</mi><mn>2</mn></msubsup><mo>/</mo><mi>g</mi><msub><mi>M</mi><mi>Pl</mi></msub></math> on the gauge boson mass <math><msub><mi>m</mi><mi>V</mi></msub></math>, where <math><mi>g</mi></math> is the coupling constant of the gauge field, <math><msub><mi>M</mi><mi>Pl</mi></msub></math> is the reduced Planck mass and <math><msub><mi>Λ</mi><mi>UV</mi></msub></math> is the ultraviolet cutoff of the effective field theory. This bound can strongly constrain new physics models involving a massive gauge boson. We also discuss how the bound depends on our high-energy assumptions.

Katsuki Aoki

Ryo Saito

Sota Sato

Satoshi Shirai

Junsei Tokuda

Masahito Yamazaki

Gravitational positivity for phenomenologists: Dark gauge boson in the swampland

Massive fields can imprint unique oscillatory features on primordial correlation functions or inflationary correlators, which is dubbed the cosmological collider signal. In this work, we analytically investigate the effects of a time-dependent mass of a scalar field on inflationary correlators, extending previous numerical studies and implementing techniques developed in the cosmological bootstrap program. The time-dependent mass is in general induced by couplings to the slow-roll inflaton background, with particularly significant effects in the case of non-derivative couplings. By linearly approximating the time dependence, the mode function of the massive scalar is computed analytically, on which we derive analytic formulae for two-, three-, and four-point correlators with the tree-level exchange of the massive scalar. The obtained formulae are utilized to discuss the phenomenological impacts on the power spectrum and bispectrum, and it is found that the scaling behavior of the bispectrum in the squeezed configuration, i.e., the cosmological collider signal, is modified from a time-dependent Boltzmann suppression. By investigating the scaling behavior in detail, we are in principle able to determine the non-derivative couplings between the inflaton and the massive particle.

Shuntaro Aoki

Masahide Yamaguchi

Analytic formulae for inflationary correlators with dynamical mass

Positivity bounds on scattering amplitudes provide a necessary condition for a low-energy effective field theory to have a consistent ultraviolet completion. Their extension to gravity theories has been studied in the past years aiming at application to the swampland program, showing that positivity bounds hold at least approximately even in the presence of gravity. A theoretical issue in this context is how much negativity is allowed for a given scattering process. We show that this issue is relevant to physics within the scope of ongoing experiments, especially in the context of dark sector physics. A detailed analysis of dark photon scenarios is provided as an illustrative example. Our results do not merely show the phenomenological importance of the theoretical study of gravitational positivity bounds but also open up an exciting possibility of exploring the nature of quantum gravity via an experimental search of the dark sector.

Phenomenological motivation for gravitational positivity bounds: A case study of dark sector physics

We study black hole extremality in nonlinear electrodynamics motivated by the Weak Gravity Conjecture (WGC) and the Festina Lente (FL) bound. For illustration, we consider the Euler-Heisenberg model and the Dirac-Born-Infeld model in asymptotically flat spacetime, de Sitter spacetime, and anti-de Sitter spacetime. We find that in all cases the extremal condition enjoys a certain monotonicity expected by the WGC. This provides evidence for the conjecture beyond the leading order corrections to the Einstein-Maxwell theory. We also study how light charged particles modify the mass-charge relation of Nariai black holes in de Sitter spacetime and discuss possible implications for the FL bound. Besides, we point out an interesting similarity between our black hole analysis and gravitational positivity bounds on scattering amplitudes.

United States

Yoshihiko Abe

Kaho Yoshimura

Black hole extremality in nonlinear electrodynamics: a lesson for weak gravity and Festina Lente bounds

We develop a framework to derive consistency constraints on gravitational Regge amplitudes based on the finite energy sum rules (FESRs), which directly connect gravitational Regge amplitudes at a finite ultraviolet scale with infrared physics without suffering from super-Planckian physics. For illustration, we consider four-point scattering of an identical massless scalar coupled to gravity. First, we derive multiple FESRs without relying on the s-t-u permutation invariance. We then make use of FESRs, crossing symmetry, and other principles such as unitarity, to derive bounds on the Regge parameters. The bounds result in infrared finite gravitational positivity bounds in four spacetime dimensions.

Finite energy sum rules for gravitational Regge amplitudes

We study higher derivative corrections to black brane thermodynamics and their implications for the weak gravity conjecture for p-form gauge fields. In particular we show that higher derivative corrections decrease tension-to-charge ratios of extremal black branes as implied by the weak gravity conjecture, if four-derivative couplings follow scattering positivity bounds. We also demonstrate that entropy corrections in the micro canonical ensemble are positive under the same assumptions. This extends earlier works in the Einstein-Maxwell theory to p-form gauge fields in general spacetime dimensions.